Thermodynamics of Copper-Oxygen System Dissolved in a Glass—Relation to Copper Ruby Formation

Abstract

The Cu2O(glass)-Cu(glass) equilibrium was studied in 25Na2O, 10Al2O3, 65B2Os glass at varied partial pressures of oxygen (pO2=10−12 to 10−17 atmosphere) and temperatures in contact with solid metallic copper. On heat-treatment, the best ruby was formed in glass melted at pO2=10−14 atmosphere, at higher pO2's no ruby colour developed, and at pO2 ≤10−15 atmosphere the glass produced progressively poorer rubies. Using the thermodynamic data estimated for the Cu2O(glass)-Cu(glass) system, possibilities for the precipitation of Cu (solid) and Cu2O (solid) are discussed. It is concluded that Cu2O (solid) is primarily responsible for the bright red ruby colour in this glass.