On the problems of the kinetic evaluation of DTA curves and non‐isothermal rate curves of one‐step reactions in solution

Abstract

AbstractThe kinetics of one‐step reactions in solution was studied non‐isothermally (linear temperature increase in the external system) by Differential Thermal Analysis (DTA) in an apparatus using a stirring technique. — Based on the assumption of a proportionality between heat flux and reaction rate, experimental DTA curves were evaluated by three methods, a) calculation of rate constants according to the formula proposed by Borchardt and Daniels [9], b) calculation of rate constants from non‐isothermal rate curves deduced from the heat balance equation, c) deriving activation data by optimum fitting of the theoretical model curves generated by numerical integration of the rate law, to the experimental curve. — In all cases studied, results obtained by the three methods are in good agreement. They are also confirmed by values reported in the literature, which are obtained by isothermal methods. However, it is not possible to extract rate constants from the decaying portion of the DTA curves, since the weight of the kinetic information is decreased with reaction progress, whereas the influence of heat conductivity is increased. The nature of the dependence of the usable curve time range on kinetics (reaction order and specific time), cell constant, heating rate, and initial concentration which was tested by re‐evaluation of the theoretically generated curves confirms our model and may serve as independent evidence for the applicability of all three methods even assuming extreme values for relevant parameters.