Low-temperature bubble formation in silica glass

Abstract

Phase separation was observed in silica glass following low-temperature heat treatment in high water vapor pressure through the formation of bubbles. Although the 6 day diffusion treatment in saturated water vapor pressure at 250°C does not normally cause phase separation, the reactive fracture surface and subsurface damage caused by polishing with cerium oxide (CeO₂) allowed for an increase in water absorption during treatment and heterogeneous nucleation of the bubbles at damaged sites. The sub-surface damage, characteristic of blunt contact damage, was only revealed when the polished sample was etched. The formation of bubbles and polishing damage were observed in two silica glasses—one containing chlorine impurities and the other containing OH impurities. Raman spectra collected after fracture or polishing and water diffusion treatment demonstrated an increase in the abundance of –OH species including silanol (SiOH) groups and an evolution in the glass structure in the bubble regions compared with the bubble-free regions. These results indicate an increase in the reactivity between water and glass fracture surfaces relative to the bulk.