Electrochemistry of sodium sulfate doped glass melts

Redox behaviors of sulfur species in sodium borate, silicate and phosphate melts doped sodium sulfate were studied by means of differential pulse volt ammetry. In the 10Na(2)O . 90B(2)O(3) melt, three reduction peaks are obser ved. The peak intensity at -400 mV, which appeared as a shoulder of the pea k at -300 mV, decreases with the elapse of time. In the early stages of mel ting, noises are superimposed on the peak beyond -600 mV. In the 30Na(2)O . 70B(2)O(3) melt, the profile of the voltammogram does not change much with time after 92 h. The voltammograms of sodium metaphosphate melt at the ini tial stage of melting have large noises beyond -600 mV, The peak at -400 mV disappears after 23 h. In the sodium berate melts, the intensity of the pe ak at -450 mV decreases and its position shifts to the positive side with a n increase in temperature, whereas the intensity of the peak at -600 mV inc reases with an increase in temperature. In the 20Na(2)O . 80B(2)O(3). 0.5 N a2S melt, the peak position shifts to the positive side with an increase in heating time due to the oxidation of S2- to SO42-. By combination of the R aman signal at 988 cm(-1) and the IR signal at 630 cm(-1), which are assign ed to the fundamental vibration of SO42-, the three peaks of the voltammogr am are assigned to the successive reductions of SO42-, SO2 and S-0 with the cathodic reduction process. The stability of SO42- increases with an incre ase in the basicity of the melts and with a decrease in temperature.