1. DIFFERENTIAL
THERMAL
ANALYSIS (DTA)
Prepared by:-
Mr. Jiten B. Patel
M.pharm(1st sem)
B.M.C.P.
2. Thermal Analysis Techniques
• 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. Types of thermal analysis
• TG (Thermogravimetric) analysis:
weight
• DTA (Differential Thermal Analysis): temperature
• DSC (Differential ScanningCalorimetry):
temperature
4. • 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.
• The related technique of Differential Scanning
Calorimetry relies on differences in energy
required to maintain the sample and reference
at an identical temperature.
5. Thermogravimetry (TG)
• Thermogravimetry is the measurement of the
mass of a sample as the temperature increases.
This method is useful for determining sample
purity and water, carbonate, and organic
content; and for studying decomposition
reactions.
6. INTRODUCTION
• 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
7. • In DTA both test sample & an inert reference
material (alumina) – controlled heating or
cooling programming
• If zero temperature difference b/w sample &
reference material – sample does not
undergo any chemical or physical change.
• If any reaction takes place temperature
difference (∆T) will occur b/w sample &
reference material
8. • A DTA curve can be used as a finger print for
identification purposes, for example,
• in the study of clays where the structural
similarity of different forms renders diffraction
experiments difficult to interpret.
9. ∆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
10. Apparatus
• The key features of a differential thermal analysis
kit are as follows
1. Sample holder comprising thermocouples,
sample containers and a ceramic or metallic
block.
2. Furnace.
3. Temperature programmer.
4. Recording system.
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14. • 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
• Temp.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
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17. Differential Thermal Analysis
Advantages:
• instruments can be used at very high
temperatures
• instruments are highly sensitive
• characteristic transition or reaction
temperatures can be accurately
determined
Disadvantages: DTA
• uncertainty of heats of fusion, transition,
or reaction estimations is 20-50%
18. Factors affect results in DTA
• Sample weight
• Particle size
• Heating rate
• Atmospheric conditions
• Conditions of sample packing into dishes
19.
20. 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
