Abstract: A method of forming a dense and crack-free hematite-containing protective layer on a metal-based substrate for use in a high temperature oxidising and/or corrosive environment comprises applying onto the substrate a particle mixture consisting of: 60 to 99 95 weight %, in particular 70 to 95 weight % such as 75 to 85 weight %, of hematite with or without iron metal and/or ferrous oxide; 1 to 25 weight %, in particular 5 8 to 20 weight % such as 8 to 15 weight %, of nitride and/or carbide particles, such as boron nitride, aluminium nitride or zirconium carbide particles; and 0 to 15 weight %, in particular 5 to 15 weight %, of one or more further constituents that consist of at least one metal or metal oxide or a heat-convertible precursor thereof.

Abstract: An anode for electrowinning of aluminium from alumina comprises a cobalt-containing metallic outer part that is covered with an integral oxide layer containing predominantly cobalt oxide CoO. The integral oxide layer can be formed by surface oxidation of cobalt from the metallic outer part before use.

Abstract: A carbon body has an aluminium-wettable outer part that is made of a carbon-rich mixture containing aluminium-reactable metal-based particles and carbon. The metal-based particles are made of metal oxide particles and/or partly oxidised metal particles. The metal of the metalbased particles is selected from iron, copper, cobalt, nickel, zinc and manganese. The carbon body can be used in an aluminium electrowinning cell, e.g. as a cathode, or in an apparatus for treating molten aluminium and is wetted by molten aluminium during use.

Abstract: A cell for electrowinning a metal, in particular aluminium, from a compound thereof dissolved in an electrolyte (30) comprises an anode (40) and a cathode (10,11) that contact the electrolyte (30), the cathode (10,11) being during use at a cathodic potential for reducing thereon species of the metal to be produced from the dissolved compound. The electrolyte (30) further contains species of at least one element that is liable to contaminate the product metal (20) and that has a cathodic reduction potential which is less negative than the cathodic potential of the metal to be produced. The cell further comprises a collector (50) for removing species of such element (s) from the electrolyte (30).

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: A cell for the electrowinning of a metal (70) from a compound thereof dissolved in a molten electrolyte comprises: a thermally insulated cell trough (10,20) and a thermally insulated cell cover (30) which are arranged to contain an electrolyte (40) and maintain it in a substantially crustless molten state; and a feeder (50) for feeding a particulate (60) of the metal compound to the molten electrolyte (40). The feeder (50) comprises a feeding tube (51) extending into the cell trough (10,20) and has a tubular end portion (52) which is located between the molten electrolyte (40) and the insulating cell cover (30) and which has a substantially horizontal axial direction. The feeder (50) is arranged to feed the particulate (60) into the feeding tube (51), along the feeding tube (51) and through an opening (53) in the tubular end portion (52) from where it is delivered over the molten electrolyte (40).

Abstract: A cell for the electrowinning of aluminium (50) form alumina dissolved in a molten electrolyte comprise a generally horizontal cell bottom (5), preferably aluminium-wettable, on which a pool of product aluminium (50) is collected from at least one electrically conductive cathodic element (10) having aluminium-wettable cathode surfaces (11). The cathodic element comprises an inclined cathodic wall (10) in the electrolyte (60) above the generally horizontal cell bottom (5). The cathodic wall (10) has an upwardly-oriented inclined face (11) that forms a sloping upper aluminum-wettable drained active cathode surface on which aluminium is produced and drains into the aluminium pool (50), and a downwardly-oriented inclined face (12) which is in contact with the molten electrolyte (60) and which overlies the aluminium pool (50). The aluminium pool (50) covers substantially the entire cell bottom (5) including underneath the cathodic wall (10).

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 forming a dense and crack-free hematite-containing protective layer on a metal-based substrate for use in a high temperature oxidising and/or corrosive environment comprises applying onto the substrate a particle mixture consisting of: 60 to 99 95 weight %, in particular 70 to 95 weight % such as 75 to 85 weight %, of hematite with or without iron metal and/or ferrous oxide; 1 to 25 weight %, in particular 5 8 to 20 weight % such as 8 to 15 weight %, of nitride and/or carbide particles, such as boron nitride, aluminium nitride or zirconium carbide particles; and 0 to 15 weight %, in particular 5 to 15 weight %, of one or more further constituents that consist of at least one metal or metal oxide or a heat-convertible precursor thereof.

