Thermal Analysis & Rheology · ii TA INSTRUMENTS TGA 2950 '1995, 1996, 1997, 2000 by TA Instruments, Inc. 109 Lukens Drive New Castle, DE 19720 Notice The material contained in this

TA INSTRUMENTS TGA 2950 i

Thermal Analysis & Rheology

TGA 2950

Thermogravimetric Analyzer

Operator’s Manual

PN 925602.001 Rev. D (Text and Binder)PN 925602.002 Rev. D (Text Only)Issued July 2000

TA INSTRUMENTS TGA 2950ii

©1995, 1996, 1997, 2000 byTA Instruments, Inc.109 Lukens DriveNew Castle, DE 19720

Notice

The material contained in this manual is be-lieved adequate for the intended use of thisinstrument. If the instrument or procedures areused for purposes other than those specifiedherein, confirmation of their suitability must beobtained from TA Instruments. Otherwise, TAInstruments does not guarantee any results andassumes no obligation or liability. This publica-tion is not a license to operate under or arecommendation to infringe upon any processpatents.

TA Instruments Operating Software and Mod-ule, Data Analysis, and Utility Software andtheir associated manuals are proprietary andcopyrighted by TA Instruments, Inc. Purchasersare granted a license to use these softwareprograms on the module and controller withwhich they were purchased. These programsmay not be duplicated by the purchaser withoutthe prior written consent of TA Instruments.Each licensed program shall remain the exclu-sive property of TA Instruments, and no rightsor licenses are granted to the purchaser otherthan as specified above.

TA INSTRUMENTS TGA 2950 iii

Table of ContentsNotes, Cautions, and Warnings................xii

Hotline Numbers........................................xiv

Safety............................................................xv

Using This Manual..................................xviii

CHAPTER 1: Introducingthe TGA 2950 ............................................ 1-1

Introduction................................................. 1-3

Components .......................................... 1-4

The 2950 Instrument ................................... 1-5

2950 Display ........................................ 1-5

2950 Keypad ........................................ 1-6

HEATER Switch ......................... 1-10POWER Switch ........................... 1-10

Accessories ............................................... 1-11

Gas Switching Accessory ................... 1-11

Other Accessories .............................. 1-11

Specifications ............................................ 1-12

TA INSTRUMENTS TGA 2950iv

Table of Contents(continued)

CHAPTER 2: Installingthe TGA 2950............................................ 2-1

Unpacking/Repacking the 2950 ................... 2-3

Unpacking the 2950 .............................. 2-3

Repacking the 2950 ............................... 2-6

Installing the Instrument ............................. 2-7

Inspecting the System........................... 2-8

Choosing a Location ............................ 2-9

Filling the Heat Exchanger................. 2-10

Connecting Cables and Gas Lines...... 2-12

Heat Exchanger Cableand Water Lines ........................... 2-12GPIB Cable .................................. 2-15Purge Lines .................................. 2-17Cooling Gas Line ......................... 2-18Power Cable ................................. 2-19

Unpacking the Balance ............................. 2-20

Installing the Hang-Down Wires .............. 2-22

Aligning the SampleHang-Down Wire ............................... 2-25

Adjusting the Sample Platform ................. 2-29

Starting the 2950 ........................................ 2-30

Shutting Down the 2950 ............................ 2-32

TA INSTRUMENTS TGA 2950 v


CHAPTER 3: Running Experiments..... 3-1

Overview ..................................................... 3-3

Before You Begin ................................ 3-3

Calibrating the TGA ................................... 3-5

Temperature Calibration ...................... 3-5

Weight Calibration ............................... 3-6

Sample Platform Calibration ................ 3-6

Running a TGA Experiment ....................... 3-7

Experimental Procedure ....................... 3-7

Preparing Samples ............................... 3-8

Selecting Sample and Tare Pans .... 3-8Taring the Sample Pan ................... 3-9

Automatic Tare ..................... 3-10Manual Tare .......................... 3-10

Loading the Sample ............................ 3-11

Setting Up an Experiment .................. 3-14

Setting Up Accessories ...................... 3-15

Using the Air Cool Option.......... 3-16Using a Purge Gas ...................... 3-16Using the GasSwitching Accessory .................. 3-19

Starting an Experiment ....................... 3-20

TA INSTRUMENTS TGA 2950vi


Stopping an Experiment ..................... 3-21

Unloading the Sample ................. 3-21

Use in an Oxygen-Free Atmosphere ......... 3-22

Purge Gas System............................... 3-22

Instrument Set-Up .............................. 3-23

CHAPTER 4: Technical Reference....... 4-1

Description of the TGA 2950 ..................... 4-3

Components......................................... 4-5

Balance .......................................... 4-6Sample Loading Assembly ............ 4-8Furnace .......................................... 4-9

TGA Standard Furnace ........... 4-9EGA Furnace ........................ 4-11

Cabinet ......................................... 4-13Heat Exchanger............................ 4-15

Theory of Operation ................................. 4-16

Status Codes ............................................. 4-17

TA INSTRUMENTS TGA 2950 vii


CHAPTER 5: Maintenanceand Diagnostics......................................... 5-1

Overview ..................................................... 5-3

Routine Maintenance .................................. 5-4

Inspection ............................................. 5-4

Cleaning the Instrument ....................... 5-4

Cleaning the Furnace Housing ............. 5-5

TGA Standard Furnace Only ......... 5-5

Heat Exchanger .................................... 5-6

Maintaining HeatExchanger Coolant ........................ 5-6Draining and Refillingthe Water Reservoir ....................... 5-6

Replacing the Thermocouple ...................... 5-9

Removing andReinstalling the Furnace ........................... 5-11

Furnace Removal ............................... 5-11

Furnace Replacement ......................... 5-14

Diagnosing Power Problems ..................... 5-16

Fuses ................................................... 5-16

Power Failures .................................... 5-18

TA INSTRUMENTS TGA 2950viii


TGA Test Functions ................................. 5-19

The Confidence Test .......................... 5-19

Replacement Parts .................................... 5-21

Appendix A: Ordering Information ..... A-1

Appendix B: High ResolutionTGA Option .............................................. B-1

Overview .................................................... B-5

Option Installation ..................................... B-6

Using Hi-ResTM TGA ................................. B-7

Background ......................................... B-7

The TA Instruments Hi-ResTM

Technique ............................................ B-8

The Hi-ResTM Ramp Segment .................... B-9

Calcium Oxalate Example Scans ...... B-13

Advanced Hi-ResTM Techniques .............. B-18

What Can Be Resolved andWhat Cannot? .................................... B-18

Unresolved Transitions ..................... B-19

Selecting a Hi-ResTM Technique ....... B-22

TA INSTRUMENTS TGA 2950 ix


Dynamic Rate Hi-ResTM Ramp.......... B-22

Constant Reaction RateHi-ResTM Ramp.................................. B-23

Weight Gain Experiments ................. B-26

Signature Analysis ............................ B-27

Sample Quantity and Orientation ...... B-28

Exposed Surface Area ................ B-28Bubble Formation ....................... B-29

Thermocouple Placement ........................ B-32

Data Analysis Effects .............................. B-32

Derivative Plots ....................................... B-33

Adjusting Heating Rate ........................... B-34

Adjusting Resolution Setting ................... B-37

Useful Resolutions Settings .............. B-39

Temperature Calibration .......................... B-41

Hi-ResTM Transition Temperatures ... B-42

Hi-ResTM Sensitivity Segment ................. B-43

TA INSTRUMENTS TGA 2950x


Understanding Sensitivity Setting ..... B-44

Adjusting Sensitivity inDynamic Rate Mode ......................... B-45

Adjusting Sensitivity in ConstantReaction Rate Mode .......................... B-47

Abort Segment ......................................... B-51

Stepwise Isothermal Heating............. B-53

Hi-ResTM TGA Examples......................... B-58

Mixture of Bicarbonates.................... B-58

Dynamic Rate Scans ................... B-59

Varying Resolution Setting ........ B-61

Varying Sensitivity Setting......... B-62

Constant Reaction Rate Scans .... B-63

Stepwise Isothermal Scans ......... B-65

Monosodium Glutamate .................... B-68

Banana Taffy ..................................... B-69

Plastic Laboratory Tubing................. B-71

References ............................................... B-75

TA INSTRUMENTS TGA 2950 xi


APPENDIX C: TGA 2950Autosampler Option ................................ C-1

Introducing the Auto TGA......................... C-3

Getting Started ........................................... C-4

The TGA 2950 Instrument ......................... C-6

Calibrating the Auto TGA ....................... C-10

Running Experiments .............................. C-11

Preparing the Samples ....................... C-12

Selecting Sampleand Tare Pans ............................. C-12Taring the Sample Pans .............. C-13

Loading the Samples ......................... C-16

Setting Up an Experiment ................. C-18

Manual Operation ............................. C-19

Tracking the TGAAutosampler Status ........................... C-19

Interrupting a Run ............................. C-20

TA INSTRUMENTS TGA 2950xii


Appendix D: TGA 2950EGA Furnace Option .............................. D-1

Introducing the EGA Furnace .................... D-3

EGA Furnace Specifications ............... D-5

Installing the EGA Furnace ....................... D-6

First-Time Installation ........................ D-6

Removing and Reinstalling theEGA Furnace .................................... D-14

EGA Furnae Removal................. D-14EGA Furnace Installation ........... D-16

Connecting the Spectrometer................... D-18

Using the EGA Furnace ........................... D-21

Cleaning the Quartz Furnace Tube .......... D-22

Index ............................................................ I-1

TA INSTRUMENTS TGA 2950 xiii

Notes, Cautions,and Warnings

This manual uses NOTES, CAUTIONS, andWARNINGS to emphasize important andcritical instructions.

A NOTE highlights important information aboutequipment or procedures.

A CAUTION emphasizes a procedure that maydamage equipment or cause loss of data if notfollowed correctly.

A WARNING indicates a procedure thatmay be hazardous to the operator or to theenvironment if not followed correctly.

NOTE:

ttttt CAUTION:

!WARNING

TA INSTRUMENTS TGA 2950xiv

Hotlines

To TA Instruments

For Technical Assistance ........ (302) 427-4070

To Order Instrumentsand Supplies ............................ (302) 427-4040

For Service Inquiries............... (302) 427-4050

Sales ...................................... (302) 427-4000

TA INSTRUMENTS TGA 2950 xv

Safety

Electrical SafetyYou must unplug the instrument before doingany maintenance or repair work; voltagesexceeding 120 volts AC are present in thissystem.

High voltages are present in this instru-ment. If you are not trained in electricalprocedures, do not remove the cabinetcovers unless specifically instructed to doso in the manual. Maintenance and repairof internal parts must be performed only byTA Instruments or other qualified servicepersonnel.

After transport or storage in humid condi-tions, this equipment could fail to meet allthe safety requirements of the safetystandards indicated. Refer to the NOTE onpage 2-9 for the method used to dry outthe equipment before use.

Chemical SafetyUse only the purge gases listed in Table 1.4 inChapter 1. Use of other gases could causedamage to the instrument or injury to theoperator.

Do not use hydrogen or any other explosivegas in the TGA 2950 furnace or the TGA2950 EGA furnace.

Oxygen can be used as a purge gas in the TGA2950. However, the furnace must be keptclean so that volatile hydrocarbons (whichmight combust) are removed.

!WARNING

!WARNING

!WARNING

!WARNING

TA INSTRUMENTS TGA 2950xvi

Safety(continued)

The TGA 2950 furnace assembly contains alayer of refractory ceramic fiber (RCF)insulation. This insulation is completelyencapsulated within the ceramic subassem-bly, which is not meant to be disassembled.If the subassembly should break in such away as to expose the RCF insulation, werecommend that you dispose of it as youwould any refractory material.

If you are routinely evaluating materials inthe TGA that lose a large amount of volatilehydrocarbons (e.g., lubricating oils), youneed to clean the furnace more frequentlyto prevent dangerous buildup of debris inthe furnace.

If you are using samples that may emitharmful gases, vent the gases by placingthe instrument near an exhaust.

The TGA 2950 EGA furnace assembly alsocontains refractory ceramic fiber (RCF)insulation. This insulation is enclosedwithin the furnace housing. The furnacehousing should only be disassembled forreplacement of EGA furnace sample tube orfurnace assemblies. Refer to instructionsprovided with the sample tube or furnacereplacement kits for procedures for han-dling RCF insulation.

!WARNING

!WARNING

!WARNING

!WARNING

TA INSTRUMENTS TGA 2950 xvii

Thermal Safety

After running an experiment, allow the openfurnace and thermocouple to cool down beforeyou touch them.

During a sample run, the furnace base (seeFigure 1.1) can be hot enough to burn skin.Avoid contact with the furnace base duringexperiments.

Mechanical Safety

Keep your fingers and all other objects outof the path of the furnace when it is mov-ing. The furnace seal is very tight.

!WARNING

!WARNING

TA INSTRUMENTS TGA 2950xviii

Using This ManualChapter 1 Describes your TGA 2950

instrument and its acces-sories and specifications.

Chapter 2 Describes how to unpackand install the TGA andhow to connect the TGAto the rest of your system.

Chapter 3 Describes how to runTGA experiments and setup the accessories.

Chapter 4 Provides technicalinformation and explainsprin-ciples of TGAoperation.

Chapter 5 Describes how to performroutine maintenance,replace the thermocouple,remove and reinstall thefurnace, and diagnosepower problems; alsoprovides an explanationof the confidence test.

Appendix A Lists TA Instrumentsoffices that you cancontact to place orders,receive technical assis-tance, and request service.

Appendix B Describes the HighResolution option includ-ing installation, useage,applications, etc.

TA INSTRUMENTS TGA 2950 xix

Using This Manual(continued)

Appendix C Provides instructionsneeded to operate theTGA Autosampler optionto automatically load andrun samples.

Appendix D Provides instructionsneeded to install and usethe EGA furnace with theTGA 2950.

TA INSTRUMENTS TGA 2950xx

TA INSTRUMENTS TGA 2950 1–1

CHAPTER 1: Introducing theTGA 2950

Introduction................................................. 1-3

Components .......................................... 1-4

The 2950 Instrument ................................... 1-5

2950 Display ........................................ 1-5

2950 Keypad ........................................ 1-6

HEATER Switch ......................... 1-10POWER Switch ........................... 1-10

Accessories ............................................... 1-11

Gas Switching Accessory ................... 1-11

Other Accessories .............................. 1-11

Specifications ............................................ 1-12

Introducing the TGA 2950

TA INSTRUMENTS TGA 29501–2


IntroductionYour TA Instruments ThermogravimetricAnalyzer (TGA) 2950 is a thermal weight-change analysis instrument, used in conjunctionwith a TA Instruments thermal analysis control-ler and associated software, to make up athermal analysis system.

The Thermogravimetric Analyzer 2950 mea-sures the amount and rate of weight change in amaterial, either as a function of increasingtemperature, or isothermally as a function oftime, in a controlled atmosphere. It can be usedto characterize any material that exhibits aweight change and to detect phase changes dueto decomposition, oxidation, or dehydration.This information helps the scientist or engineeridentify the percent weight change and correlatechemical structure, processing, and end-useperformance.

Your controller is a computer that performs thefollowing functions:

• Provides an interface between you and theanalysis instruments

• Enables you to set up experiments andenter constants

• Stores experimental data• Runs data analysis programs.

Introduction



Components

The TGA 2950 has five major components,illustrated in Figure 1.1:

• The balance, which provides precisemeasurement of sample weight. Thebalance is the key to the TGA system.

• The sample platform, which loads andunloads the sample to and from thebalance.

• The furnace, which controls the sampleatmosphere and temperature.

• The cabinet, where the system electronicsand mechanics are housed.

• The heat exchanger, which dissipates heatfrom the furnace.

Figure 1.1TGA 2950 Components

HeatExchanger Furnace

Thermocouple

BalanceChamber

Keypad

DisplayHeaterSwitch

PowerSwitch

SamplePlatform

Cabinet


The 2950 InstrumentThe parts of the TGA 2950 instrument thatprovide for operator control are:

· The instrument display· The instrument keypad.

Figure 1.2TGA 2950Display and Keypad

2950 Display

The TGA instrument display is the lighted areaof the keypad (Figure 1.2). It contains two rowsof 20 characters each.

During normal operation, the display is seg-mented into three areas. The left eight charac-ters on the upper line show the instrumentstatus; the right nine characters show the sampletemperature; and the bottom line is a realtimesignal display (e.g., weight).

TGA 2950 Thermogravimetric Analyzer

Standby 23.25°CWeight 238.247 mg

The 2950 Instrument



NOTE:

A pound sign (#) after the weight signal indi-cates that the balance reading has not yetstabilized. When the weight stabilizes, thepound sign will disappear.

2950 Keypad

The instrument keypad (see Figure 1.2) containsthe keys found in Table 1.1 and the HEATERand POWER switches

Experiment information and instrument constantsare entered from the controller keyboard, not theinstrument keypad.

Table 1.1TGA 2950 KeypadFunction Keys

Key/Function Explanation

SCROLL Scrolls the realtimesignals shown on thebottom line of the display.For more details on theexperiment, refer to statusand signal displays on thecontroller.

TARE Zeros the displayedweight of an emptysample pan: automaticallyloads the pan from thesample platform, raisesthe furnace to protect thepan from air currents,weighs the pan, stores theweight as an offset, andthen unloads the pan.

(table continued)


The 2950 Instrument

∆

Table 1.1TGA 2950 KeypadFunction Keys(continued)


LOAD Loads a sample pan fromthe sample platform onto thebalance.

UNLOAD Unloads the sample panfrom the balance onto thesample platform.

∆FURNACE Toggles between the

furnace closed (up) andfurnace open (down)functions, depending onwhere the furnace iswhen you press the key.This key can be pressedwhile the furnace ismoving to reverse thedirection of movement.

START Begins the experiment. Thisis the same function as Starton the controller.

Forced Start can be done bypressing the START keywhile the status line displays“Set Up.” Forced startbegins collecting dataduring instrument setup.

(table continued)



Table 1.1TGA 2950 KeypadFunction Keys(continued)


STOP If an experiment isrunning, this key ends themethod normally, asthough it had run tocompletion; i.e., themethod-end conditionsgo into effect and the datathat has been generated issaved. This is the samefunction as Stop on thecontroller.

If an experiment is notrunning (the instrument isin a stand-by or method-end state), the STOP keywill halt any activity (aircool, all mechanicalmotion, etc.).

REJECT If an experiment isrunning, SCROLL-STOPends the method normal-

(Hold down ly, as though it had run toSCROLL and completion; i.e., thepress STOP) method-end conditions go

into effect and the datathat has been generated isdiscarded. This is thesame function as Rejecton the controller.

(table continued)


The 2950 Instrument

NOTE:

Table 1.1TGA 2950Keypad Function Keys(continued)


The SCROLL keyoperates normally(scrolls the realtimesignals) until the STOPkey is pressed.

If an experiment is notrunning, SCROLL-STOPworks like the STOP key.

AUTO SELECT This key appears only oninstruments with anautosampler installed.See Appendix C fordetails.

Automatic Keypad Functions

Some of the TGA instrument keys automaticallyperform additional functions under certainconditions:

• START automatically loads the sample panand closes the furnace, if necessary, beforebeginning the experiment.

• TARE, LOAD, and UNLOADautomatically open the furnace ifnecessary.

• START can be pressed while a sampleLOAD is in progress.



HEATER Switch

The HEATER on/off switch (see Figure 1.2)turns the power to the instrument heater on andoff. This switch should be in the ON (1) positionbefore you start an experiment.

The light in the HEATER switch will glow only whenan experiment is in progress.

POWER Switch

The POWER switch (see Figure 1.2) turns thepower to the instrument on and off.

NOTE:


Accessories

Gas SwitchingAccessory

The TA Instruments Gas Switching Accessorycan be used to turn the purge gas on and off or toswitch between two different purge gases duringTGA experiments.

Evolved GasAnalysis Furnace

The TGA 2950 EGA furnace is an accessory tothe instrument which allows you to performcombined TGA and evolved gas analysisexperiments.

Other Accessories

The TGA can be used with many standardanalytical accessories offered by various manu-facturers, including vacuum, FTIR, mass spec-trometers, gas chromatographs, and evolved gasanalyzers. Consult the appropriate local instru-ment manufacturer for further information.

Accessories



SpecificationsTables 1.2 through 1.4 contain the technicalspecifications for the TGA 2950.

Table 1.2TGA 2950Operating Parameters

Temperature range 25oC to 1000oC

Thermocouple Platinel II*

Heating ratewith standard furnace 0.1 to 100oC/minwith EGA furnace 0.1 to 50°C/min

*Platinel II is a registered trademark ofEngelhard Industries.

Table 1.3TGA 2950InstrumentCharacteristics

Operating line voltage 115 volts,50/60 Hz

Energy consumption 1.5 kVA


Specifications

ttttt CAUTION:

Table 1.4Sampling System

Sample pansTypes Platinum, Alumina

(Al20

3), Aluminum

Volume capacity Platinum: 50 µL,100 µLAlumina: 100 µL,250 µL, 500 µLAluminum 100 µL

Weighing capacity1 1.0 gm

Balance measurement2

Resolution 0.1 µgAccuracy < + 0.1%

Ranges 100 mg range:0.1 µg _ 100 mg1000 mg range:1 µg _ 1000 mg

1 The total mechanicalcapacity of the balance is5 gm. In order to avoiddamaging the balanceassembly, never allow thetotal weight of the sample,tare weight, hang-downwires, and pans to exceed5 gm.

2 The TGA balance mechanism is sensitiveto changes in the surrounding room tempera-ture. For optimum accuracy, you mustregulate the ambient temperature.

(table continued)



!WARNING

Table 1.4(continued)

Furnace AtmospherePurge gases Helium, nitrogen,

oxygen, air, argon3

Purge rate Up to 100 cc/min

3 Do not use hydrogen orany other explosive gas inthe TGA 2950 furnace orthe TGA 2950 EGA furnace.Oxygen may be used. How-ever, the furnace must bekept clean of volatile hydro-carbons to prevent combus-tion.


CHAPTER 2: Installing theTGA 2950

Unpacking/Repacking the 2950 ................... 2-3

Unpacking the 2950 .............................. 2-3

Repacking the 2950 ............................... 2-6

Installing the Instrument ............................. 2-7

Inspecting the System........................... 2-8

Choosing a Location ............................ 2-9

Filling the Heat Exchanger................. 2-10

Connecting Cables and Gas Lines ...... 2-12

Heat Exchanger Cableand Water Lines ........................... 2-12GPIB Cable .................................. 2-15Purge Lines .................................. 2-17Cooling Gas Line ......................... 2-18Power Cable ................................. 2-19

Unpacking the Balance ............................. 2-20

Installing the Hang-Down Wires .............. 2-22

Aligning the SampleHang-Down Wire ............................... 2-25

Adjusting the Sample Platform ................. 2-29

Starting the 2950 ........................................ 2-30

Shutting Down the 2950 ............................ 2-32

TA INSTRUMENTS TGA 2950

Installing the 2950

2–2


Unpacking/Repackingthe 2950

These instructions are also found as separateunpacking instructions in the shipping box.

You may wish to retain all of the shippinghardware, the plywood, and boxes from theinstrument in the event you wish to repack andship your instrument.

Unpacking the 2950

Refer to Figures 2.1 to 2.3 while unpacking yourinstrument.

