Behavior of water in glass during crystallization

The presence of water in glass has a large influence on the rate of crystallization. Furthermore, water can diffuse into or out of a glass during the heat-treatment for crystallization and influence the crystallization behavior of the glass surface. Water diffusion in a lithium alumino-silicate (LAS) glass and the corresponding LAS based transparent glass-ceramic was investigated using IR spectroscopy. IR spectra of water-related species changed drastically during crystallization, from an exclusively hydroxyl peak to a peak possibly containing molecular water. Both water solubility and diffusion coefficient were lower in the glass-ceramic than in the glass. These results were attributed to the expulsion of water from the crystalline phase and segregation into the remaining glassy phase, resulting in a high water concentration in the glassy phase.