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: A cell for the electrowinning of aluminium by the electrolysis from an aluminium compound dissolved in a molten electrolyte (50), comprises: (I) a plurality of non-carbon anodes (10), each anode being suspended in operating in the molten electrolyte by an anode stem (11) that connects the anode (10) to a positive current source; and (II) a thermic insulating cover (60,60?) which covers the electrolyte (50) and through which each anode stem (11) extends from the positive current source to an anode (10). The insulating cover (60,60?) comprises a plurality of movable sections (60) that together cover a substantial part of the electrolyte (50). Each movable section (60) covers a corresponding portion of the electrolyte (50) that is located therebelow and that can be uncovered by moving the corresponding movable section (60).

Abstract: An anode for the electrowinning of aluminium by the electrolysis of alumina in a molten fluoride electrolyte has an electrochemically active integral outside oxide layer obtainable by surface oxidation of a metal alloy which consists of 20 to 60 weight % nickel; 5 to 15 weight % copper; 1.5 to 5 weight % aluminium; 0 to 2 weight % in total of one or more rare earth metals, in particular yttrium; 0 to 2 weight % of further elements, in particular manganese, silicon and carbon; and the balance being iron. The metal alloy of the anode has a copper/nickel weight ratio in the range of 0.1 to 0.5, preferably 0.2 to 0.3.

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 method of manufacturing a component, in particular an aluminium electrowinning anode, for use at elevated temperature in an oxidising and/or corrosive environment comprises: applying onto a metal-based substrate layers of a particle mixture containing iron oxide particles and particles of a reactant-oxide selected from titanium, yttrium, ytterbium and tantalum oxides; and heat treating the applied layers to consolidate by reactive sintering of the iron oxide particles and the reactant-oxide particles to turn the applied layer into a protective coating made of a substantially continuous reacted oxide matrix of one or more multiple oxides of iron and the metal from the reactant-oxide. The metal-based substrate comprises at its surface during the heat treatment an integral anchorage-oxide of at least one metal of the substrate.

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: The invention relates to a thermally insulating structural component (10) such as a cover of a container (5), in particular a molten salt electrolytic cell which component (10) is inert and resistant to corrosive media (1) at high temperature in the form of liquids, vapours and/or gases, in particular NaAlF4, AlF3, HF or O2, and which during use is exposed to such corrosive media (1). The component (10) comprises thermal insulating material (30) shielded from the corrosive media (1) by an openly porous or reticulated alumina structure (20) which is made impermeable by a compact filler material (15) resistant and inert to the corrosive media and comprising compacted particles of refractory material, in particular alumina cement. The structural component (10) can have a top metallic shell (40) which extends over the thermal insulating material (30) and downwards along lateral sides of the component (10). The insulating material (30) can be secured to the alumina structure (20) through nuts (50) and bolts (60).

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 long-lasting metal-based oxygen-evolving anode (10) for the electrowinning of aluminium from alumina dissolved in a molten electrolyte, has a plurality of electrochemically active anode members (15,15′) spaced apart and parallel to one another. Each anode member (15) can comprise a bottom part (15a) which has a substantially constant width over its height and which is extended upwardly by a tapered top part (15b for guiding a circulation a of electrolyte (30) thereon. The bottom part (15a) is usually made of a metal alloy with a substantially flat oxide bottom surface (16) which is electrochemically active for the oxidation of oxygen.

Abstract: A cell for the electrowinning of aluminium (50) from alumina, comprises an inclined plate-like or grid-like open anode structure (25) which has a generally v-shaped configuration in cross-section. The anode structure (25) has a downwardly-oriented sloping electrochemically active surface that is generally v-shaped in cross-section and spaced above an upwardly-oriented corresponding sloping cathode surface (11) by an anode-cathode gap (40) in which alumina dissolved in a circulating electrolyte (60) is electrolysed. The anode structure (25) has a plurality of anode through-passages (45) distributed thereover for an up-flow of alumina-depleted electrolyte (60) from the anode-cathode gap (40).