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4 Anadolu University Materials Science and Engineering Department MLZ 306 Materials Processing Laboratory-II 2015-2016 Course Instructors Prof. Dr. Cemail AKSEL Prof. Dr. Ferhat KARA Prof. Dr. Gürsoy ARSLAN Assoc. Prof. Dr. Dilek TURAN Assoc. Prof. Dr. A. Tuğrul SEYHAN Assist. Prof. Dr. Emrah DÖLEKÇEKİÇ Assist. Prof. Dr. G. İpek NAKAŞ Laboratory Instructors Res. Assist. Özlem TUZLACI Res. Assist. Umut SAVACI Res. Assist. K. Burak DERMENCİ Res. Assist. S. Çağrı ÖZER Res. Assist. Hande MARULCUOĞLU Res. Assist. H. Şule ÇOBAN Res. Assist. Burak DEMİR Celal ÇELEBİ Ramazan KALE Merve GEÇGİN Ufuk AKKAŞOĞLU Ayşegül AKYÜREKLİ Gülden TOK Şükran GÜRCAN Course Coordinator Dr. H. Boğaç POYRAZ

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4

Anadolu University

Materials Science and Engineering Department

MLZ 306

Materials Processing Laboratory-II

2015-2016

Course Instructors Prof. Dr. Cemail AKSEL Prof. Dr. Ferhat KARA Prof. Dr. Gürsoy ARSLAN Assoc. Prof. Dr. Dilek TURAN Assoc. Prof. Dr. A. Tuğrul SEYHAN Assist. Prof. Dr. Emrah DÖLEKÇEKİÇ Assist. Prof. Dr. G. İpek NAKAŞ

Laboratory Instructors Res. Assist. Özlem TUZLACI Res. Assist. Umut SAVACI Res. Assist. K. Burak DERMENCİ Res. Assist. S. Çağrı ÖZER Res. Assist. Hande MARULCUOĞLU Res. Assist. H. Şule ÇOBAN Res. Assist. Burak DEMİR Celal ÇELEBİ Ramazan KALE Merve GEÇGİN Ufuk AKKAŞOĞLU Ayşegül AKYÜREKLİ Gülden TOK Şükran GÜRCAN

Course Coordinator Dr. H. Boğaç POYRAZ

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MLZ 306 Materials Processing Laboratory-II

Instructors: MLZ 306 P Assoc. Prof. Dr. A. Tuğrul SEYHAN

MLZ 306 S Prof. Dr. R. Ferhat KARA

MLZ 306 W Prof. Dr. Gürsoy ARSLAN

MLZ 306 X Assoc. Prof. Dr. Dilek TURAN

MLZ 306 Y Assist. Prof. Dr. Emrah DÖLEKÇEKİÇ

MLZ 306 Z Prof. Dr. Cemail AKSEL

MLZ 306 T Assist. Prof. Dr. G. İpek NAKAŞ

Coordinator: Dr. H. Boğaç POYRAZ

GRADING TABLE

Exam Exam Type Percentage of Exam

II. MIDTERM

6 Quizzes* (Exp#1, Exp#2, Exp#3,

Exp#4, Exp#5, Exp#6) 50 %

FINAL 6 Reports*

(Exp#1, Exp#2, Exp#3, Exp#4, Exp#5, Exp#6)

50 %

*No quiz and report for Experiment #7.

IMPORTANT NOTE : Minimum qualifying grade in this course is 50.

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Experiment ? Time ? Where ? Instructors ?

EXP #1

a) Heat Treatment of Steels 1 – 2 pm

MatSE Metallography Lab.-2 #MLZ 118

Umut SAVACI

Özlem TUZLACI

b) Microstructure Analysis in Metallic Materials 2 – 3 pm

c) Jominy – End Quench Test 3 – 4 pm

d) Hardness Testing Techniques 4 – 5 pm MatSE Metallography Lab.-1 #MLZ 119

EXP #2 a) NDT Experiments 2 – 3.30 pm Faculty of Aeronautics and Astronautics

A Block, Materials Lab.

Celal ÇELEBİ

b) Fatigue-Charpy Impact-Tension Testing 3.30 – 5 pm Ramazan KALE

EXP #3 a) Sonic Modulus 1 – 3 pm MatSE Lab.

#MLZ 232 Merve GEÇGİN S. Çağrı ÖZER

b) Porosimetry 3 – 5 pm MatSE Lab. #MLZ/S 207

Hande MARULCUOĞLU Ufuk AKKAŞOĞLU

EXP #4 a) Electrolytic Reduction of Zinc 1 – 3 pm

MatSE Process Lab. #MLZ 123

K. Burak DERMENCİ H. Şule ÇOBAN

b) Corrosion and Cathodic Protection 3 – 5 pm

EXP #5 a) Electrical & Structural Characterization of Thin Films and Coatings 1 – 3 pm MatSE Thin Film Lab.

#MLZ 129 Burak DEMİR

b) Electrical Property Measurements 3 – 5 pm MatSE Lab. #MLZ 232

Ayşegül AKYÜREKLİ Burak DEMİR

EXP #6 Polymer Processing 1 – 5 pm MatSE Polymer Lab. #MLZ 130 Şükran GÜRCAN

EXP #7 Standard Tests 2 – 5 pm Ceramic Research Center, Standard Tests Lab. Gülden TOK

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MLZ 306 Materials Processing Laboratory-II SCHEDULE

12.02.2016 Lab Meeting (MLZ M1) All groups

19.02.2016 Technical Excursion – (BİLECİK DEMİR ÇELİK A.Ş.) All groups

26.02.2016 Rotative Experiments

Report Submission Due By

04.03.2016

Group P - NDT Experiments,Fatigue-Charpy Impact-Tension Tests Group S - Standard Tests Group W - Polymer Processing Group X - Elec. & Struc. Charac. of Thin Films and Coatings - Electrical Property Measurements Group Y - Electrolytic Reduction of Zinc - Corrosion and Cathodic Protection Group Z - Sonic Modulus - Porosimetry Group T - Heat Treatment-Microstructure Analysis-Jominy-Hardness Testing

04.03.2016 Rotative Experiments

Report Submission Due By

11.03.2016

Group P - Heat Treatment-Microstructure Analysis-Jominy-Hardness Testing Group S - NDT Experiments, Fatigue-Charpy Impact-Tension Tests Group W - Standard Tests Group X - Polymer Processing Group Y - Electrical & Structural Characterization of Thin Films - Electrical Property Measurements Group Z - Electrolytic Reduction of Zinc - Corrosion and Cathodic Protection Group T - Sonic Modulus - Porosimetry

11.03.2016 Rotative Experiments

Report Submission Due By

25.03.2016

Group P - Sonic Modulus - Porosimetry Group S - Heat Treatment-Microstructure Analysis-Jominy-Hardness Testing Group W - NDT Experiments, Fatigue-Charpy Impact-Tension Tests Group X - Standard Tests Group Y - Polymer Processing Group Z - Electrical & Structural Characterization of Thin Films - Electrical Property Measurements Group T - Electrolytic Reduction of Zinc - Corrosion and Cathodic Protection

1st Midterm Week (14-19 March, 2016)

25.03.2016

Rotative Experiments

Report Submission Due By 01.04.2016

Group P - Electrolytic Reduction of Zinc - Corrosion and Cathodic Protection Group S - Sonic Modulus - Porosimetry Group W - Heat Treatment-Microstructure Analysis-Jominy-Hardness Testing Group X - NDT Experiments, Fatigue-Charpy Impact-Tension Tests Group Y - Standard Tests Group Z - Polymer Processing Group T - Electrical & Structural Characterization of Thin Films - Electrical Property Measurements

01.04.2016

Rotative Experiments

Report Submission Due By 08.04.2016

Group P - Electrical & Structural Characterization of Thin Films - Electrical Property Measurements Group S - Electrolytic Reduction of Zinc - Corrosion and Cathodic Protection Group W - Sonic Modulus – Porosimetry Group X - Heat Treatment-Microstructure Analysis-Jominy-Hardness Testing Group Y - NDT Experiments, Fatigue-Charpy Impact-Tension Tests Group Z - Standard Tests Group T - Polymer Processing

08.04.2016 Rotative Experiments

Report Submission Due By

15.04.2016

Group P - Polymer Processing Group S - Electrical & Structural Characterization of Thin Films - Electrical Property Measurements Group W - Electrolytic Reduction of Zinc - Corrosion and Cathodic Protection Group X - Sonic Modulus - Porosimetry Group Y - Heat Treatment-Microstructure Analysis-Jominy-Hardness Testing Group Z - NDT Experiments, Fatigue-Charpy Impact-Tension Tests Group T - Standard Tests

15.04.2016

Rotative Experiments

Report Submission Due By 06.05.2016

Group P - Standard Tests Group S - Polymer Processing Group W - Electrical & Structural Characterization of Thin Films - Electrical Property Measurements Group X - Electrolytic Reduction of Zinc - Corrosion and Cathodic Protection Group Y - Sonic Modulus - Porosimetry Group Z - Heat Treatment-Microstructure Analysis-Jominy-Hardness Testing Group T - NDT Experiments, Fatigue-Charpy Impact-Tension Tests

2nd Midterm Week (25-30, April, 2016) 06.05.2016 Technical Excursion – (not confirmed, to be announced later) All groups

13.05.2016 Technical Excursion – (not confirmed, to be announced later) All groups

Final Week (14-27, 2016)

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GENERAL INSTRUCTIONS FOR MLZ 306 MATERIALS PROCESSING LABORATORY-II

1. There will be one midterm and one final exam regarding to this course. All quizzes and

experiment reports will contribute to the overall grade. The midterm exam will cover “6 quizzes” (Exp#1, Exp#2, Exp#3, Exp#4, Exp#5, Exp#6) and the final exam will cover “6 reports” (Exp#1, Exp#2, Exp#3, Exp#4, Exp#5, Exp#6). There will be no quiz and report for the Exp#7.

2. It is extremely important that you read each experiment and basic references prior to the lab. The lab instructor will ask general questions during the lab to test your understanding of the lab.

3. It is obligatory to wear laboratory apron unless the lab instructor tells otherwise. Students

without aprons (lab coats) will not be admitted to the laboratory. 4. The lab groups must be present in the room/building where the lab will take place (stated

in the lab manual) 5 minutes before the lab starts. Students are obliged to learn the location of the labs before the labs begin.

5. All labs (except Exp#7) will be evaluated with a quiz and a report. It’s definitely obligatory

to have the lab. manual with you and read the corresponding lab. chapter before coming to the lab.

6. Before each lab. (except Exp#7) starts, there will be a quiz composed of 2-3 questions. 7. Students are responsible to submit the lab reports to the corresponding lab instructor’s box

on Friday until 12:00. These are not formal reports although neatness, organization, ect., of the report, as well as proper execution of the experiment will count towards your grade. The lab instructor will grade the lab. reports within a week and will post the results. If you wish to discuss the grade, make an appointment to see the lab instructor at his/her convenience. A copy of the graded reports will be handed to you upon your request if needed.

8. The nature of working in groups implies that there should be cooperation and discussion

between members of the group and the lab instructor. It is, however, expected that when students prepare their reports, that they do so individually using their own words and interpretation. Plagiarizing or blatant copying of a report or reference will result in an automatic zero for that lab for the first offense. A second offense will result in an automatic FF grade for the course.

9. Students must attend each lab on the specified group. The students will be admitted to the

class within the first half an hour. Lab reports must be handed in on time; otherwise 10% will be deducted from the mark for each day late.

10. Minimum qualifying grade for this course is determined as 50. 11. Lab. manuals will be available on the department web-site: http://matse.anadolu.edu.tr

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12. Instructions for Informal Lab Reports

(a) Each experiment should be organized in the report neatly and carefully;

For example;

Student Name : Student Number : Date: Lab. Group Number :

I. Experiment Name II. Equipment & Materials

III. Experimental Methods & Procedures IV. Important Parameters V. Results and Discussion

VI. Conclusions VII. Notes

VIII. References (if used)

(b) All the above will be neatly written, pasted, taped, etc. into the lab. report. (c) The reports must be written in English and will be prepared by handwriting, hand-drawing, and/or by the use of a computer. This will be announced by the lab instructor at the end of each experiment.

(d) The reports will not exceed “2 PAGES”, excluding Tables and Figures. Reports exceeding 2 pages will not be taken into account (unless the lab instructor requests otherwise).

(e) The reports will cover only 1-page of background information, if necessary. The second page will include the activities performed during the laboratory hour, comments, and the answers to the lab instructor’s questions and demands, if any.

*The requests of the lab instructors may be different from what is written in “General Instructions”. In that case, the reports will be prepared according to the requests of the lab instructors. If the lab. report is prepared by the use of a computer, both the hardcopy and digital copy will be handed to the corresponding lab. instructor.

