Effect of B2O3 on the crystallization, structure and properties of MgO-Al2O3-SiO2 glass-ceramics

The formation of alpha-cordierite glass-ceramics in the MgO-Al2O3-SiO2 system without and with addition of B2O3 was investigated. Moreover, the effects of different contents of B2O3 on the crystallization behavior, structure variation, thermal and physical properties of glass-ceramics were studied, and the action mechanism of B2O3 was systematically discussed by XRD, FT-IR and XPS. The results show that a proper amount of B2O3 shortens the crystallization route and reduces formation temperature of alpha-cordierite, which further promotes the direct precipitation of alpha-cordierite in MAS system. The glass-ceramics undergo the phase transitions from intermediate phases of MgO center dot Al2O3 center dot SiO2 and Mg0.6Al1.2Si1.8O6 to pure alpha-cordierite without the addition of B2O3. However, the pure alpha-cordierite directly precipitates in the glass-ceramics adding 4 mol% B2O3 without intermediate phases. Low B2O3 content (4 mol%) promotes the crystallization of alpha-cordierite, while high B2O3 content (8-12 mol%) inhibits it, which is accompanied by the increase of thermal expansion coefficient from 1.70 x 10(-6) degrees C-1 to 3.72 x 10(-6) degrees C-1 and the decrease of Vickers hardness from 9.4 GPa to 6.9 GPa. B2O3 is confirmed to be very important in controlling the crystallization process of alpha-cordierite in this glass-ceramics system, and this study is helpful for providing the reference value for others to choose B2O3 and its content.