Title 34. THERMAL ANALYSIS.pdf ✅

PHARMD GURU Page 2  Calorimetry is the process of measuring the amount of heat released or absorbed during a chemical reaction and the device is known as calorimeter.  Watson and O'Neill developed this thermal analysis in 1960 and then introduced it in 1963 commercially at Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. PRINCIPLE: The basic principle involved in DSC is that this technique is used to study what is the effect of heating on the polymers/samples. It examines the thermal transitions of polymer or sample when heated. For example, this technique can be employed to study the effect of heating on a crystalline polymer, glass transitions, and crystallization. The sample and reference materials are heated by separate heaters at the same temperature throughout the experiment. The energy which is required to obtain zero temperature difference between sample and reference is measured. INSTRUMENTATION: FIG: SCHEMATIC REPRESENTATION OF DSC APPARATUS  The DSC measurement requires a sample and a reference.  Modern DSC sample and reference pans are small and usually made of aluminum. They may or may not have lids.  Sample size is generally 1-10 mg and the reference pan is left empty, but an inert reference material may be used.

PHARMD GURU Page 4  The differential heat flow into the pans is directly proportional to the difference in the thermocouple signals.  The sample temperature is measured by the alumel/chromel thermocouple under the sample position.  This temperature is an estimated sample temperature because the thermocouple is not inserted into the sample itself.  The accuracy of this temperature will depend on the thermal conductivity of the sample and its container, the heating rate, and other factors.  The sample and reference pans both have lids and the reference pan is an empty pan. 2) POWER COMPENSATED DSC: FIG: POWER COMPENSATED DSC  The major difference in power compensated DSC instruments is that, two separate heating elements are used for the sample and the reference.  A change in temperature between the sample and the reference serves as the signal to “turn on” one of the heaters, so that the sample and the reference stay at the same temperature.  When a phase change, reaction, glass transition, or similar event occurs in the sample, the sample and reference temperatures become different.  This causes extra power to be directed to the cell at the lower temperature in order to heat it.