Differential Thermal Analysis

For analytical students
Differential thermal analysis is a technique through which we can measure the change in temperature as a function of time or temperature
you can surely get concept of this technique along with the applications of this technique

1. USMAN ALI 1

2. ANALYTICAL CHEMISTRY PRESENETED BY USMAN ALI & UMAR RAFIQUE TO Sir. AJMAL BHATTI Sb Government College Gujranwala 2 USMAN ALI

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4. Limitations Of TGA The Chemical or physical changes which are not accompanied by the change in mass on heating are not indicated in thermogravimetric analysis During TG, Pure fusion reaction, crystalline transition, glass transition, crystallization and solid state reation with no volatile product would not be indicated because they provide no change in mass of the specimen. 4 USMAN ALI

5. 1.Principle Differential Thermal analysis is a technique in which the temperature of the substance under investigation is compared with the temperature of a thermally inert material such as a -alumina, and is recorded with furnace temperature as the substance is heated or cooled at a predetermined uniform rate. The principle of method consists in measuring the change in temperature associated with physical or chemical changes during the gradual heating of the substance. 5 USMAN ALI

6. Phenomena causing changes in Temperature Physical: Adsorption (exothermic) Desorption (endothermic) A change in crystal structure ( endo – or exothermic) Crystallization (exothermic) Melting (endothermic) Vaporization (endothermic) Sublimation (endothermic) 6 USMAN ALI

7. Chemical: Oxidation (exothermic) Reduction (endothermic) Break down reactions ( endo – or exothermic) Chemisorption (exothermic) Solid state reactions ( endo – or exothermic) Generally speaking, phase transitions, dehydration, reduction and some decomposition reactions produce endothermic effects whereas crystallization, oxidation and some decomposition reaction produce exothermic effects. 7 USMAN ALI

8. Historical Aspects: In 1899 Robert Austen improved this technique by introducing two thermocouples, one placed in sample and other in the reference block. This technique was later on modified by Burgess(1909), Norton(1939), Grim(1951), Kerr(1948), Kauffman(1950), Fold Vari (1958). 8 USMAN ALI

9. Characteristics Of DTA Curves 9 USMAN ALI

10. Characteristics Of DTA Curves Temperature of the sample is greater for an exothermic reaction, than that of reference, for endothermic the sample temperature lags behind that of reference The peak temperature corresponds to the maximum rate of heat of evolution. It does not represent the maximum rate of reaction nor the completion of the exothermic process. 10 USMAN ALI

11. Characteristics Of DTA Curves DTA curves are not only help in the identification of materials but their peak areas provide quantitative information regarding mass of sample, heat of reactions (Enthalpy change) and factors such as sample geometry and thermal conductivity. If latter two factors are expressed by a factor “K” called calibration factor, then peak area can be expressed as: Peak Area (A) = ±∆ H m K 11 USMAN ALI

12. Instrumentation: 12 USMAN ALI

13. Instrumentation: 1. Source of Uniform Heating: Nichrome (up to 1300 C ) Platinum and its alloys (up to 1750 C ) Molybdenum (up to 2000 C ) 2. Temperature Regulating System: Electronic Temperature Regulators 3. Specimen Holder: Pt, Ni, stainless steel, Ag and alloy such as Pt- Rh Ceramic material: sintered alumina, silica 13 USMAN ALI

14. Instrumentation: 4. Measurement of Temperature: Rare metal alloys Pt - Rh (Pt 10% - Rh 13%) used as thermocouple W - Mo also used as thermocouple 5. Temperature Recording System: Galvanometric Observation ( For few samples) Automatic pen Ink electronic Recorder 14 USMAN ALI

15. Factors Affecting DTA Curves: DTA is a dynamic temperature technique. Therefore, a large number of factors can affect. These factors can be divided into the two groups: Instrumental factors Sample factors 15 USMAN ALI

16. Factors Affecting DTA Curves: Instrumental Factors: Size and shape of sample holder Sample holder material Heating rate of sample Sensitivity of recording system Location of thermocouple in the sample Atmosphere around sample 16 USMAN ALI

17. Factors Affecting DTA Curves: Sample characteristics: Amount of sample Particle size Packing density Heat capacity Thermal conductivity Degree of crystallinity Dilutes of diluents Swelling and shrinking of sample 17 USMAN ALI

18. Factors Affecting DTA Curves: 18 USMAN ALI

19. Interpretation of DTA Curve 19 USMAN ALI

20. Applications The important applications of DTA are: Rapid identification of the composition of mixed clays Studying the thermal stabilities of inorganic compounds Critically examining in a specific reaction whether a new compound is actually formed or the product is nothing but an unreacted original substance 20 USMAN ALI

21. Applications DTA offers a wide spectrum of useful investigations related to reaction kinetics, polymerization, solvent -retention, phase-transformations, solid-phase reactions and curing or drying properties of a product 21 USMAN ALI

22. Thank You ! USMAN ALI 22