As2Se3 melt crystallization studied by quadratic approximation of nucleation and growth rate temperature dependence

The constant heating rate crystallization of As2Se3 undercooled melt was measured by the differential scanning calorimetry. The nonlinear regression analysis of conversion temperature dependence was performed in frame of the classical nucleation theory supposing the normal 3D growth. The parameters of temperature dependence of nucleation rate and growth rate were determined by three step process. First the simple parabolic model was used to estimate the maximum and width of nucleation/growth rate temperature dependence. Then the obtained parabolic curves were fitted by the theoretical ones. In the third step, the obtained parameters were used as zero estimates for nonlinear regression analysis of experimental data. The results obtained by using conversion degree alpha were compared with the results obtained by using the -ln(1 - alpha) transformed function. Although both treatments give comparable results the use of -ln(1 - alpha) input data is preferred due to better numerical stability of nonlinear regression treatment.