Optimum loading of molybdenum electrodes in corrosive glass melts

Abstract

At given current density, the voltage between electrodes and the generated power increase with the equipment size providing the geometrical similarity is maintained. The current density affects the corrosion rate of molybdenum electrodes to a different degree depending on the type of molten glass. In minimizing the corrosion of electrodes, the total loss of electrodes which is proportional to their area and to the linear corrosion rate should be considered, the corrosion rate depending on the temperature near the electrode surface. It was found experimentally that under the conditions of a maximum suppression of corrosion phenomena in 24 % lead glass by a current of reduced frequency, the corrosion rate will not significantly depend on the current density. On the basis of a parabolic approximation for the found temperature dependence of the corrosion rate of molybdenum electrodes in 24 % lead glass and on the basis of model measurements investigating the dependence of surface temperature of electrodes on their area in a specific arrangement of the given furnace and for constant power input, a semi-empirical equation was derived, describing the relation between the total electrode loss rate Q and the total electrode area A (1/ϱ) Q̇ = α/A+ ß+ γA . The course of this relationship which passes through a minimum has been calculated for the given furnace. The calculated area corresponding to a minimum electrode loss rate is in good agreement with the area of electrodes placed in the operating furnace on long-term experience. The calculated value of the electrode loss rate in this minimum does not differ from the operational evidence more than the deviations of individual series of laboratory experiments.