Effects of ZnO on crystallization, microstructures and properties of BaO-Al2O3-B2O3-SiO2 glass-ceramics

A novel glass-ceramic, BaO-ZnO-Al2O3-B2O3-SiO2, with high coefficient of thermal expansion (CTE) was prepared by the solid-state method. Crystalline phases are quartz (major), cristobalite (minor), and bazirite (minor). Results via whole pattern fitting indicate that crystallinities slightly vary within 33.6-39.3 %, but mass fractions of phases greatly change versus ZnO content. ZnO cannot remarkably promote the crystallization of Ba-Al-B-Si glass. Thermal expansion curves become linear, since the phase transformation from quartz to cristobalite is effectively suppressed by ZnO. An empirical equation of CTE versus temperature and ZnO content was built further. The densification mechanism reveals because Zn2+ with higher field strength increases glass viscosity and hinders ion diffusion, shrinkage rates and densities decrease with ZnO. Flexural strength (sigma) and electrical properties thus significantly deteriorate. The sample with 3 wt% ZnO sintered at 950 A degrees C achieves excellent performances: CTE = 12.24 ppm/A degrees C, sigma A = 153.3 MPa, and epsilon = 5.7, tan delta = 0.0004, rho = 4.4 x 10(12) Omega cm.