Low temperature synthesis of non-crystalline solids of the system SrO-SiO2

Non-crystalline solids within the liquid-liquid immiscibility region in the system SrO-SiO₂ have been prepared from a gel obtained by the hydrolysis of silicon tetramethoxide with an aqueous solution of strontium nitrate. The gel which was porous and translucent at room temperature increased in transparency with heating due to the collapse of micropores until it became completely clear. The gel became opaque again due to the precipitation of α-quartz at higher temperatures. The critical temperatures below which clear solids were obtained fell on a line connecting the glass transition temperatures of vitreous silica and those of SrO-SiO₂ glasses prepared by melting. The density and refractive index of the pore-free, clear glassy solid, changed continuously with the SrO content along lines connecting those of vitreous silica and SrO- SiO₂ glasses of high SrO content prepared by melting. The maximum amount Sr²⁺ which could be introduced using an aqueous solution as the starting material corresponded to a composition of 10 SrO · 90 SiO₂ by weight.