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EXPERIMENT # 1: HEAT TREATMENT OF STEELS – MICROSTRUCTURE ANALYSIS IN METALLIC MATERIALS – JOMINY - END QUENCH TEST – HARDNESS TESTING TECHNIQUES (a) HEAT TREATMENT OF STEELS Objective: Investigation of conventional heat treatment procedures used to tailor the

properties of steels. Effects of heat treatment and different cooling conditions on microstructure and hardness.

Materials: AISI 4140 alloy steel, heat treatment oil (Petrofer isorapid 277hm) Equipment: Box furnace, oil and water baths. BACKGROUND

Metals and alloys for many structural and mechanical applications need to be hard, strong and tough. These required properties are dependent mainly on composition, and microstructure of the steel. In microstructure, the size and distribution of the phases and grains controls the mechanical properties. For a metal finer grains in the microstructure yields with greater hardness, strength and toughness. But the mechanical properties depend strongly on the phases present than the grains.

Heat treatment is a combination of heating and cooling operations applied to any metal or alloy in the solid state in order to obtain desired microstructure and mechanical properties. The microstructure of any heat treated metal is deduced using Continuous Cooling Transformation (CCT) which is related to the Time-Temperature-Transformation (TTT) diagrams of the selected metal sample. The CCT diagram for 4140 steel is shown in Figure 1. EXPERIMENTAL PROCEDURE

Heating the furnace

Placing the steel samples into the furnace

Stop the heating of furnace

Quenching with water

Quenching with oil

Cooled at furnace

Cooled at air

Sample Preparation

Microstructure Investigation

Hardness Tests

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Figure 1. CCT diagram of 4140 steel. [1]

Figure 2. TTT diagram of 4140 steel [2]

References: [1] Voort, G.F.V., Atlas of Time-Temperature Diagrams for Irons and Steels [2] ASM, Atlas of isothermal transformation and cooling transformations diagrams.

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(b) MICROSTRUCTURE ANALYSIS IN METALLIC MATERIALS Objective: The purpose of this laboratory is to acquaint students with the manner in

which metallurgical specimens are prepared for metallographic study, to correlate the relationship between the schematic sketches and the actual appearances of the microstructures.

Materials: A set of polished and etched identified and unidentified metal specimens. Equipment: Metallographic preparation facilities and metallurgical microscopes.

BACKGROUND

Introduction

A properly prepared metallographic sample can be aesthetically pleasing as well as revealing from a scientific point of view. The purpose of this practical is to understand how to prepare and interpret metallographic samples systematically. The process is illustrated below.

• Gather information about chemical composition, heat treatment, processing, phase diagram.

• Cut representative sample, noting plane of section relative to prominent features (e.g. long direction of rod).

• Mount sample, grind and polish. • Examine unetched sample. • Etch lightly and examine again. • Etch further if necessary. • Compare with microstructure expected from equilibrium phase diagram

You are provided with these samples: hypo-eutectoid steel, eutectoid steel, hyper- eutectoid steel, martensite steel, pearlitic-ferritic grey cast iron, laminar (flake) graphite grey cast iron, Spheroidal (nodular) graphite cast iron, white cast iron, brass (alloy of copper and zinc).

Sample Mounting

Small samples can be difficult to hold safely during grinding and polishing operations, and their shape may not be suitable for observation on a flat surface. They are therefore mounted inside a polymer block This can be done cold using two components which are liquid to start with but which set solid shortly after mixing. Cold mounting requires very simple equipment consisting of a cylindrical ring which serves as a mould and a flat piece of glass which serves as the base of the mould. The sample is placed on the glass within the cylinder and the mixture poured in and allowed to set Cold mounting takes about 40 minutes to complete.

In hot-mounting the sample is surrounded by an organic polymeric powder which melts under the influence of heat (about 200 oC). Pressure is also applied by a piston, ensuring a high quality mould free of porosity and with intimate contact between the sample and the polymer. This is not the case with cold mounting where the lack of proper contact and the presence of porosity can cause problems such as the entrappment and seepage of etchant during the final stages of preparation. Consequently, hot-mounting should be the preferred way of

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encapsulating specimens assuming that time and resources permit, and assuming that the heat involved in the process does not influence the sample .

Grinding and Polishing

Grinding is done using rotating discs covered with silicon carbide paper and water. There are a number of grades of paper, with 180, 240, 400, 1200, grains of silicon carbide per square inch. 180 grade therefore represents the coarsest particles and this is the grade to begin the grinding operation. Always use light pressure applied at the centre of the sample. Continue grinding until all the blemishes have been removed, the sample surface is flat, and all the scratches are in a single orientation. Wash the sample in water and move to the next grade, orienting the scratches from the previous grade normal to the rotation direction. This makes it easy to see when the coarser scratches have all been removed. After the final grinding operation on 1200 paper, wash the sample in water followed by alcohol and dry it before moving to the polishers.

The polishers consist of rotating discs covered with soft cloth impregnated with diamond particles (6 and 1 micron size) and an oily lubricant. Begin with the 6 micron grade and continue polishing until the grinding scratches have been removed. It is of vital importance that the sample is thoroughly cleaned using soapy water, followed by alcohol, and dried before moving onto the final 1 micron stage. Any contamination of the 1 micron polishing disc will make it impossible to achieve a satisfactory polish.

Etching

The purpose of etching is two-fold. Grinding and polishing operations produce a highly deformed, thin layer on the surface which is removed chemically during etching. Secondly, the etchant attacks the surface with preference for those sites with the highest energy, leading to surface relief which allows different crystal orientations, grain boundaries, precipitates, phases and defects to be distinguished in reflected light microscopy.

2% Nital Ferric Chloride Sodium Hydroxide Steel Stainless steel Aluminium & alloys - Copper & alloys Zinc & alloys - - Magnesium & alloys

A polished sample is etched using a cotton tip dipped in the etchant. Etching should always be done in stages, beginning with light attack, an examination in the microscope and further etching only if required. If you overetch a sample on the first go then the polishing procedure will have to be repeated.

Metallographic Imaging Modes

The reflected light microscope is the most commonly used tool for the study of the microstructure of metals. It has long been recognized that the microstructure of metals and alloys has a profound influence on many of the properties of the metal or alloy. Mechanical properties (strength, toughness, ductility, etc.) are influenced much more than physical properties (many are insensitive to microstructure). The structure of metals and alloys can be viewed at a wide range of levels - macrostructure, microstructure, and ultra-microstructure.

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In the study of microstructure, the metallographer determines what phases or constituents are present, their relative amounts, and their size, spacing, and arrangement. The microstructure is established based upon the chemical composition of the alloy and the processing steps.

Microstructures

• Microstructures of Steel

Steel is an alloy consisting mostly of iron, with a carbon content between 0.2 and 1.7 or 2.04% by weight (C:1000–10,8.67Fe), depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten. Carbon and other elements act as a hardening agent, preventing dislocations in the iron atom crystal lattice from sliding past one another. Varying the amount of alloying elements and form of their presence in the steel (solute elements, precipitated phase) controls qualities such as the hardness, ductility and tensile strength of the resulting steel. Steel with increased carbon content can be made harder and stronger than iron, but is also more brittle. The maximum solubility of carbon in iron (in austenite region) is 2.14% by weight, occurring at 1149 °C; higher concentrations of carbon or lower temperatures will produce cementite. Alloys with higher carbon content than this are known as cast iron because of their lower melting point. Steel is also to be distinguished from wrought iron containing only a very small amount of other elements, but containing 1–3% by weight of slag in the form of particles elongated in one direction, giving the iron a characteristic grain. It is more rust-resistant than steel and welds more easily. It is common today to talk about 'the iron and steel industry' as if it were a single entity, but historically they were separate products.

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Microstructure of hyper eutectoid steel

• Microstructures of Cast Irons

Cast irons with a composition equivalent to about 4.3% C solidify as a eutectic. Because cast irons are not simple binary Fe-C alloys, it is usual practice to calculate the carbon equivalent (CE) value which is the total carbon content plus one-third the sum of the silicon and phosphorus contents. If the CE is > 4.3, it is hypereutectic; if it is < 4.3, it is hypoeutectic.

In the Fe-C system, the carbon may exist as either cementite, Fe,C, or as graphite. So the eutectic reaction is either liquid transforming to austenite and cementite at about 1130°C or liquid transforming to austenite and graphite at about 1135°C. Addition of elements such as silicon promote graphite formation. Slow cooling rates promote graphite formation, while higher rates promote cementite. The eutectic grows in a cellular manner with the cell size varying with cooling rate which influences mechanical properties.

Gray lron Figure 1 shows interdendritic flake graphite in a hypoeutectic alloy where proeutectic austenite forms before the eutectic reaction. This type of graphite has been given many names. In the US it is referred to as Type D (ASTM A247) or as undercooled graphite. It was thought that the fine size of the graphite might be useful, but it is not technically useful as it always freezes last into a weak interdendritic network.

Figure 2 shows more regularly-shaped graphite flakes in an alloy of higher carbon content, although still hypoeutectic. While flake lengths in Figure 1 are roughly 15-30µm, flake lengths in Figure 2 are in the 60-120µm range. Figure 3 shows somewhat coarser flakes (250-500µm length range) in a higher carbon content cast iron .

Other graphite forms are also observed. For example, Figure 4 shows disheveled graphite flakes in a casting. Note that a few nodules are present. This appears to be a mix of B- and D-type flakes. Figure 5 shows a hypereutectic gray iron where very coarse flakes form before the eutectic which is very fine. This is similar to C-type graphite.

Nodular Iron

The addition of magnesium ('inoculation') desulfurizes the iron and causes the graphite to grow as nodules rather than flakes. Moreover, mechanical properties are greatly improved over gray iron; hence, nodular iron is widely known as 'ductile iron'.

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Nodule size and shape perfection can vary depending upon composition and cooling rate. Figure 6 shows fine nodules, about 15-30µm in diameter, while Figure 7 shows coarser nodules (about 30-60µm diameter) in two ductile iron casts . Note that the number of nodules per unit area is much different, about 350 per mm2 vs.125 per mm2, respectively.

Compacted Graphite

Compacted graphite is a more recent development made in an effort to improve the mechanical properties of flake gray iron. Figure 8 shows an example where the longest flakes are in the 60-120µm length range. Compare these flakes to those shown in Figures 2 and 3.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

(c) JOMINY - END QUENCH TEST Objective: Understanding the effect of cooling rate on the hardness and formation of

hardenability curve of the selected steel sample. Materials: AISI 4140 alloy steel test sample (ASTM A225). Equipment: Box furnace, jominy end quench test apparatus BACKGROUND

The Jominy End-Quench test is a standard procedure in order to measure hardenability of steel. Hardenability is a term that is used to describe the ability of an alloy to be hardened by the formation of martensite as a result of a given heat treatment. The hardenability of a steel depends on: (1) the composition of the steel (2) the austenitic grain size (3) the structure of the steel before quenching.

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In general hardenability increases with carbon content and with alloy content. The most important factor influencing the maximum hardness that can be obtained is mass of the metal being quenched. In a small section, the heat is extracted quickly, thus exceeding the critical cooling rate of the specific steel and this part would thus be completely martensitic. The critical cooling rate is that rate of cooling which must be exceeded to prevent formation of nonmartensite products. As section size increases, it becomes increasingly difficult to extract the heat fast enough to exceed the critical cooling rate and thus avoid formation of nonmartensitic products. Hardenability of all steels is directly related to critical cooling rates [1].

Experimental Procedure

AISI 4140 steel test sample prepared according to the ASTM A255 [2] test standard (Figure 1). Preheated samples are placed to the test set-up system and then water is sprayed to the sample as shown in Figure 2 for maximum of 10 minutes. After cooling to the room temperature, two flats 180° apart shall be ground to a minimum depth of 0.015 in. (0.38 mm) along the entire length of the bar and Rockwell C hardness measurements made along the length of the bar. Hardness measurements are made for the first 50 mm (2 in.) along each flat for the first 12.8 mm, hardness readings are taken at 1.6-mm intervals, and for the remaining 38.4 mm every 3.2 mm. A hardenability curve is produced when hardness is plotted as a function of position from the quenched end.

Figure 1. Jominy Test Sample[3] Figure 2. Jominy Test set-up[2]

References [1] http://web.itu.edu.tr/~arana/jominy.pdf [2] ASTM A255-10 standard test methods for determining hardenability of steel [3] Shackelford, IF, Introduction to materials science

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(d) HARDNESS TESTING TECHNIQUES Objective: Investigation of conventional heat treatment procedures used to tailor the

properties of steels. Effects of heat treatment and different cooling conditions on microstructure and mechanical properties.

Materials: AISI 4140 alloy steel heat treated test samples. Equipment: Hardness Test Equipment (EMCOTEST M1) Rockwell Hardness Testing

Rockwell hardness testing is the most widely used method for determining hardness, primarily because the Rockwell test is simple to perform and does not require highly skilled operators. By use of different loads (forces) and indenters, Rockwell hardness testing can determine the hardness of most metals and alloys, ranging from the softest bearing materials to the hardest steels. Readings can be taken in a matter of seconds with conventional manual operation and in even less time with automated setups. Optical measurements are not required; all readings are direct [1].

