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The endothermic decomposition of thaumasite from Mothae which has been investigated by DTA and TG shows a peak temperature of 138--203 ~ and reaction orders of 0.45--1.00, depending on the heating rate employed. The activation energy of the reaction was found to be about 19 kcal/mole; the enthalpy is 246 cal/g.The decomposition seems to be divided into one reaction with n = 0.90, immediately followed by one with n = 1.59. The first reaction is attributed to the loss of H20, the second one to the (partial) release of OH and CO2.

Prior to evaluating DTA curves a thorough investigation of different types of specimen holders and cell blocks should be made, which means a quantitative appraisal of heat transfer conditions. The empirical approach makes use of the thermal analogue of Ohm's law, where R = thermal resistance. Calculation of R gave a graphical correction of about 1 ram, which stresses the merit of computer calculation. Very small differences of the values for R between platinum and alumina sample holders were observed. R was experimentally determined at 500 ~ and 1000 ~ by means of UO2 and BaCO3.A rigorous comparison of various approaches in investigations of kinetics is needed to clear up the controversy between isothermal versus dynamic experimental methods. DTA methods, which are simple and time-saving, might be of use in such a project. Prior to evaluating DTA curves a thorough investigation of different types of specimen holders and cell blocks must be accomplished. This means that a quantitative appraisal of heat transfer conditions existing in an actual block should be made. A close examination of the total peak area including the exponential tail of a DTA curve, i.e. that part returning from the peak to the baseline, may make it possible to calculate the parameters of the apparatus. Thus the kinetic effects might be separated from the main diffusivity of the system, and the existing theories, (e.g. Piloyan et al.) for kinetic calculations might be tested.There have been a number of mathematical treatments of DTA curves. The investigation of thermal characteristics of DTA cell blocks has received less attention.In 1954