Differential thermal analysis

DTA

1. Differential Thermal A nalysis Khawar yaqoob M13-330

2. Thermal analysis When a material is heated its structural and chemical composition can undergo changes such as fusion, melting, crystallization, oxidation, decomposition, transition, expansion and sintering. Using Thermal Analysis such changes can be monitored in every atmosphere of interest. The obtained information is very useful in both quality control and problem solving.

3. Techniques for thermal analysis Thermogravimetric Analysis (TGA) Differential Thermal Analysis (DTA ) Differential Scanning C alorimetry (DSC)

4. Differential Thermal Analysis (DTA) In Differential Thermal Analysis, the temperature difference that develops between a sample and an inert reference material is measured, when both are subjected to identical heat – treatments This is a comparison method Analytical method for recording the difference in temperature (∆T) b/w a substance and an inert reference material as a function of temperature or time Any transformation – change in specific heat or an enthaply of transition can be detected by DTA In DTA both test sample & an inert reference material (alumina) – controlled heating or cooling programming

5. Differential Thermal Analysis (DTA) DTA is used by analysts for analyzing certain properties like: • Glass transition temperature • C hemical reactions • Crystalline phase changes • Decomposition of glass batch materials

6. ∆T VS Temp. Sharp Endothermic – changes in crystallanity or fusion Broad endotherms - dehydration reaction Physical changes usually result in endothermic curves Chemical reactions are exothermic

7. Phenomena causing changes in temperature

8. Apparatus Differential thermal analysis mainly consist of 1. Sample holder comprising thermocouples, sample containers and a ceramic or metallic block . 2. Furnace. 3. Temperature programmer. 4. Recording system.

9. DTA apparatus

10. Diagram

11. Procedure Heart of the analysis – heating block Identical pair of cavities for the sample, ref. material Whole unit is set in an oven- control pressure Thermocouple is place directly in contact with the sample and another in contact with the reference Temperature of the block is raised, the temperature of the sample & reference follow Zero temp. difference – no physical or chemical change If any reaction – difference in ∆T

12. Graphical Representation

13. Factors affect results in DTA

14. Factors that influence DTA curve

15. DTA Advantages: Instruments can be used at very high temperatures Instruments are highly sensitive Characteristic transition or reaction temperatures can be accurately determined Accurate Low detection limit (up to 10-7 g) Reliable data Easy to use Rather cheap Minimal sample preparation Disadvantages: Uncertainty of heats of fusion, Transition or reaction estimations is 20-50% Destructive Limited range of samples Time consuming Usually not qualitative

16. Applications Quantitative identification and purity assessment of materials are accomplished by comparing the DTA curve of sample to that of a reference curve Impurities may be detected by depression of the M.P

17. Applications Pharm industry Food industry Cosmetic industry Polymer industry Research and Development Ceramic industry

18. Limitations Δ T determined not so accurate (2,3 0C) Very small value of Δ T cannot be determined and quantified Due to heat variation between sample and reference makes it less sensitive