Figure 1. Principles of Rockwell Hardness Testing

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The Rockwell hardness test is a very useful and reproducible one provided that a number of

simple precautions are observed. Most of the points filled below apply equally well to the other

hardness tests:

• The indenter and anvil should be clean and well seated.

• The surface to be tested should be clean and dry, smooth, and free from oxide. A rough-

ground surface is usually adequate for the Rockwell test.

• The surface should be flat and perpendicular to the indenter.

• Tests on cylindrical surfaces will give low readings, the error depending on the

curvature, load, indenter, and hardness of the material. Theoretical and empirical

corrections for this effect have been published.

• The thickness of the specimen should be such that a mark or bulge is not produced on

the reverse side of the piece. It is recommended that the thickness be at least 10 times

the depth of the indentation. The spacing between indentations should be three to five

times the diameter of the indentation.

• The speed of application of the load should be standardized. This is done by adjusting

the dashpot on the Rockwell tester. Variations in hardness can be appreciable in very

soft materials unless the rate of load application is carefully controlled [2].

Brinell Hardness Testing

The brinell hardness testing is a simple indentation test for determining the hardness of

a wide variety of materials. The test consists of applying a constant load (force) usually

between 500 and 3000 kgf. for a specified time (10 to 30 s) using a 5- or 10-mm-diam hardened

steel or tungsten carbide ball on the flat surface of a workpiece. The time period is required to

ensure that plastic flow of the work metal has ceased. After removal nf the load, the resultant

recovered round impression is measured in millimeters using a low-power microscope [1].

Hardness is determined by taking the mean diameter of the indentation (two readings

at right angles to each other) and calculating the Brinel hardness number (BH) by dividing the

applied load by the surface area of the indentation according to the following formula:

𝐵𝐻 =𝐹

𝜋2𝐷. (𝐷 − 𝐷! − 𝐷!!)

Where;

BH= the Brinell hardness number

F = the imposed load in kg

D = the diameter of the spherical indenter in mm

Di = diameter of the resulting indenter impression in mm

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Vickers Hardness Testing

The Vickers indenter (Fig. 2) is a highly polished, pointed, square-based pyramidal

diamond with face angles of 136o. With the Vickers indenter, the depth of indentation is about

one seventh of the diagonal length.

When the mean diagonal of the indentation has been determined the Vickers hardness

may be calculated from the formula, but is more convenient to use conversion tables. The

Vickers hardness should be reported like 800 HV/10, which means a Vickers hardness of 800,

was obtained using a 10 kgf force. Several different loading settings give practically identical

hardness numbers on uniform material, which is much better than the arbitrary changing of

scale with the other hardness testing methods. The advantages of the Vickers hardness test are

that extremely accurate readings can be taken, and just one type of indenter is used for all types

of metals and surface treatments. Although thoroughly adaptable and very precise for testing

the softest and hardest of materials, under varying loads, the Vickers machine is a floor

standing unit that is more expensive than the Brinell or Rockwell machines [3].

Figure 2. Diamond pyramid indenter used for the Vickers test and resulting

indentation in the workpiece

The indenter employed in the Vickers test is a square-based pyramid whose opposite

sides meet at the apex at an angle of 136º. The diamond is pressed into the surface of the

material at loads ranging up to approximately 120 kilograms-force, and the size of the

impression (usually no more than 0.5 mm) is measured with the aid of a calibrated microscope.

The Vickers number (HV) is calculated using the following formula:

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𝐻𝑉 =2𝐹 sin 136

!

2𝑑! → 𝐻𝑉 = 1.854

𝐹𝑑!

Where;

F= Load in kgf

d = Arithmetic mean of the two diagonals, d1 and d2 in mm

HV = Vickers hardness

Knoop Hardness Testing

The Knoop indenter (Fig. 3) is a highly polished, rhombic-based pyramidal diamond

that produces a diamond-shaped indentation with a ratio between long and short diagonals of

about 7 to 1. The pyramid shape used has an included longitudinal angle of 172° 30' and an

included transverse angle of 130° 0'. The depth of the indentation is about 1/30th of its length

[1].

Figure 3. Pyramidal Knoop indenter and resulting indentation in the work piece

The diamond indenter employed in the Knoop test is in the shape of an elongated four-

sided pyramid, with the angle between two of the opposite faces being approximately 170º and

the angle between the other two being 130º. Pressed into the material under loads that are often

less than one kilogram-force, the indenter leaves a four-sided impression about 0.01 to 0.1 mm

in size. The length of the impression is approximately seven times the width, and the depth is

1/30 the length. Given such dimensions, the area of the impression under load can be calculated

after measuring only the length of the longest side with the aid of a calibrated microscope. The

final Knoop hardness (HK) is derived from the following formula [3]:

𝐻𝐾 = !!= !

!"! Where;

P= the applied load, k gf

A= the unrecovered projected area of indentation, mm2

L= the measured length of long diagonal, mm

C= constant to 0.07028

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Fracture Toughness

Fracture toughness is an indication of the amount of stress required to propagate a

preexisting flaw. It is a very important material property since the occurrence of flaws is not

completely avoidable in the processing, fabrication, or service of a material/component. Flaws

may appear as cracks, voids, metallurgical inclusions, weld defects, design discontinuities, or

some combination thereof. Since engineers can never be totally sure that a material is flaw free,

it is common practice to assume that a flaw of some chosen size will be present in some

number of components and use the linear elastic fracture mechanics (LEFM) approach to

design critical components. This approach uses the flaw size and

features, component geometry, loading conditions and the material

property called fracture toughness to evaluate the ability of a

component containing a flaw to resist fracture [4].

A parameter called the stress-intensity factor (K) is used to

determine the fracture toughness of most materials. A Roman numeral

subscript indicates the mode of fracture and the three modes of

fracture are illustrated in the image to the right. Mode I fracture is the

condition in which the crack plane is normal to the direction of largest

tensile loading. This is the most commonly encountered mode and,

therefore, for the remainder of the material we will consider KI

The stress intensity factor is a function of loading, crack size,

and structural geometry. The stress intensity factor may be represented

by the following equation [4]:

Figure 4. Fracture toughness

𝐾! = 𝜎 𝜋𝑎𝛽

Where:

KI =is the fracture toughness

σ=is the applied stress in MPa or psi

a=is the crack length in meters or inches

β=is a crack length and component geometry factor that is different for each specimen

and is dimensionless.

References

[1] ASM Metal Handbook Volume 08 Mechanical Testing and Evaluation [2] http://www.key-to-steel.com/Articles/Art140.htm [3] http://www.gordonengland.co.uk/hardness/vickers.htm [4] http://www.ndted.org/EducationResources/CommunityCollege

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EXPERIMENT # 2: NDT EXPERIMENTS - FATIGUE-CHARPY IMPACT-TENSION TESTING

(a) NON-DESTRUCTIVE TESTING (NDT)

Objective: The objective of the experiment is to introduce the use and the importance of non-destructive testing methods.

BACKGROUND

Non-destructive tests (NDT) are inspection methods which are usually used to search for the presence of defects in components, without causing any effects on the properties of the components. The types of defects detectable are cracks, porosity, voids, inclusions, etc.

Modern NDT is used by manufacturers to: ensure product integrity and reliability; prevent failure, accidents and saving lives; make profit for users; ensure customer satisfaction; aid in better product design; control manufacturing process; lower manufacturing costs; maintain uniform quality level; ensure operational readiness.

The table below shows the types of NDT methods used today.

Commonly Used Methods Other Methods Ultrasonics Visual Methods Radiography Acoustic Emission Dye Penetrant Thermography Magnetic Particle Inspection Holography Eddy Current

1) Basic Principles Of Ultrasonic Testing

Mechanical vibrations can be propagated in solids, liquids and gases. The actual particles of matter vibrate, and if the mechanical movements of the particles have a regular motion, the vibration can be assigned a frequency in cycles per second, measured in hertz (Hz), where 1 Hz = 1 cycle per second. If this frequency is within the approximate range 10 to 20,000 Hz, the sound is audible; above about 20 kHz, "the sound" waves are referred to as ultrasound or ultrasonics.

The ultrasonic principle is based on the fact that solid materials are good conductors of sound waves. The waves are not only reflected at the interfaces but also by internal flaws (material separations, inclusions,etc.).

As an example of a practical application, if a disc of piezoelectric materials is attached to a block of steel (Figure 1a), either by cement or by a film of oil, and a high- voltage electrical pulse is applied to the piezoelectric disc, a pulse of ultrasonic energy is generated in the disc and is propagated into the steel. This pulse of waves travels through the metal with some spreading and some attenuation and will be reflected or scattered at any surface or internal discontinuity such as an internal flaw in the specimen. This reflected or scattered energy can be

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detected by a suitably-placed second piezoelectric disc on the metal surface and will generate a pulse of electrical energy in that disc. The time- interval between the transmitted and reflected pulse is a measure of the distance of the discontinuity from the surface, and the size of the return pulse can be a measure of the size of the flaw. This is the simple principle of the ultrasonic flaw detector and the ultrasonic thickness gauge. The piezoelectric discs are the "probes" or "transducers"; sometimes it is convenient to use one transducer as both transmitter and receiver. In a typical ultrasonic flaw detector the transmitted and received pulses are displayed in a scan on a timebase on an oscilloscope as shown in Figure 1b.

2) Radiography (Rt)

Radiography involves the use of penetrating gamma or X-radiation to examine parts and products for imperfections. An X-ray generator or radioactive isotope is used as a source of radiation. Radiation is directed through a part and onto film or other imaging media. The resulting shadowgraph shows the dimensional features of the part. Possible imperfections are indicated as density changes on the film in the same manner as a medical X-ray shows broken bones.

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3) Dye Penetrant

Penetrant testing is used to test non-ferrous materials such as aluminum and stainless steel. Different test methods are available ranging from visible red/water washable penetrant systems to complex emulsifier penetrant systems. Various sensitivities are selected based on the product and customer requirements. Components can be tested in-house or on site. We are expert in setting up specific testing programs for our clients.

Common uses would be:

• Non-ferrous parts can readily be tested using this method • Aircraft components • Non-ferrous castings • Finished machined components

4) Magnetic Particle Testing (Mt)

This NDE method is accomplished by inducing a magnetic field in a ferromagnetic material and then dusting the surface with iron particles (either dry or suspended in liquid). Surface and near-surface imperfections distort the magnetic field and concentrate iron particles near imperfections, previewing a visual indication of the flaw.

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5) Electromagnetic Testing (Et) Or Eddy Current Testing

Electrical currents are generated in a conductive material by an induced alternating magnetic field. The electrical currents are called eddy currents because they flow in circles at and just below the surface of the material. Interruptions in the flow of eddy currents, caused by imperfections, dimensional changes, or changes in the material's conductive and permeability properties, can be detected with the proper equipment.

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(b) FATIGUE-CHARPY IMPACT-TENSION TESTING Objective: The objective of the charpy impact experiment is to evaluate the energy

absorbing characteristics of metal materials at room temperature using the Charpy impact method. The object of the fatigue test is to comprehend how fatigue conditions affect metals and to determine the fatigue life of the specimen. The object of the tension testing is to determine the tensile properties for various metallic samples using the American Standard Test Methods (ASTM).

Materials: V-notch charpy impact samples and fatigue samples. A set of metallic specimens prepared according to the tension testing standards.

Equipment: Impact testing machine for charpy impact test. Mechanical testing

machine for fatigue test. Instron Universal Testing Machine for tension.

(a) Charpy Impact Test Introduction Charpy impact test is a method for evaluating the toughness and notch sensitivity of engineering materials. It is usually used to test the toughness of metals, but similar tests are used for polymers, ceramics and composites. The test measures the energy absorbed by the fractured specimen. This absorbed energy is a measure of a given material's toughness.

Test specimen

The test specimen is 55 mm long, with cross section 10x10 mm, and has a V-notch 2 mm deep of 45° included angle and a root radius of 0.25 mm.

Test procedure

1. Pulling the pendulum at a known height and engaging the safety latch

2. Clamping the specimen in the machine

3. Releasing the pendulum

4. Reading the result from the indicator

(b) Fatigue Testing

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Introduction:

In many applications, materials are subjected to vibrating or fluctuating forces. The behavior of materials under such load conditions differs from the behavior under a static load. Designers are faced with predicting fatigue life, which is defined as the total number of cycles to failure under specified loading conditions, since the material is subjected to repeated load cycles (fatigue) in actual use. Fatigue testing data is used to predict cycle number of crack initiation and crack propagation behavior.

Test specimen

The fatigue test specimen is center crack tension (CCT) type and was made by 2024-T3 aluminum alloy. The width (W), length (L) and thickness (B) of the specimens are 90, 300, 6 mm, respectively. The specimen was machined according to ASTM E 647 recommendation (Fig. 1). Figure 1: The fatigue crack growth CCT specimen geometry (dimensions mm). Test procedure

1. Selecting test parameters and calculating maximum and average load values 2. Clamping the specimen 3. Inputting test parameters to the MAX program controlling the test machine 4. Starting the test 5. Monitoring and measuring the crack length by the traveling microscope.

