A criterion for determining the mechanism of solid state reactions from TG data-constancy of the pre-exponential factor

Abstract

For incorrect mechanisms, the computed values of A vary as a function of the heating rate; the correct mechanism, however, yields a constant A.

Some problems concerning the evaluation of non-isothermal kinetic parameters

“…9 The analytical form off(a) is the one that leads to the same value of the preexponentiai factor A, for various linear heating rates [ 14].…”

“…There are significant differences among the E values obtained for various mechanisms and the values of E agree with those obtained by means of isoconversional methods only for mechanism R1. It is to be noted that R 1 is the mechanism used to simulate the thermogravimetric data [14]. …”

“…(11)) will be applied to thermogravimetric data from reference [14], for the dehydration of calcium oxalate monohydrate and for the thermooxidative degradation of an unsaturated polyester resin (resin A). For the first and third cases, where the activation energy is constant, the analytical form offla) will be obtained by help of the criterion suggested in the previous paragraph.…”

“…Isothermal studies of the thermooxidative degradation of resin A [17] have shown thatf(tx) has the form: (14) where n>l and Amm, x is the maximum weight loss in the considered change.…”

On the use of Diefallah’s composite integral method for the non-isothermal kinetic analysis of heterogeneous solid-gas reactions

“…Some relatively recent papers [2][3][4][5][6] evidenced the importance of the isoconversional methods (model-free methods), which allow to obtain the dependence of the activation energy on the degree of conversion without the knowledge of the analytical form of f(α) (kinetic model). In order to find f(α) or g(α) there were suggested: (1) procedures for discrimination from a pre-established set of functions of conversion after E was evaluated by means of an isoconversional method [7][8][9][10][11][12][13];…”