SINTERING AND PROPERTIES OF O-CENTER-DOT-AL2O3-CENTER-DOT-4SIO(2)-BOROSILICATE GLASS COMPOSITES

Sintering, glass crystallization, microstructure, and the resulting pr operties of spodumene-borosilicate glass composites were investigated. Densities >90% could be obtained for samples sintered below 1000 degr ees C. Samples that contained more low-viscosity glass densified at lo wer temperatures, and significant density reduction was observed at hi gher temperatures. Samples that contained high-viscosity glass densifi ed only at higher temperatures. When glasses of different viscosity we re added, the densification of the composites was improved. There was interdiffusion between spodumene and glass. Cristobalite crystallized from the pure glasses. Addition of spodumene changed the major phase c rystallized to anorthite or alpha-quartz as a result of dissolution of spodumene into glass. Composites that contained glass of higher silic a content showed more crystallization. As sintering temperatures incre ased, the amount of crystallization decreased, due to dissolution of g lass into spodumene. The spodumene particles showed angular shape with smooth and straight sides. The spodumene-glass composites showed a di electric constant in the range of 5-6, a loss tangent generally <1%, a nd a CTE value in the range of 2-5.6 X 10(-6) K-1. Codoping of glasses with different viscosity effectively improved the densification and p roperties of the composites.