CRYSTALLIZATION OF Y3AL5O12 FROM AN OXYNITRIDE GLASS MONITORED BY HIGH-TEMPERATURE X-RAY-DIFFRACTOMETRY

It is well established that the glassy phase in a beta-SiAlON material , with addition of Y2O3, can be crystallized to yttrium aluminium garn et (Y3Al5O12-YAG) by a post-sintering heat treatment. The crystallizat ion of the YAG phase from an oxynitride glass with composition 46.1 wt % Y2O3, 26.3 wt% Al2O3, 21.6 wt% SiO2 and 6 wt% Si3N4 was studied by m eans of high-temperature X-ray diffractometry. The kinetics of the cry stallization were monitored in terms of the (420)) YAG peak area versu s isothermal soaking time at 1150 degrees C during different heat trea tments. The crystallization of the YAG phase was found to proceed as a surface crystallization. The results are relevant to developing impro ved crystallization treatments for glasses with potential for crystall ization to YAG-based glass-ceramics and for heat treatments of YAG/bet a-SiAlON materials. Copyright (C) 1996 Elsevier Science Ltd