300

90

17 2a

6

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(a) Tensile Testing

Introduction: When a specimen is loaded so that the resultant force passes through the centroid of the specimen cross-section, the loading is categorized as axial and can be either tensile or compressive. Tests determine material properties. When materials for engineering projects are procured, the engineer often must specify material property requirements to the manufacturer. After the material is received it is generally good practice, if not mandatory, to perform acceptance tests to verify the material properties before the materials are used. Therefore, it is important to understand which material properties are relevant and how those properties are obtained. Results from simple tension tests, similar to the test described in this experiment, can provide information from which several material properties can be determined. The experiments to be completed for Tension I will illustrate the usefulness of the simple tension test and demonstrate the mechanical behavior of materials. What is Tension Test ? Method for determining behavior of materials under axial stretch loading. By pulling on something, you will very quickly determine how the material will react to forces being applied in tension. As the material is being pulled, you will find its strength along with how much it will elongate. Data from test are used to determine elastic limit, elongation, modulus of elasticity, proportional limit, reduction in area, tensile strength, yield point, Yield Strength and other tensile properties. Procedures for tension tests of metals are given in ASTM E-8. Methods for tension tests of plastics are outlined in ASTM D-638, ASTM D-2289 (high strain rates), and ASTM D-882 (thin sheets). Why Perform a Tensile Test or Tension Test? You can learn a lot about a substance from tensile testing. As you continue to pull on the material until it breaks, you will obtain a good, complete tensile profile. A curve will result showing how it reacted to the forces being applied. The point of failure is of much interest and is typically called its "Ultimate Strength" or UTS on the chart.

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Hooke's Law For most tensile testing of materials, you will notice that in the initial portion of the test, the relationship between the applied force, or load, and the elongation the specimen exhibits is linear. In this linear region, the line obeys the relationship defined as "Hooke's Law" where the ratio of stress to strain is a constant, or . E is the slope of the line in this region where stress (σ) is proportional to strain (ε) and is called the "Modulus of Elasticity" or "Young's Modulus". Modulus of Elasticity The modulus of elasticity is a measure of the stiffness of the material, but it only applies in the linear region of the curve. If a specimen is loaded within this linear region, the material will return to its exact same condition if the load is removed. At the point that the curve is no longer linear and deviates from the straight-line relationship, Hooke's Law no longer applies and some permanent deformation occurs in the specimen. This point is called the "elastic, or proportional, limit". From this point on in the tensile test, the material reacts plastically to any further increase in load or stress. It will not return to its original, unstressed condition if the load were removed. Yield Strength A value called "yield strength" of a material is defined as the stress applied to the material at which plastic deformation starts to occur while the material is loaded. Strain You will also be able to find the amount of stretch or elongation the specimen undergoes during tensile testing This can be expressed as an absolute measurement in the change in length or as a relative measurement called "strain". Strain itself can be expressed in two different ways, as "engineering strain" and "true strain". Engineering strain is probably the easiest and the most common expression of strain used. It is the ratio of the change in length to the original length,

. Whereas, the true strain is similar but based on the instantaneous length of the specimen as the

test progresses, , where Li is the instantaneous length and L0 the initial length. Ultimate Tensile Strength One of the properties you can determine about a material is its ultimate tensile strength (UTS). This is the maximum load the specimen sustains during the test. The UTS may or may not equate to the strength at break. This all depends on what type of material you are testing. . .brittle, ductile, or a substance that even exhibits both properties. And sometimes a material may be ductile when tested in a lab, but, when placed in service and exposed to extreme cold temperatures, it may transition to brittle behavior.

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Testing Procedure We will serve to introduce the Instron testing equipment and testing procedures. For the experiment, a 8 mm nominal diameter hot rolled steel sample will be tested to failure. Load versus- strain diagrams will be produced during the test and this diagram will subsequently be used to determine material properties. The student will learn how to properly conduct a tension test and obtain the relevant material properties from the results. Further, the student will discover how different materials behave under similar loading conditions as well as how material properties differ. REPORT REQUIREMENTS: For the material tested please determine and tabulate the following properties: a. Proportional Limit b. Yield Strength c. Ultimate Strength d. Modulus of Elasticity e. Percent elongation f. Percent reduction in area g. Provide stress versus strain plot, appropriately labeled, for specimen tested h. Briefly summarize, in words, tension test.

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EXPERIMENT # 3: SONIC MODULUS-POROSIMETRY Objective: The objective of the experiments is to introduce various testing

techniques available in the department.

(a) Sonic Modulus

There are basically two ways to measure elastic properties, of which Young’s, bulk, and

shear moduli are most common.

The first way is to measure strain in response to some quasi statically applied stress,

commonly in conjunction with strength testing. There are several limitations to this, an

important one is that often only Young’s modulus is obtained. Another is that since most

ceramics have high moduli and hence low stains, using the easiest measurement of strains, i.e.,

from test machine head travel, is generally grossly inaccurate due to substantial parasitic

deflections of the loading train being of similar or greater magnitude as the specimen strains.

The second and generally preferred method of measuring elastic properties is but one of

two sets of wave motion measurements. These are versatile, often being applicable on

components, and generally offer good accuracy and other advantages. One basic way of doing

this by transmission of ultrasonic waves, or transmission and reflection of pulses (i.e.,

pulse echo). Thus, elastic properties can be calculated from the material density (ρ) and

measurable velocities of longitudinal (νl) and shear waves (νs). Another basic way of measuring

elastic properties by wave methods is by resonance vibration of specimens [1].

The velocity of ultrasonic pulses, travelling in a solid material, depends on the density,

elastic properties and on the different phases present inside the material, thus the quality could

be related to its measurement. Ultrasonic testing is applied to measure elastic stiffness,

mechanical properties and defect’ presence in concrete, refractories and ceramic materials, etc

[2].

The greatest advantage of ultrasonic velocity measurements is the nondestructive

determination of elastic moduli. Assuming that the samples used in this analysis are isotropic,

standard velocity-elasticity relations can be used to calculate the various moduli. These

relations are:

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E = νl2 ρ(1+σ)(1-2σ)/(1-σ)

G = νs2 ρ

σ = (1-2b2)/(2-2b2)

K = E/[3(1-2σ)]

where νl is the longitudinal wave velocity (m/s), νs the shear wave velocity (m/s), E the

Young’s modulus (pascals), G the shear modulus (pascals), σ the Poisson’s ratio, K the bulk

modulus (pascals) and b= νs/ νl [3].

The Nature of Sound

Sound waves are mechanical vibrations involving movement within the medium in

which they are travelling. The particles in the medium vibrate, causing it to distort, thus

transferring energy from particle to particle, along the wave path [4].

Longitudinal waves: Particles oscillate parallel to the direction of propagation. In aluminum νl=

6.25 X 103 m/s [5].

Figure 1. Longitudinal waves [6]

Shear waves: Particles oscillate transverse to the direction of propagation. In aluminum νl= 3.1

X 103 m/s [5].

Figure 2. Shear waves [6]

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Test Materials

Different ceramic materials (densities must be known).

Test Procedure

1- Propagation time (t) of longitudinal waves’ measurement for pulse-echo mode.

2- Propagation time (t) of shear waves’ measurement for pulse-echo mode.

3- Thickness (d) measurement of ceramic materials.

4- Ultrasonic wave velocity calculation for pulse-echo mode (ν=2d/t).

5- Calculation of elastic properties.

References 1. RICE, R.W., Porosity of Ceramics, M. Dekker, New York, 24-25 (1998).

2. ROMAGNOLI, M., BURANI, M., TARI, G. and FERREIRA, J.M.F., A Non-destructive Method to Assess

Delamination of Ceramic Tiles, Journal of the European Ceramic Society, 27, 1631-1636 (2007).

3. KULKARNI, N., MOUDGIL, B. and BHARDWAJ, M., Ultrasonic Characterization of Green and Sintered

Ceramics: I, Time Domain, American Ceramic Society Bulletin, 73, 146-153 (1994).

4. Ultrasonic Non-destructive Testing, Published by: The Institution of Metallurgist, The Chameleon Press,

London, 10 (1983).

5. Encyclopedia of Applied Physics, Testing Equipment-Mechanical to Topological Phase Effects, Wiley-VCH

Verlag GmbH, 21, 39 (1997).

6. www.cen.bris.ac.uk/projects/eqteach97/waves2.htm (19.10.2007)

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(b) Mercury Porosimetry

Figure 1. Mercury porosimetry

Mercury porosimetry characterizes a material’s porosity by applying various levels of pressure

to a sample immersed in mercury. The pressure required to intrude mercury into the sample’s

pores is inversely proportional to the size of the pores.

Analysis Technique

To perform an analysis, the sample is loaded into a penetrometer, which consists of a sample

cup connected to a metal-clad, precision-bore, glass capillary stem. The penetrometer is sealed

and placed in a low pressure port, where the sample is evacuated to remove air and moisture –

the user controls the speed of the evacuation and there’s no need for a separate preparation unit.

The penetrometer’s cup and capillary stem are then automatically backfilled with mercury.

Excess mercury is automatically drained back into the internal reservoir; only a small amount

remains in the penetrometer.

As pressure on the filled penetrometer increases, mercury intrudes into the sample’s pores,

beginning with those pores of largest diameter. This requires that mercury move from the

capillary stem into the cup, resulting in a decreased capacitance between the now shorter

mercury column inside the stem and the metal cladding on the outer surface of the stem.

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The instrument automatically collects low pressure measurements over the range of pressures

specified by the operator. Then, the penetrometer is moved to the high pressure chamber, where

high pressure measurements are taken. Data are automatically reduced using the low and high

pressure data points, along with values entered by the operator, such as the weight of the

sample and the weight of the penetrometer loaded with mercury.

Proven Science

Mercury porosimetry is based on the capillary law governing liquid penetration into small

spaces. This law, in the case of a non-wetting liquid like mercury, is expressed by the

Washburn equation:

𝐷 =−2𝛾. 𝑐𝑜𝑠𝜃

𝑃

where D is the pore diameter, P is the applied pressure, the surface tension of mercury and

the contact angle between the mercury and the sample, all in consistent units. The volume of

mercury V penetrating the pores is measured directly as a function of applied pressure. This P-

V information serves as a unique characterization of pore structure.

The Washburn equation assumes that all pores are cylindrical. Although pores are rarely

cylindrical in reality, this equation provides a practical representation of pore distributions,

yielding very useful results for most applications.

As pressure increases during an analysis, pore size is calculated for each pressure point and the

corresponding volume of mercury required to fill these pores is measured. These measurements

taken over a range of pressures give the pore volume versus pore size distribution for the

sample material.

If decreasing pressure are included in the analysis, extrusion data are also calculated using the

Washburn equation. Extrusion P-V curves usually differ from intrusion curves because of

mercury entrapment and because there is no driving force to bring the mercury out of the pores

during the extrusion phase of the analysis. Differences between intrusion curves and extrusion

curves can be used to characterize channel restrictions and the structure or shape of pores.

Pore diameters may be offset toward larger values on extrusion curves because receding

contact angles are smaller than advancing contact angles. This results in equivalent volumes of

γ φ

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mercury extruding at lower pressures than those at which the pores were intruded. Also, pore

irregularities, such as enlarged chambers and “ink-well” structures sometimes trap mercury.

Comprehensive Results

Mercury porosimetry can determine a broader pore size distribution more quickly and

accurately than other methods. Comprehensive data provide extensive characterization of

sample porosity and density. Available results include:

• Total pore volume • Incremental volume • Differential volume • Log-differential volume • % of total volume • Total pore surface area • Incremental area • Median or mean pore diameter • Pore size distributions and % porosity • Sample densities (bulk and skeletal)

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EXPERIMENT # 4: a) ELECTROLYTIC REDUCTION OF ZINC Objective: The objective of the electrolytic reduction of Zinc experiment is to have

a basic knowledge of electrolytic reduction concept, Faraday Law and terms of Electrochemical cell, Faraday Efficiency, Polarization, Hydrogen Overvoltage, EMF Series, Nernst Diffusion Layer. During experiment, you will be introduced the effects of effective surface area, impurities present in the solution, temperature and electrolysis time.

Materials: Zinc sulfate solution (65 g/l Zn+2 containing ZnSO4 ve 130 g/l free H2SO4), Al cathodes, Pb anodes

Equipment: - DC Power Supply

- Multimeter - Glass beaker, electrode holders, cables etc.

Electrolysis:

Faraday defined the electrolysis as a chemical work done by electric current generated

in DC power supply and pass through electrolyte. Conductive materials such as electrolytes can

be divided into two main subgroups. One group of conductive materials (metals, alloys, metal

oxides, graphite etc.) conduct electric current without chemically changed. Other group of

materials (ionic conductors) conducts with the help of ionic transport. An electrolytic cell

consists of electrolyte, electrodes (anode, cathode) and DC supply. Figure 1 shows schematic

view of electrolysis system.