Have an assistant help you unpack thisunit. Do not attempt to do this alone.

Figure 2.1Shipping Boxes

NOTE:

!WARNING

Unpacking/Repacking the 2950


Installing the 2950

2–4

1. Open the shipping carton and remove theaccessory box.

2. Remove the cardboard packing insert.

3. Stand at one end of the box with yourassistant facing you at the other end. Liftyour end of the unit out of the box as yourassistant lifts his/her end.

4. Place the unit on a lab bench with one sidehanging over the edge of the bench (seeFigure 2.2). Someone must be holdingonto the unit at all times while it is in thisposition.

Figure 2.2Removing the PlywoodBoard

5. While your assistant holds the unit, use awrench to remove the two nuts and washersfrom the bottom. Then lift and rotate theunit so that the other end hangs over theedge of the bench. Someone must holdonto the unit at all times while it is in


this position. While your assistant holds theunit, remove the two nuts and washers fromthe other side.

6. Slide the unit completely onto the lab bench.Have your assistant hold one side up whileyou unscrew and remove the black rubbershipping feet from the bottom. Then rotatethe unit and remove the shipping feet fromthe other side in the same manner.

7. Have your assistant lift the entire unit whileyou slide the plywood board out from underthe unit.

8. Have your assistant lift one side of the unitwhile you use a wrench to install twomounting feet on the other side (see Figure2.3). Rotate the unit and install the tworemaining mounting feet in the same man-ner.

9. Remove the furnace clamp before turning onthe power to the unit.

Figure 2.3Installing theMounting Feet

Unpacking/Repacking the 2950


Installing the 2950

2–6

Repacking the 2950

To pack and ship your instrument, use thehardware retained during unpacking and reversethe instructions found on pages 2-3 to 2-5.


Installingthe Instrument

Before shipment, the TGA 2950 instrument isinspected both electrically and mechanically sothat it is ready for operation upon proper instal-lation. Installation involves the followingprocedures, described in this chapter:

· Inspecting the system for shipping damageand missing parts

· Filling the heat exchanger· Connecting the TGA to the TA Instruments

controller· Connecting the heat exchanger cable and

water lines, purge gas lines, accessories, andpower cable

· Unpacking the balance· Installing the hang-down wires· Leveling the instrument and aligning the

hang-down wires· Adjusting the sample platform.

If you wish to have your TGA installed by a TAInstruments Service Representative, call for aninstallation appointment when you receive yourinstrument.

To avoid mistakes, read this entire chapterbefore you begin installation.

Installing the Instrument

ttttt CAUTION:


Installing the 2950

2–8

Inspectingthe System

When you receive your TGA 2950, look overthe instrument and shipping container carefullyfor signs of shipping damage, and check theparts received against the enclosed shipping list.

• If the instrument is damaged, notify thecarrier and TA Instruments immediately.

• If the instrument is intact but parts aremissing, contact TA Instruments.

A list of TA Instruments phone numbers can befound in Appendix A of this manual.


Choosinga Location

Because of the sensitivity of TGA experiments,it is important to choose a location for theinstrument using the following guidelines. TheTGA should be:

In ... a temperature-controlled area.... a clean, vibration-free environ-

ment.... an area with ample working and

ventilation space.On ... a stable work surface.Near ... a power outlet (115 volts AC,

50 or 60 Hz, 15 amps). A stepup/down line transformer maybe required if the unit is oper-ated at a higher or lower linevoltage.

... your TA Instruments thermalanalysis controller.

... compressed lab air and purgegas supplies with suitableregulators and flowmeters.

Awayfrom ... dusty environments.

... exposure to direct sunlight.

... direct air drafts (fans, room airducts).

... poorly ventilated areas.

... noisy or mechanical vibrations.

Drying out the instrument may be needed, if it hasbeen exposed to humid conditions. It is importantto be certain that the instrument ground isadequately connected to the facilities ground forsafe operation.

Run the following method to dry out the instrument(refer to Chapter 4 for further information):

1 Ramp at 10°C/min to 400°C2 Isothermal for 30 min.


NOTE:


Installing the 2950

2–10

Filling theHeat Exchanger

The heat exchanger contains a liquid reservoirthat supplies the instrument with coolant todissipate heat from the furnace. The coolantexits the heat exchanger through the supply line,circulates to the furnace, and comes back to thereservoir via the return line as seen in Figure 2.4(for instructions on how to connect the waterlines, turn to page 2-12). To fill the heat ex-changer, follow the directions given below.

Figure 2.4Rear Panel ofHeat Exchanger

1. Unscrew the water reservoir cap on the heatexchanger (see Figure 2.4).

Screws

HeatExchangerCable

Water Reservoir Cap


Figure 2.5Heat ExchangerBottle

2. Add TA Instruments TGA Conditioner (PN952377.901) into the water reservoir bottle.Refer to the instructions on the bottle for theamount of conditioner to add to the reser-voir. Then fill the bottle to the inner rim(see Figure 2.5) with distilled water.

After the system has been started, recheck thelevel of water in the reservoir bottle and refill tothe inner rim if necessary.

Do not put any liquid other than distilledwater in the heat exchanger reservoir.

3. Replace and tighten the water reservoir cap.


Fill to bottle’s inner rim.

NOTE:

!WARNING


Installing the 2950

2–12

Connecting Cablesand Lines

To connect the cables and water and gas lines,you will need access to the TGA instrument’srear panel. All directional descriptions arewritten on the assumption that you are facing theback of the instrument.

Connect all cables before connecting the powercords to outlets. Tighten the thumbscrews on allcomputer cables.

Whenever plugging or unplugging power cords,handle them by the plugs, not by the cords.

Protect power and communications cablepaths. Do not create tripping hazards bylaying the cables across accessways.

Heat Exchanger Cableand Water Lines

1. Locate the cooling accessory connector onthe left rear of the instrument cabinet(Figure 2.6).

2. Connect the heat exchanger cable to theconnector. The heat exchanger cable is theonly cable that fits into this connector.

NOTE:

tttttCAUTION:

!WARNING


Figure 2.6TGA 2950Connector Panel

3. Remove the water lines from the packing.

4. Connect one end of the water line marked“SUPPLY” to the connector labeled “SUP-PLY” on the right side of the instrumentcabinet.

5. Connect the other end of the water linemarked “SUPPLY” to the connector labeled“SUPPLY” on the heat exchanger.

6. Connect one end of the unmarked water lineto the connector labeled “RETURN” on theright side of the instrument cabinet.

7. Connect the other end of the unmarkedwater line to the connector labeled “RE-TURN” on the heat exchanger.



Installing the 2950

2–14

Figure 2.7 illustrates the correct water lineconnections for the TGA and heat exchanger.

Figure 2.7Heat Exchanger WaterLine Connections

8. Plug in the power cable and turn on thepower switch for the heat exchanger.

Air trapped in the heat exchanger system must bepurged before starting the first run. After installa-tion of the TGA is complete, turn on the instru-ment by placing the HEATER and POWER switchesin the ON position. Then start the heat exchangerpump by turning on Air Cool from the controller.Refill the coolant reservoir as needed. Repeat thisprocess until all the air has been purged fromthe system and the instrument stops reporting an“Err 119.”

NOTE:


GPIB Cable

1. Locate the GPIB connector on the right rearof the TGA instrument (see Figure 2.6).

2. Connect the GPIB cable to the connector.The GPIB cable is the only cable that fitsinto the connector.

3. Tighten the hold-down screws on theconnector.

4. Connect the other end of the GPIB cable tothe controller or to the GPIB cable ofanother TA Instruments instrument con-nected to the controller. (For more informa-tion, see your controller manual.)

5. Select an address from 1 to 9. Then use thebinary address switches on the TGA connec-tor panel to set the desired address (SeeTable 2.1). Figure 2.8 on the next pageshows a instrument address of 7.

If you have a multi-instrument system, eachinstrument must have a different a differentaddress.

If you change the address after the TGA ispowered on, you must press the TGA’sReset button to enter the new address. Waituntil the instrument completes its startupdisplays, then reconfigure the instrumentwith the controller to bring the instrumentback online.

The instrument’s GPIB address is displayed duringstart up and can also be viewed on theinstrument’s status display.

NOTE:


NOTE:


Installing the 2950

2–16

4/86010161-26C

ADDRESS1 2 3 4 5O

N

Table 2.1Binary Address Settings

Address Switch Pattern1 2 3 4 5

1 0 0 0 0 12 0 0 0 1 03 0 0 0 1 14 0 0 1 0 05 0 0 1 0 16 0 0 1 1 07 0 0 1 1 18 0 1 0 0 09 0 1 0 0 1

*0 = OFF; 1 = ON

Figure 2.8Binary Address Switches(Showing an Address of 7)


Purge Lines

Do not use any liquid in the purge lines.

1. Locate the FURNACE PURGE and BAL-ANCE PURGE fittings on the right side ofthe TGA instrument back (Figure 2.9).

Figure 2.9TGA PURGE Fittings

2. Make sure that the pressure of your purgegas source does not exceed the manufactur-ers’ recommended pressures for flowmetersand other regulated devices you are using.

If you are using laboratory purge, rather thanbottled purge, you will need to install an externaldrier.

The use of corrosive gases is not recommended.

!WARNING

NOTE:

tttttCAUTION:

Furnace Purge

Balance Purge



Installing the 2950

2–18

Use of an explosive gas as a purge gas isdangerous and is not recommended for thisinstrument. For a list of the purge gases thatcan be used with the TGA instrument, seeChapter 1. Oxygen may be used as a purgegas, but the furnace must be kept clean ofvolatile hydrocarbons to prevent combustion.

3. Connect a length of 1/4-inch I.D. flexibletubing from each of the PURGE fittings to aflowmeter (consult your compressed gasvendor for specific requirements). Thenconnect each flowmeter to the purge gassource.

4. The recommended setting for the purge rateis 100 mL per minute or less. The flowdistribution should be as follows: (a) for thestandard furnace, 40 percent to the balancechamber and 60 percent to the furnace, and(b) for the EGA furnace, 10 percent to thebalance and 90 percent to the furnace.

Cooling Gas Line1. Locate the COOLING GAS fitting, a 1/4-

inch compression fitting on the left side ofthe TGA cabinet back, marked with a 120psig maximum warning label (Figure 2.10).

Figure 2.10TGA COOLINGGAS Fitting

!WARNING


2. Make sure your compressed lab air source isregulated to between 25 and 120 psig and isfree of oil and water vapors.

3. Connect a compressed lab air line to theCOOLING GAS fitting.

Nitrogen may also be used as a cooling gas.

Power Cable

1. Make sure the TGA POWER switch (Figure2.11) is in the Off (0) position.

Figure 2.11TGA POWER Switch

2. Plug the power cable into the TGA.

Before plugging the TGA power cable into the walloutlet, make sure the instrument is compatiblewith the line voltage. Check the label on the backof the unit to verify the voltage.

3. Plug the power cable into the wall outlet.

NOTE:


ttttt CAUTION:


Installing the 2950

2–20

Unpackingthe Balance

When unpacking the balance, be careful not todamage the balance arm or hang-down loops.

1. Using the 7/64-inch ball driver supplied inyour TGA accessory kit, loosen and removethe six screws securing the balance chamberfaceplate to the instrument.

2. Take off the faceplate.

3. Loosen and remove the thumbscrew holdingthe balance cover on the sample (left) sideof the balance mechanism (Figure 2.12), andtake off the cover.

Figure 2.12Interior of BalanceChamber Before Unpacking

BalanceCover

SampleSide

TareSide

TareTube

BalanceCoverScrew

Hang-DownLoop

t CAUTION:


4. Using tweezers, remove the foam insertfrom around the screw hole (Figure 2.13):

a. Gently compress the foam with thetweezers, being careful not to touch thebalance.

b. Remove the foam insert from thebalance chamber.

Figure 2.13Removal of FoamInsert from BalanceChamber

5. Replace the sample side cover and screw.

6. Repeat the procedure to remove the foaminsert in the tare (right) side of the balance.

Unpacking the Balance

FoamInsert


Installing the 2950

2–22

Installing theHang-Down Wires

During installation, take care not to bend thehang-down wires or damage the hang-down loops.

1. Turn on the TGA instrument.

2. Press the FURNACE key to lower thefurnace.

3. Locate the sample hang-down wire in yourTGA Accessory Kit.

4. Hold the wire in your hand so that thedoubly bent top hook is pointing to the leftand the bottom hook is pointing to the right.

5. Carefully insert the bottom of the hangdownwire into the top of the furnace far enoughso that you can insert the top of the wire intothe thermocouple tube without bending thewire (Figure 2.14).

Figure 2.14Installing the SampleHang-Down Wire

t CAUTION:


6. Thread the hang-down wire up through thethermocouple tube into the balance cham-ber, and hook the top of the wire over thetop of the tube (see Fig. 2.14).

To make the hang-down loops easier to see, wesuggest sliding a piece of white paper into thebalance chamber behind each loop before you hookthe hang-down wire into it. (Do not forget toremove the paper when finished.)

7. Grasp the top hook of the hang-down wirewith brass tweezers. Being careful to keepthe top hook pointing to the left, pass thedouble bend through the hang-down loop sothe wire is hanging from the loop.

8. Unscrew and remove the tare tube.

9. Locate the tare hang-down wire in youraccessory kit.

10. Hold the wire in your hand so that thedoubly bent top hook is pointing to the leftand the bottom hook is pointing to the right.

11. Using brass tweezers, insert the tare hang-down wire into the balance chamber on thetare side and down through the hole abovethe tare tube connection, taking care not tobend the wire (Figure 2.15 on next page).

12. Being careful to keep the top hook pointingto the left, pass the double bend through thehang-down loop so the wire is hanging fromthe loop.

NOTE:

Installing the Hang-Down Wires


Installing the 2950

2–24

13. Select the sample pan you will use in yourexperiments, and load one of the same sizeand type onto the tare hang-down wire.

14. Replace the tare tube and finger-tighten it tocompress the O-ring seal.

You are now ready to align the hang-downwires.

Figure 2.15Installing the TareHang-Down Wire


Aligning the SampleHang-Down Wire

To avoid weight signal noise, the TGA instru-ment must be level so that the sample pan andhang-down wire hang inside the furnace andthermocouple tube without touching them. Theangle at which the pan hangs is very sensitive toslight irregularities in benchtop surfaces, so it isimportant that you select a sturdy table or benchfor your TGA.

Once you have your TGA in a satisfactorylocation, adjust the top and bottom of the samplehang-down wire and level the instrument usingthe following procedures.

To align the top of the sample hang-down wire:

1. Place an empty sample pan on the sampleplatform.

2. Press the LOAD key on the instrumentkeypad. The TGA will automatically lowerthe furnace (if necessary), move the sampleplatform over to the furnace, and load thepan onto the balance.

If the pan will not automatically load, placepan manually (using brass tweezers) on thesample hang-down wire and continue withthe procedure. Use the Instrument ControlSample Platform Adjust procedure tocorrect loading after completing samplehang-down wire alignment.



Installing the 2950

2–26

3. Check to see whether the top end of thesample hang-down wire is hanging freelyand roughly centered within the top of thethermocouple tube inside the balancechamber.

4. If the wire is not roughly centered inside thethermocouple tube, turn the balance adjust-ment screw (Figure 2.16) with the 7/64-inchball driver until the wire is centered.

Turning the balance adjustment screwclockwise will move the wire backwards;turning the screw counterclockwise willmove the wire frontwards.

Figure 2.16Location of Balance Adjustment Screw


To align the bottom of the hang-down wire:

1. Press the FURNACE key to raise thefurnace just to the bottom of the sample pan,and press STOP.

2. Check the alignment of the sample panwithin the furnace. It should hang freely,roughly centered, and should not be touch-ing the sides of the furnace or the thermo-couple tube (Figure 2.18).

3. If the sample pan is not centered and hang-ing freely within the furnace, level the TGAinstrument by adjusting the feet on thebottom. Turn the feet clockwise to lengthenor counterclockwise to shorten the legs.Continue adjusting until the pan hangscorrectly.

Figure 2.18Aligning the SamplePan in the Furnace


ThermocoupleTube

SamplePan Sample

Pan

Furnace

FurnaceHousing

FurnaceBase

TOP VIEW

Sample PanShould be Centered

Within Furnace


Installing the 2950

2–28

4. Press the FURNACE key to lower thefurnace.

5. Press the UNLOAD key to remove thesample pan from the furnace.

6. Replace the balance chamber faceplate andits 6 screws.

If you had to load the sample pan manuallyin order to align it in the furnace, you shouldnow adjust the sample platform using theprocedure described on the next page.


Adjusting theSample Platform

If the sample hang-down wire fails to pick up asample pan during an automatic loading proce-dure, you will need to adjust the position of thesample platform, using the Sample PlatformAdjust procedure. This procedure is part of theInstrument Control software program. Refer tothe online help and documentation for furtherinformation on adjusting the sample platformshown in Figure 2.19.

This procedure assumes that the instrument hasbeen properly levelled (see page 2-26) and that thesample hang-down wire is straight.

Figure 2.19Sample PlatformAssembly

NOTE:

Adjusting the Sample Platform


Installing the 2950

2–30

Starting the 29501. Check all connections between the TGA

2950 and the controller. Make sure eachcomponent is plugged into the correctconnector.

2. Press the instrument POWER and HEATERswitch to the ON (1) position. The instru-ment will run an internal confidence test,which is run each time you power on theunit.

The HEATER and POWER indicator lamps mayflicker under low AC voltage conditions.

3. Watch the instrument display during theconfidence test for any error messages thatmay be indicated. If an error occurs, make anote of the test number in which the erroroccurred, and call TA Instruments forservice.

After the confidence test, the screen will brieflydisplay the system status, indicating the amountof data storage memory available and the GPIBaddress. Next follows the copyright display, andthen the standby display, shown in Figure 2.20.

NOTE:


Figure 2.20TGA 2950Standby Display

4. Bring the instrument online with the TAcontroller.

Allow the TGA to warm up for at least 30 minutesbefore performing an experiment.


Standby 23.25°CWeight 238.247 mg

NOTE:

Starting the TGA 2950


Installing the 2950

2–32

Shutting Downthe 2950

Before you decide to power down your instru-ment, consider the following:

� All of the components of your thermalanalysis system are designed to be poweredon for long periods.

� The electronics of the TGA and thecontroller perform more reliably if powerfluctuations caused by turning units on andoff are minimized.

For these reasons, turning the system and itscomponents on and off frequently is dis-couraged.

When you finish running an experiment on yourinstrument and wish to use the thermal analysissystem for some other task, leave the instrumenton; it will not interfere with whatever else youwish to do.

If you do need to power down your instrumentfor any reason, simply press the POWER andHEATER switches to the OFF position.


CHAPTER 3: Running Experiments

Overview ..................................................... 3-3

Before You Begin ................................ 3-3

Calibrating the TGA ................................... 3-5

Temperature Calibration ...................... 3-5

Weight Calibration ............................... 3-6

Sample Platform Calibration ................ 3-6

Running a TGA Experiment ....................... 3-7

Experimental Procedure ....................... 3-7

Preparing Samples ............................... 3-8

Selecting Sample and Tare Pans .... 3-8Taring the Sample Pan................... 3-9

Automatic Tare ..................... 3-10Manual Tare .......................... 3-10

Loading the Sample ........................... 3-11

Setting Up an Experiment .................. 3-14

Setting Up Accessories ...................... 3-15

Using the Air Cool Option ......... 3-16Using a Purge Gas ...................... 3-16Using the GasSwitching Accessory .................. 3-19

Running Experiments


Starting an Experiment....................... 3-20

Stopping an Experiment ..................... 3-21

Unloading the Sample ................. 3-21

Use in an Oxygen-Free Atmosphere......... 3-22

Purge Gas System .............................. 3-22

Instrument Set-Up .............................. 3-23


OverviewThis chapter provides step-by-step instructionson how to run TGA experiments. Explanationsof terminology and how the instrument operatesare given in Chapter 4, �Technical Reference.�

All of your TGA experiments will have thefollowing general outline. In some cases, not allof these steps will be performed.

� Entering experiment informationthroughthe TA controller (sample andinstrument information)

� Creating and selecting the thermal method� Selecting and taring the sample pan� Loading the sample� Setting the purge gas flow rate� Starting the experiment� Unloading the sample at the end of the

experiment.

To obtain accurate results, follow procedurescarefully and check calibration periodically(once a month).

Before You Begin

Before you set up an experiment, ensure that theTGA and the controller have been installedproperly. Make sure you have:

� Made all necessary cable connectionsbetween the TGA and the controller

� Connected heat exchanger cable and waterlines

Overview

Running Experiments


� Connected all gas lines� Powered on each unit� Installed all appropriate options� Configured the instrument online with the

controller� Become familiar with controller operations� Calibrated the TGA, if necessary.


Calibrating the TGATo obtain accurate experimental results youshould calibrate the instrument when you firstinstall it. For the best results, however, youshould recalibrate periodically.

Three types of calibration are needed for theTGA 2950: temperature, weight, and sampleplatform calibration. All three calibrationprocedures are performed through the Instru-ment Control software. This section provides abrief description of these types of calibration, fordetails refer to the online help and documents.

TemperatureCalibration

Temperature calibration is useful for TGAexperiments in which precise transitiontemperatures are essential. To temperaturecalibrate the TGA, you need to analyze a high-purity magnetic standard for its curie tempera-ture, and then enter the observed and correctvalues in the temperature calibration table (seethe online help and documentation for furtherinformation). The standard most often used isnickel with a curie temperature of 354.4°C(NIST Certificate for GM761). The observedand correct temperatures correspond to theexperimental and theoretical transition tempera-tures (e.g., curie temperature) of the calibrant.From one to five temperature calibration points(pairs of observed and correct temperaturepoints) can be entered in the calibration table.A multiple-point calibration is more accurate thana one-point calibration.

Calibrating the TGA

Running Experiments


Weight Calibration

Weight calibration should be performed on theTGA at least once a month. The weight calibra-tion procedure calibrates both the 100 mg and1 gram weight ranges. The calibration param-eters are stored internally in the instrument.

You must be sure to determine the exact weightof the calibration weights before they are used tocalibrate the instrument.

The Instrument Control weight calibrationfunctions guide you through the calibrationprocedure step-by-step, see the online help anddocumentation for further information.

Sample PlatformCalibration

The sample platform adjustment procedure isused if the sample hang-down wire fails to pickup a sample pan during an automatic loadingprocedure. The sample platform must beadjusted so that the instrument can properly loadand unload the sample pans.

To avoid weight signal noise, the TGA must belevel so that the sample pan and hang-down wirehang inside the furnace and thermocouple tubewithout touching them. The Instrument Controlsample platform adjust functions take you step-by-step through the procedure, see the onlinehelp and documentation for further information.

NOTE:


Running aTGA Experiment

Experimental Procedure


� Selecting the pan type and material� Loading the pan� Taring the empty sample pan� Loading the sample into the pan� Entering experiment information through

the TA controller (sample and instrumentinformation).

� Creating and selecting the thermal methodon the controller.

� Attaching and setting up externalaccessories as required (e.g., purge gas, GasSwitching Accessory).

� Starting the experiment.

Running a TGA Experiment

Running Experiments


Preparing Samples

TGA experiments utilize different types ofsample pans, depending upon the type ofmaterial that you are analyzing.

