Pressure induced nucleation in a Li 2O · 2SiO 2 glass

Abstract

The concentration of nuclei ( N v) in a Li 2O · 2SiO 2 (LS 2) glass was measured using a newly developed differential thermal analysis technique, after densifying the glass at 1, 3, or 6 GPa pressure at 400 °C for 20 min. N v increased from 38×10 12 m −3 for an as-melted glass to 82×10 12 m −3 for a glass subjected to a pressure of 1 GPa, and remained nearly constant with further increase of pressure of up to 6 GPa. This increase in N v is equivalent to nucleating this LS 2 glass at the temperature (455 °C) of its maximum nucleation rate for 2 h. The average effective activation energy for crystallization for the densified glasses, 292±10 kJ/mol, was also the same as that of the (undensified) glass nucleated at 455 °C for 2 h, but was significantly smaller than that (358±10 kJ/mol) for an as-melted (undensified and unnucleated) glass. The present results show that applying an external pressure on this LS 2 glass shifts its nucleation curve to lower temperatures causing nuclei to form even at 400 °C. A decrease in viscosity at all temperatures with the application of pressure is suspected to be a reason for the enhanced nucleation observed for this LS 2 glass.