Effect of glass composition on interaction between alkali–silicate glass and WC mold

For the molding process of optical glass, to investigate the effect of glass composition on the interaction between the glass preform and the mold, we examined the fusion phenomenon at various alkali–(boro-)silicate glass/mold interfaces. Glass samples were heated to 800 °C on a tungsten carbide plate in a nitrogen atmosphere, then the migration of the mold and glass constituents near the interface was investigated by electron probe microanalyzer (EPMA). It was found that when Q, the ratio of the molar number of oxygen atoms in the glass to the field strength of the cations, is low, the glass and WC mold are barely fused. When Q is high, glass fuses to the mold accompanied with the migration of tungsten and sodium atoms near the interface. This phenomenon is interpreted as follows: increasing the value of Q accelerates the oxidization of W and the reduction of Na, and then the oxidation layer on the glass/mold interface leads the fusion.