Selecting Sampleand Tare Pans

Three kinds of sample pans are available for theTGA 2950, platinum, alumina ceramic, andaluminum. The platinum pans come in 50 and100 µL sizes, the ceramic pans come in 100,250, and 500 µL sizes, and the aluminum pansare 100 µL in size. The criteria for choosing asample pan are as follows:

� For most experiments, platinum is thedesirable choice. It is easy to clean anddoes not react with most organics andpolymers. Ceramic pans are more porousand are therefore more easily contaminated.There are some conditions, however, inwhich other types pans are desirable, asexplained below.

� Use ceramic pans for samples that mightamalgamate or react with platinum (e.g.,metals, corrosives, inorganics).

� Use aluminum pans when disposability isdesired. Aluminum pans are meant forone-time use in experiments that do not goabove 600°C and for samples that do notreact with aluminum.


� If your sample will melt during theexperiment, use a pan that is deep enough toprevent spilling (the deepest pan is the 500µL ceramic pan).

The platinum and ceramic pan types are reus-able. To clean between experiments, use aBunsen burner or a propane torch, or run the panthrough a hot thermal program in the TGA toburn out any residue. Aluminum pans aredisposable, do not attempt to clean and reusethem.

Once you have selected the proper sample pan,remove the tare tube, and using brass tweezers,put the same type and size pan on the tare hook.Use the first step in the weight calibrationprocedure to mechanically tare the balance.

Taring theSample Pan

Taring the sample pan ensures that the weightmeasured by the balance reflects the weight ofthe sample only. You should tare the sample panbefore each experiment, even if you use thesame pan in consecutive experiments.

When you tare a pan, the TGA reads the weightof the empty pan and then stores the weight asan offset, which is subtracted from subsequentweight measurements. For optimum accuracy,the weight reading must be stable before it isaccepted as an offset. If you use the automatictare procedure, the TGA will determine whenthe weight reading is sufficiently stable; or youcan determine the acceptability of the weightreading by taring the system manually. Both tareprocedures are explained here.


Running Experiments


Automatic Tare

Because the TGA 2950 has two weight ranges,taring is done for both ranges. The tare weight isstored by the instrument for the appropriateweight range.

1. Place the empty sample pan on the sampleplatform.

2. Press the TARE key on the instrumentkeypad. The TGA will automatically loadthe pan, raise the furnace (to protect the panfrom air currents), weigh the pan, store theweight as the offset for each weight range,and unload the pan.

Manual Tare

Manual tare operates in the weight range indi-cated, by storing the current reading as an offset,and estimates the tare weight for the otherweight range (typically the 1-gm range). Theestimate is accurate if the TGA 2950 has beentared or weight-calibrated recently.

1. Place the empty sample pan on the sampleplatform.

2. Press the LOAD key to load the pan ontothe balance.

3. Press the FURNACE key to close thefurnace, to protect the pan from air currents.

4. Observe the weight reading on thecontroller's Signal Display window (SignalA Weight).

5. Wait for the Signal A Weight to stabilize,and then choose Auto Zero to store thedisplayed weight as the offset.


Loading the Sample

After taring the sample pan, load the sample intothe TGA furnace as follows:

1. Place the sample in the sample pan, andposition the pan on the sample platform(Figure 3.1).

The wire on the bottom of the sample panshould align with the groove in the panhole, sothat the sample pan can be picked up by thesample hang-down wire.

Always use brass tweezers to handle the samplepans.

Manually loading the sample pan onto the hang-down wire may damage the balance mechanism.

Figure 3.1Sample PanReady to Load

NOTE:

t CAUTION:


Thermocouple

SampleHook

FurnaceHousing

SamplePan

SamplePanHolder

SamplePlatform

Running Experiments


2. Press the LOAD key. The TGA will auto-matically load the sample pan onto thebalance.

3. Position the thermocouple at the edge of thesample pan, rather than in the middle, forbest results (Figure 3.2).

The position of the thermocouple should be thesame as it was during temperature calibration.

Figure 3.2Adjusting theThermocouple

NOTE:

Thermocouple

Sample Hook

Sample Pan

Furnace

Thermocoupleshould be about2 mm frompan surface.


4. Press the FURNACE key to close thefurnace by moving it up around the sample(Figure 3.3).

Figure 3.3Furnace inClosed Position


Running Experiments


Setting Up anExperiment

Once you have prepared the sample, the nextstep in your experiment is to enter the neededinformation in the TA controller. All of thecontroller functions described in this section areaccessed through the Instrument Control. Referto the online help and documentation to learnhow to perform the following steps.

1. Select the Instrument.

2. Select the Instrument Mode.

3. Enter Sample Information.

4. Enter Instrument Information.

5. Create and Select Thermal Methods.

The first time you use your TGA you will needto create at least one thermal method to controlexperiments. Each method is made of severalsegments, or individual instructions (e.g.,Equilibrate, Ramp), that control the state of theinstrument.


Setting UpAccessories

If your experiment requires external accessories,ensure that they are turned on, and make anynecessary adjustments before you start yourexperiment. Make sure that the system canachieve the conditions of all segments in themethod.

This section describes how to use the followingaccessories with the TGA 2950:

· Air cool option· Purge gas· TA Instruments Gas Switching Accessory· Evolved Gas Analysis (EGA) Furnace

(see also Appendix D).

For the TGA HiResTM Option, see Appendix B,and for the TGA Autosampler, see Appendix C.

The TGA can also be used with other acces-sories, such as vacuum, FTIR, gas chromato-graphs, mass spectrometers, and evolved gasanalyzers. Consult the appropriate local instru-ment manufacturer for further information.


Running Experiments


Using theAir Cool Option

You can program the system to air-cool thefurnace automatically at the end of the experi-ment by selecting the air cool method-endcondition as one of your instrument parameters(see the online help and documentation forfurther information.). After the air cool isactivated, it will continue to run for the desiredtime.

Before you start an experiment that uses the aircool option, ensure that the supply valve fromthe air source is open and that the pressure isregulated to between 25 and 120 psig. Nitrogencan also be used as a cooling gas.

If you are using the EGA furnace, Air Cool can beused with the furnace closed. However, if thetemperature is above 500°C, the EGA furnace willcool naturally until it is 500°C or less, then Air Coolwill begin.

Using a Purge GasYou can control the sample atmosphere duringTGA experiments by connecting a purge gas tothe system. Purge gas is distributed separatelyto two parts of the TGA: the furnace and thebalance chamber.

The balance purge maintains a positive pressurein the balance chamber to prevent decomposi-tion products from contaminating the sensitivebalance mechanism. The balance purge flowsfrom the balance chamber via two routes: downthe thermocouple tube and through an outlet inthe balance chamber to the right of the thermo-couple tube. It then exits across the sample panalong with the furnace purge.

NOTE:


The purge flow through the furnace is horizontalto the sample (see Figure 3.4), permitting rapidremoval of decomposition products from thesample environment.

Figure 3.4Furnace Purge

You can choose nitrogen, oxygen*, helium, air, orargon for your purge environment. Do not useany other gases in the TGA 2950. See the�Chemical Safety� section on page xv for furtherdetails.

Do not use hydrogen or any other explosivegas in the TGA 2950 furnace or the TGA 2950EGA furnace. *Oxygen may be used as a purgegas, but the furnace must be kept clean ofvolatile hydrocarbons to prevent combustion.

Do not use any liquid in the purge lines.

Purge gas can be obtained from a pressurizedcylinder or an in-house supply source. Gassupplied from an in-house source should bepassed through a sieve dryer to remove anytrace of moisture before it enters the TGA.

!WARNING

!WARNING


Running Experiments


It is important to maintain the proper ratio offlow rates between the balance chamber and thefurnace housing. Having the separate balancechamber purge prevents decomposition gasesfrom entering the balance chamber. The recom-mended setting for the purge rate is 100 mL perminute or less. When you use the standard TGA2950 furnace, the flow distribution should be 40percent to the balance chamber and 60 percent tothe furnace. When you use the TGA 2950 EGAfurnace, the flow distribution should be 10percent to the balance chamber and 90 percent tothe furnace.

To maintain this flow distribution, you will needto connect a flowmeter to each of the purgefittings on the back of the TGA instrument. Setthe purge gas flow rates by adjusting thesemeters. The PURGE port goes to the TGAfurnace, and the BALANCE PURGE goes to thebalance chamber.

Before you start the purge gas, make sure thatthe desired gas is connected to the purge ports,that all lines are clear, and that your supply ofpurge gas is sufficient for the experiment.

Always maintain constant purge flow rates anddistribution throughout your experiment;changing the purge during an experiment canaffect the data.


Using the GasSwitching Accessory

You can use the Gas Switching Accessory toturn the purge gas on and off or to switchbetween two different purge gases during a TGAexperiment. Before starting and experiment thatuses the Gas Switching Accessory, make sure itspower switch is on, and make sure the necessarygas sources are properly connected.

The Gas Switching Accessory can be controlledby the Gas segment in the method (see the onlinehelp and documentation for further information).

Connect the Gas Switching Accessory to thepurge port only, when switching between gasesduring an experiment. Attach the inert gas toGAS 1 and the other gas to GAS 2.

Consult your Gas Switching Accessoryoperator�s manual for further instructions.


Running Experiments


Starting anExperiment

Before you start the experiment, ensure that theTGA 2950 is online with the controller and youhave entered all necessary experimental param-eters.

Once the experiment is started, operations arebest performed at the controller keyboard. TheTGA 2950 is very sensitive to motion and mightpick up the vibration caused by pressing a key onthe instrument keypad.

Start the experiment by pressing the START keyon the instrument keypad, or selecting start onthe TGA Instrument Control program (see theonline help and documentation for furtherinformation). When you press the START key,the system automatically loads the sample panand closes the furnace if necessary, and thenruns the loaded method to completion.

Forced StartIf you wish to start collecting data duringinstrument setup, you can use the forced startfeature. This is most useful for samples thatloose a significant amount of weight during theset-up period (i.e., samples with volatile sol-vents). When a forced start is initiated, thecurrent sample weight is stored as the initialweight, data collection is started immediately,and the instrument status changes from �Set Up�to �Started.� The methods begin when thenormal set-up procedures are completed.

To begin a forced start, press START on theinstrument keypad while the status line displays�Set Up.�

NOTE:



Stoppingan Experiment

If for some reason you need to discontinue theexperiment, you can stop it at any point bypressing either the STOP key on the TGA 2950keypad or Stop on the on the TGA InstrumentControl program (see the online help and docu-mentation for further information). Anotherfunction that stops the experiment is Reject.However, the Reject function discards all of thedata from the experiment; the Stop functionsaves any data collected up to the point at whichthe experiment was stopped.

The Heat Exchanger will continue to run as long asthe Air Cool option is activated or until the indi-cated temperature is below 50oC.

The REJECT function discards all experiment data.

Unloadingthe Sample

If you select the method-end option that enablesthe furnace to open and unload at the end of theexperiment, the TGA will automatically unloadthe sample at the end of the run. (See the onlinehelp and documentation for further information.)If you need to unload the sample manually, waituntil the run and all method-end operations arecomplete, and then press the UNLOAD key.The sample pan may not line up with the sampleplatform groove at method end.

NOTE:

t CAUTION:

Running Experiments


Use in an Oxygen-Free Atmosphere

If you choose to perform TGA experiments inan oxygen-free atmosphere, a few extra precau-tions to the purge gas system and instrumentsetup are necessary to ensure an oxygen-freeenvironment.

Purge Gas System

When performing TGA experiments in anoxygen-free atmosphere, take the followingprecautions:

� Use a high purity, inert gas of grade 5 orbetter. It may be necessary to use anoxygen trap in-line, depending on the puritygrade.

� Choose a 2-stage regulator of diaphragmconstruction for high purity applications.

� Use copper or stainless steel tubing from thegas regulator, to the flowmeters, and to theTGA purge inlet ports.

� Allow the TGA to prepurge (under closedconditions) for at least 30 minutes after firstturning on your purge gas.

� Increase the standard purge rate during thistime to 100 mL/minute flow into thebalance chamber and 100 mL/minute intothe furnace.


Instrument Set-Up

When performing TGA experiments in anoxygen-free atmosphere, take the followingsteps to set up your instrument:

� Readjust your flowmeter(s) for standardoperating flow rates: (a) for the standardfurnace, 40 mL/minute flow into balancechamber and 60 mL/minute into the furnaceor (b) for the EGA furnace, 10 mL/mintueinto the balance chamber and 90 mL/minuteinto the furnace.

� Tare sample pan (as needed).

� Load sample and close system

� Purge 20 minutes, if possible, beforestarting a run.

� When run is complete, allow the furnace tocool in the closed position until the temp-erature is less than 350°C. This can beautomatically programmed into yourmethod; after last segment add anequilibrate at 350°C step. Another option isto change method end conditions to leavefurnace closed at method end.

� When using air or oxygen during anexperiment, introduce new gas throughfurnace purge port only and switch back tonitrogen before cooling down.

When the TGA is idle, leave the system closed andcontinue purging with nitrogen.

Use in an Oxygen-Free Atmosphere

NOTE:

Running Experiments



CHAPTER 4: Technical Reference

Description of the TGA 2950 ..................... 4-3

Components ......................................... 4-5

Balance .......................................... 4-6Sample Loading Assembly ............ 4-8Furnace .......................................... 4-9

TGA Standard Furnace ........... 4-9EGA Furnace ........................ 4-11

Cabinet ......................................... 4-13Heat Exchanger ............................ 4-15

Theory of Operation ................................. 4-16

Status Codes ............................................. 4-17

Technical Reference



Descriptionof the TGA 2950

The TGA 2950 operates on a null balanceprinciple. Physically attached to a taut-bandmeter movement, the balance arm is maintainedin a horizontal reference position by an opticallyactuated servo loop. When the balance is in anull position, a flag located on top of the balancearm blocks an equal amount of light to each ofthe photodiodes (the light is supplied by aconstant current infrared LED). As sampleweight is lost or gained, the beam becomesunbalanced, causing an unequal amount of lightto strike the photodiodes. The unbalancedsignal, called the error signal, is acted upon bythe control circuitry and reduced to zero, ornulled. This is accomplished by an increase ordecrease in the current to the meter movement,causing it to rotate back to its original position(null position). The change in current necessaryto accomplish this task is directly proportional tothe change in mass of the sample. This current isconverted to the weight signal.

The TGA 2950 has two weight ranges: 1 gm and100 mg. Both ranges are continuous over theirweight loss operating range, which means thatthe entire weight loss range can be viewedwithout any loss of information. The weight lossoperating ranges are:

• 1 gm to 0 µg for the 1 gm range• 100 mg to 0.0 µg for the 100 mg range.

Description of the TGA 2950

Technical Reference


Negative weight (tare imbalance) is limited to150 mg in the 1 gm range, and to 15 mg in the100 mg range. Range control is automatic.

During normal operation of the TGA, the samplemay evolve gases. To prevent back diffusion ofthese liberated gases to the balance chamber, thebalance chamber is purged with an inert gas(standard furnace = 40 mL/min, EGA furnace =10 mL/min). An inert gas must be used toprevent contamination or corrosion of thebalance.

Heating rate and sample temperature are mea-sured by the thermocouple located above thesample.


Components

The TGA 2950 has five major components,illustrated in Figure 4.1: the balance, the sampleloading assembly, the furnace, the cabinet, andthe heat exchanger.

Figure 4.1TGA 2950 Components

The balance, the most important part of theTGA system, provides precise measurement ofthe sample weight. The sample loading assem-bly automatically loads and unloads samplesfrom the TGA balance. The furnace controls thesample atmosphere and temperature. Thecabinet contains the system electronics andmechanics. The heat exchanger dissipates heatfrom the furnace.


Technical Reference


Balance

The TGA balance assembly (Figure 4.2) consistsof the balance meter movement, the balancearm, the balance arm sensor, the hang-downwire assemblies, the sample pan, and the tarepan.

Figure 4.2TGA Balance Assembly

The balance meter movement is a taut-bandmeter movement to which the balance arm isattached.

The balance arm is a rhombic piece of alumi-num attached to the meter movement. It is in anull balance system. A hang-down loop isattached to each end to hold the hang-downwires.

Balance ArmSensor

Hang-Down WireAssembly

Sample Pan

Balance Arm

Balance MeterMoverment

Tare Pan


The balance arm sensor is a printed circuitboard assembly that detects the null position ofthe meter movement. The balance beam sensoris mounted above the balance arm. It is used inconjunction with the analog circuitry to maintaina null position.

The TGA has two hang-down wire assemblies:one for the tare pan and one for the sample pan.Each assembly consists of a hang-down wire andloop. The hang-down wire has hooks at each endand connects the pan to the loop. The loop haseyelets at each end; it is used to connect thehang-down wire to the balance arm. The longerhang-down wire (4 inches) is for the sample pan.

Sample pans are available in platinum in 50,and 100 µL sizes, alumina ceramic in 100, 250,and 500 µL sizes, and aluminum in 100 µL. Allpans are 0.4 inches in diameter.

The tare pan holds the counter-balance weightthat mechanically subtracts out the weight of thesample pan and hang-down wire.


Technical Reference


Sample Loading Assembly

The sample loading assembly (Figure 4.3) is aplatform that pivots the sample pan to thefurnace area, where the pan engages the hang-down wire from the balance assembly. It alsopivots the platform away from the furnace areafor easy sample loading and unloading.

Figure 4.3Sample Loading Assembly


FurnaceTwo types of furnaces may be used with theTGA 2950 instrument, the standard TGAfurnace, or the Evolved Gas Analysis (EGA)furnace. The EGA Furnace (see Appendix D) isan optional accessory that allows you to connecta spectrometer to the instrument so that thegases evolved by sample decomposition can beanalyzed.

TGA Standard Furnace

The TGA standard furnace (Figure 4.4) consistsof a furnace housing, a heater, and a furnacebase that moves these parts up (to closed posi-tion) and down (to open position).

Figure 4.4TGA Furnace


Technical Reference


The stainless steel furnace housing has a purgeopening on either side to allow gas flow orevacuation. Purge gas enters through a purgefitting on the right side of the furnace housing. Itthen passes through an opening in the heater,flows around the sample pan, and exits throughopenings on the opposite side of the furnacehousing and heater. From here, the evolved gascan be sent through appropriate connections toan external analyzer, if desired.

The heater is a resistance-wound unit of lowthermal mass alumina material that can beheated and cooled rapidly. Controlled heatingrates of up to 100°C per minute can be obtained,to an upper limit of 1000°C.

Cooling air enters through the holes in the baseof the furnace assembly at the completion of testruns, if desired.

A Platinel II* thermocouple extends throughthe bottom of the balance chamber, down alongthe hang-down wire, and is positioned just abovethe sample pan, where it monitors the sampleenvironment temperature.

The furnace base moves the furnace assemblyup around the sample pan to the closed position,or down away from the sample pan to the openposition.


EGA Furnace

The (Evolved Gas Analysis) EGA furnaceconsists of a quartz glass sample tube sur-rounded by an electric resistance heater, both ofwhich are contained within a water-cooledfurnace housing. The housing is mounted to afurnace base that raises and lowers the furnacefor sample loading and unloading. See Figure 4.5.

Figure 4.5EGA Furnace

The sample tube has a purge gas inlet thatpasses through the right side of the furnacehousing. A fitting on the left side of the housingallows connection of a transfer line to carryexhaust gas to a spectrometer such as a FTIR.Because the heater is external to the sampletube, evolved gases from sample decomposition


Technical Reference


within the sample tube do not come in contactwith the resistance elements or the furnaceceramic refractory.

Cooling air enters through the furnace base andpasses upward between the outside of thesample tube and the inside of the furnace,completely separating the cooling air from thesample and the sample zone.

The furnace is a resistance heater wound onalumina ceramic, which allows sample zonetemperatures as high as 1000°C with heatingrates up to 50°C/min.

The thermocouple and furnace base are thesame as those described above for the standardTGA furnace.

*Platinel II is a registered trademark ofEngelhard Industries.


Cabinet

The TGA cabinet (Figure 4.6) consists of thecabinet housing, the instrument display andkeypad, the electronics compartment, the purgeand cooling gas fittings, and the rear panel.

Figure 4.6TGA Cabinet Components

The TGA cabinet housing consists of a basecasting, a rear cover, and a sample preparationtray. The base casting is one-piece casting ofheavy-weight aluminum, designed to provide astable platform for the TGA instrument parts.The rear cover is injection molded using aheavy-gauge thermoplastic material, designedfor easy cleaning. The removable samplepreparation tray is located on the right side ofthe instrument. The tray is designed to keepliquids from spilling into the instrument.


ElectronicsCompartment

Cooling GasFitting

Rear Panel

Instrument Displayand Keypad

Technical Reference


The instrument display and keypad aredescribed in Chapter 1.

The electronics compartment contains theelectronics that control the instrument functions.

Two purge fittings are located on the left sideof the instrument back, one for the balancechamber and one for the furnace housing.

The cooling gas fitting is located on the rightside of the instrument back and is for furnacecool-down air.

The rear panel (Figure 4.7) has the signal andpower connections for the instrument, the fuses,the ready light, the address switches, and theReset button.

Figure 4.7Rear Panel


Heat Exchanger

The heat exchanger (Figure 4.8) consists of afan, a radiator, a water reservoir, a pump, atemperature switch, and a flow switch.

The fan blows cool air through the radiator.

The radiator exchanges heat between the waterand air.

The water reservoir holds additional water thatmay be required by the system.

The pump pushes the water through the system.

The temperature switch detects over-tempera-ture conditions, which could be caused byfailure of the fan.

The flow switch detects lack of flow, whichcould be caused by failure of the pump or a leakin the system.

Figure 4.8Heat Exchanger


Water ReservoirBottle Temperature

SwitchRadiator

FlowSwitch

FanPump

Technical Reference


Theory of OperationThermogravimetric analysis (TGA) is a thermalanalysis technique for measuring the amount andrate of change in sample mass as a function oftemperature and time. It is used to characterizeany material that exhibits weight loss or phasechanges as a result of decomposition, dehydra-tion, and oxidation. Two modes are commonlyused for investigating thermal stability behaviorin controlled atmospheres: (1) dynamic, inwhich the temperature is increased at a linearrate, and (2) isothermal, in which the tempera-ture is kept constant.


Status Codes

Status CodesStatus codes are character strings that arecontinuously displayed at the top left of theTGA instrument display. These codes tell youwhat segment in the method is currently beingperformed by the instrument.

Table 4.1Status Codes

Code Meaning

Air Cool The furnace air cool linehas been opened to coolthe furnace.

Calib The TGA is in calibrationmode.

Closing The furnace assembly isclosing.

Cold The instrument heatercannot supply heat fastenough to keep up withthe thermal program. Thismay be caused by a largeballistic jump in theprogram, a faulty heater,or a faulty control thermo-couple signal.

Complete The thermal method hasfinished.

(table continued)

Technical Reference



Code Meaning

Cooling The heater is cooling, asspecified by a Rampsegment.

Ending The method is completeand the EGA furnace iscooling until it can AirCool or open and unload.

Equilb The temperature is beingequilibrated to the desiredset point.

Err n An error has occurred.The instrument displaywill give the error codenumber (n, a two-or-three-digit code); thecontroller screen will alsoshow the complete errormessage.

Heating The heater temperature isincreasing, as specified bya Ramp segment.

Holding Thermal experimentconditions are holding;the program is suspended.Choose Start to continuethe run.

