Abstract: A metallic aluminium electrowinning anode structure has initially an iron-based alloy outer part with an active anode surface which is essentially metallic and free of any ceramic compounds of metals from the metallic. The anode structure undergoes a conditioning treatment that includes: substantially preventing the essentially metallic active surface free of said ceramic compound from reacting with any reactable species, in particular oxygen and fluorine species, until immersion into a molten electrolyte containing oxygen ions; immersing into the molten electrolyte the metallic anode structure with its essentially metallic active surface free of said ceramic compounds; and polarising the immersed metallic anode structure to form on the metallic anode structure a dense and coherent integral iron-based oxide layer which is electrochemically active for the oxidation of oxygen and which inhibits diffusion of oxygen towards the metallic anode structure.

Abstract: An anode of a cell for the electrowinning of aluminium comprises a nickel-iron alloy substrate having a nickel metal rich outer portion with an electrolyte pervious integral nickel-iron oxide containing surface layer which adheres to the nickel metal rich outer portion of the nickel-iron alloy and which in use is electrochemically active for the evolution of oxygen. The oxide surface layer has a thickness such that, during use, the voltage drop therethrough is below the potential of dissolution of nickel-iron oxide. The nickel metal rich outer portion may contain cavities some or all of which, after oxidation, are partly or completely filled with iron oxides to form iron oxide containing inclusions.

Abstract: A method of inhibiting dissolution of a transition metal alloy anode (40) of an aluminium electrowinning cell comprises providing a barrier layer (11,20,50,50?) on a non-anodic structural cell material (15), such as carbon, and electrolysing alumina dissolved in a molten electrolyte (30). The non-anodic structural material is able to supply an oxidisable by-product to the electrolyte and/or is active for reducing electrolyte species exposed to the structural material into an oxidisable by-product, such as sodium metal or carbon dust. However, the barrier layer inhibits the presence in the molten electrolyte (30) of the oxidisable by-product that constitutes an agent for chemically reducing the anode's transition metal oxides and anodically evolved oxygen.

Abstract: An anode of a cell for the electrowinning of aluminium comprises a nickel-iron alloy substrate having an openly porous nickel metal rich outer portion whose surface is electrochemically active. The outer portion is optionally covered with an external integral nickel-iron oxide containing surface layer which adheres to the nickel metal rich outer portion of the nickel-iron alloy and which in use is pervious to molten electrolyte. During use, the nickel metal rich outer portion contains cavities some or all of which are partly or completely filled with iron and nickel compounds, in particular oxides, fluorides and oxyfluorides.

Abstract: A cell for the electrowinning of aluminium comprising one or more anodes (10), each having a metal-based anode substrate, for instance comprising a metal core (11) covered with an metal layer 12, an oxygen barrier layer (13), one or more intermediate layers (14; 14A, 14B) and an iron layer (15). The anode substrate is covered with an electrochemically active transition metal oxide layer, in particular an iron oxide-based outside layer (16) such as a hematite-based layer, which remains dimensionally stable during operation in a cell by maintaining in the electrolyte a sufficient concentration of iron species and dissolved alumina. The cell operating temperature is sufficiently low so that the required concentration of iron species in the electrolyte (5) is limited by the reduced solubility of iron species in the electrolyte at the operating temperature, which consequently limits the contamination of the product aluminium by iron to an acceptable level.

Abstract: An anode of a cell for the electrowinning of aluminium comprises a nickel-iron alloy substrate having an openly porous nickel metal rich outer portion whose surface is electrochemically active. The outer portion is optionally covered with an external integral nickel-iron oxide containing surface layer which adheres to the nickel metal rich outer portion of the nickel-iron alloy and which in use is pervious to molten electrolyte. During use, the nickel metal rich outer portion contains cavities some or all of which are partly or completely filled with iron and nickel compounds, in particular oxides, fluorides and oxyfluorides.

Abstract: An iron-based metal anode for the electrowinning of aluminium by the electrolysis of alumina in a molten fluoride electrolyte has an electrochemically active integral outside oxide layer on an iron-based alloy that consists of 75 to 90 weight % iron; 0.5 to 5 weight % in total of at least one rare earth metal, in particular yttrium; 1 to 10 weight % aluminium; 0 to 10 weight % copper; 0 to 10 weight % nickel; and 0.5 to 5 weight % of other elements. The total amount of aluminium, copper and nickel is in the range from 5 to 20 weight %; and the total amount of rare earth metal(s), aluminium and copper is also in the range from 5 to 20 weight %. The electrochemically active surface layer is predominantly of iron oxide that slowly dissolves into the electrolyte during operation and is maintained by progressive slow oxidation of iron at the interface of the bulk metal of the alloy with the oxide layer.

