Patent ID: 6638412
Filing Date: 2003-10-28
Classification: C25C

Abstract:
A method of inhibiting dissolution of an oxygen-evolving anode of a cell for the production of aluminium from alumina dissolved in a sodium ion-containing molten electrolyte comprising a cathodic material that is predominately active for the reduction of sodium ions rather than aluminium ions, the oxygen-evolving anode comprising a transition metal-containing alloy having an integral oxide layer containing predominantly one or more transition metal oxides which slowly dissolve in the electrolyte and are compensated by oxidation of the alloy at the alloy/oxide layer interface,said method comprising providing a sodium-inert layer on the sodium-active cathodic material and electrolysing the dissolved alumina whereby oxygen is anodically evolved and aluminium ions rather than sodium ions are cathodically reduced on the sodium-inert layer to inhibit the presence in the molten electrolyte of soluble cathodically-produced sodium metal that constitutes an agent for chemically reducing said transition metal oxides and evolved oxygen, the sodium-inert layer being used as a dissolution inhibitor of the anode by its effect in inhibiting reduction of said transition metal oxides by sodium metal and in maintaining the evolved oxygen at the anode at a concentration such as to produce at the alloy/oxide layer interface stable and coherent transition metal oxides having a high level of oxidation.