Measurement of the oxygen diffusion coefficient in a glass melt by the EMF method

The oxygen diffusion coefficient in a soda-lime-silica glass melt was measured by the EMF method with Pt and zirconia electrodes. The atmosphere was changed from air to N-2 and then back to air, and the resulting EMF changes were monitored. In addition, oxygen diffusion profiles were numerically simulated and compared with experimental curves. The lead of the Pt electrode must be covered with insulating material to measure the penetration of oxygen in the melt from the surface. When silica was used as the insulator, the curve of EMF change showed relatively good agreement with the simulated curve. On the other hand, when alumina was used, a much more rapid EMF change was observed and the experimental and simulated curves did not agree. It was concluded that this was due to electronic conduction in alumina at high temperatures and that alumina should not be used for the insulator. The diffusion coefficient of oxygen in the melt could be estimated by comparing the activity change curve with a simulated curve. The resulting diffusion coefficient in 70SiO(2)-20Na(2)O-10CaO at 1200degreesC was 6x10(-6) cm(-1). Possible reasons for errors are discussed. In a melt containing Sb2O3, a reliable result could not be obtained because of the smaller EMF change.