The Influence of Low Current Densities on Anode Performance

Abstract

While the dominant amount of electrolysis occurs on the bottom surface of aluminium smelting anodes, the sides of the anodes contribute up to one-third of the electro-active area. This zone contributes to the electrolytic process, but has an ever decreasing current density, also it is subjected to more vigorous agitation as the waves of anode gas bubbles rise near the vertically oriented surfaces. Some studies have suggested that most of the dusting of anodes occurs on this face, although the explanations are based on carboxy reaction. By performing a laboratory scaled investigation of the consumption rate of different quality carbon anodes, it is evident that low current density contributes significantly to the development of a roughened surface profile. The consumption rate simultaneously accelerates although its extent is clearly dependent on carbon quality. The differential reactivity was greater for some coke types and low baking temperatures.

Several methods for assessing anode performance have been developed and correlated with standard tests especially the carboxy reactivity test. The correlations show the tests are sensitive methods of assessing the total performance of an electrode, including its tendency to dusting.