Characteristic kinetic parameters in solid → solid + gas reactions. Compensation effects

Abstract

The influence of experimental factors on thermogravimetric results using both dynamic and isothermal or quasi-isothermal methods has been extensively studied in the last few years (see for example ref. 1 and refs. cited therein). The interest in this kind of study is to acquire enough experimental data under very well-defined conditions to establish a general experimental procedure as well as a theoretical methodology [ 2,3]. Two characteristic parameters are especially influenced by experimental conditions: the activation energy and the pre-exponential factor [4]. For instance, the values found in the literature for the activation energy and preexponential factor of CO&a range from 37 to 377 kcal mole-’ and lo*1066, respectively. ZsSko [5] observed an interesting dependence between both magnitudes, and explained it as arising from a “compensation” effect in the sense that an increase in the activation energy implies an increase in the probability of nucleation. The purpose of this paper is to present a detailed study on the existence of this compensation effect in a solid + solid + gas reaction. We show that this‘ &f&t is common to dynamic as well as isothermal procedures, in contrast ‘to previously reported studies [ 61.