Nucleation and Growth of Sodium Disilicate Crystals in Sodium Disilicate Glass

A high‐temperature microscope for use with transmitted or reflected light up to × 400 magnification and up to 1400°C. was constructed. Nucleation and crystal growth in sodium disilicate glass was studied with this microscope. Heterogeneous nucleation occurred at the interface between the glass and the platinum heating element from 450° to 870° C. with a maximum at 600° C. Heterogeneous nucleation also occurred at the glass‐atmosphere interface from 25° to 375° C. as a result of surface reactions with water vapor. No homogeneous nucleation was observed. Linear growth rates of α and β sodium disilicate crystals were measured from 600° to 870° C. in two sodium disilicate glasses. Metastable growth of both α and β was observed, and growth rates of α and β were the same at a given temperature for a given glass. An equation relating fluidity and undercooling to growth rate was applied.