Abstract: A cell for the electrowinning of aluminium comprising one or more anodes (10), each having a metal-based anode substrate, for instance comprising a metal core (11) covered with an metal layer 12, an oxygen barrier layer (13), one or more intermediate layers (14, 14A, 14B) and an iron layer (15). The anode substrate is covered with an electrochemically active iron oxide-based outside layer (16), in particular a hematite-based layer, which remains dimensionally stable during operation in a cell by maintaining in the electrolyte a sufficient concentration of iron species. The cell operating temperature is sufficiently low so that the required concentration of iron species in the electrolyte (5) is limited by the reduced solubility of iron species in the electrolyte at the operating temperature, which consequently limits the contamination of the product aluminium by iron to an acceptable level.

Abstract: A cell for the electrowinning of aluminum using anodes (10) made from a alloy of iron with nickel and/or cobalt is arranged to produce aluminum of low contamination and of commercial high grade quality. The cell comprises a cathode (20) of drained configuration and operates at reduced temperature without formation of a crust or ledge of solidified electrolyte. The cell is thermally insulated using an insulating cover (65,65a,65b,65c) and an insulating sidewall lining (71). The molten electrolyte (30) is substantially saturated with alumina, particularly on the electrochemically active anode surface, and with species of at least one major metal present at the surface of the nickel-iron alloy based anodes (10). The cell is preferably operated at reduced temperature from 730° to 910° C. to limit the solubility of these metal species and consequently the contamination of the product aluminum.

Abstract: A refractory boride body or coating made of a boride of titanium, chromium, vanadium, ziconium, hafnium, niobium, tantalum, molybednum and cerium is produced from a slurry of the refractory boride or a precursor in a collidal carrier preferably composed of two more different grades of the same colloidal carrier selected from colloidal alumina, yttria, ceria, thoria, zirconia, magnesia, lithia, monoaluminum phosphate and cerium acetate. The slurry can also comprise an organic additive selected from polyvinyl alcohol; polyacrylic acid; hydroxyy propyl methyl cellulose; polythylene glycol; ethylene glycol, butyl benzyl phthalate; ammonium polymethacrylate and mixtures thereof. The retractory boride body or coated body is useful as a component of aluminum electrowinning cells.

Abstract: A method of protecting during the start-up procedure a cathode (1) of a cell for the electrowinning of aluminium where the cathode (1) is optionally coated with an aluminium-wettable refractory material (2) and on which cathode, in use, aluminium is produced. The start-up procedure comprises applying before preheating the cell one or more start-up layers (3) on the aluminium-wettable refractory coating (2). The start-up layer(s) form(s) a temporary protection (3) against damage of chemical and/or mechanical origin to the aluminium-wettable coating (2), this temporary protection (3) being in intimate contact with the aluminium-wettable coating (2) and being eliminated before or during the initial normal operation of the cell. The layers of the temporary protection (3) may be obtained from at least one pliable foil of aluminium having a thickness of less than 0.

Abstract: A drained cathode cell for the electrowinning of aluminium comprises a cell bottom (20) arranged to collect product aluminium and thermic insulating sidewalls (55,55′) lined with a molten electrolyte resistant sidewall lining (50) which is made of material liable to react with molten aluminium, in particular containing silicon carbide, silicon nitride or boron nitride. The thermic insulating sidewalls (55,55′) inhibit formation of an electrolyte crust on the lining (50), whereby the lining (50) is exposed to molten electrolyte. The cell bottom (20) has a peripheral surface from which the insulating sidewalls (55,55′) extend generally vertically to form, with the cell bottom, a trough for containing molten electrolyte and aluminium produced on at least one drained cathode (32).

Abstract: A process for the electrowinning of aluminium from alumina dissolved in a fluoride-based molten electrolyte in a cell operating at reduced temperature, typically below 870° C., utilising nickel-alloy based anodes, in particular nickel-iron alloy anodes. The electrolyte contains AlF3 in such a high concentration, usually above 20 weight %, in addition to cryolite, that fluorine-containing ions rather than oxygen ions are oxidised on the anodes. However, only oxygen is evolved, the evolved oxygen being derived from the dissolved alumina present near the anodes. The anodes may be porous at the surface so as to provide a high active surface area for operation at low current density.

