Low expansion copper aluminosilicate glasses

The thermal expansion coefficients of Cu₂O---Al₂O₃---SiO₂ glasses have been measured. These glasses have very low expansion coefficients similar to that for SiO₂ glass, but their liquids temperatures are much lower. It was possible to reduce the liquids temperature by the addition of 2 mol% of Na₂O while maintaining low expansivity. In order to explain the low expansivity, the effects of cation size, valence, the Cu²⁺/Cu⁺ ratio, bond strength and phase separation were examined. Phase separation was observed in these glasses which probably consisted of a copper-rich dispersed phase and a network former-rich matrix phase. It was concluded that the overall expansion coefficients of the glasses were governed by the low expansion matrix phase.