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 species and dissolved alumina.

Abstract: An anode of a cell for the electrowinning of aluminum comprises an iron-nickel alloy body or layer whose surface is oxidized to form a coherent and adherent outer iron oxide-based layer, in particular hematite, the surface of which is electrochemically active for the oxidation of oxygen ions and which reduces diffusion of oxygen from the electrochemically active surface into the iron-nickel alloy body or layer. The anode may be kept dimensionally stable during cell operation by maintaining a sufficient amount of dissolved alumina and iron species in the electrolyte to prevent dissolution of the outer oxide layer of the or each anode and by reducing the electrolyte operating temperature to limit dissolution of iron and by reducing the electrolyte operating temperature to limit dissolution of iron species in the electrolyte.

Abstract: A bipolar cell for the electrowinning of aluminum has bipolar electrodes each comprising a carbon cathode body having on one side an active surface on which aluminum is produced and connected on the other side through an oxygen impermeable barrier layer to an electrochemically active anode layer having an oxygen evolving iron oxide-based outer surface. The anode layer may comprise a metal-based anode substrate and a transition metal oxide-based outside layer, in particular an iron oxide-based outside layer, which either is an applied layer or is obtainable by oxidising the surface of the anode substrate which contains iron. During operation, the anode layer can be kept dimensionally stable by maintaining in the electrolyte a concentration of transition metal species which are present as one or more corresponding transition metal oxides in the electrochemically-active layer.

Abstract: A non-carbon, metal based slow-consumable anode of a cell for the electrowinning of aluminum self-forms during normal electrolysis an electrochemically-active oxide-based surface layer (20). The rate of formation (35) of the layer (20) is substantially equal to its rate of dissolution (30) at the surface layer/electrolyte interface (25) thereby maintaining its thickness substantially constant, forming a limited barrier controlling the oxidation rate (35). The anode (10) usually comprises an alloy or iron at least one of nickel, copper, cobalt or zinc which during use forms an oxide surface layer (20) mainly containing ferrite.

Abstract: A drained cathode cell for the electrowinning of aluminium comprises a cell bottom (20) arranged to collect product aluminium and thermic insulating sidewalls (40) lined with a molten electrolyte resistant sidewall lining (50), in particular containing silicon carbide, silicon nitride or boron nitride. The thermic insulating sidewalls (40) 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 zone from which the insulating sidewalls (40) 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). The peripheral zone of the cell bottom (20) is arranged to keep the product aluminium from contacting and reacting with the molten electrolyte resistant sidewall lining 50).

Abstract: A non-carbon, metal-based slow-consumable anode of a cell for the electrowinning of aluminium self-forms during normal electrolysis an electrochemically-active oxide-based surface layer (20). The rate of formation (35) of the layer (20) is substantially equal to its rate of dissolution (30) at the surface layer/electrolyte interface (25) thereby maintaining its thickness substantially constant, forming a limited barrier controlling the oxidation rate (35). The anode (10) usually comprises an alloy of iron with at least one of nickel, copper, cobalt or zinc which during use forms an oxide surface layer (20) mainly containing ferrite.

Abstract: An open-pored body (11), in particular a carbon component of an aluminum production cell, which is to be exposed to oxidizing conditions or chemical attack at high temperatures is treated to protect the body against oxidation or corrosion at high temperature by impregnating the surface of the body at about ambient temperature with a hot non-saturated liquid (10). This liquid contains a treating agent at a temperature above the temperature of the body. The concentration of treating agent in the hot liquid is such that when the liquid is cooled, before it reaches the temperature of the body, the liquid saturates and treating agent precipitates. A pressure differential is applied to cause the liquid to impregnate into the surface pores of the body (11) and precipitate a layer of the treating agent from the liquid inside the body by cooling as it impregnates the pores of the body.

Abstract: A carbon body, in particular a prebaked anode of an electrolytic cell for the production of aluminum by the electrolysis of alumina in a molten fluoride electrolyte, is treated over its surfaces to improve the resistance thereof to deterioration during operation of the cell by air and oxidizing gases released at the anode, by immersing the body in a treating liquid containing a soluble boron compound and at least one additive from the group consisting of aluminum compounds, calcium compounds, sodium compounds, magnesium compounds, silicon compounds, elemental carbon, and elemental aluminum, said additive being in the form of a powder, in suspension such as a colloid, or in solution, e.g., at 80° to 120° C. The same treatment can also be applied to a carbon mass forming a Söderberg anode and to cell sidewalls. The additives increase strength and improve oxidation resistance compared to impregnation with boric acid alone.

