Ceramics-Silikáty 46, (4) 133 - 139 (2002)

The molybdenum corrosion and lead precipitation rates together with the overall electrode current were investigated in terms of the potential of the molybdenum electrode in three glass melts. Two of them contained 24 wt.% lead oxide, one of them containing also a small addition of arsenic oxide, and the third glass melt was free from lead oxide. The comparison of the rate of precipitating lead, of the corrosion rate and of the total electrode current in the melt free from arsenic oxide showed that molybdenum is for the most part transferred into the glass melt in the form of Mo(VI) even at potentials substantially more negative than the rest corrosion potential. The stationary polarization curves obtained for all the three glass melts exhibited courses typical of passivation. In the case of melts containing lead oxide the passivation already set in at the rest corrosion potential, or in the presence of arsenic oxide even at a more negative potential. Alternating current can affect the corrosion and lead precipitation rate in various glass melts in both directions. The accelerating effect always occurs in parallel with reduction of the mean electrode potential and vice versa. The effect of the electrode potential, of the alternating current and of the content of alkalies on the corrosion rate in the glass melts, can be explained by affecting the presence or layer thickness of molybdenum dioxide on the electrode.