Differential Thermal Analysis
Khawar yaqoob
M13-330
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.
Techniques for thermal analysis
Thermogravimetric Analysis (TGA)
Differential Thermal Analysis (DTA)
Differential Scanning Calorimetry (DSC)
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
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
∆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
Phenomena causing changes in temperature
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.
DTA apparatus
Diagram
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
Graphical Representation
Factors affect results in DTA
Factors that influence DTA curve
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
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
Applications
Pharm industry Food industry Cosmetic industry
Polymer industry Research and Development Ceramic industry
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