Crystallization Kinetics of Apatite and Powellite in a Borosilicate Glass Under Thermal Gradient Conditions

The aim of this work is to determine the impact of a thermal gradient on the crystallization kinetics of apatites (Ca2Nd8(PO4)(SiO4)5O2) and powellite (CaMoO4) in a borosilicate glass containing rare earth elements and molybdenum, typically incorporated in nuclear waste glasses. An automated SEM allows the acquisition of images over a large area of glass samples submitted to isothermal or thermal-gradient heat treatments. The images are then processed by image analysis, allowing the extraction of crystal morphological parameters. The evolution of these parameters is plotted versus time and temperature. The comparison of data from glass samples which have undergone an isothermal heat treatment with samples treated in a thermal gradient allows us to determine the impact of the thermal gradient.