PROCESS AND APPARATUS FOR MEASURING ENTHALPY CHANGES BY MEANS OF DIFFERENTIAL THERMAL ANALYSER (DTA) APPARATUS, OPERATING WITH QUASI-ISOTHERMAL HEATING TECHNIQUE

摘要

The invention relates to a temperature controlling process and apparatus for investigation of thermal phase transformations, wherein a sample (2) and a reference substance (1) are placed into a furnace (3) with rising temperature of a predetermined rate operated by a programmed temperature controller (4), the temperatures of sample (2) and reference substance (1) are sensed by temperature sensors (5, 6), the difference between the temperatures (Ts; Tr) of the sample (2) and reference substance (1) is determined by a temperature difference measuring device (9), the output signal being Q-DTAt, which, in turn, is coupled to an element forming a signal proportional to the temperature difference, and when a difference between the temperature of the sample (2) T'?s? and that of the reference substance (1) T'?r? is generated, these are measured by the known quasi-static heating technique, and a difference is kept between them automatically and controlled by the transformation itself continuously at such a value that the transformation should take place at a constant rate orders of magnitude smaller than in the other known solutions. The essence of the invention lies in that the integration of signal Q-DTAt obtained as a function of time and proportional to the difference in the temperatures of the sample (2) T'?s? and reference substance (1) T'?r?, then transforming the signal INTEGRAL Q-DTAt obtained at the output of integrating unit (18) as a function of time into a signal depending on the temperature of the sample, INTEGRAL Q-DTAT.