Sintering of cordierite-borosilicate glass composites

The sintering and properties of cordierite-borosilicate glass composites we re investigated. For the composites with greater than or equal to 35% low-v iscosity glass, the sintered densities decreased with the increasing sinter ing temperature above 850 degrees C. No crystallization of the glass was fo und. For the composites with 50-90 wt% high-viscosity glass, the sintered d ensities remained nearly constant (>95%) in a wide sintering temperature ra nge. However, cristobalite crystallized from the glass phase, resulting in an undesirably high coefficient of thermal expansion. Presintering processi ng and a lower heating rate improved the densification of the composites wi th low-viscosity glass while limiting that of the composites with high-visc osity glass. This result is explained by the difference in crystallizabilit y between these two glasses. As low- and high-viscosity glass powders were simultaneously added, the density reduction was reduced and the coefficient of thermal expansion was closer to that of Si because of the absence of cr istobalite phase. The dielectric constant of all the composites was in the typical range of 4.9-5.7 at 1 MHz.