Effect of Titanium Dioxide on Crystallization Behavior and Properties of MgO–Al₂O₃–SiO₂ Glass–Ceramics

Cordierite glass–ceramics exhibit low dielectric constant, dielectric loss and thermal expansion. The stoichiometric cordierite MgO–Al₂O₃–SiO₂ (MAS) glass is due to the surface crystallization. In this paper, MAS glass–ceramics with various contents of TiO₂ as a nucleation agent were prepared by a melting method and subsequent heat treatment. The effect of TiO₂ content on the crystallization behavior and properties was investigated. The results show that the glass transition temperature and the first crystallization peak temperature decrease with the increase of TiO₂ content, indicating that TiO₂ can effectively promote the crystallization. TiO₂ enters into the glass network structure, and facilitates the formation of μ-cordierite and magnesium aluminum titanate crystalline phases in the glass, and then form α-cordierite at a higher temperature. The crystallization mechanism of glass with more than 5% (in molar fraction) TiO₂ becomes the bulk crystallization. As TiO₂ content increases to 10%, the glass–ceramics heat-treated at 800 ℃ for 10 h and 1000 ℃ for 5 h have a high density of 2.95 g/cm³, a hardness of 9.67 GPa, and a thermal conductivity of 2.13 W/(m·K). At 8.2–12.4 GHz, its dielectric constant is 6.3–6.5 and the dielectric loss fluctuates from 10^–2 to 10^–3. At 1 MHz, the dielectric constant is 10.8 and the dielectric loss is 0.0244.