Preparation Of Glass-Ceramics With Needle-Like Apatite Crystals Of Different Aspect Ratios And Their Behaviour During Extrusion

Glass-ceramics containing needle-like apatite crystals were produced from glasses in the system Si02-Al203-Ca0-P205-K20-F-. Crystallization was achieved by rapid heating to 1200 deg C and keeping the sample for 0.5 to 15h. 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 behaviour 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.