Differential thermal analysis under quasi-isothermal, quasi-isobaric conditions (Q-DTA) - Examinations using 'transformation-governed heating control' and 'self-generated atmosphere' (TGHC-SGA)

摘要

The course of conventional DTA or DSC curves is rather characteristic of the experimental conditions then of the transformation itself. The course of Q-TA(T) curves taken by the Q-DTA measuring technique is not deteriorated by these factors when using the "transformation-governed heating control" (TGHC). In this technique, namely, the temperature of the sample is governed by the transformation itself based on the feed-back principle so that the relay-switch system of the Q-DTA apparatus sensing the change of the Q-DTA(t) signal governs the heating control unit in a way, in which the transformation proceeds with a predetermined, very small and strictly constant rate by providing the suitable difference between the temperatures of the sample and the furnace. In order to normalise the experimental conditions, for decomposition reactions a particular, so-called "labyrinth crucible" should also be used, which provides a "self-generated atmosphere" already at the beginning of the reaction, and keeps the partial pressure of gaseous decomposition products constant at their maximum value of 100 kPa till the end of the transformation. This way, the unique normal characteristic temperature of reactions and transformations, together with reaction heat belonging to them can be measured, and the course of transformations free of every foreign influence can also be recorded. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 14]