OXIDATION-REDUCTION EQUILIBRIUM IN COPPER PHOSPHATE-GLASS MELTED IN AIR

Copper phosphate glasses with 40, 50, and 60 mol% CuO in batch were melted in air at 1000-degrees, 1100-degrees, and 1200-degrees-C using quartz or alumina crucibles, and the [Cu2+]/[Cu(total)] ratio variations with melting time were measured. Glasses were oxidized during melting and reached equilibrium [Cu2+]/[Cu(total)] ratios which were independent of melting temperature and identical for the 40 and 50 mol% CuO content glasses. Structural considerations seemed to have determined oxidation-reduction equilibrium rather than an equilibrium redox reaction. Also, the effects of crucible type on the oxidation-reduction balance were examined. It was found that a quartz crucible is more inert and has less effect on the oxidation-reduction equilibrium of glass than an alumina crucible. Crucible contamination and phosphorus vaporization were found to diminish as the CuO content in the batch was increased.