(table continued)


Status Codes


Code Meaning

Hot The temperature isbeyond the set point, andthe instrument cannotremove heat fast enoughto follow the thermalprogram. This is usuallycaused by a large ballisticjump to a lower tempera-ture.

Initial The temperature is beingequilibrated to the desiredset point. When thetemperature has reachedequilibrium, the statuswill change to Ready.

Iso The thermal program isholding the current tem-perature isothermally.

Jumping The heater is jumpingballistically to the setpoint temperature.

Load The TGA is loading asample pan onto thebalance.

No Power No power is being appliedto the heater. Check theheater switch and fuse.

(table continued)

Technical Reference



Code Meaning

Opening The furnace assembly isopening.

Ready The system has equili-brated at the initialtemperature and is readyto begin the next segment.Choose Start to continuethe method.

Reject The experiment has beenterminated and the dataerased.

Repeat The method is executing arepeat loop that does notinvolve temperaturecontrol segments.

Set Up The system is loading thesample, closing thefurnace, and letting theweight stabilize beforebeginning the first seg-ment.

Stand by The method and method-end operations are com-plete.

(table continued)


Status Codes


Code Meaning

Started The TGA is still settingup to start the experiment(see Set Up above), butthe initial weight has beenmeasured and data collec-tion has begun. Thethermal method will startwhen the normal setupprocess has been com-pleted.

Tare The TGA is measuringthe weight differencebetween an empty samplepan and the tare pan. Themeasured weight is usedas an offset so that thedisplayed weight valueindicates the weight of thesample only.

Temp °C The heater is in stand-bymode, and the experimenthas been terminated.

Temp* Temperature calibration isin effect. The heater is instand-by mode, and theexperiment has beenterminated.

Unload The TGA is unloading asample from the balance.

Weight # The weight reading is notstable.

Technical Reference



CHAPTER 5: Maintenance andDiagnostics

Overview ..................................................... 5-3

Routine Maintenance .................................. 5-4

Inspection ............................................. 5-4

Cleaning the Instrument ....................... 5-4

Cleaning the Furnace Housing ............. 5-5

TGA Standard Furnace Only ......... 5-5

Heat Exchanger .................................... 5-6

Maintaining HeatExchanger Coolant ........................ 5-6Draining and Refillingthe Water Reservoir ....................... 5-6

Replacing the Thermocouple ...................... 5-9

Removing andReinstalling the Furnace ........................... 5-11

Furnace Removal ............................... 5-11

Furnace Replacement ......................... 5-14

Diagnosing Power Problems ..................... 5-16

Fuses ................................................... 5-16

Power Failures .................................... 5-18


Maintenance and Diagnostics

5–2

TGA Test Functions ................................. 5-19

The Confidence Test .......................... 5-19

Replacement Parts .................................... 5-21


OverviewThe procedures described in this section are thecustomer’s responsibility. Any further mainte-nance should be performed by a representativeof TA Instruments or other qualified servicepersonnel.

Because of the high voltages in this instru-ment, untrained personnel must not at-tempt to test or repair any electricalcircuits.

Overview

!WARNING



5–4

RoutineMaintenance

Inspection

Examine the instrument periodically to keep itfree of dust, debris, and moisture. Keep thefurnace area clean. Any sample spillage ofresidue should be removed before the nextexperiment.

Cleaningthe Instrument

You can clean the TGA instrument keypad asoften as you like. The keypad is covered with asilk-screen Mylar* overlay that is reasonablywater resistant but not waterproof or resistant tostrong solvents or abrasives.

A household liquid glass cleaner and papertowel are best for cleaning the instrumentkeypad. Wet the towel, not the keypad, with theglass cleaner, and then wipe off the keypad anddisplay.


Cleaning theFurnace Housing

Do not touch the EGA furnace sample tubewith your bare fingers. Skin oils may causedevitrification of the quartz glass, resultingin severely reduced sample tube life. Donot insert instruments inside the sampletube to scrape or chip contaminants fromthe sample tube as breakage may result.

TGA StandardFurnace Only

To ensure long furnace life, we recommend thatyou clean the furnace housing at least once amonth to remove condensation materials. Followsteps 1-6 to remove furnace housing (page 5-8and 5-9). Disconnect the purge line and invertthe furnace housing over paper towels. Clean theinside with a solvent and cotton squabs. Be sureto dry the housing and purge ports with air toremove any solvent traces before replacing thefurnace housing. Follow the instructions on page5-10 and 5-11 for replacing the standard furnacehousing. After replacing the furnace, heat theTGA to 900°C to remove any remaining solvent.

If you are routinely evaluating materials in theTGA that lose a large amount of volatilehydrocarbons (e.g., lubricating oils), you needto clean the standard furnace more frequentlyto prevent dangerous buildup of debris in thefurnace. This is particularly important if youare using oxygen as a purge gas.

Routine Maintenance

!WARNING

!WARNING



5–6

Heat ExchangerThe heat exchanger does not require any mainte-nance other than to maintain the level andquality of the liquid coolant. If the level dropstoo low, or the coolant becomes contaminated,this could result in problems with your instru-ment.

Do not put any liquid other than distilledwater and TA Conditioner in the heatexchanger reservoir.

Maintaining HeatExchanger Coolant

You should check the level and condition of theheat exchanger coolant periodically. We recom-mend routine checks every three to six months,depending on use of the instrument.

Add distilled water to the reservoir, if necessary,to keep the reservoir at least 2/3 full. If algaegrowth is visible, drain the reservoir bottle, refillit with distilled water, and add TA InstrumentsTGA Conditioner, as described in the nextsection.

Draining and Refillingthe Water Reservoir

Drain and refill the heat exchanger waterreservoir as follows:

1. Turn off the POWER switch and disconnectthe heat exchanger cable and water linesfrom the instrument cabinet (see Chapter 2for instructions).

!WARNING


2. Unscrew and remove the water reservoircap.

3. Drain the coolant and flush out the systemas follows:

a. Lift the heat exchanger and dump outthe contents of the water reservoirbottle.

b. Fill the bottle to 2/3 full with distilledwater only and replace the cap.

c. Reconnect the heat exchanger cable andwater lines to the instrument cabinet.

d. Turn on the POWER switch.

e. Turn on the pump by activating AirCool and allow the water to circulate forseveral minutes.

f. Turn off the pump by deactivating AirCool, and check the clarity of the waterin the reservoir bottle.

g. If the water clarity is still unacceptable,disconnect the heat exchanger cable andwater lines from the instrument cabinet,and repeat steps a through f.

h. Continue repeating this procedure untilyou are satisfied with the clarity of thewater in the bottle after it has circulated.

4. Dispose of the water and fill the bottlewith TGA Conditioner (PN 952377.901)and fresh distilled water as directed inChapter 2.

Routine Maintenance



5–8

5. Turn on the pump again by activating AirCool, and circulate the water until the airbubbles disappear from the water lines.(You may see “Err 119” on the instrumentdisplay until all the air has been removed.)

6. Replace and tighten the water reservoir cap.


Replacing theThermocouple

1. Unload the sample pan and open the fur-nace.

2. Using the ball driver supplied in your TGAaccessory kit, loosen and remove the sixscrews securing the balance chamberfaceplate to the instrument.

3. Take off the faceplate.

4. Push the thermocouple up from the bottom,to feed it back into the balance chamber(Figure 5.1).

Figure 5.1Removing theThermocouple

5. Unplug the thermocouple from its connectorand remove the thermocouple from thebalance chamber.

Replacing the Thermocouple



5–10

6. Plug the new TGA thermocouple into theconnector.

7. Thread the new thermocouple down throughthe hole next to the thermocouple tube.

8. Thread the end of the thermocouple justthrough the ceramic disk at the end of thethermocouple tube.

9. Load a sample pan to make sure that the endof the thermocouple does not touch it(Figure 5.2).

Figure 5.2Checking Positionof Thermocouple

10. Make sure that the hang-down wire does nottouch the top of the thermocouple inside thebalance chamber.

11. Replace the balance chamber faceplate andscrews.


Removing andReinstallingthe Furnace

To remove or reinstall the furnace, you will haveto remove the furnace arm from its connectioninside the slot on the front of the instrumentcabinet.

Furnace Removal

To remove the furnace use the following proce-dure:

1. Press the FURNACE key to open thefurnace completely.

2. With the ball driver supplied in your TGAAccessory Kit, loosen the two screws oneach side of the furnace arm connection,within the slot on the front of the instrumentcabinet.

In Figure 5.3 on the next page, the furnace arm/base has been removed to better show thelocation of the screws and alignment of thecleats.

To obtain access to the upper left screw and cleat,loosen the three hold-down screws on the furnacebase. Rotate the furnace housing gently counter-clockwise to move the coolant connections awayfrom the front of the cabinet slot.

Removing and Reinstalling the Furnace

NOTE:



5–12

Figure 5.3Aligning Cleats forRemoval ofFurnace Arm/Base

3. Rotate each screw to turn the D-shaped cleatso that the flat edge of the cleat is alignedvertically and parallel with the groove in thefurnace arm (Figure 5.3).

4. While holding the furnace base in one hand,press the FURNACE key to raise thefurnace about 1/4 of the way up, and pressSTOP.

5. Unplug and remove the furnace arm/basefrom the instrument cabinet (Figure 5.4).

6. Loosen the hold-down screws, if necessary,and remove the furnace housing from thefurnace base, being careful not to disturb thecoolant connections. Lay the furnacehousing on the front ledge of the cabinet.


Figure 5.4Removing Furnaceand Housingfrom Cabinet

7. Unplug the Air Cool line from the bottom ofthe furnace arm/base (Figure 5.4). Thefurnace arm/base is now completely free ofthe instrument.

When you remove the Air Cool line, do not let itslip back into the instrument cabinet.


NOTE:



5–14

Furnace Replacement

To replace or reinstall the furnace:

1. Plug the Air Cool line into the bottom of thefurnace arm/base.

2. Slip the furnace housing over the furnacearm/base and tighten the three hold-downscrews only enough to keep the housing andbase together while you reinstall them.

Before trying to reconnect the furnace arm to theplug inside the cabinet slot, it may help to backeach of the four screws inside the slot out onemore complete turn, again aligning the flat edge ofeach cleat so that it is parallel with the groove onthe furnace arm. (Loosening the screws one moreturn each will give you a bit more room to maneu-ver the arm into its connection.) In order to loosenthe screws, press the FURNACE key to lower theconnection so that you can reach it through thewide part of the slot. When you have aligned thecleats, press the FURNACE key again to raise thefurnace about 1/4 of the way up.

3. Plug in the furnace arm.

4. Continuing to hold the furnace base, pressthe FURNACE key to lower the furnacecompletely.

5. Using the ball driver, tighten the two screwson either side of the furnace arm connection,making sure that the curved edges of all fourcleats engage the groove on the furnace arm.

NOTE:


To obtain access to the upper left screw and cleat,rotate the furnace housing gently counterclock-wise. This will move the purge and coolant connec-tions away from the front of the cabinet slot.

7. Rotate the furnace housing clockwise until itis aligned correctly, and tighten the threehold-down screws completely.

NOTE:




5–16

DiagnosingPower Problems

Fuses

The TGA contains internal fuses that are notuser serviceable. If any of the internal fusesblows, a hazard may exist. Call your TA Instru-ments service representative.

The only fuses that you should service yourselfare the external fuses, located on the TGA’s rearpanel. Both are housed in safety-approved fusecarriers, labeled F1 and F2 (Figure 5.5).

Always unplug the instrument before youexamine or replace the fuses.

Figure 5.5Fuse Locations

!WARNING

Fuse 1 Fuse 2


Fuse 1 is in the circuit between the main electri-cal input and the POWER switch. All power forinternal operations and instrument functions,except heater power, passes through this fuse. Ifthis fuse blows, you will get no response fromthe instrument when you attempt to turn it on.

Fuse 2 protects the heater coils in the furnace.Because fuse 2 does not power the internallogic, you may not know that this fuse is blownuntil you try to heat a sample; the TGA passesthe confidence test with fuse 2 open.

Fuse 2 is always checked at the beginning of amethod. Power supplied by this circuit isswitched by a computer-controlled relay as wellas by the HEATER switch located on theinstrument’s front panel. When both devices areactive, the light in the HEATER switch willglow.

Diagnosing Power Problems



5–18

Power Failures

A power failure caused by a temporary drop inline voltage results in one of two responses bythe TGA instrument:

If the drop is fairly large and of long duration(20 milliseconds or more), the system will resetand go into its power-up sequence when powerresumes.

If the drop is small or of short duration, thesystem may halt, and you may see “Err F02” onthe display. This message means that the systemhas detected a power failure and has shut down.The instrument will not restart until it is reset.To reset, press the Reset button on the TGA’sback panel.

If “Err F02” appears at start-up and remainseven after you have tried to restart the instru-ment, the detection circuitry itself is probably atfault. Do not try to repair it yourself; call yourTA Instruments service representative.

The TGA is designed for a nominal line voltageof 115 volts AC (+ 10%), 50 or 60 Hz. It shouldnot be operated outside this range. Low linevoltage may result in poor instrument operation;high line voltage may damage the instrument.


TGA 2950Test Functions

The TGA 2950 has three levels of test anddiagnostic functions:

• The confidence test that is run every timethe instrument is started.

• Cycling test functions that continuously testspecific.

• A manufacturing verifier test mode thatcoordinates and logs the results of asequence of confidence test and drift runs.

These test functions are always present in theinstrument. They are designed to aid manufac-turing and service in checking and repairing theinstrument.

The Confidence Test

The TGA confidence test is run each time theinstrument is turned on or reset. The confidencetest checks most of the computer and interfacecomponents in the system.

When the confidence test is running, the numberof the test currently being performed is shownon the display. The test number appears as atwo-digit hex number on the lower right of thedisplay. This number is changed as each newtest is started. Most of the tests are very brief, sotheir test numbers may not be apparent.

A standard TGA system takes about 12 secondsto run the confidence test. The longest tests arethe RAM tests, which take about 6 seconds.

TGA 2950 Test Functions



5–20

After the tests are completed, a sign-on messageis displayed for 3 seconds. The system thenstarts running, and the Ready light on the backof the instrument glows.

If an error is detected, an error message is postedon the bottom line of the display. Nonfatal errorsare displayed for 3 seconds, and then the confi-dence test continues. A fatal error occurs when acircuit essential to the operation of the instru-ment has failed the confidence test; the instru-ment cannot reliably perform any furtherfunctions. The system stops when the fatal erroris posted, and the Ready light remains off.

Table 5.1 summarizes the primary confidencetests for the TGA. If any errors occur during theconfidence test, call your TA Instrumentsservice representative.

Table 5.1TGA Confidence Test

Test Number Area Being Tested

— CPU logic30 CMOS RAM4n Program memory5n CPU board I/O

functions6n DRAM data storage

memory70 GPIB test82 Keypad testAn Analog board testsBn Drive board testsD0 Saved memory

checksum


Replacement Parts

ReplacementParts

Replacement parts for the TGA 2950 are avail-able from TA Instruments and are listed in Table5.2.

Table 5.2List of TGA2950 Parts

Part Number Description

952018.906 100 µL platinum samplepan kit

952018.907 100 µL ceramic samplepan kit

952040.901 Sample hang-down wire952040.902 Tare hang-down wire952011.906 Class M calibration

weight kit (100 mg and1 gm)

269931.001 Class M cal. wt. 100 mg269931.002 Class M cal wt. 1 gm952018.908 50 µL platinum sample

pan kit952323.902 100 µL aluminum sample

pan kit952018.909 250 µL ceramic sample

pan kit952018.910 500 µL ceramic sample

pan kit952384.901 TGA Temperature

Calibration kit952385.901 TGA nickel reference

material952013.901 Furnace assembly952014.901 Balance assembly952017.001 Tare tube

(table continued)



5–22

∆



952310.901 Motor drive PCB952060.901 Analog PCB952068.901 Sample thermocouple

assembly952080.901 Sample motor assembly952081.902 Furnace sensor952081.903 Furnace ∆ sensor952081.904 Sample position sensor952082.901 Furnace motor assembly952121.001 Work surface tray952183.901 Aluminum temperature

calibration standard900905.901 Calcium oxalate sample990806.901 Air purge valve assembly952324.001 TGA 2950 keypad

assembly990820.010 Instrument keypad990828.901 Power supply assembly990850.901 Central processor PCB990880.901 Communications PCB990870.901 Triac drive PCB259508.000 Brass tweezers259509.000 Spatula, curved, 165 mm

long265303.001 Instrument display265749.001 O-ring, bottom of furnace

housing200063.029 O-ring, bottom cap plate

of furnace269845.001 O-ring, furnace housing to

balance chamber269920.002 Balldriver, 0.050-inch269920.026 Balldriver, 7/64-inch

(table continued)


Replacement Parts



269930.001 Class C calibration weightkit (1 mg to 500 mg)

952160.901 TGA 2950 CoolingAccessory

952160.903 Heat exchanger fan/assembly

952162.901 Cooling Accessory tubing952166.901 Cooling Accessory water

reservoir bottle952172.901 Cooling Accessory pump

assembly952161.901 Flow switch assembly269932.001 Solid state relay952377.901 Conditioner Kit



5–24

TA INSTRUMENTS TGA 2950 A–1

Appendix A: Ordering Information

Email address: http://www.tainst.com; click on�Answerman� icon.

TA Instruments, Inc.109 Lukens DriveNew Castle, DE 19720Telephone: 1-302-427-4000 or 1-302-427-4040Fax: 1-302-427-4001

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Appendix A

TA INSTRUMENTS TGA 2950A–2

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TA INSTRUMENTS TGA 2950 B–1

Hi-ResTM Option

Appendix B:High ResolutionTM TGA Option

Overview .................................................... B-5

Option Installation ..................................... B-6

Using Hi-ResTM TGA ................................. B-7

Background ......................................... B-7

The TA Instruments Hi-ResTM

Technique ............................................ B-8

The Hi-ResTM Ramp Segment .................... B-9

Calcium Oxalate Example Scans ...... B-13

Advanced Hi-ResTM Techniques .............. B-18

What Can Be Resolved andWhat Cannot? .................................... B-18

Unresolved Transitions ..................... B-19

Selecting a Hi-ResTM Technique ....... B-22

Dynamic Rate Hi-ResTM Ramp.......... B-22

Constant Reaction RateHi-ResTM Ramp.................................. B-23

Weight Gain Experiments ................. B-26

Signature Analysis ............................ B-27

Appendix B

B–2 TA INSTRUMENTS TGA 2950

Sample Quantity and Orientation ...... B-28

Exposed Surface Area ................ B-28Bubble Formation ....................... B-29

Thermocouple Placement ........................ B-32

Data Analysis Effects .............................. B-32

Derivative Plots ....................................... B-33

Adjusting Heating Rate ........................... B-34

Adjusting Resolution Setting ................... B-37

Useful Resolutions Settings .............. B-39

Temperature Calibration .......................... B-41

Hi-ResTM Transition Temperatures ... B-42

Hi-ResTM Sensitivity Segment ................. B-43

Understanding Sensitivity Setting ..... B-44

Adjusting Sensitivity inDynamic Rate Mode ......................... B-45

Adjusting Sensitivity in ConstantReaction Rate Mode .......................... B-47

Abort Segment ......................................... B-51

Stepwise Isothermal Heating............. B-53


Hi-ResTM Option

Hi-ResTM TGA Examples......................... B-58

Mixture of Bicarbonates.................... B-58

Dynamic Rate Scans ................... B-59

Varying Resolution Setting ........ B-61

Varying Sensitivity Setting ......... B-62

Constant Reaction Rate Scans .... B-63

Stepwise Isothermal Scans ......... B-65

Monosodium Glutamate .................... B-68

Banana Taffy ..................................... B-69

Plastic Laboratory Tubing ................. B-71

References ............................................... B-75

Appendix B



Hi-ResTM Option

OverviewThis appendix describes how to use the HighResolution option for the TGA 2950 instrument.

Some of the benefits provided by the Hi-ResTM

option are:

· Improved Transition Resolution· Faster Survey Scans· Enhanced Signature Analysis Capability· Transition Temperatures Closer to

Isothermal Values· Increased Method Programming Versatility

The Hi-ResTM option provides three methodprogramming steps (segments) which are usedfor the high resolution TGA capability. Thenew method segments are:

· High Resolution Ramp· High Resolution Sensitivity· Abort Next Segment

With the addition of these segments, methodprogramming becomes more versatile andpowerful than ever before. The Hi-ResTM rampcan be used alone as a simple single-segmentmethod, or the method segments can be com-bined with more traditional segments, such asconstant heating rate ramps and timed isother-mal periods, for maximum programming flex-ibility.

What these segments do and how to use them tocontrol TGA experiments and improve transitionresolution is described in the following sections.For further details regarding creating methods,refer to the online help and documentation.

Appendix B


OptionInstallation

The Hi-ResTM TGA option is field installable byqualified service personnel (see separate instal-lation procedure included with the Hi-ResTM

option kit). The following items are required:

· Version 2.0 or higher TGA 2950 InstrumentSoftware (Included in Kit)

· Version 8.2 or higher controller operatingsystem

· Instrument �Software Option� circuit board(Included in Kit)

· Hi-ResTM TGA software option key(Included in Kit)

A TGA instrument with Hi-ResTM capabilityproperly installed can be identified by the �Hi-Res TGA Installed� message on the instrumentdisplay screen following the confidence test, andby the letters �HR� in the instrument identifica-tion string on the configuration screen of thecontroller (e.g., �TGA 2950 HR V2.0A�).


Hi-ResTM Option

Using Hi-ResTM TGA

Background

TGA is particularly useful for observing thethermal decomposition of compounds. Whenindividual thermal decompositions occur at wellseparated temperatures, quantitative informationabout sample composition can be obtained fromthe percent weight change at each transition.However, many TGA decomposition transitionsoverlap or appear drawn out in temperature dueto the time-dependent nature of the reactionstaking place. This overlap substantially reducesthe ability to obtain an accurate measurement ofweight change and reaction temperature.

It has long been known that using very slowheating rates will improve the separation ofsome overlapping transitions and, thus, increasethe resolution of the TGA scan. Anothertechnique to increase resolution is to increasefurnace temperature until the onset of decompo-sition and then hold temperature isothermallyuntil the decomposition is complete. Afterwhich, the temperature is raised again until thenext decomposition begins, and so on until thefinal temperature of interest is reached. A thirdtechnique to increase resolution is controllingthe furnace temperature in such a way as tomaintain a preselected constant reaction rate (%/minute). This results in slower or even negativeheating rates during a transition which gives thereaction more time to reach completion beforethe next transition is encountered.

Appendix B


The major drawback to these techniques is thatthey increase substantially the total time requiredfor a measurement, thereby reducing laboratoryproductivity. Moreover, increasing measurementtime often reduces the accuracy and reliability ofthe analysis. This is due to exposing the sampleto high temperatures for long periods of timewhich may cause slow time-dependent changessuch as oxidation and absorption, or exposure tochanging ambient conditions such as humidityand pressure.

The TA InstrumentsHi-ResTM Technique

The TA Instruments Hi-ResTM technique,dynamic rate TGA (DRTGA), differs fromprevious control techniques in that the heatingrate of the sample material is dynamically andcontinuously modified in response to changes inthe rate of decomposition of the sample so as tomaximize weight change resolution. Thistechnique allows the use of very high maximumheating rates during Hi-ResTM ramp segmentswhile avoiding transition temperature overshoot.Typical Hi-ResTM ramps often take the same orless time to complete than a comparable con-stant heating rate experiment run at a lowerheating rate, while providing improved resolu-tion.


