Affiliation: | a Department of Industrial Chemistry, Faculty of Engineering, Mie University, Kamihama, Tsu, Mie, 514, Japan b Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto, 611, Japan |
Abstract: | The behavior of copper ions in the Cu2O·Al2O3·4SiO2 (in moles) glass on heating in air at temperatures up to 500°C was studied. When the glass, in which about 90% of Cu was present as Cu+ ions, was heated in air above 300°C, a CuO layer was formed on the surface. The amount of CuO was increased with heating temperature and time, corresponding to the decrease in weight of the glass. Furthermore, the fraction of Cu2+ ions in the glass increased. These observations suggest that oxygens do not diffuse into the glass, but Cu+ ions migrate to the surface from the interior to balance the surplus positive charge produced by the oxidation of Cu+ to Cu2+ ions inside the glass. The following reaction scheme for the formation of the CuO layer was proposed; 2Cu+(interior) + 21O2(surface) → Cu2+(interior) + CuO(surface). |