Alcan International Limited

Alcan Research and Development Limited

Ernest W Dewing

Adam J Gesing

Raman Radha Sood

Frederick W Southam

Douglas J Wheeler

Jean-Paul R Huni

David N Mitchell

Douglas N Reesor

William R Bennett

Peter Alexander Wales

John Sulzer

Thomas M Clere

Pervez J Bamji

Aniket Pant

Charles J Rogers

Alan D McLeod

Ethan A Hollingshead

Thomas G Edgeworth

Louis J Manfredo

Stephen H Keeley

Thomas J Hudson

Joseph K Walker

Donald L De Respiris

Eric Robert Wallace

A process and apparatus for melting metals that react rapidly with air at elevated temperatures to form a stable metal oxide and/or that contains a metal oxide prior to being exposed to elevated temperature, while reducing metal losses due to oxidation or the presence of the oxides. The process involves melting the metal in the presence of a molten metal salt metal salt mixture while electrolyzing metal oxide contained in the salt metal salt mixture to convert the oxide to elemental metal. The process requires an metal salt mixture which contains at least 25% by weight, and more preferably 100% by weight, of metal fluoride and which, for the metal being melted, has a composition which remains substantially unchanged during the electrolysis process. The fluoride improves oxide solubility in the metal salt mixture, making it possible to increase current densities without producing anode effects. The stable composition makes it possible to use the metal salt mixture for prolonged periods without change. The apparatus consists of a single vessel having an interior volume divided at least into a melting zone and an electrolysis zone by a heat-resistant partition which allows the metal salt mixture to be recirculated between those zones. The process and apparatus can be used for melting metals, metal matrix composites reinforced by metal oxides and metal foams stabilized by metal oxide particles.

Process and apparatus for melting metals and composites while reducing

A process is described for producing an aluminum grain refiner, such as Al-Ti-B grain refiner. Molten aluminum is continuously flowed as a bottom layer along a substantially horizontal or slightly inclined trough. Titanium or boron compounds reducible by aluminum or a mixture of such compounds is added to the surface of the aluminum layer such that a discrete separate layer of these is formed on top of the aluminum layer. Reaction between the aluminum and the titanium and/or boron compounds occurs along the interface between the layers and this reaction may, if desired, be aided by providing relative movement between the layer of molten aluminum and the layer of titanium and/or boron compounds. A surface layer of spent reaction product is removed and a stream of aluminum alloyed with titanium and boron is collected.

Production of an aluminum grain refiner

A method of refining lithium-containing aluminum scrap metal. An electrolytic cell is formed using molten scrap as the anode, lithium or Al-Li as the cathode and a chloride-based lithium electrolyte. The cell is operated at a temperature of about 700.degree. C. and the lithium is transferred from the scrap to the cathode. The depletion of lithium in the scrap is signalled by an abrupt rise in voltage of the cell. The remaining scrap at the anode can be used in the same way as conventional aluminum scrap and the pure Li or Al-Li alloy formed at the cathode can be used as new material for the Al-Li alloy market.

Refining of lithium-containing aluminum scrap

In an aluminium reduction cell including a cell lining and embedded therein at least one cathode current collector including a high temperature section comprising an electrically conducting refractory material such as titanium diboride, generally in conjunction with molten aluminium metal, corrosion is a problem. The invention provides a substance to protect the collector section. The substance may be a liquid impermeable layer e.g. particulate material impregnated with a molten fluoride-or chloride-containing salt mixture; for a getter such as particulate aluminium to react chemically with gaseous corrosive species. Combinations of these substances may be used, optionally in conjunction with a solid layer such as an alumina or aluminium metal tube.

Aluminium reduction cell

A method of purifying aluminum contaminated with cerium or other rare earth metal comprises bringing the molten metal into contact with a halogenating agent. Preferred halogenating agents are aluminum fluoride for reducing cerium levels to around 0.1% to 0.3%, and chlorine gas for reducing cerium levels still further, and these may advantageously be used in sequence. Particulate aluminum fluoride may be introduced into the vortex of a stirred body of the molten metal. The controlled addition of chlorine may be effected by bubbling a mixture of chlorine and an inert gas into a body of the molten metal. The cerium contamination may arise from the use of a dimensionally stable anode comprising cerium dioxide in an aluminum reduction cell.

Method of producing aluminum

The invention concerns cells for production of Al by electrolysis of an alumina-containing electrolyte based on cryolite and having a lining based on alumina for containing the electrolyte. A layer containing an alkali or alkaline earth metal compound, e.g. sodium aluminate, is included in the lining, preferably around the 880.degree. C. isotherm when the cell is in operation. On penetration of the lining by the electrolyte, the compound dissolves in or reacts with the electrolyte so as to raise the solidus and reduce or prevent further penetration.