Figure 1. Electrolysis system

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The EMF cell converts the chemical reaction energy into electrical energy. The

following equation gives the relation between Gibbs free energy change (ΔG) and potential (E):

∆𝐺 = −𝑛 × 𝐹 ×𝐸

where n is the number of electrons passing through cell and F is Faraday constant

(96500 Coulomb). Since metals always give electrons n must be positive digit as well as

Faraday constant. If ΔGcell = 0, it states the equilibrium. Positive ΔGcell states that reaction is

impossible without any external manipulation. Electrolysis makes positive Gibbs free energy

change reactions possible with the help of applied current so they convert electrical energy into

chemical energy.

The potential difference between two plates (anode/cathode) dipped into electrolyte is

called cell voltage. The potential difference between one of the electrodes and electrode with

known potential (reference electrode) is called single electrode potential or half-cell voltage.

Standard potentials of elements given in EMF series are potentials measured with respect to

Standard Hydrogen Reference Electrode (SHE).

Faraday Law gives the relation between consumed electrical energy and chemical

work. It shows the equivalent-gram metal collected in the cathode by 1 Faraday (96500

Coulomb) current passing through electrolyte or molten salt and the equation:

𝑚 𝑔 =𝐴!"× 𝐼 × 𝑡𝑧 × 96500

m: the mass of collected metal in the cathode (g) AZn: Atomic weight of Zn (g/mole) I: Applied current (A) t: Electrolysis time (s) z: Valence electron of collected metal

Positive (+) pole of DC current supply is called anode and negative (-) pole is cathode.

During electrolysis, anions (negatively charged ions) move towards anode, and cations

(positively charged ions) move towards cathode. Oxidation occurs in anode (anodic reaction)

whereas reduction takes place in cathode (cathodic reaction).

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Total cell voltage (ET) in an electrolytic cell:

𝐸! = 𝐸! + 𝐸! + 𝜂! + 𝜂! + (𝐼×𝑅)

EA : Standard electrode potential of anode EK : Standard electrode potential of cathode ηA : Overvoltage of anode ηA : Overvoltage of cathode (I x R) : Resistive losses

If current is passing in the electrolytic system, electrode potential (Ei) will be different

comparing to its original potential (E0). This phenomenon is named Overvoltage (polarization)

and can be formulized:

𝜂 = 𝐸! − 𝐸!

Main overvoltage types are;

• Diffusion Overvoltage

• Chemical Reaction Overvoltage

• Charge Transfer Overvoltage

• Crystallization Overvoltage

Metal ions can travel through cathode via diffusion, convection and migration. When the

electrode is polarized, the surface concentration of the species that is either being oxidized or

reduced falls to zero. Additional material will then diffuse to the electrode (cathode) surface

towards this region of lower concentration. This lower/higher concentration region is called

Nernst Diffusion Layer (δ). Resulting concentration-distance gradient at the electrode surface is

represented in Figure 2. The width of the Nernst diffusion layer is not a function of current.

Increasing current density reduces the bulk solution concentration – electrode surface

concentration difference as well as it reduces Nernst diffusion layer.

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Figure 2. Nernst Diffusion Layers on Electrodes and Concentration Gradient Between Electrodes

Metallic Zinc Production

More than %90 of total Zinc production is from sulphureted ores. Concentrated sulphureted

ores are first calcined and leached with sulphuric acid. Iron in the solution then precipitated via

jarosite, hematite and/or goethite processes. After that, solution is purified by removing

impurities (Cd, Ni, Co, Cu etc.) via cementation with Zn powder. Solution treatment and

purification are crucial steps for electrowinning of zinc from sulphureted ores because 4 main

groups of materials can present in the solution:

Ø Elements below Zn in EMF series: These have higher electronegativity than Zn (K, Na,

Ca, Mg, Al, Mn). However, they’re impossible to collect on cathode surface. Molten

salt electrolysis is used to produce these metals.

Ø Elements between Zinc and Hydrogen:

o Pb, Cd, Ta, Sn: Easily reduce on cathode. Impure the cathode material

o Fe, Co, Ni: Difficult to reduce on cathode because hydrogen overvoltage on

these metals is lower than Zn.

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Ø Elements above H in EMF Series: Reduces Hydrogen overvoltage (Cu, As, Sb, Te, Ge,

In etc.)

Ø Metals resolve Zinc into the solution producing local cell: (Ni, Cu, Co, As, Sb)

The final step for metallic Zinc production is electrolytic reduction. Reactions below take

place in electrodes:

Zn2+ + 2e- = Zn0 (cathodic reaction) -0.76V (vs. SHE)

SO42- + H2O = SO4

2- + 2H+ + 2e- + ½ O2 (anodic reaction) +1.23V (vs. SHE)

Zn2+ + SO42- + H2O = Zn0 + SO4

2- + 2H+ + 2e- + ½ O2 (total reaction) -1.99V (vs. SHE)

Excluding kinetic factors, the voltage needed from DC source is 1.99 Volt.

Thermodynamically, it’s impossible to reach metallic zinc from aqueous solutions.

Because, elements below Hydrogen in EMF series, result in reduction of H+ ions to H2. The

overvoltage needed to form gaseous H2 in the system can be defined as Hydrogen Overvoltage.

It makes electrolytic reduction of Zn kinetically possible. Three main steps of gaseous H2

formation is electron transfer in Hydrogen ion (Volmer reaction), formation of Hydrogen

molecule (Tafel Reaction) and transition to gaseous phase.

• Effect of Impurities on Electrolytic Reduction of Zinc:

Cleanliness of electrolytic solution is the most crucial part of electrolytic reduction

systems. Impurities in the solution can be divided into 2 sub-groups of impurities more noble

than Zinc and impurities more active than Zinc according to EMF Series. If impurities more

noble than Zinc are presented in the solution, they will be reduced before Zn, when external

current is applied. It reduces purity and current efficiency of collected Zn metal in cathode.

However, impurities more active than Zn don’t cause any problem because they’re impossible

to be reduced on cathode. They need specific production methods (e.g. Molten Salt

Electrolysis) to collect.

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• Effect of Temperature on Electrolytic Reduction of Zinc:

Temperature strongly effects kinetics of electrolytic systems. Metallic Zn collection and

H2 formation occurs at the cathode side of electrolytic reduction of Zn. Increasing

temperature enhances the reaction rate of Hydrogen Overvoltage. In other words, with

increasing temperature, more spaces in active cathode surface occupied with H2

formation and less spaces to collect metallic Zn.

Electrolytic reduction of Zn in industrial scale requires very high current density levels

between 600-1000 A/m2.

Experimental Procedure:

Figure 3. Experimental Setup

In Figure 3, 300 ml electrolyte is put into three 500 ml glass beakers that contain one Pb

anode and one Al cathode and 65 g/l Zn+2 containing ZnSO4 based electrolyte of each. First cell

will be at 60°C whereas second and third cells will be set up at room temperature. The

electrolyte at the third cell has 1 g/l Fe3+ or 3 g/l Cu2+ ions. Three electrolysis cells are

connected in series and current densities between 600-1000 A/m2 are applied. Here the wetted

(effective) surface areas of the electrodes should be especially paid attention. Each hour, Al

cathodes are washed, dried in drying oven and weighed to find out the amount of deposited

metal.

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EMF SERIES (vs SHE)

Au/Au+Pt/Pt2+Pb/Pb4+Ag/Ag+Rh/Rh2+Cu/Cu2+As/As3+Sb/Sb3+Bi/Bi3+H2/2H+Fe/Fe3+Pb/Pb2+Sn/Sn2+Ni/Ni2+Co/Co2+Cd/Cd2+Fe/Fe2+Zn/Zn2+Mn/Mn3+Al/Al3+Ti/Ti2+Ca/Ca2+Li/Li+

1.701.200.800.7990.60.340.300.240.200.0-0.04-0.126-0.140-0.23-0.27-0.402-0.44-0.763-1.05-1.66-1.75-2.84-3.01

Hydrogen Over

Voltage

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b) CORROSION AND CATHODIC PROTECTION Objective: The objective of Corrosion and Cathodic Protection experiment is to have a basic knowledge on corrosion, corrosion cell, corrosion current, electrical double layer and effect of cathodic surface area on corrosion current. Materials:

Ø 3 Zn plates with 2 cm2 effective area

Ø Cu plates with 2, 10 and 30 cm2 effective area

Ø %3.5 NaCl solution

Equipments:

Ø Calomel electrode

Ø Multimeter

BACKGROUND

Metals are found in nature as a metallic compounds. Production of a metals and alloys is a

matter of “material-energy-knowledge”. However, metals have high tendency to form its

metallic compounds giving a reaction in its environment. As a result of that, physical, chemical,

mechanical and electrical properties will change. We often call that “damage”. Corrosion is

defined as degradation and damage of materials in its environment. Corrosion is a self-driven

reaction. We don’t need to give energy from outsource. Corrosion in atmosphere, aqueous

solutions, even under soil, is called aqueous corrosion. If there’s no water (e.g. High

temperature, gas-metal reactions), this type of corrosion is high temperature corrosion. Besides

them, there are also corrosion of organic liquids and molten metal corrosion.

Corrosion is a kind of electrochemical reaction. It’s based on electron transfer, so the

electron transfer system in corrosion is named corrosion cell. Typical corrosion cell consists of;

• Anode, the metal which is oxidized,

• Cathode, the metal that is reduced or consume the produced electrons at surface,

• Electrolyte, solution which provides ionic conduction,

• Interface layer, the layer that oxidation and reduction reactions take place

• Electrical conductor transfers electrons transporting from anode to cathode.

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The current that flow in corrosion cell is named as corrosion current (icor). In corrosion

cell, rate of oxidation and reduction reaction are equal to each other (ianode = icathode = icor). If

there is no reduced material in the cell, since the produced electrons are not consumed,

corrosion does not take place. In other words, if there is no cathodic reaction or cathodic

reaction is prevented, corrosion reaction does not occur. Additionally, corrosion reaction does

not take place if there is no;

• electrical connection between anode and cathode,

• contact of anode or cathode with the solution,

• conductor.

Dissolution rate of metal (corrosion rate) is determined by the reduction rate. The

corrosion rate (icor) decreases when the amount of reduced material in solution decreases, since

corrosion rate is controlled by the cathodic reaction rate (icathode).

In corrosion, if anode and cathode is apart from each other, metal only decomposed at

anode. In this situation selective or regional corrosion occur and this type of corrosion cell is

named as macrocorrosion cell. At some situations even an atomic size point defects act as both

anode and cathode, as a result of this metal corrodes uniformly.

Ø Corrosion Prevention

The corrosion behavior of metal surfaces can be changed either by coating or by

cathodic protection. Cathodic protection methods are based on 2 approaches. First one is using

sacrificial anode that more active metal (sacrificial anode) is presented in the system. Other

approach is using external current source that changes anode to cathode in the electrochemical

system.

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Experimental Procedure:

Surfaces of the three Zn plates are cleaned, dried and weighed. Surface of the Cu plate

with 2 cm2 area is cleaned, dried and weighed. One of the 2 cm2 active surface area Zn plate is

weighed, put into a 400 ml beaker with % 3,5 NaCl solution. This sample is taken out of the

solution, washed, dried and weighed.

Another weighed 2 cm2 Zn plate is coupled with 10 cm2 Cu plate and put into a 400 ml

beaker with % 3,5 NaCl solution. During this operation current is recorded for 15 minutes by

zero resistant amperemeter. At the end of the experiment Zn plate is washed, dried and

weighed.

One of the other weighed 2 cm2 Zn plate is coupled with 30 cm2 Cu plate and put into a

400 ml beaker with %3,5 NaCl solution. During this operation current is recorded for 15

minutes by zero resistant amperemeter. At the end of the experiment Zn plate is washed, dried

and weighed. The experimental setup is shown in Figure 1.

Figure 1. Experimental setup for corrosion and cathodic protection

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EXPERIMENT #5 - ELECTRICAL & STRUCTURAL CHARACTERIZATION OF THIN FILMS & COATINGS - ELECTRICAL PROPERTY MEASUREMENTS (a) Electrical & Structural Characterization of Thin Films

Objective: The objective is to learn thin film deposition processes (e.g. sputtering).

Main purpose of the experiment is to learn what is vacuum and why it is

necessary for thin film deposition. Understanding the main important

parameters effecting thin film properties (Table 7.5.1 in the pdf file). It is

also the basis of a number of scientific instrumental techniques with

atomic resolution, the scanning probe microscopy techniques such as

STM, AFM.

Equipment: - Low vacuum sputtering tool (Au coating)

- High vacuum sputtering tool

- FPP- Four point probe

- ATM - STM

Materials: Au/Pd deposition on glass, Si, SiO2 and insulating ceramic substrates

using low and high vacuum tools.

