Effect of starting materials of nucleation agents on crystallization of CaO–Al2O3–SiO2 glass

The effect of the starting materials of the nucleation agents for glass–ceramics (GCs) was explored. The number of hexagonal platy particles of metastable-CaAl₂Si₂O₈ in CaO–Al₂O₃–SiO₂ (CAS) GCs was increased by changing the sizes of molybdenum oxide (MoO₃) and carbon particles used as starting materials of the nucleation agents. X-ray diffraction patterns indicated that all of GC specimens display reflections attributed to metastable-CaAl₂Si₂O₈ solely. In addition, scanning electron microscopy (SEM) revealed that, compared with the CAS GC with precipitated hexagonal platy particles of metastable-CaAl₂Si₂O₈ (CAS GC-H) prepared using MoO₃ particles with a Brunauer–Emmett–Teller (BET) surface area of 3.5 m²/g and 10–50 μm carbon particles, CAS GC-Hs prepared using MoO₃ particles with a BET surface area of 1.2 m²/g or carbon fibers 10–50 μm in length and ∼5 μm in diameter resulted in approximately a twofold increase in the number of platy particles of metastable-CaAl₂Si₂O₈ and a decrease in the average particle size from 13 to 11 μm. The microstructures of the CAS GC-Hs are closer looks. In addition, no major differences in volume fractions estimated using the binarized SEM images are observed between those GC specimens. These results indicated that the starting materials of nucleation agents affect the crystallization of CAS GCs.