1986 Volume 94 Issue 1088 Pages 425-431
Though it is well recognized that the knowledge on electrolysis of glass is important to understand ionic behavior of molten glass and to operate an electric melting furnace, there have been few investigations on the decomposition voltage of molten glass. In this paper, electrolytic behavior in the molten sodium borate glass system was investigated by measuring current-potential curves on Pt electrodes. The effects of water were also studied. The products on the Pt test electrode were identified both by direct observation during electrolysis and by EPMA analysis for the electrode-glass interface after polarization. Moreover, conceivable decomposition reactions were determined by comparing with the theoretical decomposition voltages. In the system containing small amounts of water (xNa2O⋅(10-x)B2O3, x=1-5), experimental decomposition voltages were 1.3-1.6V at 1000°C, which increased with increasing Na2O. In the system introduced much water (xNa2O⋅(10-x) H3BO3, x=1-3.33), experimental decomposition voltages were around 1.6V, which decreased slightly with increasing Na2O content. In the system containing small amounts of water, at the platinum cathode, noticeable bubbles due to the discharge of sodium ions (b.p. of Na=883°C) could not be observed at any applied potentials, but occasional and small bubble formation was observed due to the liberation of hydrogen gases which were decomposition products of water as an impurity. In this case, boron elements were produced at the cathode by the discharge of borate anions. In the system introduced much water, hydrogen gas evolution was observed prior to the reduction of borate anions. On anodic polarization, oxygen gases evolved. Comparison between experimental decomposition voltages and theoretical ones indicated that the most probable decomposition reactions might be such reactions as Na2B4O7→2NaBO2+2B+3/2O2 and Na2B6O10→Na2B4O7+2B+3/2O2.
