An alternative treatment of non-isothermal transformation kinetics.: Application to the crystallization of the Cu0.03Ge0.20Te0.77 alloy

Non-isothermal differential scanning calorimetry is frequently employed to study the kinetics of the transformation reactions and, in particular, the crystallization of the glassy alloys. Such data are analyzed by the Kissinger method, which was originally derived for the study of homogeneous reactions. The consensus in the literature, in several decades, was that such applications (i.e., to heterogeneous solid state transformations) of the Kissinger method are not valid. In the present work the principal objections to these applications are addressed and alternative derivations of theoretical results are provided. These results demonstrate that the Kissinger method is valid for heterogeneous reactions of the type described by the Johnson-Mehl-Avrami equation in the isothermal case. Isothermal and non-isothermal data on crystallization of the Cu0.03Ge0.20Te0.77 glassy alloy are presented. These experimental results and the discussions presented here help to clarify the effects of incubation times in non-isothermal transformation kinetics and provide a further demonstration of validity of the generalized Johnson-Mehl-Avrami theory for the description of heterogeneous solid state transformations. (C) 1999 Elsevier Science B.V. All rights reserved.