Alcan International Limited

Claude Allaire

Bohdan Gnyra

John McIntyre

Tom J Hudson

Pierre Tremblay

Lionel Talbot, Deceased

A barrier layer for prevention of solid fluorides penetration, e.g. NaF, from the interior of an aluminum production cell holding a fluoride-containing melt into a refractory layer intended to provide heat and electrical insulation for the cell. The barrier layer contains CaO, which may be derived from a CaO precursor such as calcite (CaCO.sub.2) by decomposition during cell start-up. Since CaO does not appear to react with sodium fluoride (NaF), and indeed according to thermodynamic calculations seems incapable of doing so at cell operating temperatures, it is effective for preventing the penetration of that compound when the latter is in the solid state. The barrier layer makes it possible to use insulating low cost refractories which are attacked by solid fluorides in the cell wall lining with improvement of the life of such materials. The barrier layer also keeps fluorides out of the refractory materials so that these materials can be disposed of in conventional land-fill sites without risk of causing pollution due to leaching of fluoride salts.

Barrier layer against fluoride diffusion in linings of aluminum

The amount of electrically conductive material in the bottom floor lining of a conventional aluminum reduction cell is reduced by using a non-conductive lining material in its place. The non-conductive material separates the remaining electrically conductive regions from the sidewall linings of the cell and preferably confines the electrically conductive material to the 'anode shadow' region of the cell floor. In another embodiment joints between the conductive and non-conductive regions are positioned such that they are covered by cell freeze (solid electrolyte) during operation of the cell. This prevents liquid cell contents penetrating the joint and adversely affecting the cell lining, thus shortening the life of the cell. The non-conductive material preferably comprises a particulate alumina mixture made up of large shapes which firmly compact together and smaller particles which fill the remaining voids. Optionally, the mixture may be bonded together with amorphous alumina, in which case the mixture can also be used for cell wall linings. The linings can be used in reduction cells of conventional design and reduces undesirable magnetohydrodynamic effects as well as pollution hazards caused by conventional carbonaceous cell linings.

Linings for aluminum reduction cells

Aluminum electrolysis cell having a refractory lining, said lining being produced by calcining red mud obtained as a byproduct of the Bayer process of producing alumina, grinding the calcined product to form particles of -4 Tyler mesh, mixing the ground product with a binder (e.g. colloidal silica, colloidal alumina, sodium silicate or sodium aluminate) and sufficient water to produce a formable mixture. The mixture is formed into a shaped product, fired and used, for example, as a monolithic lining, to form the internal surface of the aluminum electrolysis production cell.

Electrolysis cell and refractory material therefor

A process for producing a refractory material and to the material so-produced. The process comprises calcining red mud obtained as a by-product of the Bayer process of producing alumina, grinding the calcined product to form particles of -4 Tyler mesh, mixing the ground product with a binder (e.g. colloidal silica, colloidal alumina, sodium silicate or sodium aluminate) and sufficient water to produce a formable mixture. The mixture is then formed into a desired shape and fired, preferably after curing and drying. The resulting fired products have good resistance to high temperatures and to corrosive chemicals such as cryolite. Consequently, the products can be used as refractory linings for aluminium production cells, and in similar applications.

Refractory material produced from red mud

The amount of electrically conductive material in the bottom floor lining of a conventional aluminum reduction cell is reduced by using a non-conductive lining material in its place. The non-conductive material separates the remaining electrically conductive regions from the sidewall linings of the cell and preferably confines the electrically conductive material to the 'anode shadow' region of the cell floor. The non-conductive material preferably comprises a particulate alumina mixture made up of large shapes which firmly compact together and smaller particles which fill the remaining voids. Optionally, the mixture may be bonded together with amorphous alumina, in which case the mixture can also be used for cell wall linings. The linings can be used in reduction cells of conventional design and reduces undesirable magnetohydrodynamic effects as well as pollution hazards caused by conventional carbonaceous cell linings.

The non-destructive testing of materials, particularly coarse grain materials such as the carbonaceous materials used in the anodes and cathodes of an aluminium smelting furnace, using longitudinal compression waves employs a waveguide to apply the waves to a specimen, the and specimen having a cross-sectional dimension Dg of between 3 and 5 times the material average grain size Dg. Alternatively, or in addition, the waves used preferably are of effective wavelength from about 30Ds to 50Ds. Alternatively, or in addition, the effective wavelength of the waves is preferred to be approximately equal to the length of the sample; the necessary very long samples may be obtained by connecting a plurality of smaller elementary samples end-to-end. The apparatus may include a controllable furnace for cycling the sample to determine the change with temperature of the physical characteristic that is being measured. The methods and apparatus employ relatively low frequencies, in the sonic range, and high powers; although particularly suited for measurements with coarse grain materials they are also very effective with more usual fine grain materials, such as ceramics.

Methods and apparatus for non-destructive testing of materials using

The amount of electrically conductive material in the bottom floor lining of a conventional aluminum reduction cell is reduced by using a non-conductive lining material in its place. The non-conductive material separates the remaining electrically conductive regions form the sidewall linings of the cell and preferably confines the electrically conductive material to the 'anode shadow' region of the cell floor. The non-conductive material preferably comprises a particulate alumina mixture made up of large shapes which firmly compact together and smaller particles which fill the remaining voids. Optionally, the mixture may be bonded together with amorphous alumina, in which case the mixture can also be used for cell wall linings. The linings can be used in reduction cells of conventional design and reduces undesirable magnetohydrodynamic effects as well as pollution hazards caused by conventional carbonaceous cell linings.

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Chicoutimi-Nord, Canada

Claude Allaire