A theoretical method to analyze the glass-crystal transformation kinetics under non-isothermal regime: Application to crystallization of the Ge0.13Sb0.23Se0.64 glassy alloy

A theoretical method has been considered to determine the suitable form of the glass-crystal transformation function, and to calculate the kinetic parameters by using differential scanning calorimetry data, obtained from experiments carried out under non-isothermal regime. 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 volume 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 relationships leads to a straight line, whose slope and intercept allow to obtain the activation energy and the frequency factor, respectively. The theoretical method has been applied to the crystallization kinetics of the Ge0.13Sb0.23Se0.64 glassy alloy and it has been found that the kinetic model of normal grain growth is most suitable to describe the crystallization of the quoted alloy. The values obtained for the activation energy, E, and the logarithm of the frequency factor, K0, have been 188.3 kJ mol−1 and 36.7 (K0 in s−1), respectively. The phases at which the alloy crystallizes after the thermal process have been identified by X-ray diffraction. The diffractogram of the transformed material suggests the presence of microcrystallites of Sb2Se3 and GeSe, remaining in a residual amorphous matrix.