Some surface and interfacial phenomena encountered in aluminium electrolysis

Surface or interfacial tension causes several effects that are important for the understanding of the Hall-Heroult process. Some of these phenomena are analyzed in the present paper. A formula for the calculation of the meniscus formed at the metal - bath sideledge boundary is derived. It is shown that large alumina bath agglomerates may be present at the metal surface due to the interfacial tension. The propagation of capillary and gravity waves at the interface is addressed. Furthermore, it is shown that adsorption of water into commercial alumina conforms with the BET isotherm up to about 40 - 50 percent relative humidity, followed by the absorption of up to 20 weight percent water by pore condensation at water vapour pressures still below saturation. Marangoni convection can occur due to interfacial tension gradients between the parts of the cathode that are inside and outside the projection of the anode.