Theoretical study on the mechanism and transformation kinetics under non-isothermal conditions. Application to the crystallization of Sb 0.12As 0.36Se 0.52 glassy alloy

Abstract

A procedure has been developed to determine the reliable form of the glass-crystal transformation function, and to deduce the kinetic parameters by using differential scanning calorimetry data, obtained from experiments performed under non-isothermal conditions. It is an integral method, which is based on a transformation rate independent of the thermal history and expressed as the product of two separable functions of absolute temperature and the fraction transformed. Considering the same temperatures for the different heating rates, one obtains a constant value for temperature integral, and, therefore, a plot of a function of the volume fraction transformed versus the reciprocal of the heating rate leads to a straight line with an intercept of zero, if the reaction mechanism is correctly chosen. Besides, by using the first mean value theorem to approach the temperature integral, one obtains a relationship between a function of the temperature and other function of the volume fraction transformed. The logarithmic form of the quoted relationship leads to a straight line, whose slope and intercept allow to obtain the activation energy and the frequency factor. The method developed has been applied to the crystallization kinetics of the Sb 0.12As 0.36Se 0.52 glassy alloy and it has been found that the kinetic model of normal grain growth is the most suitable to describe the crystallization of the quoted alloy. The mean values obtained for the activation energy and the frequency factor have been 27.36 kcal mol −1 and 1.5×10 9 s −1, respectively.