Water diffusion in lead silicate and sodium lead silicate melts

Water diffusion in lead silicate melts has been measured at temperatures ranging from 800 to 1200°C for compositions containing 35 to 65 mol% PbO. The diffusivity of water increases with increasing PbO concentration and with experimental temperature, with values ranging from 1×10−6 to 5×10−5 cm2/s. Water diffusion was also measured at 1200°C for three series of sodium lead silicate melts. The diffusivity of water increases with decreasing SiO2 content. The results of this study are compared to those for water diffusivity in sodium silicate and soda lime silicate melts. The relation between water diffusivity and melt viscosity is considered for all four glass forming systems. It is demonstrated that the correlation between water diffusivity and melt viscosity only occurs for very limited ranges of temperature and melt composition. As has been found for many other systems, the glass transformation temperatures of the lead silicate and sodium lead silicate glasses decrease with increasing water concentration in the glass.