Crystallization of rod-shaped fluoroapatite from glass melts in the systemSiO2-Al2O3-CaO-P2O5-Na2O-K2O-F-

Glasses in the system SiO2-Al2O3-CaO-P2O5-Na2O-K2O-F- were crystallized at temperatures in the range of 900-1200 degrees C. Depending on the chemical composition, besides the main phase formed which is fluoroapatite, other cr ystalline phases, such as CaF2 and nepheline, were observed. Although, the glasses were phase separated, consisting of a silica-rich matrix and a P2O5 - and CaO-enriched droplet-phase, at some chemical compositions, strong ani sotropic apatite crystals were obtained. Here, high temperatures were favor able in order to obtain, elongated crystals. The aspect ratios of the fluor oapatite crystals obtained were up to 12:1. (C) 1999 Elsevier Science B.V. AU rights reserved.