1994, Durschang, Bernward R., Carl, Gunter, Rüssel, Christian, Marchetti, Kurt, Roeder, Erwin

Glass-ceramics with oriented crystals have been produced from a lithium disilicate glass system by extruding the nucleated glass below the crystallization temperature, and subsequent heat treatment to achieve high-crystalline glass-ceramics. The extruded glass was found to possess a small amount of ahgned, elongated lithium disilicate crystallites and anisotropic stresses. The resulting glassceramic shows a high orientation of the needle-shaped Li₂Si₂O₅ crystals with their c-axis parallel to the extrusion direction. The degree of crystallographic orientation was found to be decreased for samples with an additional heat treatment slightly above Tg, placed between the extrusion process and the crystallization. The crystal alignment of specimens extruded below crystallization temperature is significantly higher than the alignment o f extruded glass-ceramic.

1997, Habelitz, Stefan, Carl, Gunter, Rüssel, Christian, Marchetti, Kurt, Roeder, Erwin, Eifler, Dieter, Hergt, Rudolph

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.