A HIGH-TEMPERATURE X-RAY-DIFFRACTION STUDY OF THE CRYSTALLIZATION OF AMORPHOUS BALL-MILLED ZIRCON

The crystallisation pathways for zircon and other oxide mixtures which had been ball milled were examined by high temperature powder X-ray d iffraction. Zircon, zircon-alumina and zirconia-silica mixtures were p artially or completely amorphised by prolonged milling. Upon heating, full recrystallisation of zircon as a nanocrystalline phase was observ ed before rapid grain growth occurred. Crystallisation was found to oc cur by heterogeneous nucleation with simultaneous slow grain growth by coalescence. Zirconia-silica and zircon-alumina milled mixtures also formed a transient tetragonal zirconia phase during heating, which rea cted with silica to form zircon. The zirconia-silica system in particu lar crystallised zircon at a significantly lower temperature than repo rted previously for other solid-state preparation techniques. (C) 1997 Elsevier Science B.V.