Generalization of the Avrami equation for the analysis of non-isothermal transformation kinetics. Application to the crystallization of the Cu0.20As0.30Se0.50 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 Kissing er method, which was originally derived for the study of homogeneous reacti ons. The consensus in the literature, in several decades, was that such app lications (i.e. to heterogeneous solid state transformations) of the Kissin ger method are not valid. In the present work the principal objections to t hese applications are addressed and alternative derivations of theoretical results are provided. These results demonstrate that the Kissinger method i s valid for heterogeneous reactions of the type described by Johnson-Mehl-A vrami equation in the isothermal case. Isothermal and non-isothermal data o n crystallization of the Cu0.20As0.30Se0.50 glassy alloy are presented. The se experimental results and the discussions presented here help to clarify the effects of incubation times in non-isothermal transformation kinetic an d provide a further demonstration of validity of the generalized Johnson-Me hl-Avrami theory for the description of heterogeneous solid state transform ations. (C) 2000 Elsevier Science Ltd. All rights reserved.