Differential thermal analysis (DTA) is a thermal analysis technique that measures the temperature difference between a sample and an inert reference material as they are heated or cooled under identical conditions. DTA can detect physical and chemical changes in a material that involve changes in heat flow, such as fusion, decomposition, and glass transitions. The DTA technique involves placing a sample and inert reference material in contact with thermocouples in a heating block. As the block is heated, any difference in temperature between the sample and reference due to an endothermic or exothermic reaction in the sample is measured and plotted against temperature or time. DTA is useful for applications in materials characterization, pharmaceuticals, polymers, ceramics, and

2. Differential Thermal
Analysis
Khawar yaqoob
M13-330

3. 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.

4. Techniques for thermal analysis
 Thermogravimetric Analysis (TGA)
 Differential Thermal Analysis (DTA)
 Differential Scanning Calorimetry (DSC)

5. 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

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

7. ∆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

8. Phenomena causing changes in
temperature

9. 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.

10. DTA apparatus

11. Diagram

12. 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

13. Graphical Representation

15. Factors affect results in DTA

16. Factors that influence DTA curve

17. 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

18. 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

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

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