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 = 770°C) and is fully sintered before the crystallisation occurrence (880°C). 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 m) fired at 900°C. 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 × 10^–4 at 1 MHz and a thermal expansion coefficient of 4.5 × 10^–6°C^–1. Furthermore, the microwave characteristics were measured at 10 GHz with the results of K = 9.8, Q _f = 2250, and temperature coefficient of resonant frequency _f = –30 ppm/°C.