The effect of additives on the crystallization and sintering of 2MgO-2Al₂O₃-5SiO₂ glass-ceramics

Crystallization and sintering behaviour of three cordierite (2MgO-2Al₂O₃-5SiO₂) glasses containing different amount of additives were investigated and compared by using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Archimedes method. The stoichiometric 2MgO-2Al₂O₃-5SiO₂ (MAS) glass and the 2MgO-2Al₂O₃-5SiO₂ glass containing 3 wt% of B₂O₃ and 3 wt% of P₂O₅ (MASBP) showed two exotherms (one for μ-cordierite formation from a glass and the other for α-cordierite formation from the μ-cordierite phase), whereas the 2MgO-2Al₂O₃-5SiO₂ glass containing 2 wt % of B₂O₃, 2 wt% of P₂O₅, and 2 wt % of TiO₂ (MASBPT) showed only a single exotherm representing α-cordierite formation. By using Kissinger, Augis-Bennett, Ozawa, and modified Kissinger methods, the activation energy values for α-cordierite formation in the MASBP and MASBPT glasses were determined as 310 ± 6 and 326 ± 13 kJ mol^-1, respectively, whereas that in the MAS glass was determined as 868 ± 5 kJ mol^-1. The MASBPT glass showed the lowest peak temperature value for α-cordierite formation (980°C) amongst the three glasses. Both the MASBP and MASBPT glasses showed excellent sintering behaviour (> 99.7% of theoretical density).