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
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.
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
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
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
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