ISSN 0862-5468 (Print), ISSN 1804-5847 (online) 

Ceramics-Silikáty 42, (3) 132 - 140 (1998)


CORROSION OF MOLYBDENUM ELECTRODES IN LEAD GLASS MELTS - PART 2 - EFFECT OF POTENTIAL AND TRANSFER OF ALTERNATING CURRENT BY THE ELECTRODE
 
Matěj Jiří 1, Hulínský Václav 2, Mamo Kassaye 2
 
1 Laboratory of Inorganic Materials of the Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic and Institute of Chemical Technology, Technická 5, 166 28 Prague
2 Department of Glass and Ceramics, Institute of Chemical Technology, Technická 5, 166 28 Prague

A comparison of the values of corrosion of molybdenum electrodes shows that the rest corrosion current is substantially lower than the mean value of alternating current over the current density range of 0.1 - 9 A/cm considered. The efficiency of hypothetical alternating-current electrolysis amounts to only 12 to 24 %. The alternating current is probably for the most part transferred by a reversible reaction. The dependence of corrosion rate of molybdenum in glass melts containing PbO on frequency exhibits a twin minimum whose frequencies decrease with the total content of alkalies while being independent of the Na₂O : K₂O ratio. The corrosion rate, separation of lead and the total current all exhibit a substantial increase when the potential is reduced by 200 to 300 mV compared to the rest potential, i.e. at -840 to -940 mV with respect to the oxygen electrode. Oxidation of Mo occurs even under these conditions. The separation of lead ceases when the potential is increased by 100 mV. The reaction of the molybdenum oxidation products with the alkalies in the glass melt probably plays a significant role in the entire corrosion process as well as in the alternating current transfer between the molybdenum electrode and the glass melt.


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