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7/30/2019 Differential Thermal Analysis (DTA).ppt
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DIFFERENTIAL THERMALANALYSIS (DTA)
Presented By
Mr. Shaise Jacob
Faculty
Dept. of Pharmaceutical Analysis
Nirmala College of Pharmacy
Muvattupuzha, Kerala
India
E mail - [email protected]
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Types of thermal analysis
TG (Thermogravimetric) analysis:
weight
DTA (Differential Thermal Analysis):temperature
DSC (Differential ScanningCalorimetry):temperature
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In Differential Thermal Analysis, the
temperature difference that developsbetween a sample and an inert referencematerial is measured, when both are subjected
to identical heat - treatments. The related technique ofDifferential Scanning
Calorimetryrelies on differences in energyrequired to maintain the sample and reference
at an identical temperature.
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Thermogravimetry (TG)
Thermogravimetry is the measurement of themass of a sample as the temperature increases.This method is useful for determining samplepurity and water, carbonate, and organic
content; and for studying decompositionreactions.
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INTRODUCTION
This is a comparison method
Analytical method for recording thedifference in temperature (T) b/w asubstance and an inert reference material asa function of temperature or time
Any transformation change in specific heat
or an enthaply of transition can be detectedby DTA
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In DTA both test sample & an inert referencematerial (alumina) controlled heating orcooling programming
If zero temperature difference b/w sample &
reference material sample does notundergo any chemical or physical change.
If any reaction takes place temperaturedifference (T) will occur b/w sample &reference material
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A DTA curve can be used as a finger print foridentification purposes, for example,
in the study of clays where the structural
similarity of different forms renders diffractionexperiments difficult to interpret.
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T VS Temp.
Sharp Endothermic changes in crystallanity or fusionBroad endotherms - dehydration reaction
Physical changes usually result in endothermic curves
Chemical reactions are exothermic
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Apparatus
The key features of a differential thermalanalysis kit are as follows
1. Sample holder comprising thermocouples,sample containers and a ceramic or metallic
block.
2. Furnace.3. Temperature programmer.
4. Recording system.
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Heart of the analysis heating block
Identical pair of cavities for the sample, ref.material
Whole unit is set in an oven- control pressure
Thermocouple is place directly in contact withthe sample and another in contact with the
reference Temp.of the block is raised, the temperature of
the sample & reference follow
Zero temp. difference no physical or chemicalchange
If any reaction difference in T
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Differential Thermal Analysis
advantages:
instruments can be used at very hightemperatures
instruments are highly sensitive
characteristic transition or reactiontemperatures can be accuratelydetermined
disadvantages:
uncertainty of heats of fusion, transition,or reaction estimations is 20-50%
DTA
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Factors affect results in DTA
Sample weight
Particle size
Heating rate
Atmospheric conditions
Conditions of sample packing into dishes
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Applications
Quantitative identification and purityassessment of materials are accomplished bycomparing the DTA curve of sample to that ofa reference curve
Impurities may be detected by depression ofthe M.P
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