Theoretical analysis on the mechanism and transformation kinetics under non-isothermal conditions

Abstract

Abstract A procedure has been developed for analyzing the evolution with time of the volume fraction crystallized and reaction mechanism and for calculating the kinetic parameters at non-isothermal transformations in materials involving formation and growth of nuclei. Considering the assumptions of extended volume and random nucleation, a general expression of the fraction crystallized as a function of the time has been obtained in isothermal crystallization processes. The application of the crystallization rate equation to the non-isothermal processes has been carried out under the restriction of a nucleation which takes place early in the transformation and the nucleation frequency is zero thereafter. In these conditions, the correct reaction mechanism has been obtained plotting the logarithmic form of various kinetic equations versus the reciprocal temperature, and choosing that equation, which gives the plot with the best fit to a straight line. The kinetic parameters, activation energy and frequency factor, have been deduced from the slope and intercept of the above-mentioned straight line. The theoretical method developed has been applied to the crystallization kinetics of the semiconducting Sb 0.16 As 0.36 Se 0.48 alloy, thus obtaining values for the quoted parameters that agree very satisfactorily with the calculated results by other mathematical treatments. This fact shows the reliability of the theoretical method developed.