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ELECTRICAL AND STRUCTURAL

CHARACTERIZATION OF THIN FILMS & COATINGS

Anadolu University, Faculty of Engineering, Department of Materials Science and Engineering

Supervisor and Instructor: Assoc. Prof. Dr. Ing. Ramis Mustafa ÖKSÜZOĞLU

Authors: Associated Prof. Dr. Ramis Mustafa ÖKSÜZOĞLU, M.S. Phys. Eng. Mustafa YILDIRIM

Page Number

CONTENTS ....................................................................................................................... iii 1. INTRODUCTION .......................................................................................................... 1-2 2. VACUUM SCIENCE AND TECHNOLOGY ............................................................... 2-4 3. THIN FILM FORMATION ............................................................................................ 4-6 4. THIN FILM DEPOSITION TECHNIQUES .................................................................. 6-7 5. SPUTTERING PROCESS ........................................................................................ 7 5.1. DC Sputtering .............................................................................................................. 7-8 5.2. RF Sputtering ............................................................................................................... 8-9 5.3 Magnetron Sputtering ................................................................................................... 9 6. THIN FILM CHARACTERISATION TECHNIQUES ................................................. 9-10 6.1. Atomic Force Microscope (AFM) ............................................................................... 10-11 6.2. X-Ray Reflectometry (XRR) ...................................................................................... 11-12 6.3. Four Point Probe (FPP) (Sheet Resistance (R) and Resistivity (ρ) ............................. 13 7. REFERENCES ............................................................................................................... 13

1. INTRODUCTION

Thin films are fabricated by the deposition of individual atoms on a substrate. A thin film is defined

as a low-dimensional material created by condensing, one-by-one, atomic/molecular/ionic species of

matter. The thickness is typically less than several microns. Thin films differ from thick films. A thick

film is defined as a low-dimensional material created by thinning a three-dimensional material or

assembling large clusters/aggregates/grains of atomic/molecular/ionic species. Historically, thin films

have been used for more than a half century in making electronic devices, optical coatings,

instrument hard coatings, and decorative parts. The thin film is a traditional well-established material

technology. However, thin film technology is still being developed on a daily basis since it is a key

in the twenty-first century development of new materials such as nanometer materials and/or a

man -made super lattices.

Thin film materials and devices are also available for minimization of toxic materials since the

quantity used is limited only to the surface and/or thin film layer. Thin film processing also saves on

energy consumption in production and is considered an environmentally benign material technology for

the next century. Thin film technology is both an old and a current key material technology [3]. In all

deposition techniques and application of thin films the vacuum technologies are imperative.

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2. VACUUM SCIENCE AND TECHNOLOGY

Virtually every thin-film deposition and processing method or technique employed to characterize

and measure the properties of films requires either a vacuum or some sort of reduced-pressure ambient.

For example, there are plasma discharges, sustained at reduced gas pressures, in which many important

thin-film deposition and etching processes occur. Evacuated spaces are usually populated by uncharged

gas atoms and molecules [2].

The net result of the continual elastic collisions and exchange of kinetic energy is that a steady-state

distribution of molecular velocities emerges given by the celebrated Maxwell - Boltzmann formula.

f (v) = 1/n (dn / dv) = 4/π1/2(M/2RT)3/2 v2exp – Mv2/2RT (2.1)

This centrepiece of the kinetic theory of gases states that the fractional number of molecules f(v)

here n is the number per unit volume in the velocity range v to v + dv , is related to their molecular

weight (M) and absolute temperature (T). In this formula the units of the gas constant R are on a per-

mole basis.Momentum transfer from the gas molecules to the container walls gives rise to the forces that

sustain the pressure in the system. Kinetic theory shows that the gas pressure, P, is related to the mean-

square velocity of the molecules and thus, alternately to their kinetic energy or temperature.

P = nMv-2/3NA = nRT/NA (2.2)

where NA is Avogadro's number. From the definition of n, n/NA is the number of moles per unit

volume and therefore, (2.2) is an expression of the perfect gas law. Definitions of some units together

with important conversions include

1 atm = 1.013 x 106 dynes/cm2 = 1.013 x 105 N/m2 = 1.013 x 105 Pa

1 torr = 1 mm Hg = 1.333 x 103 dynes/cm2 = 133.3 N/m2 = 133.3 Pa

1 bar = 0.987 atm = 750 torr.

The mean distance travelled by molecules between successive collisions, called the mean-free path,

λmfp, is an important property of the gas that is dependent on the pressure. One collision will occur under

the condition that πdc2 λmfp n=1, For air at room temperature and atmospheric pressure, λmfp ~ 500Å,

assuming dc ≈ 5 Å.

A molecule collides in a time given by λmfp/v, and under the above conditions, air molecules make

about 1010 collisions per second. As a result of collisions, they are continually knocked to and fro,

executing a zigzag motion and accomplishing little net movement. Since n is directly proportional to P, a

simple relation for ambient air is [1,2]:

λmfp = 5 x 10-3 / P (2.3)

with λmfp given in centimeters and P in torr. At pressures below 10-3 torr, λmfp is so large that

molecules effectively collide only with the walls of the vacuum chamber. A most important quantity

that plays a role in both vacuum science and vapor deposition is the gas impingement flux Φ . It is a

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measure of the frequency with which molecules impinge on or collide with a surface, and should be

distinguished from the previously discussed molecular collisions in the gas phase. The number of

molecules that strike an element of surface, perpendicular to a coordinate direction, per unit time and

area is given by

Φ = 0 ∫ ∞ vx dnx (2.4)

A useful variant of this formula is

Φ = 3.513 x 1022 P/(MT)1/2 molecules / cm2-s (2.5)

when P is expressed in torr.

As an application of the preceding development, consider the problem of gas escaping the vessel

through a hole of area A into a region where the gas concentration is zero. The rate at which molecules

leave is given by ΦA and this corresponds to a volume flow per second (V) given by ΦA/n cm3/s. Upon

substitution of (2.2) and (2.5), we have

V = 3.64 x 103 (T/M)1/2 A cm3 / s. (2.6)

For air at 298 K this corresponds to 11.74 liters/s, where A has units of cm2. In essence we have just

calculated what is known as the conductance of a circular aperture. As a second application, consider

the question of how long it takes for a surface to be coated by a monolayer of gas molecules. This is

an issue of great importance when attempting to deposit or grow films under extremely clean conditions.

The same concern arises during surface analysis of films, which is performed at very low pressures in

order to minimize surface contamination arising from the vacuum chamber environment. This

characteristic contamination time, tc, is essentially the inverse of the impingement flux. Thus, for

complete monolayer coverage of a surface containing some 1015 atoms/cm2, the use of (2.5) yields

tc = 1015/3.513 x 1022 . (MT)1/2/P = 2.85 x 10-8 / P. (MT)1/2s (2.7)

with P measured in torr. In air at atmospheric pressure and ambient temperature a surface will

acquire a monolayer of gas in 3.49 x 10-9s assuming all impinging atoms stick. A condensed

summary of the way system pressure affects the gas density, mean free path, incidence rates, and

monolayer formation times is conveniently displayed in Fig.2.1.

The pressure scale is arbitrarily subdivided into corresponding low, medium, high, and ultrahigh vacuum

domains, each characterized by different requirements with respect to vacuum hardware (e.g., pumps,

gauges, valves, gaskets, feed throughs). Of the film deposition processes, evaporation requires a vacuum

mainly in ultrahigh regimes, whereas sputtering between the high and low-pressure and chemical vapour

depositions are accomplished at the border between the medium and high vacuum ranges. In the low-

pressure molecular-flow regime the situation is little changed from that of an isolated chamber where the

perfect gas law applies. At the higher pressures in the viscous-flow regime, gas flow is governed by the

laws of compressible fluid dynamics. Conductance, throughputs, and pumping speeds are now

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complicated functions of pressure. With the exception of chemical vapour deposition this labour script is

exclusively concerned with the easier-to-model low- pressure chambers. Attaining low system pressures

is largely a matter of connecting a high vacuum-backing pump combination to the chamber via high-

conductance ducts. Oil diffusion, turbo molecular, cryo-, and ion pumps produce the low pressures,

while rotary, Roots, and sorption pumps are necessary to provide the necessary fore pressure for

operation of the former. Assorted valves, cold traps, and gauges round out the complement of required

vacuum hardware [2].

3. THIN FILM FORMATION

Any thin-film deposition process involves three main steps: 1. Production of the appropriate atomic,

molecular, or ionic species. 2. Transport of these species to the substrate through a medium. 3.

Condensation on the substrate, either directly or via a chemical and/or electrochemical reaction, to form

a solid deposit. The Steps in Film Formation: 1. Thermal accommodation; 2. Binding; 3. Surface

diffusion; 4. Nucleation; 5. Growth; 6. Coalescence; 7. Continued growth. Depending on the

thermodynamic parameters of the deposit and the substrate surface, the initial nucleation and growth

stages (4 and 5) of the many observations of film formation have pointed to three basic growth modes

may be described as (a) island type, called Volmer-Weber type, (b) layer type, called

Fig. 2.1 Molecular density, incidence rate, mean free path, and monolayer formation time as a function of pressure.

Frank-van der Merwe type, and (c) mixed type, called Stranski-Krastanov type [3]. These are illustrated

schematically in Fig.3.1. Island growth occurs when the smallest stable clusters nucleate on the substrate

and grow in three dimensions to form islands. This happens when atoms or molecules in the deposit are

more strongly bound to each other than to the substrate. Many systems of metals on insulators, alkali

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halide crystals, graphite, and mica substrates display this mode of growth [1]. The opposite

characteristics are displayed during layer growth.

Here the extension of the smallest stable nucleus occurs

overwhelmingly in two dimensions resulting in the

formation of planar sheets. In this growth mode the atoms

are more strongly bound to the substrate than to each other.

The first complete monolayer is then covered with a

somewhat less tightly bound second layer. Providing the

decrease in bonding energy is continuous toward the bulk

crystal value, the layer growth mode is sustained [1].

The layer plus island or Stranski-Krastanov (S.K.)

growth mechanism is an intermediate combination of the aforementioned modes. In this case, after

forming one or more mono layers, subsequent layer growth becomes unfavorable and islands form. The

transition from two- to three-dimensional growth is not completely understood, but any factor that

disturbs the monotonic decrease in binding energy characteristic of layer growth may be the cause. For

example, due to film-substrate lattice mismatch, strain energy accumulates in the growing film. When

released, the high energy at the deposit-intermediate layer interface may trigger island formation. This

growth mode is fairly common and has been observed in metal-metal and metal-semiconductor systems

[1].

At an extreme far removed from early film formation phenomena is a regime of structural effects

related to the actual grain morphology of polycrystalline films and coatings. This external grain structure

together with the internal defect, void or porosity distributions frequently determines many of the

engineering properties of films. For example, columnar structures, which interestingly develop in

amorphous as well as polycrystalline films, have a profound effect on magnetic, optical, electrical, and

mechanical properties [1].

4. THIN FILM DEPOSITION TECHNIQUES

Typical deposition processes are physical and chemical. The physical process is composed of the

physical vapour deposition (PVD) processes, and the chemical processes are composed of the chemical

vapour deposition (CVD) process (Fig. 4.1).

Fig. 3.1 Thin film growth models

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Fig. 4.1 Schematic representation of physical and chemical vapor deposition

In particular by the necessity to deposit insulating and passivating films, the CVD is served as a

powerful processing method. PVD processes (often just called thin film processes) are atomistic

deposition processes in which material is vaporized from a solid or liquid source in the form of atoms or

molecules, transported in the form of a vapour through a vacuum or low pressure gaseous (or plasma)

environment to the substrate where it condenses. Typically, PVD processes are used to deposit films

with thicknesses in the range of a few nanometers to micrometers; however they can also be used to

form multilayer coatings, graded composition deposits, very thick deposits and freestanding structures.

The substrates can range in size from very small to very large such as the 10” x 12” glass panels used for

architectural glass. The substrates can range in shape from flat to complex geometries such as

watchbands and tool bits. Typical PVD deposition rates are 10–100Å (1–10 nanometers) per second.

PVD processes can be used to deposit films of elements and alloys as well as compounds using reactive

deposition processes. The main categories of PVD processing are thermal evaporation, sputter

deposition, ion plating and arc vapour deposition. In this script the sputtering process is used as a main

thin film deposition process in the Thin film Laboratory.

5. SPUTTERING PROCESS

For convenience sputtering processes are divided into four major categories: namely, DC, RF and

magnetron. Magnetron sputtering is practiced in DC and RF as well as reactive variants and has

significantly enhanced the efficiency of these processes. Because magnetron sputtering is now the

dominant method of physically depositing films by plasma methods, it merits a section all its own. The

thin films that deposit are derived from target cathodes which play an active role in the plasma. Mainly

sputtering process described in fig.5.1 [2].

