Corrosion of refractory materials in molten lead-silicate glasses

The corrosion resistance of refractory materials in molten optical glasses has been systematically studied. The temperature dependence of the corrosion rate for various refractories in three lead-bearing glasses (VS92: 72% SiO2, 14% PbO, 10% K2O; TF5: 61% SiO2, 36% PbO; and STF11: 20% SiO2, 65% PbO, 12% B2O3) was investigated. The corrosion increased with increase in PbO content, and is also greatly influenced by the viscosity, which governs the convection intensity and the contact layer thickness. The high fluidity and corrosiveness of STF11 are due to linking of the Pb2+ ions with the (SiO4) and (BO4) tetrahedra. The effect of composition of a sintered Al2O3-SiO2 refractory on corrosion resistance is shown; a corundum refractory is the most resistant in all three glasses, and corrosion increases with SiO2 content. An Arrhenius equation described the temperature dependence of the corrosion rate for TF5 and STF11 glasses. High activation energies characterise the corrosion of most refractories in TF5. The corrosion activation energies of sintered, cast, and single crystal corundum refractories are compared. High corrosiveness is expected for glasses whose compositions do not provide a three-dimensional Si-O tetrahedron network and instead give rise to structures characteristic of island silicates. 5 refs.