ORIENTED MICA GLASS-CERAMIC BY EXTRUSION AND SUBSEQUENT HEAT-TREATMENT

Glass-ceramics with oriented mica crystals have been produced by extru ding a fluorophlogopite glass and subsequent thermal treatment. During extrusion predominantly the intermediate phase norbergite (Mg3F2SiO4) and besides small quantities of phlogopite mica crystals (Na/KMg3F2Si 3AlO10) crystallized. Heat treatments at temperatures around the maxim um crystallization rate resulted in an oriented crystallization of phl ogopite as proved by electron microscopy and XRD analysis. The plate-l ike crystals are aligned with their basal planes parallel to the direc tion of extrusion. The degree of orientation was studied by X-ray pole figure measurements. The (003) planes show strong ring-fibre texture. The degree of orientation decreased if the crystallization was realiz ed at lower temperatures and lower crystallization rates. The alignmen t mechanism is discussed.