Abstract: An anode of a cell for the electrowinning of aluminium has a nickel-iron alloy outer portion which during use is covered with an integral iron-based oxide surface layer. The nickel-iron alloy outer portion comprises one or more rare earth metals that are substantially insoluble in nickel and iron. These rare earth metals are present in the outer portion in an amount which provides during use controlled diffusion of iron from the outer portion to the integral iron-based oxide surface 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 drained-cathode cell for the electrowinning of aluminium comprises one or more anodes (14) suspended over one or more cathodes (16). The or each anode (14) and cathode (16) respectively have a sloped V-shaped active anode surface (22) and parallel sloped inverted V-shaped drained cathode surfaces (18) facing one another and spaced apart by two sloped inter-electrode gaps (20), arranged so the electrolyte circulates upwardly in the sloped inter-electrode gaps (20) assisted by anodically produced gas and then returns from a top part (22′) to a bottom part (22″) of each inter-electrode gap (20) along an electrolyte path (26,27,36,37).

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 material, for instance used as an aluminium-wettable component (21,21′, 41,41′, 51), in particular of a cell for the electrowinning of aluminium (60), comprises an openly porous or reticulated ceramic structure whose surface during use is exposed to and wetted by molten aluminium. The structure is made of ceramic material inert and resistant to molten aluminium, such as alumina, and an aluminium-wettable material that comprises metal oxide and/or partly oxidised metal, in particular of manganese, iron, cobalt, nickel, copper or zinc, which is/are reactable with molten aluminium to form a surface layer containing alumina, aluminium and metal derived from the metal oxide and/or partly oxidised metal. The ceramic structure comprises a coating of the aluminium-wettable material on the inert and resistant ceramic material, or is made of a mixture of the inert and resistant material and of the aluminium-wettable ceramic material.

Abstract: A cell for the electrowinning of aluminium comprises a horizontal carbon cathode bottom (11) having an aluminium-wettable surface coating (25) and a series of plates (21) made of aluminium-wettable reticulated porous material, typically foams, filled with aluminium and placed flat on the aluminium-wettable surface coating (25). During use, a thin bottom layer of aluminium (22) wets the aluminium-wettable surface coating (25) on top of the cathode bottom (11) and a bottom part of the porous aluminium-filled plates (21). A top layer of aluminium (23) is formed above the porous aluminium-filled plates (21). The cell may be operated with metal anodes (10) possibly protected with a cerium oxyfluoride coating when operated above about 910°-930° C.

Abstract: An anode for use in a cell for the electrowinning of aluminum from alumina comprises a substrate with a core having an outer portion made of nickel covered with a barrier layer for inhibiting diffusion of fluoride species oxygen species to the core and preventing diffusion of constituents from the core during use. The barrier layer is made of silver and an electrochemically active noble metal miscible with nickel and silver, e.g. gold or palladium. The anode is coated with an electrochemically active surface layer which can be made of one or more cerium compounds.

Abstract: The invention relates to an optical element comprising a substrate which is provided with a transparent layer comprising an organic polymer network and one or more photochromic compounds, in which the transmission of the optical element in the visible wavelength range changes in response to a variation of incident light, while the transparent layer comprising photochromic compounds is provided with a protective coating on the side remote from the substrate side.

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 cell for the electrowinning of aluminium comprises a plurality of metal-based anodes facing and spaced apart from an aluminium-wettable drained cathode surface on which aluminium is produced. The drained cathode surface is formed along the cell by upper surfaces of a series of juxtaposed carbon cathode blocks, the cathode blocks extending across the cell. The drained cathode surface is divided into quadrants by a longitudinal aluminium collection groove along the cell and by a central aluminium collection reservoir across the cell. Pairs of quadrants across the cell are inclined in a V-shape relationship, the collection groove being located along the bottom of the V-shape and arranged to collect molten aluminium draining from the drained cathode surface and evacuate it into the aluminium collection reservoir during cell operation.

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 cell for the electrowinning of aluminium comprises a plurality of metal-based anodes facing and spaced part from an aluminium-wettable drained cathode surface on which aluminium is produced. The drained cathode surface is formed along the cell by upper surfaces of juxtaposed carbon cathode blocks, the cathode blocks extending across the cell. The drained cathode surface is divided into quadrants by a longitudinal aluminium collection groove along the cell and by a central aluminium collection reservoir across the cell. Pairs of quadrants across the cell are inclined in a V-shape relationship, the collection groove being located along the bottom of the V-shape and arranged to collect molten aluminium draining from the drained cathode surface and evacuate it into the aluminium collection reservoir during cell operation.

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: 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: 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: 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: A non-carbon, metal-based, high temperature resistant, electrically conductive and electrochemically active anode of a cell for the production of aluminum has a metal-based substrate to which an adherent coating is applied prior to its immersion into the electrolyte and start up of the electrolysis by connection to the positive current supply. The coating is obtainable from one or more layers applied from: a liquid solution, a dispersion in a liquid or a paste, a suspension in a liquid or a paste, and a pasty or non-pasty slurry, and combinations thereof with or without one or more further applied layers, with or without heat treatment between two consecutively applied layers when at least two layers are applied.

Abstract: A cell of advanced design for the production of aluminium by the electrolysis of an aluminium compound dissolved in a molten electrolyte, has a cathode (30) of drained configuration, and at least one non-carbon anode (10) facing the cathode both covered by the electrolyte (54). The upper part of the cell contains a removable thermic insulating cover (60) placed just above the level of the electrolyte (54). Preferably, the cathode (30) comprises a cathode mass (32) supported by a cathode carrier (31) made of electrically conductive material which serves also for the uniform distribution of electric current to the cathode mass (32) from current feeders (42) which connect the cathode carrier (31) to the negative busbars.

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.