Low temperature sintering and crystallisation behaviour of low loss anorthite-based glass-ceramics

Anorthite-based glass-ceramics including TiO2 as nucleating agent were melted and quenched in this study. The effect of particle size on the sintering behaviour of glass powders was investigated in order to obtain low-temperature sintered glass-ceramics. Anorthite glass-ceramic starts to densify at the transition temperature of glass (T-g = 770degreesC) and is fully sintered before the crystallisation occurrence (880degreesC). Therefore, a dense and low-loss glass-ceramic with predominant crystal phase of anorthite is achieved by using fine glass powders (D-50 = 0.45 mum) fired at 900degreesC. The as-sintered density approaches 99% theoretical density and the apparent porosity is as low as 0.05 Vol%. The dense and crystallized anorthite-based glass-ceramic exhibits a fairly low dielectric loss of 4 x 10(-4) at 1 MHz and a thermal expansion coefficient of 4.5 x 10(-6)degreesC(-1). Furthermore, the microwave characteristics were measured at 10 GHz with the results of K = 9.8, Of = 2250, and temperature coefficient of resonant frequency tau(f) = -30 ppm/degreesC. (C) 2003 Kluwer Academic Publishers.