Hi-ResTM Option

The Hi-ResTM

Ramp SegmentThe new Hi-ResTM ramp segment varies theheating/cooling rate of the furnace in response tochanges in the rate of decomposition of thesample so as to improve weight change resolu-tion. The new segment has the followingformat:

Ramp <rate>°C/min res <res_setting> to<temp>°C

where:

<rate> is the maximum ramp heating rate(0.01 to 200°C/minute)

<res_setting> is the resolution setting(-8.0 to +8.0)

<temp> is the ramp final temperature(-200 to 1000°C)

example:

Ramp 50.00°C/min res 4.0 to800.00°C

The Hi-ResTM ramp segment operates similarlyto the traditional constant heating rate rampsegment, except that the heating rate is varieddynamically during the ramp in response to thederivative of weight change (%/minute). Aspercent/minute increases, heating rate is de-creased. As percent/minute decreases, heatingrate is increased. The heating rate is constrainedto the range 0.001°C/minute (minimum) to the

Appendix B


maximum specified in the ramp segment. Theresolution setting is a unitless number used toselect the most useful band of percent/minutevalues for proportional heating rate control.

Higher resolution settings select lower percent/minute values, and generally result in increasedresolution and longer experiment times. Lowersettings have the opposite effect.

Resolution settings may be selected anywhere inthe range of -8.0 to +8.0. Positive settingsindicate that dynamic rate mode is to be usedduring the ramp. Negative settings indicate thatconstant reaction rate mode is to be used. Moredetails on using each mode is covered in theAdvanced Hi-ResTM Techniques section.

Positive resolution settings are the most univer-sally useful settings and the least likely to haveundesirable side effects. Although there are nohard and fast rules about which resolutionsetting to use for a given experiment, there aresome general guidelines which will be helpful.

It has already been stated that higher resolutionsettings usually provide better resolution resultsand lower settings the reverse. The closer thesetting is to zero the larger the derivative ofweight change (%/minute) must be for a reduc-tion in heating rate to occur. In fact, a resolutionsetting of exactly zero completely disables theapplication of the Hi-ResTM technique, resultingin a normal constant heating rate ramp at themaximum rate specified.

A resolution setting of +1.0 will produce a TGAscan at 50°C/minute that roughly approximatesthe resolution obtained by a constant heatingrate scan at 20°C/minute. In other words, you


Hi-ResTM Option

can zip through baseline sections of your scan ata higher heating rate while slowing down onlyfor transitions and still get the resolution of theslower heating rate scan. For scans whichcontain a large amount of baseline this can resultin very significant overall time savings with noloss of resolution. The same speed/resolutionrelationship applies to other heating rates aswell.

Higher resolution settings apply the Hi-ResTM

technique more aggressively by reacting tosmaller percent/minute values. Some generalrules-of-thumb for selecting resolution settingsare as follows:

1. If you are uncertain what the resolutionsetting and heating rate should be, then trysetting +3.0 and 50°C/minute. (Negativeresolution settings are covered in theAdvanced Hi-ResTM Techniques section.)

2. When trying to obtain better resolution,try progressively higher resolution settings,1.0 at a time, while leaving the heating ratefixed.

3. The most useful resolution settings are3.0 to 5.0 because they cover the mostcommonly encountered bands of percent/minute during typical decompositions. Ifyour decompositions tend to be explosivein nature, with large percent/minute peaks(greater than 50 %/minute), or if you wishto minimize experiment time, then usesettings less than 3.0. If your decompo-sitions are very gradual (less than 0.5 %/minute peaks), or if it is important to limitthe rate of decomposition, try settingsgreater than 5.0.

Appendix B


The most useful maximum heating rates are 10to 50°C/minute for positive resolution settings.However, other values are perfectly acceptablewhen required by the needs of the experiment.

Use lower heating rates when transitions arevery closely spaced in temperature, or if thesample material reacts very rapidly. A higherheating rate conventional ramp can be used toskip over baseline sections in order to shortenexperiment time. Generally speaking, you nolonger need to use very slow heating rates, lessthan 5°C/minute, because the dynamic rate Hi-ResTM technique automatically reduces heatingrate with the accompanying improvement inresolution.

There are no special method programmingconstraints on Hi-ResTM ramp segments. Theymay appear anywhere in a method that a normalramp could appear. The maximum ramp rate,resolution setting and final temperature of anexecuting Hi-ResTM ramp may be changed viathe Modify Segment feature on the controller.

Selecting the resolution setting is covered ingreater detail in the Advanced Hi-ResTM Tech-niques section.


Hi-ResTM Option

Calcium OxalateExample Scans

In this example, five TGA scans of calciumoxalate monohydrate (CaC2O4.H2O) were run innitrogen to compare the results usingconventional TGA and Hi-ResTM TGA. In allcases a single ramp or Hi-ResTM ramp segmentfrom ambient to 800°C was used for the method.

Figures B.1 and B.2 show the results of constantheating rate scans at 20°C/minute and 1°C/minute. Figures B.3, B.4 and B.5 show theresults of Hi-ResTM scans at 50°C/minute withresolution settings 3.0, 4.0 and 5.0 respectively.Figure B.6 shows a composite plot of thederivative of weight loss for each of the fivescans. The derivative smoothing window for allplots was set to 5°C.

Figure B.1

Appendix B


Figure B.2

Figure B.3


Hi-ResTM Option

Figure B.4

Figure B.5

Appendix B


Figure B.6

As can be seen in these examples, calciumoxalate has three well resolved transitionscorresponding to the loss of water (1st weightloss), carbon monoxide (2nd weight loss) andcarbon dioxide (3rd weight loss). Comparingthe 20°C/minute and the 1°C/minute scans(Figures B.1 and B.2), we see some improve-ment in resolution of the water loss (1st transi-tion), but little improvement in the other twotransitions.

Note that the transition temperatures in theslower scan are shifted to lower temperatures asexpected. The 20°C/minute scan took 39 minutesand the 1°C/minute scan took nearly 13 hours tocomplete.

(a) 1°C/min, Normal Ramp; (b) Res 5.0, 50°C/min; (c) Res 4.0, 50°C/min; (d) Res 3.0, 50°C/min; (e) 20°C/min, Normal Ramp


Hi-ResTM Option

Comparing the results of the two constantheating rate scans to the Hi-ResTM scans inFigures B.3, B.4 and B.5 we can see that theresolution 3.0 scan (Figure B.3) gave compa-rable results in two thirds the time of the 20°C/minute scan. The resolution 4.0 scan (FigureB.4) gives much improved resolution in aboutthe same time as the 20°C/minute scan, and theresolution 5.0 scan gives a dramatic improve-ment in only twice the time.

Figure B.6 shows a plot of the weight percentderivatives from each of the calcium oxalatescans overlaid on the same scale. Note howmuch taller and narrower the Hi-ResTM peaks arecompared to the conventional scans. We canalso clearly see that transition temperature isreduced by increasing the resolution setting.This effect is normal because with progressivelyhigher resolution settings, transitions are con-strained to lower decomposition rates which canonly be maintained at lower temperatures.

As can be seen in these simple examples, the Hi-ResTM ramp segment is easy to use and providessignificant resolution improvement, in the sametime frame as conventional constant heating rateTGA. The following section on Advanced Hi-ResTM Techniques contains valuable informationabout additional Hi-ResTM methods and adjust-ments which will help you obtain maximumperformance from this powerful analysis tool.

Appendix B


Advanced Hi-ResTM

TechniquesThis section discusses in greater detail how touse the Hi-ResTM features and gives specificadvice which may be helpful in setting up yourown experiments. As with any new analyticaltool, there is a learning period required duringwhich the user becomes familiar with theoptions and adjustments and gains knowledgeabout what can and cannot be expected from theanalysis.

What Can Be Resolvedand What Cannot?

�Will Hi-ResTM TGA improve the resolution ofmy transitions?� This is one of the first ques-tions asked by most people when they areintroduced to Hi-ResTM TGA. It would bewonderful, if the answer were always an un-qualified �yes�. Unfortunately, there are someapplications where resolution enhancement willbe minimal. Therefore, some criteria for select-ing likely candidates for resolution improvementis needed. Outlined below are some guidelineswhich can be employed whenever a new mate-rial is considered, or when a sample is tried andno resolution improvement is obtained. (It isworth noting that substantial productivity gainsare still possible, even if transition resolution isnot improved.)


Hi-ResTM Option

UnresolvableTransitions

The Hi-ResTM techniques provide useful tools toimprove transition resolution of many samplematerials, but some materials will show little orno resolution improvement. This is becausethese materials have transitions which cannot beseparated by time and temperature alone. Thetransitions are usually overlapped such that thecomponents of interest decompose at or verynear the same temperature and at approximatelythe same rate of reaction. For these materials itmay be necessary to employ other techniquesseparately or in conjunction with TGA, such asvacuum, switching purge gases, semi-pressur-ized sample containment, or evolved gas analy-sis.

There are some general rules-of-thumb whichwill help you decide if the material you areworking with will be a successful candidate forresolution improvement. First, do the compo-nents of the sample material decompose atsufficiently different temperatures? This canoften be determined by running a slow heatingrate survey scan of the material at 1°C/minuteand comparing the result to a 20°C/minute scanof the same material. Generally, the tempera-tures of transition will be lower in the slowerscan, but if there is no observable improvementin separation of the components, then it is likelythat Hi-ResTM TGA will not produce a signifi-cant separation of the components either.

Always consider purge gas to be a factor whenrunning survey scans or heating rate trials.Generally, nitrogen and air are the most com-mon choices for purge. In some cases, transi-tions which appear to be one large weight loss in

Appendix B


nitrogen will separate in air due to reaction withoxygen in the purge stream. Switching from airto nitrogen may help to eliminate oxidationwhich tends to counteract a simultaneous weightloss. A few materials are reactive with nitrogenand are better run in argon. Also, consider thepurity and moisture content of the purge gas.Adding or removing moisture may change therate or nature of the reactions taking place.When the nature of the sample is relativelyunknown, it is wise to repeat scans using bothair and nitrogen to see if any transitions appearor disappear, or shift in temperature or weightloss.

Another test is to determine if the componentsof the sample material have significantly differ-ent rates of decomposition. If so, it may bepossible to improve resolution using stepwiseisothermal heating, or using the constant reac-tion rate Hi-ResTM mode (negative resolutionsettings). To find out, run a conventionalconstant heating rate ramp up to the transitiontemperature and then hold isothermally. Afterthe decomposition is complete, plot the deriva-tive of weight percent versus time and look atthe shape of the curve. If both components ofthe transition are decomposing at about the samerate, then the curve will be a continuous expo-nential decay. However, if the curve appears tobe a rather rapid exponential decay, followed bya very gradual and somewhat constant rate ofweight change, then the components havedifferent reaction rates and improvement inseparation is probably achievable.


Hi-ResTM Option

A third technique, which may help to improveresolution, is to control the atmospheric pressuresurrounding the sample while in the furnace.This can be done by placing the sample in asemi-sealed container such as a hermetic DSCpan with a very small pin hole (0.1 mm diameteror less) or in a sample cup with a lid. When thesample starts to react, the evolved gas will builda slight vapor pressure inside the sample con-tainer. This pressure may reduce or stop one ormore of the overlapped reactions and, thereby,allow completion at a higher temperature. Tomake this test, simply try running the sampleusing a Hi-ResTM ramp with and without thesample containment to see if a difference inseparation can be observed. Generally, thetemperature of reaction will shift to a highertemperature, even if no improvement in separa-tion occurs. The pressure containment tech-nique is particularly helpful when using constantreaction rate Hi-res mode (negative resolutionsettings).

Appendix B


Selecting aHi-ResTM Technique

The Hi-ResTM TGA option consists of not one,but several techniques, which all have thecommon characteristic of controlling the thermalexperiment based on changes in the sampleweight. Both absolute weight change and therate of weight change can be utilized. Thesecapabilities add a whole new dimension to TGAexperiments.

Some general guidelines have already beenpresented in the previous sections on how to setsome of the parameters involved in using Hi-ResTM TGA. In the next section we considermore closely why one technique may give betterresults than another, and present additionalguidelines for selecting techniques and settingparameters.

Dynamic RateHi-ResTM Ramp

In dynamic rate Hi-ResTM mode, one or more Hi-ResTM ramp segments are used with positiveresolution settings. In this mode, the furnaceheating rate is varied between a fixed minimumand the maximum specified in the ramp seg-ment, but is never reduced to zero (isothermal).A mathematical function is used to relate therate of weight change (%/minute) to the sampleheating rate (°C/minute). Dependant variables tothis function are resolution setting, sensitivitysetting and maximum heating rate. Independentvariables are both short and long-term rates ofweight-change (%/minute), time and tempera-ture. The result is the ability to directly compute


Hi-ResTM Option

the appropriate heating rate for the currentweight change conditions.

Because the dynamic rate Hi-ResTM modereduces heating rate smoothly and only whennecessary, it is the fastest and most reliable ofthe various techniques. This mode gives goodresults with most temperature separable transi-tions. It is preferred for fast survey scans ofunknown materials over wide temperatureranges. If no other criteria exists to select a Hi-ResTM technique, then dynamic rate is thepreferred choice.

Constant ReactionRate Hi-ResTM Ramp

In constant reaction rate Hi-ResTM mode, one ormore Hi-ResTM ramp segments are used withnegative resolution settings. In this mode theheater control system varies the temperature ofthe furnace as required to maintain a constantpreselected rate of weight change (%/minute).Whenever the rate of weight change exceeds thepercent/minute threshold, the heating rate of thefurnace is reduced, even to the point of coolingif necessary. When percent/minute falls belowthe threshold the heating rate is increased up tothe maximum specified for the ramp segment.Transition resolution is improved becausesample heating is reduced or reversed duringtransitions allowing them to complete at theselected reaction rate before moving on to thenext transition. Figure B.10 on page B-49shows a good example of a material (sodiumbicarbonate) which was analyzed using aconstant reaction rate ramp at 10°C/minute withresolution setting -4.0.

Appendix B


When used with semi-pressurized samplecontainment, constant reaction rate modebecomes even more powerful. The vaporpressure which builds up inside the samplecontainer limits the rate of reaction of thesample. This allows the reaction to complete ata nearly constant rate and temperature. Thereaction progresses more uniformly throughoutthe sample because vapor pressure gradients inand around the sample material are substantiallyreduced. The onset of higher temperaturereactions is effectively suppressed until thecompletion of lower temperature reactions.

Constant reaction rate mode is preferred for anysample where it is important to limit or controlthe rate of reaction. These may include pyro-technics, self-heating reactions, auto-catalyzingreactions and gas diffusion reactions. Constantreaction rate mode is also a good choice when itis important to accurately determine the transi-tion temperature at a given reaction rate.

Another area where constant reaction rateheating can be helpful, is when the samplematerial exhibits a relatively large and some-what constant background weight change, ontowhich is superimposed a relatively small transi-tion. If the decomposition rate threshold ischosen to be close to the background percent/minute at the maximum heating rate, then theheating rate will only be changed significantlywhen the smaller transition occurs.

Derivative of weight change curves that areplotted versus temperature may appear cyclicand have negative peaks as well as positiveones. This effect is caused by the automaticapplication of cooling whenever the rate of


Hi-ResTM Option

weight change (%/minute) exceeds the specifiedset point. In many cases the appearance of thederivative curve can be improved by increasingthe derivative smoothing window in the dataanalysis program.

Constant reaction rate mode works best at lowerheating rates (1 to 10°C/minute), where signifi-cant reaction rate and transition temperatureovershoot can be avoided. Usually several scansof the same material are required to determinethe best reaction rate threshold to use. If thesample material is very reactive, or it is impor-tant not to overshoot the selected reaction rate,then even lower maximum heating rates may berequired.

This is particularly true for very small reactionrates (less than 0.1 %/minute)

Since the heater control system concentrates ona very narrow band of reaction rates, transitionswith slightly different reaction rates in the samescan are often given very different treatment.For example, a transition which falls short of the%/minute threshold may be passed at a fairlyhigh heating rate, with results similar to conven-tional constant heating rate TGA.

Whereas, a transition which just crosses the %/minute threshold may cause a significantreduction in heating rate or even reversal of theheating process. The two transitions, althoughsimilar in nature, may appear quite different on aplot of weight change versus sample tempera-ture. This effect can be observed in the weightloss curve of figure B.10 (page B-49). Note that

Appendix B


the surface water loss at 85°C and the bicarbon-ate transition at 100°C are treated quite differ-ently. This effect is most noticeable at lowsensitivity settings. The effect can be reduced oreliminated by using multiple ramp segments inthe method, each tailored to the needs of specifictransitions. Increasing sensitivity setting mayalso be helpful. (See the section entitled �Ad-justing Sensitivity Setting in Constant ReactionRate Mode�).

Weight GainExperiments

It is important to note that, while most TGAwork involves decomposition analysis, someapplications involve weight gain such as inoxidation studies. The Hi-ResTM heating controltechniques apply equally well to weight gains asto weight losses. In this case, the absolute valueof the weight change signal is used for control.Weight gains of up to 200% can be accommo-dated. The rates of weight gain (%/minute) andtheir relationship to heating rate, resolutionsetting and sensitivity setting are exactly thesame as for weight loss. No special parametersor controls are needed for Hi-ResTM weight gainanalysis. Combinations of weight gain andweight loss in the same TGA scan are handledautomatically. It is important to recognize,however, that when weight gain and weight losstransitions overlap, the resultant weight changeis additive and may not be separable.


Hi-ResTM Option

Signature Analysis

For many materials it will not be possible toseparate overlapped transitions sufficiently toallow quantitative analysis of weight change.However, this does not mean that no usefulinformation can be gained from the TGA scan ofthe material. It is frequently the case, particu-larly in quality control work, that an exactdetermination of sample composition is notneeded. Instead, the requirement is only toidentify which material of a group of knownstandards the unknown sample most closelyresembles. Another usage is to identify lot-to-lot variation from an acceptable standard. Inboth of these cases the location, size, and shapeof the derivative of weight change peaks of theTGA scan, or the weight curve itself, is used tocreate a unique pattern or �signature� of thesample material. Signature scans of standardsand the unknown material are then compared tomake the identification or �accept/don�t accept�decision.

Since the various components of a sample, whenrun separately, usually decompose or evolve atunique and reproducible rates and temperatures,it is often felt that it should be possible todetermine exactly what is in an unknownmixture by comparison to a library of knownTGA scans of the individual components.Unfortunately, this usually does not workbecause the various components of a mixturetypically interact with one another, so that theresultant scan is unlike either material runseparately. The interactions can be chemical orphysical. Some examples are evolved gasesfrom one decomposition which slow or acceler-ate the decomposition or evolution of another

Appendix B


component (e.g., CO2 from oxidizing carbon).Molecular attractions prevent a more volatilecomponent from evolving when expected, and atthe same time hasten the evolution of anotherless volatile component (e.g., chain linkage inpolymer blends). The physical matrix of themixture may retard the evolution of a morevolatile component, which then evolves at ahigher than normal temperature and at a slowerthan normal rate (e.g., oil evaporating fromrubber). Or the components may react chemi-cally at elevated temperatures and produce newcompounds which decompose at differenttemperatures than the individual components.

Sample Quantityand Orientation

As with conventional constant heating rateTGA, sample quantity and orientation in thesample holder can be important during Hi-Resexperiments. This is particularly true if thesample is not homogeneous (e.g., a laminatedsheet or coated surface). With these types ofsamples it is wise to try scans with differentsurfaces exposed. Be aware that chopping orgrinding the material may produce an entirelydifferent result since physical or chemicalproperties may be altered.

Exposed Surface Area

Exposed surface area is often important. Whensamples melt they usually spread out over thebottom surface of the sample container. Thiswill expose more or less surface area, dependingon whether the original configuration was asingle block (area typically increases) or a


Hi-ResTM Option

powder (area typically decreases). Usually withopen sample pans it is best to try to maximizeexposed surface area at all times so that evolvedgases escape quickly and reactions proceeduniformly. This suggests the use of smallpowdered or thin samples which are uniformlydistributed in the sample vessel. When semi-pressurized sample vessels are used the issue ofexposed surface area is far less important.

Generally, sample sizes in the range of 5 to 15milligrams are recommended. If the material isself heating or auto-catalytic, then smallersample quantities may help with heating control.(This is particularly important for constantreaction rate Hi-ResTM mode.) On the otherhand, larger sample quantities (50 to 100 mg)are recommended for reactions in which a verysmall weight change (less than 1 percent) isbeing measured. For maximum weight resolu-tion it is advisable to keep sample weight belowthe TGA 2950 weight range change at 100 mg.

A problem with very large samples, whichdecompose rapidly and almost completely, isthat the furnace purge may not be able to removeall of the evolved components and some con-tamination of the furnace wall and coolingjacket may result. This may affect the remain-der of the experiment or future scans.

Bubble Formation

Whenever medium to large sample quantities arebeing run, use caution in thermocouple place-ment. Some materials, particularly polymers,will form a �skin� on the outer surface of thesample as it is heated which inhibits masstransport of the more volatile components.

Appendix B


These samples form bubbles which can rise upand touch the end of the thermocouple, ruiningthe experiment and possibly contaminating thethermocouple. Just as the largest chewing gumbubbles are produced by blowing slow pro-longed breaths, the largest gas bubbles form insamples which are gradually heated. For thisreason bubble formation is more of a concern forHi-ResTM than conventional TGA.

Another effect of bubble formation is a suddensmall unexpected change in weight and accom-panying spike in the percent/minute curve as thebubble bursts. An excellent example of bubblenoise can be seen in the scan of ethylene-vinylacetate in figures B.7 and B.8. In figure B.7 theeffect of bubble formation and bursting can beseen as a sudden drop in weight at about 400°Cduring the second weight loss. This appears inthe derivative curve as a peak shoulder. InFigure B.8 we can clearly see the formation andbursting of several large bubbles in the percent/minute curve between 65 and 85 minutes intothe run. Again, these effects tend to be morenoticeable in Hi-ResTM TGA because largerbubbles form due to the slow heating process.The best solution to bubble noise is to decreaseresolution setting and/or increase maximumheating rate. Reducing sample size may alsohelp.


Hi-ResTM Option

Figure B.7

Figure B.8

Appendix B


ThermocouplePlacement

Generally, the thermocouple should be placed 2to 5 mm above the bottom of the sample con-tainer (1 to 4 mm above the edge). Placement1 mm above the edge is recommended for mostapplications. Longer distances will not degradeheater control and are sometimes helpful inreducing any adverse effects of sample self-heating or bubble formation.

Data AnalysisEffects

Hi-ResTM TGA, due to its technique of changingheating rates dynamically, causes very signifi-cant non-linearity of data points across transitionregions when plotted versus temperature. Thisis not a problem when making plots, but whenautomatic limit selection is used during dataanalysis report generation the analysis programcan sometimes become confused about where toplace the limits. This situation can be identifiedby curve tick marks and tangent lines which arepoorly placed on the weight curve or may evenbe plotted off of the curve.

The difficulty is caused by the fixed size of thetransition onset and endset windows (the firstand last 12.5% of the analysis region). The dataanalysis program assumes that data points areuniformly distributed throughout this region. Ifthe number of data points in the baseline portionof a window is very small compared to thenumber of points in the sloped portion of thewindow (the usual case with Hi-ResTM scans)then the tangent lines will be excessively


Hi-ResTM Option

weighted toward this cluster of points and maybe nearly vertical or even fall off the curveentirely.