Abstract: A non-carbon, metal-based anode (10) of a cell for the electrowinning of aluminium, comprising an electrically conductive, high temperature resistant and oxidation resistant metal structure (11) in the form of a wire mesh or net, a foraminate sheet, a fibrous network, a reticulated skeletal structure, or a porous structure having voids, recesses and/or pores which are filled or partly filled with an electrochemically active filling (12), such as oxides, oxyfluorides, phosphides, carbides, cobaltites and cuprates making the surface of the anode (10) conductive and electrochemically active for the oxidation of oxygen ions present at the anode surface/electrolyte (5) interface.

Abstract: A method of producing a self-sustaining body of refractory boride from the group consisting of the borides of titanium, chromium, vanadium, zirconium, hafnium, niobium, tantalum, molybdenum and cerium. This body includes a refractory boride and a dried colloid from the group consisting of colloidal alumina, silica, yttria, ceria, thoria, magnesia, lithia, monoaluminium phosphate and cerium acetate and is obtained from a slurry of the refractory boride in one or more of said colloids by casting the slurry on a porous plaster layer, and drying the cast slurry by draining through the plaster, or by pressing/drying. Subsequently, the dried body is subjected to heat treatment to bond the refractory boride in the dried colloid. The bodies are useful as components of aluminium electrowinning cells.

Abstract: A non-carbon, metal-based high temperature resistant anode of a cell for the production of aluminium has a metal-based substrate coated with one or more electrically conductive adherent applied layers, at least one electrically conductive layer being electrochemically active. The electrochemically active layer contains one or more electrocatalysts fostering the oxidation of oxygen ions as well as fostering the formation of biatomic molecular gaseous oxygen to inhibit ionic and/or monoatomic oxygen attack of the metal-based substrate. The electrocatalyst can be iridium, palladium, platinum, rhodium, ruthenium, silicon, tin, zinc, Mischmetal oxides and metals of the Lanthanide series. The applied layer may further comprise electrochemically active constituents from oxides, oxyfluorides, phosphides, carbides, in particular spinels such as ferrites.

Abstract: A composite, high-temperature resistant, non-carbon metal-based anode of a cell for the electrowinning of aluminium comprises a metal-based core structure of low electrical resistance, for connecting the anode to a positive current supply, coated with a series of superimposed, adherent, electrically conductive layers. These layers consist of at least one layer on the core structure constituting a barrier substantially impervious to monoatomic oxygen and molecular oxygen; one or more intermediate, protective layers on the oxygen barrier layer which remain inactive in the reactions for the evolution of oxygen gas; and an electrochemically active layer for the oxidation reaction of oxygen ions present at the anode/electrolyte interface into nascent monoatomic oxygen, as well as for subsequent reaction for the formation of gaseous biatomic oxygen.

Abstract: A carbon body, in particular a pre-baked anode of an electrolytic cell for the production of aluminium by the electrolysis of alumina in a molten fluoride electrolyte is treated over its surfaces to improve the resistance thereof to deterioration during operation of the cell by air and oxidizing gases released at the anode, by treating the body with a treating liquid comprising a precipitable boron-containing compound and an additive, said additive being present in an amount so that substantially no separate phase from said the precipitate of said boron-containing compound is formed upon curing. Suitable boron oxide additives include colloidal alumina, silica, yttria, ceria, thoria, zirconia, magnesia, lithia, monoaluminium phosphate, cerium acetate and mixtures thereof. The same treatment can also be applied to a carbon mass forming a Soderberg anode and to cell sidewalls.

Abstract: An anode for the electrowinning of aluminium by the electrolysis of alumina dissolved in a molten fluoride electrolyte comprises a porous combustion synthesis product of nickel, aluminium, iron, copper and optional doping elements in the amounts 50-90 wt. % nickel, 3-20 wt. % aluminium, 5-20 wt. % iron, 0-15 wt. % copper and 0-5 wt. % of one or more of chromium, manganese, titanium, molybdenum, cobalt, zirconium, niobium, tantalum, yttrium, cerium, oxygen, boron and nitrogen. The combustion synthesis product contains metallic and intermetallic phases. A composite oxide surface is produced in situ by anodic polarization of the porous combustion synthesis product in a molten fluoride electrolyte containing dissolved alumina. The in situ formed composite oxide surface comprises an iron-rich relatively dense outer portion, and an aluminate-rich relatively porous inner portion.

