1999 Volume 107 Issue 1250 Pages 895-900
Redox behaviors of sulfur species in sodium borate, silicate and phosphate melts doped sodium sulfate were studied by means of differential pulse voltammetry. In the 10Na2O⋅90B2O3 melt, three reduction peaks are observed. The peak intensity at -400mV, which appeared as a shoulder of the peak at -300mV, decreases with the elapse of time. In the early stages of melting, noises are superimposed on the peak beyond -600mV. In the 30Na2O⋅70B2O3 melt, the profile of the voltammogram does not change much with time after 92h. The voltammograms of sodium metaphosphate melt at the initial stage of melting have large noises beyond -600mV. The peak at -400mV disappears after 23h. In the sodium borate melts, the intensity of the peak at -450mV decreases and its position shifts to the positive side with an increase in temperature, whereas the intensity of the peak at -600mV increases with an increase in temperature. In the 20Na2O⋅80B2O3⋅0.5Na2S 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 Raman signal at 988cm-1 and the IR signal at 630cm-1, which are assigned to the fundamental vibration of SO42-, the three peaks of the voltammogram are assigned to the successive reductions of SO42-, SO2 and S0 with the cathodic reduction process. The stability of SO42- increases with an increase in the basicity of the melts and with a decrease in temperature.
