CRYSTALLIZATION OF A Li{sub}2O·2SiO{sub}2 GLASS UNDER HIGH HYDROSTATIC PRESSURES

摘要

The crystallization behavior of a Li{sub}2O·2SiO{sub}2 (LS{sub}2) glass subjected to a uniform hydrostatic pressure of 4.5 or 6 GPa was investigated between 543 and 750°C using XRD, IR, Raman, TEM and DTA. The density of all the glasses (or glass-ceramics) subjected to high pressures was higher than that of the glass at ambient pressures (one atmosphere), and was 2.43 ±0.01 g/cm{sup}3 for the 4.5 GPa glass and between 2.52 ± 0.01 g/cm{sup}3 and 2.57 ± 0.01 g/cm{sup}3, depending upon processing temperature, for the 6 GPa glasses. The crystallization tendency for the glasses decreased (the crystal growth rate curve moved to higher temperatures) with increasing pressure. A decrease in the diffusion coefficient and/or developing additional stress at the glass-crystal interface at high pressures could be the likely reasons for suppressing the crystal growth rates. Like the glass at ambient pressure, the glass subjected to 4.5 GPa crystallized only LS{sub}2(orthorombic,Ccc2) crystals. The density of both glasses, ambient and 4.5 GPa, was smaller man that of the crystal, 2.46 ± 0.01 g/cm{sup}3. The structure of the crystals formed in the glasses that were subjected to 6 GPa pressure and whose density was higher than that of Li{sub}2O·SiO{sub}2 (LS) crystals, was complex and unknown. The structure of these crystals is believed to be a deformed LS-type, whose parameters yield a calculated crystal density of 2.61 g/cm{sup}3 which is higher than the measured density of these glass-ceramics, It is believed that crystallization of these glasses follows a route which favors forming only those crystals that are accompanied by a positive, but lowest possible density change.