Incorporation and role of halogens in silicate melts and glasses

This article provides a review on the solubility, speciation and diffusion of halogens (fluorine, chlorine, bromine and iodine) in molten silicates and their effect on the viscosity. Fluorine is the most soluble halogen in silicate melts. By replacing oxygen in tetrahedra and by coordinating with aluminum, it triggers depolymerization of the glassy network, which decreases the viscosity of silicate melt. The solubility of chlorine is favored by the presence of alkali in the melt composition. Chlorine shows affinity for the network modifiers cations such as calcium or sodium. Its effect on viscosity depends on the chemical composition, especially the proportion of alkali elements and aluminum. The solubility of bromine increases in silica-rich and alkali-rich melt. The solubility of iodine can reach 1 wt.% in a borosilicate glass in which it is associated with sodium ions. (authors)