TEMPERATURE CALIBRATION OF AN ELECTRICAL COMPENSATION DSC ON COOLING USING THERMALLY STABLE HIGH-PURITY LIQUID-CRYSTALS

Temperature calibration of DSCs is usually carried out on heating. In order to accurately control the temperature during cooling experiments , the calibration has to be carried out on cooling. Therefore, three h igh-purity, thermally stable liquid crystals were used to perform a te mperature calibration of an electrcial compensation DSC on cooling. Al l three liquid crystals have several liquid crystalline phases, and th ey all were purified to a 99.9% level. Temperatures of the isotropic t o nematic or cholesteric and the mesophase to mesophase transitions we re used. It was verified that these liquid crystals have sufficient th ermal stability for carrying out the calibration on cooling. The depen dence of the real temperature on the indicated temperature has been es tablished for all the combinations of the heating and cooling rates of practical interest. It is also shown that the van't Hoff equation can only be applied to the crystal to a liquid crystal transition, but no t to the liquid crystal to liquid crystal or liquid crystal to isotrop ic transitions.