The possibility of using the KEKAM equation :~ = 1 --exp (--ktO in the kinetics of non-isothermal transformations is discussed. Calculation methods are proposed for the determination of the kinetic exponent n from thermoanalytical curves within a chosen temperature range.It is a prevalent trend in our days to gather information, both in theoretical and practical studies, on the kinetics and on the assumed mechanism of non-isothermal transformations by the computerized analysis of some set of kinetic equations based on some accepted model conception concerning the course of the solid-state chemical reaction [1,2]. The kinetic characteristics obtained after computations (the activation energy E of the reaction, the pre-exponential factor k 0 in the Arrhenius equation, and the mechanism functionf(~) of the reaction) are presumed to have a real physical meaning. However, a fact known from the experience of isothermal kinetics must be borne in mind, namely that the true, existing kinetic curve may formally be described by a number of kinetic equations based on different or even contradictory model conceptions [3]. If, on the other hand, the kinetic curve in question cannot be described by a given kinetic equation, then the corresponding model may with certainty be excluded from considerations. However, it should be mentioned here that the kinetic characteristics (E and k0) obtained in isothermal kinetics by using different kinetic equations frequently differ only slightly [3].The situation is quite different in non-isothermal kinetics, where the kinetic characteristics E and k 0 largely depend on the form of the kinetic equation taken into account [4]:(1) dt and also on the chosen temperature program [5].This difficulty can be avoided by deliberately using a more general kinetic equation for the calculation of the kinetic characteristics all the rest following from this equation. The combined Kolmogorov-Erofeev-Kazeev-Avrami -Mampel equation (abbreviated KEKAM) [6][7][8][9][10] is one of these general equations:=-I -exp (-Ktn).(2)
The solution of the exponential integral at linear heating for the general case that the activation energy linearly depends on temperature according to E(T) = E o q-RBT is T
The method suggested by several authors for determining the mechanism of solid-1 phase transformations by linearizing the function In g(cO vs.--is more correct for T a hyperbolic temperature change than for a linear temperature change. In the latter case, the method yields reliable results only under the condition that the relationship g(~) 1 in ~q-vs.~ is linear. The well-known Horowitz-Metzger method is essentially suited for processing thermokinetic curves obtained under hyperbolic heating or cooling.In the practice of thermal analysis, linear temperature programming T = T o + at is usually applied. A hyperbolic temperature change [1, 2] liT = 1IT o -bt is much less frequent. However, in some cases of thermoldnetic analysis it is desirable, for in the case of a hyperbolic temperature change the integration of the differential equations in non-isothermal kinetics is much simpler [1,3].To For the case of linear heating T = To + at, integration of Eq. (1) o r. Thermal _Anal. 10, 1976
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