Abstract: A method of producing a self-sustaining body of refractory boride from the group consisting of the borides of titanium, chromium, vanadium, zirconium, hafnium, niobium, tantalum, molybdenum and cerium. This body includes a refractory boride and a dried colloid from the group consisting of colloidal alumina, silica, yttria, ceria, thoria, magnesia, lithia, monoaluminium phosphate and cerium acetate and is obtained from a slurry of the refractory boride in one or more of said colloids by casting the slurry on a porous plaster layer, and drying the cast slurry by draining through the plaster, or by pressing/drying. Subsequently, the dried body is subjected to heat treatment to bond the refractory boride in the dried colloid. The bodies are useful as components of aluminium electrowinning cells.

Abstract: An electrolysis cell for the production of aluminum by the electrolysis of alumina dissolved in a molten halide electrolyte using a multimonopolar arrangement of substantially non-consumable anodes and cathodes with facing operative surfaces which are upright or at a slope and are spaced in a substantially parallel relationship, enabling operation at low and/or current density with an acceptable production per unit self-lowered area. The operative surface area of the anodes and the cathodes is high due to their upright sloping configuration. Operative surfaces of the anodes and possibly of the cathodes can be increased by making them porous, preferably with their articulated skeletal structure, e.g. with a porous active part on opposite faces of a central current feeder.

Abstract: A cell for the electrowinning of aluminium by the electrolysis of alumina dissolved in a molten fluoride-based electrolyte comprises a cathode composed of a carbon body having an aluminium resistant aluminium-wettable surface layer containing particulate titanium or other refractory hard metal boride and a bonding material providing a porous layer which contains cathodic molten aluminium. Molten cathodic aluminium external to the aluminium-resistant and aluminium-wettable surface contains refractory hard metal and boron in a total concentration sufficient or just below that sufficient to inhibit dissolution into the molten aluminium of the refractory hard metal boride. Alumina is fed to the cell whereby the required amount of titanium in the aluminium results from the alumina feed while, when boron is not present in a sufficient amount, boron is added to bring the total titanium and boron content to or just below the equilibrium solubility product.

Abstract: An anode for the electrowinning of aluminium by the electrolysis of alumina dissolved in a molten fluoride electrolyte comprises a porous combustion synthesis product of nickel, aluminium, iron, copper and optional doping elements in the amounts 60-90 wt % nickel, 3-10 wt % aluminium, 5-20 wt % iron, 0-15 wt % copper and 0-5 wt % of one or more of chromium, manganese, titanium, molybdenum, cobalt, zirconium, niobium, yttrium, cerium, oxygen, boron and nitrogen. The combustion synthesis product contains metallic and intermetallic phases. A composite oxide surface is produced in-situ by anodic polarization of the porous combustion synthesis product in a molten fluoride electrolyte containing dissolved alumina. The in-situ formed composite oxide surface comprises an iron-rich relatively dense outer portion, and an aluminate-rich relatively porous inner portion.

Abstract: A prebaked carbon-based anode of an electrolytic cell for the production of aluminium, in particular by the electrolysis of alumina in a molten fluoride electrolyte, is treated over its sides and top to improve the resistance thereof to erosion during operation of the cell by oxidising gases released at the anode, by immersing the anode in a boron-containing solution containing 5-60 weight % of H.sub.3 BO.sub.3 or B.sub.2 O.sub.3 in methanol, ethylene glycol, glycerin or water with a surface-active agent, e.g. at 80.degree. to 120.degree. C. After 2-60 minutes immersion, the boron-containing solution is impregnated to a depth of 1-10 cm, usually about 2-4 cm over the top and side surfaces of the anode to be protected, producing a concentration of boron in the impregnated surface from 200 ppm to 0.35%. The same treatment can be applied to cell sidewalls.

Abstract: Neodymium and neodymium-iron alloys are obtained by electrolysis of a neodymium salt melt using magnetite as the anode material. The cathode is non-consumable or is made of iron to be consumed and form a neodymium-iron alloy. The electrolysis is preferably carried out under a protective atmosphere.