Effect of molybdenum and titanium oxides on mechanical and thermal properties of cordierite-enstatite glass-ceramics

By adding either MoO3 or TiO2 as nucleating agents, glass at the eutectic point of cordierite (2MgO·2Al2O3·5SiO2) and enstatite (MgSiO3) in the MgO-Al2O3-SiO2 ternary system was crystallized. Although bulk crystallization required adding 10 wt% TiO2, approximately 0.1-0.5 wt% of MoO3 induced bulk nucleation when the parent glass was melted under reducing conditions. For both TiO2- and MoO3-nucleated glasses, the glass-ceramics containing both cordierite-enstatite as main crystalline phases were obtained by heat-treatment at 1200 °C. The fracture toughness of the glass-ceramics nucleated by TiO2 was 1.5 times higher than that of sintered cordierite ceramics. In addition to two main crystalline phases, magnesium titanium oxide and rutile also precipitated in TiO2-nucleated glass. The additional effects of TiO2 on the properties of the glass-ceramics were identified by comparing the TiO2- nucleated glass-ceramics and MoO3- nucleated one. The addition of TiO2 slightly increased the Young's modulus of the glass-ceramics. On the other hand, since TiO2 suppressed the precipitation of enstatite, the thermal deformation of TiO2-nucleated glass-ceramic at 1100 °C was larger than that of MoO3- nucleated one. Therefore, MoO3 is the preferable nucleating agent of the glass-ceramics for application which requires high thermal endurance.