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5.1. DC SPUTTERING: The DC sputtering is also known as diode or cathodic sputtering. It is

worthwhile, however, to note how the relative film deposition-rate depends on sputtering pressure and

current. At low pressures, the cathode sheath is wide, ions are produced far from the target, and their

chances of being lost to the walls is great. The mean free electron path between collisions is large, and

electrons collected by the anode are not replenished by ion-impact-induced secondary-electron emission

at the cathode. Therefore, ionization efficiencies are low and selfsustained discharges cannot be

maintained below about 10 mtorr. As the pressure is increased at a fixed voltage, the electron mean free

path is decreased, more ions are generated, and larger currents flow. But if the pressure is too high, the

sputtered atoms undergo increased collusion scattering and are not efficiently deposited. Trade-offs in

these opposing trends, where optimum operating conditions are shaded in and include the relatively high

operating pressure of ~ 100 mtorr. During DC-diode sputtering the atoms that leave the target with

typical energies of 5 eV undergo gas scattering events in passing through the plasma gas; this is so even

at low operating pressures. As a result of repeated energy-reducing collisions they eventually thermalize

or reach the kinetic energy of the surrounding gas. This happens at the distance <xth>, is the mean

distance from the cathode sputtered atoms travel before they become thermalized, where their initial

excess kinetic energy, so necessary to provide bombardment of the depositing film, has dissipated. No

longer directed, such particles now diffuse randomly. Not only is there a decrease in the number of

atoms that deposit, but there is little compaction or modification of the resulting film structure. By virtue

of lower operating pressures the magnetron sputtering

removes these disadvantages.

Despite the fact that simple DC sputtering was historically

the first to be used and has an appealing simplicity, it is no

longer employed in production environments. The reasons are

not hard to see. For example, film deposition rates are simply

too low, e.g., a few hundred Å /min at most for many metals.

These rates cannot be appreciably raised at higher operating

Fig. 5.1 Sputtering Principle

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pressures, because in addition to more gas scattering, increased contaminant levels of O2 and H2O in

chamber gases can oxidize cathodes. Thin insulating layers that form on the target further reduce the

current and deposition rates.A fundamental problem is the small ionization cross sections at typical

electron energies in the plasma. Even at optimum operating conditions, secondary electrons emitted from

the cathode have an appreciable probability of reaching the anode or chamber walls without making

ionizing collisions with the sputtering gas [2, 10].

5.2. RF SPUTTERING: In contrast dealing with the issue of sustaining AC discharges in an

electrode-less environment, our present concern is with sputter deposition. Building on our experience

with sputtering metal films, suppose we now wish to deposit thin SiO2 films by using a quartz disk of

thickness d as the target in a conventional DC diode sputtering system. For quartz the resistivity ρ is

~1016 Ω-cm. In order to draw a current density j of 1 mA/cm2, a voltage V = pjd would have to be

dropped across the target. Assuming d = 0.1cm, substitution gives an impossibly high value of 1012 V;

the discharge extinguishes and DC sputtering will not work. If a convenient level of V = 100 V is set, it

means that a target with a resistivity exceeding 106 Ω-cm could not be DC sputtered. This impasse can

be overcome, however, if we recall that impedances of dielectric filled capacitors drop with increasing

frequency. Therefore, high-frequency plasmas ought to pass current through dielectrics the way DC

plasmas do through metal targets. And since the sputter yields are essentially similar for both target

materials, sputtering of a dielectric cathode in an AC plasma should be feasible. The trick is to sustain

the plasma while ensuring positive-ion bombardment of the cathode [2, 10].

5.3. MAGNETRON SPUTTERING: For reasons

given earlier as well as others that follow, magnetron

sputtering is the most widely used variant of DC

sputtering. Important implications of this are higher

deposition rates or alternatively, lower voltage operation

than for simple DC sputtering. Another important

advantage is reduced operating pressures. At typical

magnetron-sputtering pressures of a few millitorr, sputtered

atoms fly off in ballistic fashion to impinge on substrates.

Avoided are the gas phase collisions and scattering at high

pressures which randomize the directional character of the

sputtered atom flux and lower the deposition rate.

Therefore, for the same electrode spacing and minimum

target voltage a stable discharge can be maintained at lower pressures.

Fig. Fig. 5.2.1 RF Sputtering

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6. THIN FILM CHARACTERISATION TECHNIQUES

For the first half of this century interest in thin films centred on optical applications. The role played

by films was largely a utilitarian one necessitating measurement of film thickness and optical properties.

At first single films on thick substrates were involved. However, with the explosive growth of thin-film

utilization in microelectronics there was an important need to understand the intrinsic nature of films in

more complex materials environments. Increasingly, the benefits of multilayer film structures have been

realized in an assortment of high technology applications. Examples include multilayer metal and

insulating films in microelectronics, compound semiconductor films in optoelectronics, dielectric-film

stacks for optical coatings, and ceramic film layers in hard coatings [2]. A measurement of thin-film

properties is indispensable for the study of thin-film materials and devices. The chemical composition,

crystalline structure, and optical, electrical, and mechanical properties must be considered in evaluating

thin films [3]. Experimental techniques and applications associated with determination of “film

thickness”, “film surface morphology and structure”, “film and surface composition”, “electrical

properties of films”.

These represent the common core of information required of all films and multilayer coatings

irrespective of ultimate application. Within each of these three categories only the most important

techniques will be discussed. Beyond these characteristics there are a host of individual properties (e.g.,

thickness, structure, surface morphology and electrical conductivity) which are specific to the particular

application [2].

6.1. ATOMIC FORCE MICROSCOPE (AFM): The Atomic Force Microscope (AFM), which is

sometimes called the Scanning Force Microscope (SFM), is based on the forces experienced by a probe

as it approaches a surface to within a few angstroms. A typical probe has a 500 Å radius and is mounted

on a cantilever which has a spring constant less than that of the atom-atom bonding. This cantilever

spring is deflected by the attractive van der Waals (and other) forces and repulsed as it comes into

contact with the surface (“loading”). The deflection of the spring is measured to within 0.1 Å. By

holding the deflection constant and monitoring its position, the surface morphology can be plotted.

Because there is no current flow, the AFM can be used on electrically conductive or non- conductive

surfaces and in air, vacuum, or fluid environment. The AFM can be operated in three modes: contact,

noncontact and “tapping.” The contact mode takes advantage of van der Waal’s attractive forces as

surfaces approach each other and provides the highest resolution. In the non-contacting mode, a

vibrating probe scans the surface at a constant distance and the amplitude of the vibration is changed by

the surface morphology. In the tapping mode, the vibrating probe touches the surface at the end of each

vibration exerting less pressure on the surface than in the contacting mode. This technique allows the

determination of surface morphology to a resolution of better than 10 nm with a very gentle contacting

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pressure (Phase Imaging). Special probe tip geometries allow measuring very severe surface geometries

such as the sidewalls of features etched into

surfaces [4]. Fig. 6.1.1 Schematic illustration of AFM. The tip is

attached to a cantilever, and is raster-scanned over a surface.

The cantilever deflection due to tip-surface interactions is

monitored by a photodiode sensitive to laser light reflected at

the tip backside [9].

6.2. X-RAY REFLECTOMETRY (XRR):

Most technological applications of thin films

require films of definite thickness. This is because

most properties of thin films are thickness

dependent. Hence, determination of film thickness with high precision is very crucial for these

technologies. XRR is a non-destructive and non-contact technique for thickness determination between

2-200 nm with a precision of about 1-3Å. In addition to thickness determination, this technique is also

employed for the determination of density and roughness of films and also multilayers with a high

precision [5]. XRR method involves monitoring the intensity of the x-ray beam reflected by a sample at

grazing angles. A monochromatic X-ray beam of wavelength λ irradiates a sample at a grazing angle ω

and the reflected intensity at an angle 2θ is recorded by a detector, see figure 6.2.1. This figure illustrates

specular reflection where the condition ω = 2θ / 2 is satisfied. The mode of operation is therefore θ/2θ

mode which make sure the incident angle is always half of the angle of diffraction. The reflection at the

surface and interfaces is due to the different electron densities in the different layers (films), which

corresponds to different reflective indexes in the classical optics. For incident angles θ below a critical

angle θc , total external reflection occurs. The critical angle for most materials is less than 0.3º. The

density of the material is determined from the critical angle. Above θc the reflection from the different

interfaces interfere and give rise to interference fringes. The period of the interference fringes and the

fall in the intensity are related to the thickness and the roughness of the layer (layers in case of

multilayers). The reflection can be analyzed using the classical theory (Fresnel equation). The typical

range for these measurements are between 0º and 5º in θ [5].

Film Thickness: For incident angles greater than the X-ray beam penetrates inside the film.

Reflection therefore occurs at the top and the bottom surfaces of the film. The interference between the

rays reflected from the top and the bottom of the film surfaces results in interference fringes

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Fig. 6.2.1 θ/2θ Scan: The condition of

incident angle ω = (2θ)/2 = θ = outgoing

angle is satisfied. The detector D rotates at

twice the speed of the sample P. This

arrangement is sensitive only to the planes

parallel to the surface of the sample. The

beam makes an incident angle ω with the

surface of the sample P. The reflected

intensity at angle of 2θ is measured. Both

the rotation of the sample ω and the detector

(2θ) are about the same axis MP

(perpendicular to the drawing). The sample

is adjusted so that the rotation axis lies on the sample surface. The Detector circle is fixed through the (programmable)

detector slit (PRS, programmable receiving slit). The anode focus, F of the tube lies on the detector circle.

which does not depend on the frequency like in the case of optical spectroscopy but are angle dependent.

Due to the low amplitude reflection coefficient (ρv,h ~ 1 / sin2 θ => Rv,h = |rv,h| ~ 1 / sin4 θ ≈ 1 / θ4 ) of

interface between adjacent layers, contributions of multiply reflected beams can be neglected. The m-th

interference maximum for a path difference Δ = mλ, is located at

mλ = Δ = 2dΝx,1(θm) ≈ 2d(θ2m-2δ)-1/2 mit m∈Ν ⇔ θ2

m ≈ m2λ2/4d2+2δ = m2λ2/4d2+θ2c (6..1)

If the substrate is optically denser than the film, a phase difference of π occurs at the reflection film /

substrate interface and m is substituted with m+1/2. Employing equation (6.1) and the difference

between two neighboring maxima and minima, the thickness can be determined and is given by

d ≈ λ / { 2(θ2m+1 - θ2

C)-1/2 – (θ2m - θ2

C )-1/2 } ≈ λ / {2(θm+1 - θm } , θm >> θ2

C (6.2)

The thickness is often determined with a precision better than 1 Å for measurements exhibiting

interference fringes in a bigger angular range. [5]

6.3 FILM RESISTANCE (FOUR POINT PROBE)

The purpose of the 4-point probe is to measure the resistivity or average resistance of a thin layer or

sheet or any semiconductor material by passing current through the outside two points of the probe and

measuring the voltage across the inside two points (see Fig. 6.3.1).

Fig. 6.3.1 A view of Four-Point Probe

measuring geometry: x1 and x2 are positions,

s is distance between probes.

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Typical positions of the probe is shown above in Fig. 6.3.1 in travel and measurement

positions.

Sheet resistance measurement principles

The resistance R of a rectangular block of uniform bulk resistivity is given by: R = ρ x L / A, where

A = t x W and ρ: resistivity of the sample. R = (ρ / t) x (L / W) = Rs x (L / W), where Rs: sheet

resistance of a layer of this material. The sheet resistance is expressed in Ohm.square though strictly

speaking it should be in Ohm. Rs can be determined by four probe measurement by applying a DC

current in between the 2 outer current probes and measuring the voltage at the 2 inner voltage probes: Rs

= V/I x CF. The correction factor CF is dependent on the sample size and shape.

8. REFERENCES

[1] Ohring, M., The Materials Science of Thin Films First Edition, Academic Press, USA, 1992.

[2] Ohring, M., Material Science of Thin Films Deposition & Structure Second Edition, Academic Press, USA,

2002.

[3] Wasa, K., Kitabatake, M., Adachi H., Thin Film Materials Technology Sputtering of Compound Materials,

William Andrew Publishing, USA, 2004.

[4] Mattox, Donald M., Handbook of Physical Vapor Deposition (PVD) Processing Film Formation, Adhesion,

Surface Preparation and Contamination Control, Noyes Publication, USA, 1998.

[5] http://ia.physik.rwth-aachen.de/methods/xray/www-xray-eng.pdf

[6] http://www.bal-tec.com/products/pdf/MEDGRE.PDF

[7] http://smif.lab.duke.edu/pdf/Pt_Melting_OperatingProcedure.pdf

[8] http://www.bal-tec.com/products/pdf/QSG100.PDF

[9] http://www.farmfak.uu.se/farm/farmfyskem-web/instrumentation/afm.shtml

[10] http://www.mrsec.harvard.edu

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(b) Electrical Property Measurements Objective: Understanding the theory and application of electro-ceramic materials,

especially piezoelectric materials, and characterization of electro-ceramic materials by various equipment.

