Oriented mica glass-ceramic by extrusion and subsequent heat treatment

Glass-ceramics with oriented mica crystals have been produced by extruding a fluorophlogopite glass and subsequent therma treatment. During extrusion predominantly the intermediate phase norbergite (Mg₃F₂SiO₄) and besides small quantities of phlogo pite mica crystals (Na/KMg₃F₂Si₃AlO₁₀) crystallized. Heat treatments at temperatures around the maximum crystallization rat resulted in an oriented crystallization of phlogopite as proved by electron microscopy and XRD analysis. The plate-like crystals ar aligned with their basal planes parallel to the direction of extrusion. The degree of orientation was studied by X-ray pole figur measurements. The (003) planes show strong ring-fibre texture. The degree of orientation decreased if the crystallization was realize at lower temperatures and lower crystallization rates. The alignment mechanism is discussed.