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1. “THERMAL
ANALYSIS ”

2. Thermal Analysis
Differential Scanning
Calorimetry (DSC)
Measure heat absorbed or
liberated during heating or
cooling
Thermal Gravimetric
Analysis (TGA)
Measure change in weight
during heating or cooling

3. • Principle- measures the
temperatures and heat flows associated with transitions in
materials as a function of time and temperature in a
controlled atmosphere.
• These measurements provide quantitative and qualitative
information about physical and chemical changes that
involve endothermicor exothermicprocesses, or changes
in heat capacity.
DSC: The Technique

4. • A DSC apparatus is built
around
- a differential detector
- a signal amplifier
- a furnace
- a temperature controller
- a gas control device
- a data acquisition device
Diagram of a DSC apparatus
Sample Reference
Gas
control
Furnace
controller
four
Data
acquisition
Microvolt
amplifier
Detectors
Furnace

5. DSC measures:-
•Glass transitions
•Melting and boiling points
•Crystallisation time and temperature
•Percent crystallinity
•Heats of reactions
•Specific heat capacity
•Oxidative/thermal stability
•Reaction kinetics
•Purity

6. 6
DSC Thermogram
Temperature
HeatFlow->exothermic
Glass
Transition
Crystallisation
Melting
Cross-Linking
(Cure)
Oxidation

7. Main Sources of Errors
•Calibration
•Contamination
•Sample preparation – how sample is loaded into a pan
•Residual solvents and moisture.
•Thermal lag (interval/gap)
•Heating/Cooling rates
•Sample mass
•Processing errors

8. Sample preparation
Form of sample: bulk solid, powder (pressed), liquid.
Amount of sample: 3-5mg.
DSC Pan: Al, Pt, stainless steel, Ag, Cu, Al2O3

11. Applications of DSC
 Determination of Heat Capacity:- heat absorbance capacity of polymers
 The Glass Transition Temperature: It is a reversible transition
in amorphous material from a hard, brittle state into molten rubber
like state
 Crystallization
 Oxidative stability
 Drug analysis
 General chemical analysis Melting-point
 Polymers
 Food science In food science research, DSC is used in conjunction with
other thermal analytical techniques to determine water dynamics. Changes
in water distribution may be correlated with changes in texture.

12. • Liquid crystals: Some materials go from solid to
liquid; they go through a third state, which
displays properties of both the phases.
• This anisotropic liquid is known as a liquid
crystalline state.
• Using DSC, we can observe the small energy
changes that occur as matter transitions from a
solid to a liquid crystal and from a liquid crystal
to anisotropic liquid.

13. THERMOGAVIMETRIC ANALYSIS
(TGA)
• Principle: TGA measures the amount and the rate of weight
change of a material with respect to temperature or time in
controlled environments.
• A TGA consists of three major parts a furnace,
1. A microgram balance,
2. An auto sampler and
3. A thermocouple.
.

14. Instrument:
 Instrument used for thermogravimetry is
“Thermobalance”. Data recorded in form of curve
known as „Thermogram‟
 The furnace can raise the temperature as high as
1000°C which is made of quartz.
 The auto sampler helps to load the samples on to the
microbalance.
 The thermocouple sits right above the sample.
 Care should be taken at all times that the
thermocouple is not in touch with the sample which is
in a platinum pan.

16. TGA Curve of Calcium Oxalate

17. Sample Preparation
.
The sample weight affects the accuracy of weight loss
measurements.
Typically 10-20mg of sample is preferred in most applications.
Whereas, if the sample has volatiles 50-100mg of sample is
considered adequate.

18. Experimental Conditions -Heating Rate
• Samples are heated at a rate of 10 or 20°C/min in
most cases.
• Lowering the heating rates is known to improve the
resolution of overlapping weight losses.
Experimental Conditions -Purge gas
• Nitrogen is the most common gas used to purge samples in TGA due
to its inert nature.
• Whereas, helium provides the best baseline.
• Air is known to improve resolution because of a difference in the
oxidative stability of components in the sample.
• Vacuum may be used where the sample contains volatile components,
which helps improve separation from the onset of decomposition
since the volatiles come off at lower temperatures in vacuum.
• e.g. oil in a rubber tire product.

21. Applications of TGA
• Determination of the bound and unbound water in the suspension of Milk of
Magnesia (MoM), used as a laxative.
• Polymorphism- study of polymorphs
• Solid Dispersions and Polymeric Dosage Forms
• Drug- excipient study (interaction)