Surface crystallization of rare-earth aluminosilicate glasses

Surface crystallization in a rare-earth aluminosilicate glass (Nd2O3–Al2O3–SiO2–TiO2) was studied using an isothermal method and the crystal growth rate of the glasses was evaluated as a function of the composition. For measuring the surface crystal growth rate, two different methods: measurement of the crystal layer in the longitudinal and lateral growth direction. It was found that crystallization proceeded by surface crystallization only and TiO2 did not act as a nucleating agent. The growth rate was strongly dependent on the viscosity of glass and agreed with prediction from the Preston model using the known viscosity and melting temperature. As the Si/Nd and Si/Al ratios decreased, the crystal growth rate increased. TiO2 and Nd2O3 played the role of network modifier, which decreased the viscosity of the glass, facilitating crystallization of the rare-earth aluminosilicate glass.