Structural interpretation of the modification of soda-lime-silica glass properties by P2O5

Abstract

The influence of P2O5 addition on soda-lime-silica glass properties is discussed on the basis of a structural model. It involves two effects: Insertion of phosphate molecular complexes into the silicate network interstices, and increase in silicate network condensation. The latter results from the scavenging of sodium and calcium cations by P2O5. The properties considered in this paper are high-temperature viscosity and liquidus temperature. The P2O5 additions are in the 0.8 to 3.0 mol% range. The silica content of the glasses varies from 60 to 67 mol%, and the ratio CaO/(CaO+Na2O) from 0 to 0.85. Phosphate molecular complexes decrease the liquidus temperature and the high-temperature viscosity increasing the network condensation results in an increase in the viscosity, but its effect on the liquidus temperature depends on whether the glass composition lies on an upward or downward liquidus surface of the phase diagram.