Nucleation and growth of hexagonal CaAl2Si2O8 crystals in CaO-Al2O3-SiO2 glass

Hexagonal CaAl2Si2O8 was precipitated inside of 25CaO-20Al2O3-55SiO2 (wt%) glass by heat treatment at 1050 °C with MoO3 and carbon as nucleating agents. Transmission electron microscopy revealed that metallic molybdenum particles with sizes of ∼200 nm precipitated in the glass and served as heterogeneous nucleation sites for plane-like hexagonal CaAl2Si2O8 crystals with widths greater than 10 μm and thicknesses of ∼1 μm. The thickness direction was the c-axis of hexagonal CaAl2Si2O8.