Preparation of glass-ceramics with needle-like apatite crystals of different aspect ratios and their behavior during extrusion

Abstract

Glass-ceramics containing needle-like apatite crystals were produced from glasses in the system SiO2-Al2O3-CaO-P2O5-K2O-F- . Crystallization was achieved by rapid heating to 1200°C and keeping the sample for 0.5 to 15 h. With increasing time of heat treatment, length, L, width, W, as well as the aspect ratio, L/W, of the apatite crystals increased. This also led to an increase in the Newtonian viscosity. At higher shear rates, non-Newtonian flow behavior was observed. This effect was more pronounced with increasing aspect ratio. In all cases, the result of the extrusion process was highly oriented glass-ceramics, if it was carried out in the non-Newtonian range.