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
- 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)