Aluminium electrolytic reduction cell linings

An aluminium reduction cell includes a potlining 16, which may be of alumina, with cathode current collectors 24, 32 embedded therein. The cell floor has an array of depressions 22 with at least one collector at the bottom of each depression. The depressions are filled with metal-wettable bodies 20, e.g. 5-20 mm diameter balls of titanium diboride, sized to prevent the entry of electrolyte or sludge. The depressions may be elongate in a direction perpendicular to the horizontal magnetic field in the cell.

Aluminium reduction cells

An aluminium reduction cell includes an anode 10, electrolyte 12, a cathode 14, a potlining 16 which may be of alumina and cathode current collectors embedded therein. The collectors include a section comprising a major proportion by volume of bodies 22, e.g. of titanium diboride or a TiB.sub.2 /Al cermet, joined or surrounded by aluminium, the section being so positioned that the aluminium is at least partly fluid when the cell is in operation. The bodies, which are preferably close-packed, may be cubic or cuboid or in the form of sheets or thin slabs arranged with their major faces parallel to one another and to the axis of the collector section. The collectors show good electrical conductivity together with satisfactory resistance to magnetic stirring and impact and transverse forces.

An electrolytic reduction cell for the production of molten metal by electrolysis of a molten electrolyte, which is less dense than the molten metal includes a generally rectangular shell, one or more suspended anodes and a floor structure which supports a body of the molten metal. At least one essentially linear baffle member extends transversely of the cell and is formed with restricted flow channels for absorbing energy from the molten metal and to reduce the amplitude of the wave motion in the molten metal. The baffle may be in the form of a single member formed with apertures for metal flow restriction or may be constituted by a number of separate aligned members with metal flow channels between them.

Electrolytic reduction cells

In an electrolytic reduction cell for the production of a molten metal by electrolysis of a molten electrolyte, the product metal collects on a cathodic carbon floor having embedded steel current collector bars for leading out the cathodic current. In order to reduce the wave motion of the metal due to interaction of horizontal currents in the product metal with the magnetic fields due to currents in conductors associated with the cell, electrically non-conductive barrier members are arranged on the floor of the cell transversely of horizontal currents in the product metal. Such barrier members have at least a surface layer of material resistant to product metal and extend upwardly from the cell floor to a height approximating to the normal maximum operating level of product metal.

In a process for refining Al or Mg a stream of relatively impure molten metal is passed along one face of a grille separator having interstices of the order of 0.1-1 cm in width. The interstices are filled with a molten salt electrolyte adapted to transport ions of the selected metal (Al or Mg) to a body of refined metal on the opposite side of the separator. The relatively impure metal is made in the anode and the refined metal is the cathode. Refined metal is progressively withdrawn from the cathode. The grille separator may be arranged substantially vertical or substantially horizontal, usually with slight inclination. Passages are preferably provided in the separator to allow escape of gas generated at a metal/electrolyte interface.

Electrolytic refining of molten metal

In a process for the treatment of fume-laden carbon monoxide evolved in carbothermic reduction of alumina the fume-laden gas is contacted with particulate carbon in a fluidized bed maintained at a temperature, preferably in the range 2010.degree.-2050.degree. C. and above that at which sticky aluminium oxycarbide forms. The temperature of the bed is most conveniently controlled by the rate at which fresh carbon feed material is added to the bed. The hot gas emerging from the bed is rapidly chilled to a temperature below the solidification point of aluminium oxycarbide. This is most conveniently achieved by contact with a large excess of cool alumina/carbon mix in a stream which is continuously circulated through a heat exchange stage.

Carbothermic production of aluminium

A process for the production of aluminium in two steps:

Process for the production of aluminium

In a process for production of aluminium metal carbon monoxide gas evolved at very high temperature through reaction of aluminium carbide and alumina is cooled by contact with a molten alumina slag at a lower temperature to cause back reaction of contained aluminium suboxide and Al vapor and consequent heat transfer to the contacted molten alumina slag.

In a apparatus for the production of aluminium a molten alumina slag, containing combined carbon is circulated through one or more alternately arranged relatively low temperature zones where carbon is added to increase the combined carbon content of the slag by reaction with the alumina slag and high temperature zones where aluminium metal is released by reaction of aluminium carbide and alumina in the slag with consequent depletion of the combined carbon content. Alumina is supplied to the slag at one or more locations. The energy to drive the reactions is preferably supplied by resistance heating of the slag particularly in transit from a low temperature zone to a high temperature zone although usually additional energy is supplied to the slag in the return from a high temperature zone to the next low temperature zone. In most instances the aluminium-liberating reaction is carried out in an upwardly inclined passage and the gas evolved is employed to achieve the circulatory movement of the slag. It is a preferred feature to scrub the gas with carbon without admixed alumina to avoid formation of sticky aluminium oxycarbide in the carbon, which is subsequently added as process charge.

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Kingston, Canada

Ernest W Dewing