Improved results can be obtained by moving thetransition start and stop limits farther away fromthe transition so that the onset and endsetwindows remain completely on the baselineportion of the curve. If this fails to help, thetransition tick marks can be placed manually onthe curve.

Derivative Plots

Another data analysis problem caused byunequally spaced temperature data points isunusually shaped or flattened derivative plotsversus temperature. This is due to the assump-tion that data points are equally distributed overa moving window (the smoothing window) usedto compute the derivative. If the derivativesmoothing window is too wide, derivative peakswill flattened and apparent resolution will bereduced. If the window is too narrow, derivativepeaks will be needle sharp and noisy.

The default smoothing window is 0.2 minutesfor derivatives with respect to time (%/min and%/min/min) and 10°C for derivatives withrespect to temperature (°C/min and °C/min/min).For typical Hi-ResTM TGA scans, the quality ofderivative plots with respect to temperature canbe improved by decreasing the temperaturewindow to 5°C. If extremely sharp results aredesired, try a smaller window. Less than 1°C isnot recommended. The smoothing window fortime does not normally need adjustment. If thetime derivative seems particularly noisy, tryincreasing the window to 1 minute.

Appendix B


In conventional constant heating rate TGA, theplot of percent/minute and the plot of percent/°Care essentially identical because there is a directlinear relationship between time and tempera-ture. Percent/minute is conventionally chosenfor transition peak analysis and plotting. WithHi-ResTM TGA there is no linear relationshipbetween time and temperature because theheating rate is constantly changing. Whenplotting the derivative of weight change versustemperature for a Hi-ResTM TGA scan, youshould use percent/°C. A plot of percent/minuteversus temperature can still be useful for locat-ing minor transitions and determining the rate ofreactions.

AdjustingHeating Rate

Heating rate has long been used to controltransition resolution. The typical thermalanalyst makes most runs at 20°C/minute anddrops down to 5 or 1°C/minute for hard-to-resolve transitions, or just to see if there isanything else interesting going on that mighthave been missed in the faster scan. 1°C/minutescans are generally not routine due to theenormous amount of time required to run them.

With Hi-ResTM TGA the heating rate is variedautomatically to give the benefit of slow heatingrates during transitions and fast rates duringbaseline. However, it is still necessary tospecify a maximum heating rate. This is be-cause in Hi-ResTM TGA, just as in constantheating rate TGA, the maximum heating rateaffects the results of the experiment and, assuch, is an important adjustment to consider.


Hi-ResTM Option

Heating rate adjustment is particularly critical ifthe transitions of an overlapped group are veryclosely spaced in temperature. At 50°C/minutethe normal temperature lags in the TGA furnacecan be enough to overshoot the first transition,which may reduce separation from the othertransitions in the group. This will be mostnoticeable when the percent/minute baselinepreceding a rapid transition is relatively constantand several orders of magnitude below the peakrate of the transition. Running at 20°C/minuteinstead of 50°C/minute is recommended for mostroutine work using positive resolution settingsparticularly if only one scan can be made ofeach unknown material. Less than 10°C/minuteis usually not required.

For negative resolution settings the selection ofheating rates is usually quite different becausereaction rate overshoot must be minimized.Generally, 1, 2, 5 and 10°C/minute are the mostuseful rates to use with negative resolutionsettings. Try 5°C/minute to start.

An important difference between the dynamicrate (positive resolution setting) and constantreaction rate (negative resolution setting) Hi-ResTM mode, is that the maximum heating rateselected is only an upper limit in negative mode,but it is a gain factor in positive mode. In otherwords, in negative mode the maximum heatingrate is irrelevant to heating control, except whenthe reaction rate drops to such a low level thatheating rates higher than this maximum limit arerequired to maintain the selected percent/minute.

In negative mode, as long as the maximumheating rate is high enough to allow completionof the transition at the selected percent/minute

Appendix B


set point, and not so high as to cause percent/minute overshoot, transitions will appear largelythe same from one heating rate to the next. Aword of caution, however: always keep in mindthat the background (baseline) rate of weightchange will be accelerated at higher maximumheating rates. This will move the backgroundpercent/minute closer to the control point youhave selected with the resolution setting. Ifnoise is present in the background percent/minute, it may fool the control algorithm intothinking a transition is starting and result in apremature reduction in heating rate to avoidpredicted set point overshoot. In extreme cases,heating rate cycling can occur, particularly athigh sensitivity settings. (See Figure B.13 onpage B-61) To cure this problem reduce maxi-mum heating rate and/or sensitivity setting.


Hi-ResTM Option

AdjustingResolution Setting

The purpose of the resolution parameter is toselect the range of percent/minute values overwhich the heater control system will varyheating rate in response to changes in the rate ofweight change. In dynamic rate mode (positiveresolution settings) the range of percent/minutevalues selected by each resolution setting isfairly wide (about two orders of magnitude).This width is adjustable using the sensitivityparameter.

In constant reaction rate mode (negative resolu-tion settings) the resolution setting specifies thepercent/minute value that will be used as thecontrol set point for furnace heating. In thiscase the system will adjust heating rate asrequired to maintain this constant rate of weightchange. Table B.1 (on the next page) shows thenegative resolution settings and their associatedpercent/minute values.

Appendix B


Table B.1

Res %/min Res %/min Res %min Res %/mi

-0.1 28.2 -2.1 2.82 -4.1 0.282 -6.1 0.0282-0.2 25.1 -2.2 2.51 -4.2 0.251 -6.2 0.0251-0.3 22.4 -2.3 2.24 -4.3 0.224 -6.3 0.0224-0.4 20.0 -2.4 2.00 -4.4 0.200 -6.4 0.0200-0.5 17.8 -2.5 1.78 -4.5 0.178 -6.5 0.0178-0.6 15.8 -2.6 1.58 -4.6 0.158 -6.6 0.0158-0.7 14.1 -2.7 1.41 -4.7 0.141 -6.7 0.0141-0.8 12.6 -2.8 1.26 -4.8 0.126 -6.8 0.0126-0.9 11.2 -2.9 1.12 -4.9 0.112 -6.9 0.0112-1.0 10.0 -3.0 1.00 -5.0 0.100 -7.0 0.0100-1.1 8.91 -3.1 0.891 -5.1 0.089 -7.1 0.0089-1.2 7.94 -3.2 0.794 -5.2 0.079 -7.2 0.0079-1.3 7.08 -3.3 0.708 -5.3 0.071 -7.3 0.0071-1.4 6.31 -3.4 0.631 -5.4 0.063 -7.4 0.0063-1.5 5.62 -3.5 0.562 -5.5 0.056 -7.5 0.0056-1.6 5.01 -3.6 0.501 -5.6 0.050 -7.6 0.0050-1.7 4.47 -3.7 0.447 -5.7 0.045 -7.7 0.0045-1.8 3.98 -3.8 0.398 -5.8 0.040 -7.8 0.0040-1.9 3.55 -3.9 0.355 -5.9 0.036 -7.9 0.0036-2.0 3.16 -4.0 0.316 -6.0 0.032 -8.0 0.0032

The process of initially picking, and thenadjusting resolution setting, is not exacting orcalculated. It is based largely on experience andsome general guidelines. This is because nosingle resolution setting will give dramaticallydifferent results from all the others. The changefrom one number to another is rather gradual.Another reason you might wish to experimentwith more than one setting is that some materialsreact differently from others to increasing ordecreasing the resolution setting. This is due tothe time as well as the temperature-dependantnature of transitions, and to the interaction


Hi-ResTM Option

between the rate of weight change (%/minute)and heating rate (°C/minute). As percent/minuteincreases heating rate is reduced by the controlalgorithm, but the reduction in heating rateusually causes an accompanying reduction inpercent/minute, and vise versa. Therefore,attempting to directly compute optimal resolu-tion settings from percent/minute informationgathered from previous runs becomes a veryquestionable and usually frustrating experience.

Let us then consider what guidelines and rules-of-thumb we can use to help make the selectionprocess easier. As stated earlier in the sectionon Hi-ResTM ramps, if you do not know whatresolution setting to start with, try resolution+3.0 and 50°C/minute heating rate. This willgive a rapid scan with moderate application ofthe Hi-ResTM heating technique. Results shouldbe at least as good as a 20°C/minute conven-tional scan of the same material, and will usuallybe better. If time permits, it is often helpful tohave a constant heating rate 20°C/minute scan ofthe material available for comparison.

Useful Resolution Settings

After some experience with Hi-ResTM TGA, youwill find that the most useful resolution settingsfall within the range +3.0 to +5.0 for the positivenumbers and -3.0 to -5.0 for the negative num-bers, and that adjustment by +/-0.5 is usuallyadequate. This is similar to the situation withheating rates. You can adjust heating rate to anyvalue from 0.01 to 200.0°C/minute in steps of0.01°C but most people use 1, 5, 10, 20 and50°C/minute exclusively because a finer adjust-ment does not produce significantly differentresults. With this guideline alone we havereduced the number of resolution settings to deal

Appendix B


with from 80 to only 5 for each Hi-ResTM modewhile covering the majority of materials ofinterest.

The next step is how to proceed after the firstHi-ResTM run is complete. If the first run wasmade at resolution setting 3.0, try the second oneat 4.0. Generally, increasing resolution settingby a whole number will increase the time tocomplete the TGA scan by a factor of 2 to 5times. Therefore, you must consider whetheryou can afford the added run time as well as theextra setup time. This balance between in-creased run time and adequate resolution isusually the determining factor on what resolu-tion setting to live with.

The benefit to having more range and �resolu-tion� to the resolution setting than seems to benecessary, is that on a rare occasion a materialrequires a very fine adjustment or an extremetreatment. Don�t forget that the maximumheating rate is a factor in determining resolutionas well as the resolution setting.

Lower resolution settings allow materials whichalready have well-separated transitions to beanalyzed at super high heating rates such as200°C/minute with excellent resolution in afraction of the time required at a constant rate of20°C/minute. Resolution settings above 5.0 areuseful when exact decomposition temperaturesare needed ,or when the decompositions areexplosive in nature, or when overlapped transi-tions are extremely close but highly temperatureselective.


Hi-ResTM Option

The effect of adjusting the resolution setting indynamic rate mode while holding other experi-mental factors constant can be seen in FigureB.13 (page B-61).

TemperatureCalibration

TGA temperature calibration is useful if accu-rate transition temperatures are required. Themajor causes of temperature inaccuracy in aTGA are thermal gradients between the samplethermocouple and the sample being studied.The magnitude of these gradients is proportionalto heating rate. The Hi-ResTM TGA techniquesinherently reduce thermal gradients by slowingdown the heating rate during transitions.

Another way to reduce the effect of thermalgradients is to temperature calibrate the TGA.The general procedure for temperature calibra-tion is found in theonline help and documentation.Temperature calibration involves analyzing amagnetic standard to determine its curie tem-perature. The curie temperature corresponds tothe extrapolated endpoint on the �S� shapedthermal curve.

However, when the calibration is intended foruse with Hi-ResTM TGA experiments (i.e.,dynamic rate, constant reaction rate or stepwiseisothermal), then a slow heating rate conven-tional ramp of 5oC/minute or less should be usedfor calibration. A faster ramp rate is only usedwhen calibrating for constant heating rateexperiments. The reason for this is that the Hi-ResTM heating control system reduces theheating rate during transitions.

Appendix B


Hi-ResTM TransitionTemperatures

The TGA provides precise weight measurementscoupled with relative temperature information.The resolution setting of a Hi-ResTM rampcontrols the reaction rate of sample transitions.It is reaction rate, more than anything else,which will determine the apparent transitiontemperature of a decomposition reaction.

The shift in measured transition temperaturecaused by changing resolution setting can easilybe an order of magnitude larger than the thermalgradients you are trying to correct with calibra-tion. This effect can be clearly observed in themixture of bicarbonates example (Figure B.13,page B-61). In light of this fact, it is acceptablein many cases to simply not use temperaturecalibration when employing the Hi-ResTM TGAtechniques for decomposition analysis.


Hi-ResTM Option

Hi-ResTM SensitivitySegment

The Hi-ResTM sensitivity segment sets anadditional parameter associated with Hi-ResTM

ramp segments which can be used to adjust theresponse of the Hi-ResTM temperature controlalgorithm. This is sometimes necessary becauseof the wide variation in decomposition mecha-nisms of typical sample materials. This segmenthas the following format:

Hi-ResTM sensitivity <sens_setting>

where:

<sens_setting> is the Hi-ResTM sensitivitysetting (1.0 to 8.0)

example:

Hi-ResTM sensitivity 2.0

Hi-ResTM sensitivity segments execute immedi-ately when encountered in a method and simplyset the sensitivity setting to the new valueprovided. The last value set is used for allsubsequent Hi-ResTM ramps until a new value isset. If no Hi-ResTM sensitivity segment has beenencountered in the method before the executionof a Hi-ResTM ramp segment, then the defaultsensitivity (1.0) is used.

The sensitivity setting is a unitless number,ranging from 1.0 (lowest sensitivity) to 8.0(highest sensitivity). The setting is used by boththe dynamic rate (positive resolution setting)

Appendix B


and the constant reaction rate (negative resolu-tion setting) modes of the Hi-ResTM rampsegment. There is no limit to how many timesthe setting can be changed during a method.Increasing sensitivity setting tends to increaseexperiment time.

UnderstandingSensitivity Setting

The TGA 2950 Hi-ResTM control algorithmshave been pretuned to respond correctly to mosttransition situations with the default sensitivitysetting of 1.0. This means that in most cases itwill not be necessary to adjust sensitivity settingat all. The key is knowing when and how tomake the adjustment.

It is easy to confuse resolution setting andsensitivity setting since both values can affectthe resolution of the TGA scan. However, thereis a simple way to think of the differencebetween the two parameters.

Resolution setting controls the temperature atwhich the transition will occur (i.e., how farfrom the theoretical isothermal decompositiontemperature) by selecting the reaction rate (%/minute) at which heating rate is reduced. Thecloser the reaction is to the isothermaldecomposition temperature the lower thereaction rate and the longer the reaction willtake. You will find that you can use the resolu-tion setting to literally move the measurement oftransitions on the temperature axis. (See FigureB.13, page B-61.)


Hi-ResTM Option

Sensitivity setting controls the response of theHi-ResTM system to changes in the rate ofreaction (%/minute). Larger sensitivity settingscause the system to be more reactive or �sensi-tive� to small changes in the rate of the reaction.Lower sensitivity settings dampen this response.Generally, it is best to adjust resolution settingfirst with sensitivity set to a low value, and thenafter a good result is obtained, try increasingsensitivity to see if any resolution improvementcan be obtained.

Use caution when adjusting sensitivity sinceover adjustment can cause oscillation or anoma-lies in the weight versus temperature curve.

Adjusting Sensitivityin Dynamic Rate Mode

In dynamic rate Hi-ResTM mode (positiveresolution settings), the sensitivity setting isused to further increase the resolution of sometransitions once an appropriate resolution settinghas been determined. This is accomplished bynarrowing the range of percent/minute valuesover which the heating rate is proportionallyvaried. Higher sensitivity settings result inprogressively narrower percent/minute rangesand generally increased resolution.

In this mode the resolution setting selects thegeneral neighborhood of percent/minute valuesthat will drive changes in furnace heating rate.For example, resolution setting 3.0 selects theneighborhood of approximately 1.0 to 20.0%/minute for most of the variation in heating rate.Whereas, setting 4.5 selects 0.1 to 2.0%/minute.Sensitivity setting controls the relative width of

Appendix B


this range. Setting 1.0 allows use of the fullrange. Setting 2.0 reduces the range to aboutone half the full range. Setting 3.0 to about athird and so on up to 8.0. In general, highersensitivity settings bring the furnace to thetransition temperature more quickly but thentend to remain at that temperature longer. Inother words, higher sensitivity settings bring thecontrol closer to stepwise isothermal heating.(See �Stepwise Isothermal Heating� in thesection on using Abort Segments for moreinformation.)

The recommended procedure for adjustingsensitivity setting for dynamic rate mode is tostart with a sensitivity setting of 1.0 and adjustresolution setting to get the best separationpossible in the desired time frame. Thenincrease sensitivity to 2.0, 4.0 and 8.0 to see if auseful improvement in resolution results.

It is possible that no improvement in resolutionwill result. This is usually caused by overlappedtransitions which are weakly temperature-dependant and strongly time-dependant. In thiscase, it doesn�t matter how precisely we controlat a specific temperature, the individual compo-nents of the sample material are all going todecompose more or less together in the neigh-borhood of the decomposition temperatures wehave selected via the resolution setting. Aboutall we can do is lengthen or shorten the totaltime of decomposition by selecting larger orsmaller resolution settings.

The effect of changing sensitivity settings indynamic rate mode can be seen in Figure B.14on page B-62.


Hi-ResTM Option

Adjusting Sensitivityin Constant ReactionRate Mode

In constant reaction rate Hi-ResTM mode (nega-tive resolution settings) the sensitivity setting isused to adjust the heater control system tominimize transition temperature overshoot andheating control fluctuation. Higher sensitivitysettings result in decreased percent/minuteovershoot and tighter control at the beginning oftransitions. Lower settings have the oppositeeffect.

In this mode sensitivity setting is used to adjustthe response of the heater control system tochanges in the rate of weight change (%/minute). For materials that react gradually, lowsensitivity settings are generally preferredbecause they help dampen noise and greatlyreduce the possibility of control cycling. How-ever, when it is very important to avoid percent/minute overshoot, or if the sample is highlyreactive then higher settings will be required.The problem with too high a sensitivity settingis that control cycling or heating rate �ringing�may occur (see Figure B.11).

The recommended procedure to adjust sensitiv-ity setting for constant reaction rate mode is tostart with a sensitivity setting of 1.0 and observethe transition for percent/minute overshoot andcontrol cycling. If overshoot is acceptable, nofurther adjustment is needed. If overshoot isexcessive, increase sensitivity setting by 1.0 andrecheck overshoot and cycling. Continueincreasing sensitivity until the results areacceptable or until control cycling becomesexcessive.

Appendix B


If no satisfactory sensitivity setting can befound, the problem may be too low a resolutionsetting or too high a heating rate. Try a higherresolution setting (larger negative number) toreduce the percent/minute set point and rerun theexperiment. Set points in the range of 0.1 to1.0%/minute (resolution settings -5.0 to -3.0)generally give the best results.

If the percent/minute overshoot is primarilyassociated with the first transition of a group ofoverlapped transitions, the problem may be toohigh a maximum heating rate. Try reducing theheating rate of the Hi-ResTM ramp segment byone half and rerunning the experiment. Heatingrates in the range of 1.0 to 5.0°C/minute gener-ally give the best results.

When heating rates higher than 5.0°C/minute areused, proper adjustment of sensitivity settingbecomes critical to maintaining smooth heatingcontrol. The default sensitivity of 1.0 is usuallytoo low at these higher heating rates and typi-cally results in significant transition temperatureovershoot and heating control �ringing� asshown in Figure B.9. At high heating rates asetting of 3.0 or 4.0 will give better results formost materials. The improvement can be seen inFigure B.10. If sensitivity setting is adjusted toohigh, then continuous control cycling may resultas shown in Figure B.11. With some experi-mentation, an optimal setting can usually befound. When very high heating rates are used(greater than 10/°C/minute) it may be impossibleto completely eliminate control ringing. How-ever this should not affect the quantitativemeasurement of weight loss for the transition.


Hi-ResTM Option

Figure B.9Sensitivity Setting Too Low

Figure B.10Correct Sensitivity Adjustment

Appendix B


Figure B.11Sensitivity Setting Too High


Hi-ResTM Option

Abort SegmentThe abort segment provides a mechanism to skipover or terminate other method segments whenspecific weight change conditions are met. Thissegment has the following format:

Abort next seg if <signal> <condition><value>

where:

<signal> is the real-time measurement used todecide whether to abort or not (weight % orweight %/minute)

<condition> is the limit condition for aborting(“<“ or “>”)

<value> is the abort limit which is comparedwith the real-time signal

example:

Abort next seg if % < 20.0

Abort segments execute immediately whenencountered in a method and simply establishconditions for testing the next segment. Thespecified limit, designated by the <signal>,<condition> and <value> parameters, is testedbefore and during the execution of the nextmethod segment. If the limit is reached at thebeginning of a segment, that segment is skippedand method execution continues with the nextsegment. If the segment following the abortsegment is equilibrate, initial temperature, ramp,Hi-ResTM ramp, isothermal or step, and the limithas not been reached yet, the limit will be tested

Appendix B


at the rate of 2 times per second until the seg-ment terminates normally or the limit is reached.If the limit is reached during the execution of asegment, the remaining portion of the segment isskipped. Method execution then continues withthe next segment in the method.

The conditions for determining whether limitshave been reached for each type of limit are asfollows:

% - If the condition operator is “<“ and thesample weight percent is less than or equalto the limit percent, or if the conditionoperator is “>” and the weight percent isgreater than or equal to the limit percent,then the limit is reached. Values greaterthan 100% are permitted to accommodateweight gains.

%/min -If the condition operator is “<“ and thederivative of sample weight percent is lessthan or equal to the limit percent/minute, orif the condition operator is “>” and thederivative of weight percent is greater thanor equal to the limit percent/minute, thenthe limit is reached. Negative valuesindicateweight gain and positive valuesindicate weight loss.

Abort segments are very versatile because theycan be used in front of any method segment(including other abort segments) to dynamicallychange the execution of a method. For example,an abort segment can be used to control theswitching of a purge gas or activation of anevent relay based on the rate of reaction or theamount of weight loss. An abort segment infront of a repeat segment provides a mechanismto terminate a loop prematurely. Abort segments


Hi-ResTM Option

can be used to customize a method for a par-ticular material by allowing different ramp and/or isothermal segments to be used for each tran-sition region without regard to specific tempera-ture limits. Abort segments can be used tocontrol data storage so that file size is minimizedby turning off storage or increasing samplinginterval during baseline sections of a scan.

Abort segments provide a convenient mecha-nism for shortening experiments after the data ofinterest has been collected. For example, if aheating ramp is used to analyze a material whichhas two weight losses and the only data ofinterest is the percent weight loss during the firsttransition, then an abort segment can be used toterminate the ramp after the beginning of thesecond weight loss by specifying a “%” limitcondition. This is particularly useful for Hi-ResTM ramps because the reduced heating rateduring a weight loss causes the majority of thetransition to occur during a very narrow tem-perature range, making termination by finaltemperature difficult to predict.

StepwiseIsothermal Heating

Another useful TGA technique which can beimplemented with abort segments is transition-controlled stepwise isothermal heating. Thisprocess consists of heating a sample via a rampsegment until a certain rate of weight change isdetected, and then switching to an isothermalsegment to hold constant temperature until thetransition has completed. Then the sampleheating is continued until the next transition isdetected, whereupon, isothermal holding is

Appendix B


again initiated, and so on until the final tempera-ture is reached.

The stepwise heating technique can be easilyimplemented by placing a ramp segment fol-lowed by an isothermal segment into a “repeat tofinal temperature” loop, and preceding the rampand isothermal segments with abort segments.The abort segment preceding the ramp is setupto terminate the ramp when the “%/minute” isgreater than a specified limit. The abort seg-ment preceding the isothermal segment termi-nates the holding period when the “%/minute” isless than a second limit. An example of thistype of method is shown below.

