Effect of molybdenum and tungsten oxides on nucleation and crystallization behaviors of MgO–Al2O3–SiO2 glasses

• We have searched novel nucleating agents for MgO–Al2O3–SiO2 glass-ceramics.
• Metallic particles of molybdenum and tungsten provided bulk crystallization of glass.
• Different crystals grew on molybdenum and tungsten particles.
• Glass-ceramics with a fine microstructure were obtained using molybdenum.

To investigate the effect of novel nucleating agents, this study investigates the crystallization behavior of a MgO–Al2O3–SiO2 glass with molybdenum or tungsten oxide addition. Under a reducing condition, crystals formed in the bulk of the supercooled liquids, whereas melting in air yielded only surface crystallization. The first crystalline phase precipitated inside the glass was enstatite and Mg–petalite in glasses doped with molybdenum and tungsten oxides, respectively, whereas the surface precipitate was cordierite. Molybdenum oxide yielded a finer microstructure of the glass-ceramic than tungsten oxide. Some fractions of the nucleating agents were considered to be reduced to metallic states and dispersed through the glasses, providing heterogeneous nucleating sites for enstatite and Mg–petalite.