Prevention of dissolution of metal-based aluminium production anodes

A method of inhibiting dissolution of an oxygen-evolving anode of a cell for the production of aluminium from alumina dissolved in an molten electrolyte comprising ions of at least one metal selected from sodium, lithium and potassium, which cell comprises a cathodic material that is predominately active for the reduction of such electrolyte metal 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 layer that is inert to said electrolyte metal ions on said cathodic material and electrolysing the dissolved alumina whereby oxygen is anodically evolved and aluminium ions rather than said electrolyte metal ions are cathodically reduced on the inert layer to inhibit the presence in the molten electrolyte of soluble cathodically-reduced electrolyte metal ions that constitute agents for chemically reducing said transition metal oxides and evolved oxygen, the inert layer being used as a dissolution inhibitor of the anode by its effect in inhibiting reduction of said transition metal oxides by said cathodically-reduced electrolyte metal ions 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.

A method of inhibiting dissolution of an oxygen-evolving anode of a cell for the production of aluminium from alumina dissolved in an molten electrolyte comprising carbon-based material that is reactable with oxygen, in particular molecular oxygen, and/or carbon dioxide, or that produces carbon dust, 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 an oxygen-stable layer on the carbon-based material and electrolysing the dissolved alumina whereby oxygen is anodically evolved and aluminium ions are cathodically reduced, the oxygen-stable layer inhibiting the presence in the molten electrolyte of said carbon dust or carbon monoxide that constitutes an agent for chemically reducing said transition metal oxides and evolved oxygen to form carbon dioxide, said oxygen-stable layer being used as a dissolution inhibitor of the anode by its effect in inhibiting reduction of said transition metal oxides by said carbon dust or carbon monoxide 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.