Hydrothermal dissolution of technical grade vitreous silica in NaOH solutions to liquid water glasses with higher SiO2:Na2O ratios

Abstract

Technical grade vitreous silica was dissolved hydrothermally in NaOH lyes. Liquid sodium water glasses with silica concentrations of up to 26.4 wt % and molar SiO2:Na2O ratios of up to 3.5 were obtained. The dissolution behavior showed two temperature regimes: up to 130 °C the SiO2 content approached a final solubility limit controlled by cristobalite crystallization. Above 130 °C, crystallization of low quartz restricted solubility. The dissolution kinetics were governed by surface area reduction and saturation control according to the Noyce-Whitney law.