Crystallization of rod-shaped fluoroapatite from glass melts in the system SiO 2–Al 2O 3–CaO–P 2O 5–Na 2O–K 2O–F −

Abstract

Glasses in the system SiO 2–Al 2O 3–CaO–P 2O 5–Na 2O–K 2O–F − were crystallized at temperatures in the range of 900–1200°C. Depending on the chemical composition, besides the main phase formed which is fluoroapatite, other crystalline phases, such as CaF 2 and nepheline, were observed. Although, the glasses were phase separated, consisting of a silica-rich matrix and a P 2O 5- and CaO-enriched droplet-phase, at some chemical compositions, strong anisotropic apatite crystals were obtained. Here, high temperatures were favorable in order to obtain, elongated crystals. The aspect ratios of the fluoroapatite crystals obtained were up to 12:1.