1: Abort next seg if %/min > 0.52: Ramp 10 °C/min to 700 °C3: Abort next seg if %/min < 0.054: Isothermal for 500 minutes5: Repeat segment 1 til 700 °C

The “%/min” limit for the isothermal segment isselected to be equal to the baseline rate ofweight change encountered during the onset ofthe transition of interest via a normal constantheating rate scan of this material. (Be sure touse the same ramp rate as that selected forstepwise heating.) The “%/min” limit for theramp segment is selected to be about an order ofmagnitude greater than that selected for theisothermal segment (but not more than themaximum rate of weight change encounteredduring the transition of interest). The ramp finaltemperature and the repeat final temperature areset to the final experiment temperature. Theisothermal time is set to an arbitrary time, whichis sufficiently large such that the segment willnot terminate until the percent/minute limit hasbeen reached.


Hi-ResTM Option

Stepwise heating often improves transitionresolution because transitions are time depen-dent as well as temperature dependent.Stepwise heating gives transitions more time tocomplete, thereby, reducing overlap withneighboring transitions.

To get the maximum benefit from stepwiseheating it will be necessary to run several TGAscans to properly “tune” the reaction ratethresholds used to start and stop heating. Rela-tively slow heating rates are generally requiredto prevent transition overshoot. A rough rule-of-thumb is to use a heating rate which is about onetenth the transition temperature differencebetween the transitions being resolved. Forexample, if the transitions are separated by 10°Cthen use 1°C/min as the heating rate prior to,between and following the transitions. If precisereaction temperatures are important, then slowheating rates should always be used prior toencountering transitions of interest even thoughthey may be well separated in temperature, andthe “%/min” limit for the ramp segment shouldbe set closer to the limit for the isothermalsegment. To avoid excessively long experi-ments, higher heating rate ramps or equilibratesegments can be used to skip over baselineportions of the scan.

A disadvantage to stepwise heating is that mostexperiments take much longer in total time tocomplete than by a conventional constantheating rate scan. Another disadvantage ofstepwise heating is that the decision to leaveisothermal mode and continue heating is some-what arbitrary and may lead to incorrect assump-tions about the number and size of transitions.

Appendix B


This is particularly true for materials which havetransitions that are overlapped even at very slowheating rates (such as the sodium/potassiumbicarbonate mixture in the Examples section).As a general rule, stepwise isothermal heatingcannot be used to reliably separate transitionswhich cannot be separated by conventional TGAat very slow heating rates.

Another problem to watch out for with stepwiseheating is the creation of anomalies in theweight loss versus temperature curve. Theseappear as small unexpected secondary weightlosses following a larger transition. Theseanomalies can be caused by two factors.

The first cause is using too high a heating rate inthe ramp which follows the transition. Anysmall amount of sample material which did notfinish decomposing during the transition willnow quickly decompose due to the rapid eleva-tion of the furnace temperature. This will causethe decomposition rate (%/minute) to risesubstantially. If the rising decomposition ratecrosses the abort threshold for the ramp segmentthen a second isothermal period will be intro-duced which will appear on the weight lossversus temperature plot as a small unexplainedtransition. Generally it is best to use the sameheating rate on both sides of a transition. Thisrate can then be accelerated if desired after thefurnace temperature is some distance from thetransition.

The second cause of anomalies is leaving theisothermal holding period prematurely during atransition because the percent/minute thresholdfor aborting the isothermal segment was set toohigh. This situation leaves a significant amount


Hi-ResTM Option

of undecomposed sample material which nowaccelerates its rate of decomposition. As in thecase of too high a ramp rate, the increasingtemperature causes the remaining sample toquickly decompose which raises the rate ofweight loss (%/minute) to a high level and eithertriggers another isothermal hold period or showsup as a backside shoulder on the weight losscurve.

An example of using stepwise isothermalheating is shown in the following “Hi-ResTM

TGA Examples” section.

Appendix B


Hi-ResTM TGAExamples

Included in this section of the manual areexample TGA scans of common materials.These examples can be used to compare theresults of using Hi-ResTM TGA heating controlwith the results of conventional constant heatingrate TGA. Where possible the effects of usingthe different Hi-ResTM modes and parameters areshown.

Mixture ofBicarbonates

A mixture of potassium bicarbonate (potassiumhydrogencarbonate) and sodium bicarbonate(sodium hydrogencarbonate) was chosen todemonstrate the effects of different Hi-ResTM

techniques and parameter settings. The indi-vidual bicarbonates decompose to carbonatesbetween 100°C and 200°C with the simultaneousrelease of CO2 and H2O. Potassium bicarbonatedecomposes at approximately 50°C highertemperature than sodium bicarbonate. Whenmixed together the decompositions of the twobicarbonates are overlapped in temperature andare very difficult to resolve. You can easilymake this sample yourself by thoroughly mixingequal parts (by weight) of finely powderedpotassium bicarbonate (KHCO

3) and sodium

bicarbonate (NaHCO3). Inadequate mixing orlarge granule size will reduce weight lossreproducibility. Note that potassium bicarbon-ate is very hygroscopic. The mixture must notbe exposed to ambient humidity for long or a


Hi-ResTM Option

significant surface water transition will becomeevident between 70°C and 100°C which willaffect the overall weight loss percentages.When mixing and using this sample be sure tokeep the sample supply containers tightlycapped. Load the TGA quickly and use a drypurge gas (air, nitrogen or argon). Dry air purgeat 100 mL/min was used for all example scansshown. Sample sizes varied from 20 to 40 mg.Small variations observable in weight lossreproducibility in the example scans are largelydue to the non-homogeneity of the samplemixture and variations in ambient humidity fromrun to run.

Dynamic Rate Scans

In Figure B.12 (on the next page) we haveoverlaid the individual bicarbonate decomposi-tions (curves b and d) along with the decomposi-tion of the mixture by conventional TGA(curves a and e) and by dynamic rate Hi-resTM

TGA (curve c). Reducing the heating rate of themixture from 20°C/minute (curve e) to 1°C/minute (curve a) gave a very slight improvementin resolution. Comparing these results to the50°C/minute Hi-resTM scan we observe a signifi-cant improvement in resolution with Hi-resTM

TGA in about twice the time of the 20°C/minutescan, and about one tenth the time of the 1°C/minute scan. The method used for all scans wasa single ramp segment.

Appendix B


Figure B.12

(a) 1°C/min Normal Ramp of Mixture; (b) 20°C/min Res 4.0 Hi-ResTM

Ramp of NaHCO3; (c) 50°C/min Res 4.0 Hi-ResTM Ramp of Mixture;(d) 20°C/min Res 4.0 Hi-ResTM Ramp of KHCO3; (e) 20°C/min NormalRamp of Mixture.


Hi-ResTM Option

VaryingResolution Setting

In Figure B.13 we have overlaid the conven-tional constant heating rate decompositions ofthe bicarbonate mixture (curves a and b) withdynamic rate Hi-ResTM scans at eight differentresolution settings (curves 1 through 8). All ofthe Hi-ResTM scans were run at 50°C/minute withthe default sensitivity setting of 1.0. Note thatincreasing resolution setting increases theresolution of each transition and simultaneouslyreduces the transition temperature. The initialweight losses of approximately 1% on eachcurve are due to the evaporation of surface waterabsorbed by the mixture.

Figure B.13

(a) 1°C/min Normal Ramp; (b) 20°C/min Normal Ramp;(1-8) Resolution setting

Appendix B


VaryingSensitivity Setting

In Figure B.14 we have overlaid the 1°C/minuteconventional constant heating rate decomposi-tion of the mixture (curve a) with a dynamic rateHi-ResTM scan at four different sensitivitysettings (curves b through e). All of the Hi-ResTM scans were run at 20°C/minute with aresolution setting of 5.0. Note that increasingsensitivity setting increases the sharpness ofeach transition, but does not substantiallychange the transition temperature.

Figure B.14

(a) 1°C/min Normal Ramp; (b) Sensitivity setting 1; (c) Sensitivitysetting 2; (d) Sensitivity setting 4; (e) Sensitivity setting 8.


Hi-ResTM Option

Constant ReactionRate Scans

In Figure B.15 we have overlaid the conven-tional constant heating rate decompositions ofthe bicarbonate mixture (curves c and e) withconstant reaction rate Hi-ResTM scans at differ-ent resolution and sensitivity settings. Curve bshows the Hi-ResTM scan run in an open samplepan at resolution setting -4.0 and sensitivitysetting 1.0. For curve d (resolution -4.0) andcurve a (resolution -5.0) the sample was con-tained in a hermetic aluminum DSC sample panwith a 0.1mm pin hole in the top. All of the Hi-ResTM scans were run at 5oC/min.

Comparing curve b to curves a and d, we can seea significant improvement in resolution due tothe vapor pressure build up in the semi-hermeticsample container. Because the sample pan wasopen in curve b, there was no opportunity for avapor pressure/reaction rate equilibrium to occuras the sample decomposed resulting in onlypartial separation of the transitions. The pres-sure buildup in the closed container (Curves a &d) retarded the potassium bicarbonate decompo-sition until the sodium bicarbonate decomposi-tion had completed. As with dynamic rate mode(Figure B.13), we see that higher resolutionsetting (larger negative number) reduces transi-tion temperature.

Appendix B


Figure B.15

(a) Res -5.0, Sens 2.0, Semi-hermetic Pan; (b) Res -4.0, Sens1.0, Open Pan; (c) 1°C/min Normal Ramp; (d) Res -4.0, Sens2.0, Semi-hermetic Pan; (e) 20°C/min Normal Ramp.


Hi-ResTM Option

StepwiseIsothermal Scans

In Figures B.16 and B.17 we see the result ofstepwise isothermal scans of the bicarbonatemixture using a conventional 1°C/minute rampand the abort segment. The following methodwas used for the scan in Figure B.16:


Although this method gives apparently excellentseparation results, the quantitative value of theweight loss plateau between the two bicarbonatedecompositions is in question because there isno inflection point in the plateau and the rate ofweight loss immediately increases after theisothermal segment is aborted. This indicatesthat the two decompositions are still overlappedand that holding for a longer isothermal timeperiod during the first transition would haveresulted in a lower weight loss plateau betweentransitions.

In Figure B.17 the same stepwise isothermalmethod is repeated with the %/minute limits forthe abort segments set to smaller values (0.05%/minute for the ramp abort and 0.005%/minutefor the isothermal abort). The following methodwas used for the scan in Figure B.17:


Appendix B


The scan in Figure B.17 is a definite improve-ment over the result in Figure B.16. This isbecause the abort limit for the isothermalsegment (0.005%/minute) was chosen to beequal to the baseline %/minute immediatelypreceding the sodium bicarbonate transitionobserved in a conventional constant heating ratescan of the mixture at 1°C/minute. The theorysupporting this decision is that if the two transi-tions are separable then the rate of weight lossshould return to baseline between the transi-tions. The %/minute limit for the ramp segmentwas then chosen to be ten times larger than thatfor the isothermal segment.

Although the weight loss result in Figure B.17seems more reasonable, we are suspicious thatthe decomposition of the potassium bicarbonate(2nd transition) has already started because therate of weight loss immediately increases asheating is resumed at 88°C. Another problem isthe torturous 1300 minute time frame of theexperiment.

As can be seen by these results, caution mustalways be employed when interpreting resultsfrom stepwise isothermal heating experiments.It is usually wise to run confirming experimentsby other TGA techniques, particularly if thesample material is of relatively unknown compo-sition.


Hi-ResTM Option

Figure B.16

Figure B.17

Appendix B


Monosodium Glutamate

In Figure B.18 we analyzed Accent® brandmonosodium glutamate (MSG), a common saltused for seasoning foods, which has three wellresolved transitions below 500°C. Curves a andc show the result of conventional constantheating rate scans of MSG at 1 and 20°C/minute.Curve b shows the result of a dynamic rate Hi-ResTM scan at resolution setting 4.0 and sensitiv-ity setting 1.0. As can be seen by the derivativeof weight loss curves, the Hi-ResTM scan givesresolution comparable to the 1°C/minute scan ina fraction of the time.

Figure B.18If you should decide to run this sample, beaware that MSG foams significantly at thesetemperatures. If a sample size greater than

(a) 1°C/min Normal Ramp; (b) 50°c/min Hi-ResTM

Ramp, Res 4.0, Sens 1.0; (c) 20°C/min NormalRamp; (d) 1°C/min; (e) 50°C/min; (f) 20°C/min.


Hi-ResTM Option

about 10 mg is used, the sample material mayrise up in the pan and touch the sample tempera-ture thermocouple. If MSG is heated to tem-peratures well above 500°C, it will leave aresidue which is difficult to remove from thesample pan.

Banana Taffy

In Figures B.19 and B.20 we analyzed a sampleof artificial banana taffy, a common confection-ery product composed primarily of water andsugar, which has a number of overlappedtransitions between 100°C and 500°C. FigureB.19 shows the result of a conventional constantheating rate scan of taffy at 10°C/minute. FigureB.20 shows the result of a 50°C/minute dynamicrate Hi-ResTM scan at resolution setting 4.0 andsensitivity setting 1.0.

Figure B.19

Appendix B


Figure B.20

As can be seen by comparing the derivative ofweight loss curves in Figures B.19 and B.20, theHi-ResTM scan gives improved resolution in thesame time as the conventional scan. This ispossible because the Hi-ResTM TGA ramp heatsthe taffy sample rapidly during baseline portionsof the scan and slowly during transitions,resulting in an average heating rate of about10°C/minute. A 200°C/minute Hi-ResTM scan ofthis sample takes about the same time as a 20°C/minute conventional scan while providingresolution improvement similar to that observedwith the 50°C/minute Hi-ResTM scan.


Hi-ResTM Option

PlasticLaboratory Tubing

In Figures B.21 through B.25 we analyzed asample of Tygon® R-3603 plastic tubing, a poly-vinyl chloride (PVC) based clear flexible tubingcommonly used in laboratories and industry. Anumber of overlapped transitions are evidentbetween 100°C and 350°C, followed by two wellresolved transitions at approximately 400°C and500°C. Of interest are the changes in resolutionof the various transitions as maximum heatingrate changes in both the conventional and Hi-ResTM scans.

Observing the two conventional scans (FiguresB.21 and B.22) we see that the resolution of theinitial overlapped transitions is good in the 1°C/minute scan, but poor in the 20°C/minute scan.In contrast, the resolution of the two transitionsat 400°C and 500°C are best in the 20°C/minutescan and reduced in the 1°C/minute scan. Inboth cases, however, the small backside transi-tion at 25% to 35% weight loss is barelydiscernable. Comparing the conventional TGAresults in figures B.21 and B.22 to the 50°C/minute Hi-ResTM scan in Figure B.23, we seethat all of these transitions are better resolved inthe Hi-ResTM TGA scan in a timely fashion.

Using Figures B.23, B.24, and B.25 we cancompare the result of changing the maximumheating rate of a dynamic rate Hi-ResTM scan.Maximum heating rates of 50°C/minute (FigureB.23), 20°C/minute (Figure B.24) and 10°C/minute (Figure B.25) were used with a methodconsisting of a single Hi-ResTM ramp segment.

Appendix B


Sample size (approximately 10.45mg), sensitiv-ity setting (1.0), purge gas (100 mL/minute dryair) and sample pan (open platinum) were allheld constant from run to run.

As can be seen in the examples, the results aresimilar in each scan except that the measurementof transitions is moved to slightly lower tem-peratures as heating rate is reduced, and eachrun takes about 50% longer to complete whenheating rate is reduced by 50%. Most notice-able, however, is that transition resolution isbest in the fastest scan. This is because highermaximum heating rates allow the TGA furnacetemperature to change more quickly betweentransitions which reduces transition overlap andflattens weight loss baseline. As an addedbenefit, experiment time is reduced compared totraditional resolution enhancement techniques.Here we can see the real beauty of dynamic rateHi-ResTM TGA: better results in the same or lesstime as traditional constant heating rate TGA.

Figure B.21


Hi-ResTM Option

Figure B.22

Figure B.23

Appendix B


Figure B.24

Figure B.25


Hi-ResTM Option

ReferencesListed below are two excellent additionalreferences for specific materials and techniques.These have been chosen because they give abroad review of the techniques involved andaddress the physical and chemical processestaking place, as opposed to a specific analysis ofany one sample material. Each paper containsan extensive list of additional references forspecific materials and techniques.

1. Thermoananlytical Examinations UnderQuasi-Isothermal - Quasi-IsobaricConditions, F. Paulik & J. Paulik,Thermochimia Acta., 100 (1986) 23-59.

2. Controlled Transformation Rate ThermalAnalysis: The Hidden Face of ThermalAnalysis, J. Rouquerol, ThermochimicaActa., 144 (1989) 209-224.

Hi-ResTM is a trademark of TA Instruments, Inc.TYGON® is a registered trademark of NORTON Co.ACCENT® is a registered tradmark of PET, Inc.

Appendix B


TA INSTRUMENTS TGA 2950 C–1

TGA 2950 Autosampler Option

Appendix C: TGA 2950Autosampler Option

Introducing the Auto TGA......................... C-3

Getting Started ........................................... C-4

The TGA 2950 Instrument ......................... C-6

Calibrating the Auto TGA ....................... C-10

Running Experiments .............................. C-11

Preparing the Samples ....................... C-12

Selecting Sampleand Tare Pans ............................. C-12Taring the Sample Pans .............. C-13

Loading the Samples ......................... C-16

Setting Up an Experiment ................. C-18

Manual Operation ............................. C-19

Tracking the TGAAutosampler Status ........................... C-19

Interrupting a Run ............................. C-20

Appendix C

TA INSTRUMENTS TGA 2950C–2



Introducingthe Auto TGA

The TGA Autosampler, known as the AutoTGA, is an accessory to the TA InstrumentsThermogravimetric Analyzer (TGA) 2950 (seeFigure C.1 on the next page). It allows you toplace up to 16 samples at one time on the TGAinstrument to measure the amount and rate ofweight change in a material. Experiments areperformed as they normally would be using theTGA�but now you can run samples on acontinual basis and keep a log of the resultsusing the Autosampler screens. The six (6)standard TGA pans listed below are used withthe Auto TGA:

· 100 µL aluminum· 50 and 100 µL platinum pans and· 100, 250, and 500 µL alumina ceramic

pans.

This appendix provides information on the setup of the Auto TGA. For instructions on the useof the Auto TGA through the Instrument Controlsoftware, please refer to the online help anddocumentation for further information.

Appendix C


Figure C.1Auto TGA



GettingStarted

The Auto TGA, as an accessory to the TGA,does not alter the procedures used to start up andshut down the TGA instrument and the control-ler; refer to the procedures found in Chapter 3 ofthis manual when starting your instrument.

Appendix C


The TGA 2950Instrument

When you receive your Auto TGA, you willnotice that a key has been added to the TGAinstrument keypad�the AUTO SELECT key,shown in the figure below.

Figure C.2TGA Instrument Displayand Keypad with AutoTGA Accessory

Table C.1 on page C-5 explains the functions ofthe instrument keys when used in conjunctionwith the Auto TGA accessory.




&

Table C.1Auto TGAInstrument Keys


SCROLL Scrolls the realtimesignals shown on thebottom line of the display.For more information onthe progress of theexperiment, refer to theonline help and documen-tation.

Auto TGA function: Thiskey has an added func-tion, to act as a shift keyfor the AUTO SELECT,TARE, and LOAD keys.

AUTO SELECT Auto TGA function:Increments the next pan tobe loaded when pressedalone.

SCROLL Auto TGA function:Decrements the next panto be loaded when you

AUTO SELECT hold down the SCROLLkey while pressing AUTOSELECT.

The selected sample isloaded or tared when theappropriate key ispressed.

(table continued)

Appendix C


Table C.1(continued)


TARE Auto TGA functions:Zeros the displayedweight of an emptysample pan: automati-cally loads the pan fromthe sample platform,raises the furnace toprotect the pan from aircurrents, weighs the pan,stores the weight as anoffset, and then unloadsthe pan.

Performs a tare on theselected pan when pressedalone.

SCROLL/TARE Auto TGA function:Tares all of the pans onthe sample platform whenyou hold down theSCROLL key whilepressing TARE.

LOAD Loads the selected panfrom the sample platformonto the balance.

Auto TGA function:Loads the selected samplepan when pressed alone.

(table continued)



DFURNACE D

NOTE:

Table C.1(continued)


SCROLL/LOAD Continuously loads andunloads all of the pans onthe sample platform whenyou hold down theSCROLL key whilepressing LOAD.

LOAD functions canbe stopped by pushingthe STOP key on theinstrument keypad.

UNLOAD Functions of these re-maining keys do notchange when used withthe Auto TGA accessory;see Chapter 1.

START

STOP

REJECT(SCROLL/STOP)

Appendix C


Calibratingthe Auto TGA

When using the Auto TGA accessory, the needfor calibration remains the same�weightcalibration and temperature calibration arerecommended at least once a month or whenreplacing the thermocouple; and the platformadjustment procedure needs to be performed ifthe sample hang-down wire fails to pick up asample pan. See the online help and documenta-tion for further information.



RunningExperiments

Performing experiments with the Auto TGA issimilar in many respects to the regular operationof the TGA instrument, the exceptions areexplained in this section.


� Selecting the pan type and material� Loading the pans� Taring the empty sample pans� Loading the samples into the pans� Entering experiment information through

the TA controller (sample and instrumentinformation).

� Creating and selecting the thermal methodon the controller.

� Attaching and setting up externalaccessories as required (e.g., purge gas, GasSwitching Accessory).

� Starting the experiment.

Appendix C


Preparing the Samples

Selecting Sampleand Tare Pans

The Auto TGA can utilize the same types ofpans that are available for the TGA 2950instrument.

When you are using the Auto TGA, it is possibleto prepare from 1 to 64 different samples. Eachsample platform can hold 16 numbered samples.The four sample platforms are numbered in thefollowing ranges:

· 1-16 samples· 17-32 samples· 33-48 samples· 49-64 samples.

Once you have selected the type of pan that youwish to use, you must use the same type of panfor all of the samples on the sample platformdisk. The same type of pan that you use forexperiments must also be used as a tare pan.

Tare Pan

1. Obtain a pan of the same type and size to beused for your experiments.

2. Remove the tare tube.

3. Use brass tweezers to hang the tare pan fromthe tare hook.

4. Mechanically tare the balance using the firststep of the weight calibration procedure.



5. Replace the tare tube.

Before running any experiments on the TGAyou must tare the sample pans to ensure that theweight measured by the balance reflects theweight of the sample only. You should tare thesample pans before each experiment, even if youuse the same set of pans in consecutive experi-ments.

Taring theSample Pans

When you tare the sample pans, the TGA readsthe weight of the empty pans in their numberedorder and then stores these weights as a set ofoffsets. These offsets are subtracted fromsubsequent weight measurements for eachnumbered sample. You can tare the pansmanually or automatically as explained here.

View the Autosampler log, found on the InstrumentControl software, after taring to determine which pan, ifany, does not tare during the procedure (Error 118). Ifa tare error occurs, replace the pan and manuallyretare it.

NOTE:

Appendix C


Automatic Tare

Because the TGA 2950 has two weight ranges,taring is done for both ranges. The tare weightis stored by the instrument for the appropriateweight range.