Equipment-Materials: In electro-ceramics laboratory, it is possible to design piezoelectric, capacitive and resistive transducers, produce prototypes and measure their properties. Also behaviour of transducers under AC and DC voltages can be investigated. The equipment present in this laboratory is as follows: Agilent-54624A Osciloscope MTI-2000 Fotonic Sensor HP-4194A Impedance / Gain-Phase Analyzer WF 1944 Multifunction Synthesizer HSA-4011 High Speed Bipolar Amplifier SR830 DSP TREK-Model 6100 Piezo d33 Tester.

Background

While ceramics have traditionally been admired for their mechanical and thermal

stability, their unique electrical, optical and magnetic properties have become of increasing

importance in many key technologies including communications, energy conversion and

storage, electronics and automation. Such materials are now classified under electro-ceramics,

as distinguished from other functional ceramics such as advanced structural ceramics.

Historically, developments in the various subclasses of electro-ceramics have paralleled

the growth of new technologies. Examples include: Ferroelectrics - high dielectric capacitors,

non-volatile memories; Ferrites-data and information storage; Solid Electrolytes - energy

storage and conversion; Piezoelectrics - sonar; Semiconducting Oxides - environmental

monitoring.

Dielectric materials used for construction of ceramic capacitors include zirconium

barium titanate, strontium titanate (ST), calcium titanate (CT), magnesium titanate (MT),

calcium magnesium titanate (CMT), zinc titanate (ZT), lanthanum titanate (TLT), and

neodymium titanate (TNT), barium zirconate (BZ), calcium zirconate (CZ), lead magnesium

niobate (PMN), lead zinc niobate (PZN), lithium niobate (LN), barium stannate (BS), calcium

stannate (CS), magnesium aluminum silicate, magnesium silicate, barium tantalate, titanium

dioxide, niobium oxide, zirconia, silica, sapphire, beryllium oxide, and zirconium tin titanate.

Ferroelectricity is a physical property of a material whereby it exhibits a spontaneous

electric dipole moment, the direction of which can be switched between equivalent states by the

application of an external electric field. Ferroelectrics are key materials in microelectronics.

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Their excellent dielectric properties make them suitable for electronic components such as

tunable capacitors and memory cells.

Piezoelectricity is the ability of some materials (notably crystals and certain ceramics)

to generate an electric potential in response to applied mechanical stress. This may take the

form of a separation of electric charge across the crystal lattice. The piezoelectric effect is

reversible in that materials exhibiting the direct piezoelectric effect (the production of

electricity when stress is applied) also exhibit the converse piezoelectric effect (the production

of stress and/or strain when an electric field is applied). For example, lead zirconate titanate

crystals will exhibit a maximum shape change of about 0.1% of the original dimension. The

effect finds useful applications such as the production and detection of sound, generation of

high voltages, electronic frequency generation, microbalances, and ultra fine focusing of optical

assemblies.

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EXPERIMENT # 6 POLYMER PROCESSING AND CHARACTERIZATION Objective: In this experiment, objective is learning how thermoplastics and

thermosets are processed and understand thermal analysis techniques of polymers.

Equipment: Extrusion Electrospinning Dynamic Scanning Calorimeter Thermal Gravimetric Analysis. Materials: Low density polyethylene ( LDPE),Epoxy

a) POLYMERS

Polymers can be divided into three groups - thermoplastics, thermosets, and elastomers.

Thermoplastics

Molecules in a thermoplastic are held together by relatively weak intermolecular forces so that

the material softens when exposed to heat and then returns to its original condition when

cooled. Thermoplastic polymers can be repeatedly softened by heating and then solidified by

cooling - a process similar to the repeated melting and cooling of metals. Most linear and

slightly branched polymers are thermoplastic. All the major thermoplastics are produced

by chain polymerization.Thermoplastics have a wide range of applications because they can be

formed and reformed in so many shapes. Some examples are food packaging, insulation,

automobile bumpers, and credit cards.

• Polyethylene (Low Density) LDPE, LLDPE

Properties

Semi-rigid, translucent, very tough, weatherproof, good chemical resistance, low water

absorption, easily processed by most methods, low cost.

Applications

Squeeze bottles, toys, carrier bags, high frequency insulation, chemical tank linings, heavy duty

sacks, general packaging, gas and water pipes.

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Thermosets

A thermosetting plastic, or thermoset, solidifies or "sets" irreversibly when heated. Thermosets

cannot be reshaped by heating. Thermosets usually are three-dimensional networked polymers

in which there is a high degree of cross-linking between polymer chains. The cross-linking

restricts the motion of the chains and leads to a rigid material. A simulated skeletal structure of

a network polymer with a high cross-link density is shown at the right.

Thermosets are strong and durable. They primarily are used in automobiles and construction.

They also are used to make toys, varnishes, boat hulls, and glues.

• Epoxy (EP)

Properties

Rigid, clear, very tough, chemical resistant, good adhesion properties, low curing, low

shrinkage.

Applications

Adhesives, coatings, encapsulation, electrical components, cardiac pacemakers, aerospace

applications.

• Unsaturated Polyester (UP)

Properties

Rigid, clear, chemical resistant, high strength, low creep, good electrical properties, low

temperature impact resistance, low cost.

Applications

Boat hulls, building panels, lorry cabs, compressor housing, embedding, coating.

Elastomers

Elastomers are rubbery polymers that can be stretched easily to several times their unstretched

length and which rapidly return to their original dimensions when the applied stress is released.

Elastomers are cross-linked, but have a low cross-link density. The polymer chains still have

some freedom to move, but are prevented from permanently moving relative to each other by

the cross-links. To stretch, the polymer chains must not be part of a rigid solid - either a glass

or a crystal. An elastomer must be above its glass transition temperature, Tg, and have a low

degree of crystallinity. Rubber bands and other elastics are made of elastomers

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b) Melt Extrusion Process

Melt extrusion plays a prominent part on the plastics industry. Extrusion, unlike moulding, is a

continuous process, and can be adapted to produce a wide variety of finished or semi-finished

products, including pipe, profile, sheet, film and covered wire.

In order to produce satisfactory extrudate it is necessary to apply heat to the granules in order to

soften them and make the resulting melt capable of flow under some pressure. This is carried

out rotated in the barrel by means of gear box and variable screw drive .

Therefore the screw barrel has following functions:

• pumping

• heating

• mixing

• pressurizing

In order to make each function as effective as possible it is normal practice to divide the screw

into 3 zones:

1. feed zone at hopper end.

2. compression zone (transition) at the middle.

3. melt zone (melting zone) at the die end.

The function of the feed zone is to collect granules from the feed hopper and transport (pump)

them up the screw channel. At the same time the granules should begin to heat up and compact

and build up pressure as they advance towards screw tip (die end). For efficient pumping the

granules must not be allowed to lie in the screw channel. They must therefore show high degree

of slippage on the screw channel surface and a low degree of slippage on the barrel.

Figure 1. A principal scheme of an Extrusion Machine is shown in the picture.

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Extrusion is used mainly for thermoplastics, but elastomers and thermosets are also may be

extruded. In this case cross-linking forms during heating and melting of the material in the

extruder.

c) Electrospinning

Electrospinning uses an electrical charge to draw very fine (typically on the micro or nano scale) fibres from a liquid. Electrospinning shares characteristics of both electrosprayingand conventional solution dry spinning of fibers.[1] The process does not require the use of coagulation chemistry or high temperatures to produce solid threads from solution. This makes the process particularly suited to the production of fibers using large and complex molecules. Electrospinning from molten precursors is also practised; this method ensures that no solvent can be carried over into the final product. Process When a sufficiently high voltage is applied to a liquid droplet, the body of the liquid becomes charged, and electrostatic repulsion counteracts the surface tension and the droplet is stretched; at a critical point a stream of liquid erupts from the surface. This point of eruption is known as the Taylor cone. If the molecular cohesion of the liquid is sufficiently high, stream breakup does not occur (if it does, droplets are electrosprayed) and a charged liquid jet is formed. As the jet dries in flight, the mode of current flow changes from ohmic to convective as the charge migrates to the surface of the fiber. The jet is then elongated by a whipping process caused by electrostatic repulsion initiated at small bends in the fiber, until it is finally deposited on the grounded collector.The elongation and thinning of the fiber resulting from this bending instability leads to the formation of uniform fibers with nanometer-scale diameters.

Figure 2. Fibre formation by electrospinning

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Parameters

d) Differential Scanning Calorimeter

Introduction Thermal analysis is a term used to cover a group of techniques in which a physical property of a substance and/or its reaction product(s) is measured as a function of temperature. DSC measures the heat required to maintain the same temperature in the sample versus an appropriate reference material in a furnace. Enthalpy changes due to a change of state of the sample are determined. A number of important physical changes in a polymer may be measured by DSC. These include the glass transition temperature (Tg), the crystallization temperature (Tc), the melt temperature (Tm), and the degradation or decomposition temperature (TD). Chemical changes due to polymerization reactions, degradation reactions, and other reactions affecting the sample can be determined. A typical DSC trace showing these transitions is shown in Fig. 3.

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Table 1. Specific DTA and DSC Applications

Figure 3. A Generic DSC curce depicting several transition types

Glass Transition From a thermodynamic and mechanical point of view, the glass transition, Tg, is one of the most important parameters for characterizing a polymer system. Consequently, the determination of the Tg is usually one of the first analyses performed on a polymer system. A polymer may be amorphous, crystalline, or a combination of both. Many polymers actually have both crystalline and amorphous regions, i.e., a semicrystalline polymer. The Tg is a transition related to the motion in the amorphous regions of the polymer. Below the Tg, an amorphous polymer can be said to have the characteristics of a glass, while it becomes more rubbery above the Tg . On the molecular level, the Tg is the temperature of the onset of motion of short chain segments, which do not occur below the Tg. The glass transition temperature can be measured in a variety of ways (DSC, dynamic mechanical analysis, thermal mechanical analysis), not all of which yield the same value . This results from the kinetic, rather than thermodynamic, nature of the transition. Tg depends on the heating rate of the experiment and

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the thermal history of the specimen. Also, any molecular parameter affecting chain mobility effects the Tg. Table 16.2 provides a summary of molecular parameters that influence the Tg. From the point of view of DSC measurements, an increase in heat capacity occurs at Tg due to the onset of these additional molecular motions, which shows up as an endothermic response with a shift in the baseline.

Table 2. Structural Factors Affecting Tg Melting and Crystallization The most common applications of DSC are to the melting process which, in principle, contains information on both the quality (temperature) and the quantity (peak area) of crystallinity in a polymer. The property changes at Tm are often far more dramatic than those at Tg, particularly if the polymer is highly crystalline. These changes are characteristic of a thermodynamic first-order transition and include a heat of fusion and discontinuous changes in heat capacity, volume or density, refractive index and transparency. All of these may be used to determine Tm. Generally, the crystalline melting point of a polymer corresponds to a change in state from a solid to a liquid and gives rise to an endothermic peak in the DSC curve. The equilibrium melting point may be defined as

where ΔH, is the enthalpy of fusion and ΔS, is the entropy of fusion. In addition to determining the melting point and heat of fusion from DSC, the width of the melting range is indicative of the range of crystal size and perfection . Because crystal perfection and crystal size are influenced by the rate of crystallization, Tm depends to some extent on the thermal history of the specimen.

e) Thermal Gravimetric Analysis

Thermogravimetric analysis (TGA ) uses heat to drive reactions and physical changes in materials. TGA provides a quantitative measurement of any mass change in the polymer or material associated with a transition or thermal degradation. TGA can directly record the change in mass due to dehydration , decomposition , or oxidation of a polymer with time and temperature . Thermogravimetric curves are characteristic for a given polymer or compound because of the unique sequence of the physicochemical reaction that occurs over specific temperature ranges and heating rates and are a function of the molecular structure. The changes in mass are a result of the rupture and/or formation of various chemical and physical bonds at elevated temperatures that lead to the evolution of volatile products or the formation

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of heavier reaction products . From TGA curves, data concerning the thermodynamics and kinetics of the various chemical reactions, reaction mechanisms and the intermediate and final reaction products are obtained. Other processes that can be studied by TGA are adsorption and desorption phenomena , reactions with purge gases , ash content analysis , quantitative determination of additives (including plasticizers in polymers) , solid-state reaction composition of filled polymers , rates of evaporation , and sublimation . TGA has also been used to estimate the flame retardancy of polymers, as enhanced flame retardancy is often paralleled by increased amounts o f residual char at high temperature . Similarly, antioxidant effectiveness can be gauged by the degree to which the degradation of the polymer is pushed to higher temperatures in the air purge . The temperature at which 5 % of the starting mass has been lost is a convenient benchmark for comparing antioxidant efficiency. References http://www.substech.com/dokuwiki/doku.php?id=injection_molding_of_polymers http://faculty.uscupstate.edu/llever/Polymer%20Resources/Classification.htm http://www.pitfallsinmolding.com/extrusion1.html Polymer Synthesis and Characterization Book