Effect of the thermal history of glass melts on crystallization in lithium and sodium disilicate glasses doped with platinum as a nucleating agent

The crystallization behavior of Li2O-Na2O-2SiO2 glasses with different thermal histories was examined. The glass melts were doped with 0.005 wt% platinum, held at various temperatures (>TL) and then water-quenched, and glasses were obtained. Measurements revealed distinctly different crystallization tendencies between glasses whose melt was held at just above the liquidus temperature and glasses whose melt was held at a higher temperature. After double-stage heat treatments, the glasses were crystallized, and needle-like crystals (Li2O·SiO2) and spherical crystals (Li2O·SiO2) formed. In particular, platinum-derived nuclei promoted the generation of Li2O·SiO2 crystal. Microscopic observations showed that both crystal particles precipitating in the interior of the crystallized glasses increased in number as the holding temperature decreased. The exothermic crystallization peak of the glass held at a lower temperature appeared earlier than that of the glass with a higher holding temperature in the profile of differential thermal analysis. Additionally, the precipitated amount of Li2O·SiO2 obtained from X-ray diffraction measurement increased with decreasing holding temperature. These results suggest that the distribution of platinum colloids in glass melts varies depending on the holding temperature.