1. Place the platform on the sample arm asshown in Figure C.3. Make sure that thesmall pin is inserted in the hole in theplatform. This will seat the platformcorrectly.

2. Using brass tweezers, place each sample panin a numbered place on the platform, makingsure it is stable.

Figure C.3Loading the AutoTGA Sample Platform



3. Hold down the SCROLL key, then press theTARE key on the instrument keypad. TheTGA will perform the following tare func-tions on each pan automatically:

· Load the pan· Raise the furnace (to protect the pan from

air currents)· Weigh the pan· Store the weight as the offset for each

weight range· Unload the pan.

The Auto TGA will automatically tare each ofthe remaining pans in sequence. It should takeapproximately 45 minutes to tare all 16 pans onone sample platform. When the Auto TGA hascompleted taring each pan on the sample plat-form, the tare status message will disappear.

The advantage to using the Auto TGA is to savetime and effort; therefore, it would not be efficientto perform manual tare operations on eachsample, as that would defeat the purpose of anautomatic operation. But, if manual taring isdesired, see Chapter 3 for the procedure.

NOTE:

Appendix C


Loading theSamples

After you have done the taring procedures for allof the empty sample pans, load the samples asfollows:

1. Place each sample in the correct sample panmaking sure that you do not switch aroundthe pans on the sample platform (they havealready been tared in the numbered posi-tion).

2. Place the sample pans on the sample plat-form in their original order. Make sure thatthe wire on the bottom of the sample pansalign with the groove in the panhole, so thatthe sample pan can be picked up by thesample hang-down wire.

Always use the brass tweezers to handle thesample pans.

Manually loading the sample pan onto the hang-down wire may damage the balance mechanism.

3. Press the LOAD key. The TGA will auto-matically load the selected sample.

4. Position the thermocouple at the edge of thesample pan, rather than in the middle for thebest results (see Figure C.4).

The position of the thermocouple should be thesame as it was during temperature calibration.

NOTE:

t CAUTION:

NOTE:



5. Press the UNLOAD key. The TGA willunload the sample and be ready for auto-matic sequencing.

Figure C.4Adjusting theThermocouple

Appendix C


Setting Up anExperiment

Once you have prepared the sample, the nextstep in your experiment is to enter the neededinformation in the TA controller. All of thecontroller functions described in this section areaccessed through the Instrument Control screen.Refer to the online help and documentation tolearn how to perform the following steps.

1. Select the Instrument.

2. Select the Instrument Mode.

3. Access the Autosampler Sequence.

4. Enter Sample Information.

5. Enter Instrument Information.

If you are planning to run the Autosampler, besure to specify furnace open at method end, aswell as air cool, to cool down the furnace betweensamples.

6. Create and Select Thermal Methods.

The first time you use your TGA you will needto create at least one thermal method to controlexperiments. Each method is made of severalsegments, or individual instructions (e.g.,Equilibrate, Ramp), that control the state of theinstrument. A different method may be selectedfor each sample.

NOTE:



Manual Operation

Use the AUTO SELECT and/or SCROLL/AUTO SELECT to manually select the pan thatyou want to run, then follow the proceduresfound on in Chapter 3 to start, stop, and monitoran experiment.

For details setting up the methods consult theonline help and documentation.

Tracking the TGAAutosampler Status

To monitor the current run, observe the status ofthe Auto TGA , etc. you will need to access theTA Instruments Instrument Control software.Refer to the online help and documentation forfurther information.

Appendix C


Interrupting a Run

If you want to stop an Auto TGA run that is inprogress, you can use one of the following keyson the TGA instrument keypad:

� Stop Terminates the currentmethod and run andcauses the Auto TGA tounload the pan and startthe next run. However,the data file for theinterrupted run is saved.

� Reject Terminates the currentmethod and AS run andcauses the Auto TGA tounload the cell and startthe next run. The data filefor the interrupted run isdiscarded.

� Other options are available through thecontroller functions, see the online help anddocumentation for further information.

TGA 2950 EGA Furnace Option

TA INSTRUMENTS TGA 2950 D–1

Appendix D:TGA 2950 EGA Furnace Option

Introducing the EGA Furnace .................... D-3

EGA Furnace Specifications ............... D-5

Installing the EGA Furnace ....................... D-6

First-Time Installation ........................ D-6

Removing and Reinstalling theEGA Furnace .................................... D-14

EGA Furnae Removal ................. D-14EGA Furnace Installation ........... D-16

Connecting the Spectrometer ................... D-18

Using the EGA Furnace ........................... D-21

Cleaning the Quartz Furnace Tube .......... D-22

Appendix D

TA INSTRUMENTS TGA 2950D–2



Introducingthe EGA Furnace

The Evolved Gas Analysis (EGA) Furnace(Figure D.1) is an optional accessory that allowsyou to connect a spectrometer to the instrumentso that the gases evolved by sample decomposi-tion can be analyzed. The EGA furnace and thestandard TGA furnace can be exchanged easilyon the instrument after initial hardware installa-tion. Version 3.3B (or higher) of the TGA 2950instrument software is required for the EGAfurnace.

Figure D.1TGA 2950 EGA Furnace

Appendix D


The following description of the EGA furnace mayalso be found in Chapter 4 of this manual.

The EGA furnace consists of a quartz glasssample tube surrounded by an electric resistanceheater, both of which are contained within awater-cooled furnace housing. The housing ismounted to a furnace base that raises andlowers the furnace for sample loading andunloading.

The sample tube has a purge gas inlet thatpasses through the right side of the furnacehousing. A fitting on the left side of the housingallows connection of a transfer line to carryexhaust gas to a spectrometer such as a massspectrometer. Because the heater is external tothe sample tube, evolved gases from sampledecomposition within the sample tube do notcome in contact with the resistance elements orthe furnace ceramic refractory.

Cooling air enters through the furnace base andpasses upward between the outside of thesample tube and the inside of the furnace,completely separating the cooling air from thesample and the sample zone.

The furnace is a resistance heater wound onalumina ceramic, which allows sample zonetemperatures as high as 1000°C with heatingrates up to 50°C/min.

A Platinel II* thermocouple is positioned in thefurnace, just above the sample pan, where itmonitors the sample environment temperature.

*Platinel II is a registered trademark of EngelhardIndustries.

NOTE:



The furnace base moves the furnace assemblyup around the sample pan to the closed position,or down away from the sample pan to the openposition.

EGA FurnaceSpecifications

Refer to Table D.1 below for the specificationsof the EGA furnace. Some of these may besimilar to the standard furnace for the TGA2950.

Table D.1EGA FurnaceSpecifications

Temperature range 25°C to 1000°C

Thermocouple Platinel II*

Heating rate 0.1 to 50°C/min

*Platinel II is a registered trademark of Engelhard Industries.

Appendix D


Installingthe EGA Furnace

Make sure that you place the heater powerswitch in the off position before removingor installing the furnace on the TGA 2950instrument.

Version 3.3B (or higher) of the TGA 2950instrument software is required for the EGAfurnace.

First-TimeInstallation

The first time that you install the EGA furnaceinvolves the removal of the standard TGAfurnace and replacement of the four furnacemounting screws and cleats with those suppliedwith the EGA furnace.

After this has been completed according to thefollowing directions, you may interchange thetwo types of furnaces without changing themounting hardware. Refer to page D-13 “Re-moving and Reinstalling the EGA Furnace” forsubsequent furnace exchanges.

1. Place a drip pan to the left of the instrumentto catch the coolant that will leak from thehose connections when the standard furnaceis removed.

2. Remove the standard TGA furnace usingsteps 1 through 5 found in Chapter 5 “Re-moving and Reinstalling the Furnace.”

!WARNING



Make sure that you do not remove thefurnace from its housing.

3. Unplug the AIR COOL line from the bottomof the furnace arm/base.

When you remove the AIR COOL line, do not let itslip back into the instrument cabinet.

4. Lay the furnace assembly down on the leftside of the instrument so that the hoseconnections are positioned over the drippan. Visually note the left (AAA) and right(CCC) orientation of the water lines so thatyou do not cross them later when they arereconnected. (See Figure D.2.) Thencarefully snip the wire ties and disconnectthe cooling water lines from the housing. (Asmall amount of cooling water will drain outinto the pan when the hoses are discon-nected.)

5. Press the FURNACE key to lower thefurnace carriage completely.

6. Remove the four mounting screws and cleatsfrom the furnace carriage (see Figure D.2).

NOTE:

Appendix D


Figure D.2Removing the FurnaceCarriage Mounting Screws

7. Use the 3/32-inch ball driver supplied withthe EGA installation kit to replace thescrews with the new screws, spacers andcleats provided with the kit. Refer to FigureD.3. Replace the upper screws using thelong screws with spacers and replace thelower screws using the short screws withoutspacers.

WaterLine(CCC)

Water Line (AAA)

Water Line(CCC)

MountingScrews



Figure D.3Installing the EGA MountingScrews, Spacers, and Cleats

8. Tighten the upper two mounting screwsfully, then loosen each of them no more thanone full turn, so that the flat sides of thecleats are aligned vertically as shown inFigure D.4.

Now tighten the lower two mounting screwsfully, then loosen each of them two fullturns, plus a fraction of a turn, so that theflat sides of the cleats are aligned verticallyas shown in Figure D.4.

Cleat

Short Screw

Spacer

Cleat

Long Screw

Appendix D


Figure D.4Aligning the Cleats

Loosening the upper two mounting screwsany more than one full turn may cause thescrews to interfere with the inside of theinstrument cabinet, causing damage to theinstrument.

9. Plug the AIR COOL line into the base of theEGA furnace, then connect the two water-cooling lines, making sure that the lines arenot crossed. See Figure D.5 for the correctplacement of the lines. Be sure to install thewire ties (supplied in the kit) around thecooling lines to prevent water leakage.

!WARNING



Figure D.5Plugging in theAIR COOL Line

10. Press the FURNACE key to raise thefurnace carriage until the lower mountingscrews are below the top edge of the en-larged cutout in the instrument faceplate.Then press the STOP key.

11. Plug the EGA furnace arm into the connec-tor on the carriage and tighten the lower twomounting screws using the 3/32-inch balldriver supplied with the TGA 2950 EGA.See Figure D.6 on the next page.

Wire Ties

WaterCoolLines

AirCoolLine

Appendix D


Figure D.6Tightening theLower Mounting Screws

12. Press the FURNACE key to completelylower the furnace. Use the 3/32-inch balldriver to tighten the upper furnace mountingscrews. To reach the upper left mountingscrew, insert the ball driver between thewater connections on the left side of thefurnace housing as shown in Figure D.7.



Figure D.7Tightening theUpper Mounting Screws

13. Connect the purge hose to the gas purgeinlet on the right side of furnace.

Hold onto the glass purge tube with one handwhile you install the purge hose to avoid breakingthe glass.

14. Check the Heat Exchanger reservoir waterlevel and add water if needed. See Chapter2 “Filling the Heat Exchanger” for instruc-tions.

t CAUTION:

Appendix D


Removing andReinstallingthe EGA Furnace

Make sure that you place the heater powerswitch in the off position before removingor installing the furnace on the TGA 2950instrument.

To remove or reinstall the furnace, you will haveto remove the furnace arm from its connectioninside the slot on the front of the instrumentcabinet.

EGA Furnace Removal

To remove the EGA furnace use the followingprocedure:


2. Locate the top two mounting screws on eachside of the furnace arm connection, found inthe slot on the front of the instrument.Using the 3/32-inch ball driver suppliedwith the EGA furnace, loosen the twoscrews no more than one full turn. To reachthe upper left mounting screw, insert the balldriver between the water connections on theleft side of the furnace housing. Refer toFigure D.7 for the location of these screws.

3. Press the FURNACE key to raise thefurnace about one (1) inch and press STOP.

!WARNING



4. Loosen the bottom two mounting screwsusing the 3/32-inch ball driver supplied withthe TGA 2950 EGA. See Figure D.6.

5. Unplug and remove the EGA furnace arm/base from the instrument cabinet.

6. Unplug the AIR COOL line from the bottomof the furnace arm/base.

When you remove the AIR COOL line, do not let itslip back into the instrument cabinet.

7. Place a drip pan to the left of the instrumentto catch the coolant that will leak from thehose connections when the EGA furnace isremoved.

8. Lay the furnace assembly down on the leftside of the instrument so that the hoseconnections are positioned over the drippan. Then carefully snip the wire ties anddisconnect the cooling water lines from thehousing. (A small amount of cooling waterwill drain out into the pan when the hosesare disconnected.)

The furnace is now completely free from theinstrument.

NOTE:

Appendix D


EGA Furnace Installation

To replace or reinstall the EGA furnace:

1. Plug the AIR COOL line into the bottom ofthe furnace arm/base as shown in Figure D.5on page D-11.

2. Slip the water cooling hoses over the EGAfurnace water connections and secure themwith the wire ties.

3. Tighten the upper two mounting screwsfully, then loosen each of them no more thanone full turn, so that the flat sides of thecleats are aligned vertically as shown inFigure D.4 on page D-10.

Now tighten the lower two mounting screwsfully, then loosen each of them two fullturns, plus a fraction of a turn, so that theflat sides of the cleats are aligned verticallyas shown in Figure D.4 on page D-10.

Loosening the upper two mounting screwsany more than one full turn may cause thescrews to interfere with the inside of theinstrument cabinet, causing damage to theinstrument.

4. Press the FURNACE key to raise thefurnace carriage until the lower mountingscrews are just below the top edge of theenlarged cutout in the instrument faceplate.Then press the STOP key.

!WARNING



5. Plug the EGA furnace arm into the connec-tor on the carriage and tighten the lower twomounting screws using the 3/32-inch balldriver supplied with the EGA. See FigureD.6 on page D-12.

6. Press the FURNACE key to completelylower the furnace. Use the 3/32-inch balldriver to tighten the upper furnace mountingscrews. To reach the upper left mountingscrew, insert the ball driver between thewater connections on the left side of thefurnace housing as shown in Figure D.7 onpage D-13.

7. Connect the purge hose to the gas purgeinlet on the right side of furnace.

Hold onto the glass purge tube with one handwhile you install the purge hose to avoid breakingthe glass.

8. Check the Heat Exchanger reservoir waterlevel and add water if needed. See “Fillingthe Heat Exchanger” for instructions.

t CAUTION:

Appendix D


Connectingthe Spectrometer

The TGA 2950 EGA furnace allows you toconnect a spectrometer, such as a FTIR spec-trometer, to the instrument. To connect anyspectrometer, you will need to use a transfer line(supplied by the spectrometer manufacturer) totransport the gas evolved from the sample on theTGA to the spectrometer.

• The transfer line should be 1/8 inch indiameter to connect with a 1/8-inchSwagelokTM fitting on the exhaust gasconnection.

• The transfer line should be made of heat-resistant alloy capable of resistingcorrosion by the evolved gas and oxidationat temperatures up to 1000°C.

• The transfer line must pass through theexhaust gas fitting and a glass branch tubein the sample tube. It should end at a pointjust short of the inside diameter of thesample tube to ensure that the evolved gasesdo not condense before entering the transferline.

• The transfer line must be long enough toallow flexible movement. It mustaccommodate movement of the EGAfurnace up and down 3 5/8 inches to openand close for sample loading and unloading.(If the transfer line is not long enough, itmust be disconnected and reconnected eachtime the furnace is opened and closed.)



To connect your spectrometer to the EGAfurnace follow these steps:

1. Install a SwagelokTM nut, drive ring, andferrule on the correct length of transfer line,leaving more than two inches of transfer lineprojecting beyond the ferrule.

2. Swage the ferrule, then cut the end of thetransfer tube off so that two inches of thetube projects beyond the ferrule. See FigureD.8 below

Extending the transfer line more than two inchesbeyond the SwagelokTM fitting may cause the TGA2950 to operate improperly.

Figure D.8EGA Transfer Linewith Ferrule

3. Make sure that the end of the transfer line isstraight and free of oxide deposits beforeyou insert it into the exhaust gas connection.

Ferrule

2 inches

Drive RingTransfer Tube

Nut

NOTE:

Appendix D


4. Insert the transfer line and tighten theSwagelokTM nut to seal the connector.When you tighten the SwagelokTM nut, use a3/8-inch wrench on the exhaust fitting flatsto prevent them from turning.

If the transfer line is not straight, or hasheavy oxide deposits on it, the sample tubemay be broken as the line is inserted.

!WARNING



Using theEGA Furnace

After proper installation, the EGA furnace canbe used as you would normally use the TGAstandard furnace. No special procedures mustbe followed when preparing TGA samples,setting up methods, or running experiments.Refer to the appropriate sections in the mainmanual for information. Follow themanufacturer's instructions for the use of yourspectrometer when connected to the EGAfurnace.

Appendix D


Cleaning theQuartz Furnace Tube

If the TGA is used to evaluate materials usingan oxygen purge, the furnace should becleaned routinely to prevent build-up of volatilehydrocarbon residues that could combust.

Do not touch the furnace sample tube withyour bare fingers. Skin oils may causedevitrification of the quartz glass, resultingin severely reduced sample tube life. Donot insert metallic instruments inside thesample tube to scrape or chip contaminantsfrom the sample tube as breakage mayresult.

To clean the furnace quartz sample tube, use thefollowing procedure:

Do not disturb the hangdown wire andfurnace thermocouple located directlyabove the furnace when cleaning the fur-nace, as damage may result.


2. Remove any sample pans.

3. Remove the rubber cap located on theunderside of the furnace base.

4. Place a small cup under the furnace tube.Rinse the furnace tube using a solvent (suchas alcohol) to remove debris. The solventwill drain out of the bottom of the tube intothe cup.

!WARNING

!WARNING

!WARNING



5. Using a soft bristle brush (we recommend aflexible bottle brush), gently slide the brushup and down to clean out the inside of thefurnace tube, allowing the handle to bendfreely (see Figure D.9).

Figure D.9Cleaning theInside of theFunace Tube

6. Rinse the furnace tube with the solventagain.

7. Replace the rubber cap on the quartz tubestem when you have completed the cleaningprocedure.

8. Purge the system with nitrogen for one hour.

9. Heat the furnace to 900°C to remove anyremaining solvent.

Appendix D



Index

Index

Aaccessories 1-11

setting up 3-15

Air Cool (status code) 4-17

air-coolusing 3-16

Autosampler C-1 to C-20

Auto Zero 3-10

B

balance 1-4, 3-16, 4-6arm 4-6arm sensor 4-6unpacking 2-20

binary address switches 2-16

C

cabinet 1-4, 4-13

cableGPIB 2-15

Calib (status code) 4-17

calibration 3-5sample platform 3-6temperature 3-5weight 3-6

cleaning 3-9EGA furnace quartz tube D-22

Closing (status code) 4-17

Cold (status code) 4-17

Complete (status code) 4-17

components 1-4, 4-5

confidence test 5-19

controllerdescription 1-3

Cooling (status code) 4-18

cooling gas line 2-18

D

descriptionTGA 2950 4-3

display 1-5

E

EGA furnace 1-11, 4-11

Ending (status code) 4-18

Equilb (status code) 4-18

Index

TA INSTRUMENTS TGA 2950I–2

Evolved Gas Analysis (EGA)Furnace D-3 to D-24. See alsoEGA furnace

cleaning D-22description D-3installation D-6, D-16reinstallation D-14specifications D-5usage D-21

experimentoxygen-free atmosphere 3-22

set up 3-23procedure 3-7rejecting 3-21setting up 3-14starting 3-20stopping 3-21

F

furnace 1-4cleaning 5-5EGA 4-9, 4-11, D-1reinstalling 5-11removing 5-11standard 4-9

furnace base 4-10

furnace housing 4-10

furnace tubecleaning D-22

FURNACE up key 1-7fuses 5-16

G

gaspurge 3-16types 3-17

Gas Switching Accessory 1-11,3-19

gasesrecommended 2-17

GPIB cable 2-15

H

hang-down wires 4-7aligning 2-25installing 2-22

heat exchanger 1-4, 4-15, 5-6cables 2-12coolant 5-6filling 2-10lines 2-12water reservoir 5-6

heater 4-10, 4-12

HEATER switch 1-10

Heating (status code) 4-18

High Resolution option B-5 toB-12

Holding (status code) 4-18

Hot (status code) 4-19


Index

I

Initial (status code) 4-19

instrument.See TGA 2950

Iso (status code) 4-19

J

Jumping (status code) 4-19

K

keypad 1-6

L

linesconnecting 2-12

Load (status code) 4-19

LOAD key 1-7

M

meter movement 4-6

N

No Power (status code) 4-19

O

Opening (status code) 4-20

ordering information A-1

oxygen-free atmosphere 3-22

P

pans 3-8, 4-7cleaning 3-9unloading 3-21

parts 5-21

power problemsfailures 5-18

POWER switch 1-10

purge gas 2-18, 3-16

purge lines 2-17

R

Ready (status code) 4-20

Reject (status code) 4-20

REJECT function 1-8

Repeat (status code) 4-20

routine maintenance 5-4

S

sampleloading 3-11, 4-8preparing 3-8unloading 3-21

Index


sample pans 3-8

sample platform 1-4adjusting 2-29calibration 3-6

SCROLL key 1-6

SCROLL-STOP keys 1-8

Set Up (status code) 4-20

specifications 1-12

spectrometerconnecting to EGA furnace D-18

Stand by (status code) 4-20

START key 1-7

Started (status code) 4-21

status codes 4-17.See also name ofcode

STOP key 1-8

T

Tare (status code) 4-21

TARE key 1-6

taring 3-9automatic 3-10manual 3-10

Temp °C (status code) 4-21

Temp* (status code) 4-21

test functions 5-19

TGA 2950accessories 1-11 to 1-12address switches 2-15air cool 3-16autosampler C-3 to C-20cables

GPIB 2-15power 2-19

calibrating 3-5temperature 3-5weight 3-6

cleaning 5-4furnace 5-5

components 1-4, 4-5balance 4-6cabinet 4-13hang-down wire 4-7

confidence test 5-19description 1-3, 4-3display 1-5EGA furnace D-3 to D-23furnace

installing 5-14removing 5-11

hang-down wiresaligning 2-25

heat exchanger 4-15, 5-6filling 2-10water lines 2-12

High Resolution option B-5inspecting 2-8installing 2-7–2-19

hang-down wires 2-22


Index

TGA 2950 (cont’d)instrument characteristics 1-12keypad 1-6lines

cooling gas 2-18purge 2-17

loading samples 3-11location 2-9operating parameters 1-12power problems 5-18power switch 1-10purge gas 2-18, 3-16purge gas types 3-17repacking 2-6–2-7replacement parts 5-21routine maintenance 5-4sample pans 4-7

loading 4-8sample platform

adjusting 2-29sampling system 1-13setting up an experiment 3-14specifications 1-12starting 2-30status codes 4-17stopping 2-32tare pans 4-7test functions 5-19theory of operation 4-16thermocouple

replacing 5-9unpacking 2-3–2-6weight ranges 4-3

thermocouple 4-10, 4-12replacing 5-9

Thermogravimetric analysis 4-16

Thermogravimetric Analyzer.SeeTGA 2950

U

Unload (status code) 4-21

UNLOAD key 1-7

W

Weight # (status code) 4-21

Index


Documents

Thermal Analysis & Rheology · ii TA INSTRUMENTS TGA 2950 '1995, 1996, 1997, 2000 by TA Instruments, Inc. 109 Lukens Drive New Castle, DE 19720 Notice The material contained in this