Abstract: An aluminium-wettable protective coating on a substrate, for use at elevated temperature in an oxidising and/or corrosive gaseous and/or molten environment is disclosed. The coating (20A, 20B, 20C, 20D) is applied to protect the substrate (5, 15, 16) from liquid and/or gaseous attack. The coating comprises particles of at least one metal oxide and/or at least one partly oxidised metal in a dried and/or cured colloidal carrier and/or organic binder. The metal oxide and/or partly oxide metal is reactable with molten aluminium when exposed thereto to form an alumina matrix containing metal of said particles and aluminium. The coated substrate (5, 15, 16) may be used in an aluminium electrowinning cell an arc furnace for the recycling of steel or an apparatus for the purification of a molten metal such as aluminium, magnesium, iron or steel.

Abstract: An anode of a cell for the electrowinning of aluminium comprises a nickel-iron alloy substrate having a nickel metal rich outer portion with an electrolyte pervious integral nickel-iron oxide containing surface layer which adheres to the nickel metal rich outer portion of the nickel-iron alloy and which in use is electrochemically active for the evolution of oxygen. The oxide surface layer has a thickness such that, during use, the voltage drop therethrough is below the potential of dissolution of nickel-iron oxide. The nickel metal rich outer portion may contain cavities some or all of which, after oxidation, are partly or completely filled with iron oxides to form iron oxide containing inclusions.

Abstract: A component is made of or coated with a refractory material for use at high temperature, e.g. in an aluminium production cell, an arc furnace or an apparatus for treating molten metal. The refractory material comprises particles of a refractory metal compound selected from metal borides, silicides, nitrides, carbides and phosphides, in an oxide matrix. The oxide matrix comprises a bonding mixed oxide made of a single mixed oxide or a plurality of miscible mixed oxides. The refractory material is obtainable from a heat treated slurry that comprises: a colloidal and/or polymeric oxide carrier, suspended particles of the refractory metal compound and suspended metal oxide particles. The suspended refractory metal compound particles and the suspended metal oxide particles are both reactable with the colloidal and/or polymeric oxide to form the bonding mixed oxide.

Abstract: A drained cathode cell for the electrowinning of aluminium comprises a cell bottom (20) arranged to collect product aluminium and thermic insulating sidewalls (55,55′) lined with a molten electrolyte resistant sidewall lining (50) which is made of material liable to react with molten aluminium, in particular containing silicon carbide, silicon nitride or boron nitride. The thermic insulating sidewalls (55,55′) inhibit formation of an electrolyte crust on the lining (50), whereby the lining (50) is exposed to molten electrolyte. The cell bottom (20) has a peripheral surface from which the insulating sidewalls (55,55′) extend generally vertically to form, with the cell bottom, a trough for containing molten electrolyte and aluminium produced on at least one drained cathode (32).

Abstract: A method of inhibiting dissolution of a transition metal alloy anode (40) of an aluminium electrowinning cell comprises providing a sodium-inert layer (11,20,50,50′) on a sodium-active cathodic cell material (15), such as carbon, and electrolysing alumina dissolved in a sodium ion-containing molten electrolyte (30). Aluminium ions rather than sodium ions are cathodically reduced on the sodium-inert layer to inhibit the presence in the molten electrolyte (30) of soluble cathodically-produced sodium metal that constitutes an agent for chemically reducing the anode's transition metal oxides and anodically evolved oxygen, thereby inhibiting reduction of the anode's transition metal oxides by sodium metal and 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.

Abstract: A refractory boride body or coating made of a boride of titanium, chromium, vanadium, ziconium, hafnium, niobium, tantalum, molybednum and cerium is produced from a slurry of the refractory boride or a precursor in a collidal carrier preferably composed of two more different grades of the same colloidal carrier selected from colloidal alumina, yttria, ceria, thoria, zirconia, magnesia, lithia, monoaluminum phosphate and cerium acetate. The slurry can also comprise an organic additive selected from polyvinyl alcohol; polyacrylic acid; hydroxyy propyl methyl cellulose; polythylene glycol; ethylene glycol, butyl benzyl phthalate; ammonium polymethacrylate and mixtures thereof. The retractory boride body or coated body is useful as a component of aluminum electrowinning cells.

Abstract: A method of manufacturing an anode for use in a cell for the electrowinning of aluminium comprises oxidising before cell operation an iron-nickel alloy substrate in an oxygen-containing atmosphere, such as air, at a temperature which is at least 50° C., preferably 100° C., above the operating temperature of the cell to form on the surface of the iron-nickel substrate a coherent and adherent iron oxide-containing outer layer, in particular a hematite-containing layer having a limited ionic conductivity for oxygen ions and acting as a partial barrier to monoatomic oxygen. The outer layer is electrochemically active for the oxidation of oxygen ions and reduces also diffusion of oxygen to the iron-nickel alloy substrate when the anode is in use.