Sintering, crystallization and properties of MgO-Al2O3-SiO2 system glass-ceramics containing ZnO

The effect of replacement of Al2O3 by ZnO on the sintering and crystallization behavior of MgO-Al2O3-SiO2 system glass-ceramics was investigated. The results show that with increasing ZnO content, the melting temperature and crystallization temperature of the glass-ceramics were lowered, and the glass transition temperature firstly decreased and then increased. With the replacement of 5 and 8 wt.%, the predominant crystalline phase in the glass-ceramics was found to be alpha-cordierite and the secondary crystalline phase to be gahnite and quartz. When the replacement was increased to 11 wt.%, the predominant crystalline phase was found to be gahnite and quartz and the secondary phase to be a-cordierite. Only the sample containing 8 wt.% ZnO (abbreviated as sample Z8) can be fully sintered before 1000 degrees C. Therefore, a dense and low dielectric loss glass-ceramic with predominant crystal phase of alpha-cordierite and gahnite is achieved by using fine glass powders (D-50 = 3 mu m) fired at 900-925 degrees C. The as-sintered density approaches 97.0% theoretical density. The flexural strength of sample Z8 increases with sintering temperature, which closely corresponds to its relative density. The thermal expansion coefficient (TCE) of sample Z8 sintered at different temperatures mainly depends on its crystalline phases. The dielectric property of sample Z8 sintered at different temperatures depends on not only its relative density but also its crystalline phases. The dense and crystallized glass-ceramic Z8 exhibits a fairly low dielectric constant (5.0-5.2), a low dielectric loss (<= 10(-3)) at 1 MHz, a low thermal expansion coefficient (4.0-4.2 x 10(-6) degrees C-1), very close to that of Si (similar to 3.5 x 10(-6) degrees C-1) and a higher flexural strength (>= 125 MPa), suggesting that it would be a promising material in the electronic packaging field. (c) 2006 Elsevier B.V. All rights reserved.