The effects of 1 wt % P2O5 addition on the properties of container glass

The effects of replacing 1 wt% SiO2 by P2O5 in a typical container glass composition have been investigated. High temperature viscosity, liquidus temperature, chemical durability, thermal expansion coefficient, dilatometric softening point, glass transition temperature and density were measured to assess more fully the potential technological benefits of using small P2O5 additions in soda– lime–silica glass manufacture. High temperature viscosity measurements showed that viscosity is unaffected by the replacement of 1% SiO2 by P2O5 in these glasses. On this basis it is suggested that the predictive mathematical factor for the effect of low levels of P2O5 on glass viscosity in soda–lime–silica glasses is equal to the factor for SiO2. The liquidus temperature was reduced by 15°C upon replacement of 1% SiO2 by P2O5, indicating that the glass stability is improved. This was commensurate with results from other studies using similar levels of P2O5 addition in similar glass systems. Chemical durability was improved slightly by the introduction of P2O5 whilst the thermal expansion coefficient was unaffected. Small changes in glass transition temperature, dilatometric softening point and density were also observed. The use of low levels of P2O5 in the manufacture of container glass could prove highly beneficial. Its desirable effects on liquidus temperature and chemical durability may allow levels of components such as CaO to be increased whilst retaining the properties required of container glass. These changes could lead to environmental benefit through reductions in melting temperature.