GLASS-CERAMIC WITH PREFERRED ORIENTATION OF LI2SI2O5 CRYSTALS PRODUCED BY EXTRUSION BELOW CRYSTALLIZATION TEMPERATURE AND SUBSEQUENT HEAT-TREATMENT

Glass-ceramics with oriented crystals have been produced from a lithiu m disilicate glass system by extruding the nucleated glass below the c rystallization temperature, and subsequent heat treatment to achieve h igh-crystalline glass-ceramics. The extruded glass was found to posses s a small amount of aligned, elongated lithium disilicate crystallites and anisotropic stresses. The resulting glass-ceramic shows a high or ientation of the needle-shaped Li2Si2O5 Crystals with their c-axis par allel to the extrusion direction. The degree of crystallographic orien tation was found to be decreased for samples with an additional heat t reatment slightly above T(g), placed between the extrusion process and the crystallization. The crystal alignment of specimens extruded belo w crystallization temperature is significantly higher than the alignme nt of extruded glass-ceramic.