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Slow consumable non-carbon metal-based anodes for aluminium production cells

a production cell, non-carbon technology, applied in the direction of electrochemical machining apparatus, electrolysis components, electrolysis coatings, etc., can solve the problem of difficult to achieve full protection of alloy substrates, and achieve the effect of reducing the frequency of anode replacement and reducing carbon-generated pollution

Inactive Publication Date: 2001-08-16
MOLTECH INVENT
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0011] An object of the present invention is to provide a non-carbon, metal-based anode for the electrowinning of aluminium so as to eliminate carbon-generated pollution and reduce the frequency of anode replacement, such an anode having an outside layer well resistant to chemical electrolyte attack whose surface is electrochemically active for the oxidation of oxygen ions contained in the electrolyte and for the formation of gaseous oxygen.

Problems solved by technology

However, full protection of the alloy substrate was difficult to achieve.

Method used

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  • Slow consumable non-carbon metal-based anodes for aluminium production cells
  • Slow consumable non-carbon metal-based anodes for aluminium production cells

Examples

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Effect test

example 2

[0071] A non-carbon metal-based anode according to the invention was obtained from a 15.times.15.times.80 mm sample of a nickel-iron based alloy. The sample was made of cast alloy consisting of 79 weight % nickel, 10 weight % iron and 11 weight % copper.

[0072] The sample was pre-oxidised in air at about 1100.degree. C. for 5 hours in a furnace to form the anode with a pre-oxidised surface layer.

[0073] After pre-oxidation, the anode was immersed in molten cryolite contained in a laboratory scale cell. The molten cryolite contained approximately 6 weight % of dissolved alumina. Current was passed through the anode sample at a current density of 0.5 A / cm.sup.2. After 100 hours, the anode was extracted from the cell for analysis.

[0074] The anode was crack-free and its dimensions remained substantially unchanged. On the surface of the anode a well adherent oxide surface layer of a thickness of about 0.6 mm had grown providing an adequate protection.

example 3

[0075] This Example illustrates the wear rate of the nickel-iron containing anode of Example 2 and is based upon observations made on dissolution of nickel-based samples in a fluoride-based electrolyte.

[0076] An estimation of the wear rate is based on the following parameters and assumptions:

[0077] With a current density of 0.7 A / cm.sup.2 and a current efficiency of 94% an aluminium electrowinning cell produces daily 53.7 kg aluminium per square meter of active cathode surface.

[0078] Assuming a contamination of the produced aluminium by 200 ppm of nickel, which corresponds to the experimentally measured quantities in typical tests, the wear rate of a nickel-iron sample corresponds to approximately 1.2 micron / day. Therefore, it will theoretically take about 80 to 85 days to wear 0.1 mm of the anode.

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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.

Description

[0001] This application is a continuation of co-pending international application designating the USA, PCT / IB99 / 01358, filed on Jul. 30, 1999.[0002] This invention relates to non-carbon, metal-based, slow consumable anodes for use in cells for the electrowinning of aluminium by the electrolysis of alumina dissolved in a molten fluoride-containing electrolyte, and to methods for their fabrication and reconditioning, as well as to electrowinning cells containing such anodes and their use to produce aluminium.[0003] The technology for the production of aluminium by the electrolysis of alumina, dissolved in molten cryolite, at temperatures around 950.degree. C. is more than one hundred years old.[0004] This process, conceived almost simultaneously by Hall and Hroult, has not evolved as many other electrochemical processes.[0005] The anodes are still made of carbonaceous material and must be replaced every few weeks. During electrolysis the oxygen which should evolve on the anode surface...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C25C3/12
CPCC25C3/12
Inventor DE NORA, VITTORIODURUZ, JEAN-JACQUES
Owner MOLTECH INVENT
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