On the use of the classical rate equation in non-isothermal heterogeneous kinetics

Abstract

all the symbols having known meanings. To vindicate this drastic request, Dr. Shlensky mentions two previous articles published by him and his coworkers [2, 3]. After a careful reading of these articles we found that they actually refer to the thermal destruction of some polymeric materials, so from the very beginning the possible inapplicability of Eq. (1) should be restricted to this group of compounds. However, as Dr. Shlensky and his coworkers show in these articles, Eq. (1) correctly describes even the thermal destruction of polymers at low heating rates (below !10~ We consider these results as normal, because it is very well known that, in order to remove the disturbing effects of the heat transfer on the kinetic data, one has to work at various heating rates and to extrapolate the values of the kinetic parameters to zero heating rate. Equally, one can use such low heating rates that their further decrease no longer influences the values of the kinetic parameters. Actually, these heating rates should be low enough to ensure a kinetic regime, and high enough to ensure conditions far from equilibrium for the reaction. As shown by widespread experience, the heating rate values which fulfil these requirements should be below 10~ in agreement with the findings of Dr. Shlensky and his coworkers. It has to be pointed out that this is the field of heating rates used in non-isothermal heterogeneous kinetics. At higher heating rates, over 70~ it is normal that one can not describe the decomposition kinetics by using Eq. (1). The possibilities of using Eq. (1) to describe the thermal destruction of polymers have been critically analyzed with special emphasis on the disturbing effects generated by the changes of mechanism during heating of the sample [4]. It is noteworthy that some of the methods used in non-isothermal kinetics, based on Eq. (1), such as those given by Flynn and Wall [5] or Ozawa [6], provide evidence