Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1995-07-27
1998-02-24
Valentine, Donald R.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
427314, 252512, 204290R, C25C 308, H01B 102, B05D 302
Patent
active
057208603
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to components of aluminium production cells made of composite materials comprising ordered aluminide compounds of nickel, iron and/or titanium, for use in particular as anodes and cathodes and cell linings in aluminium production cells containing a fluoride-based molten electrolyte containing dissolved alumina and cerium species.
The invention is more particularly concerned with the production of components of aluminium production cells made of composite materials comprising ordered aluminide compounds of nickel, iron and/or titanium, by the micropyretic reaction of a mixture of reactive powders, which reaction mixture when ignited undergoes a micropyretic reaction to produce a net-shaped reaction product, it being understood that the reaction product may be used directly as an anode or cathode, or as substrate carrying an outer protective coating, or as a cell component.
BACKGROUND ART
U.S. Pat. No. 4,614,569 describes anodes for aluminium-production coated with a protective coating of cerium oxyfluoride, formed in-situ in the cell or pre-applied, this coating being maintained by the addition of cerium to the molten cryolite electrolyte. The inclusion of cerium in the substrate was proposed to promote formation of the cerium oxyfluoride coating and enhance its properties, but so far no practical way was found to effectively implement this.
U.S. Pat. No. 4,948,676 describes a ceramic/metal composite material for use as an anode for aluminium production particularly when coated with a protective cerium oxyfluoride based coating, comprising mixed oxides of cerium and one or more of aluminium, nickel, iron and copper in the form of a skeleton of interconnected ceramic oxide grains interwoven with a metallic network of an alloy or an intermetallic compound of cerium and one or more of aluminium, nickel, iron and copper. The production methods included reactive sintering, reactive hot-pressing and reactive plasma spraying of a metal powder mix optionally including some oxides. The described process conditions led to a complex porous microstructure which through dissolution and redeposition of cerium provided a self-healing effect when the anode is first used. However, difficulties were encountered in controlling the porosity of this microstructure.
U.S. Pat. No. 4,909,842 discloses the production of dense, finely grained composite materials with ceramic and metallic phases by self-propagating high temperature synthesis (SHS) with the application of mechanical pressure during or immediately after the SHS reaction. The ceramic phase may be carbides or borides of titanium, zirconium, hafnium, tantalum or niobium, silicon carbide or boron carbide. The intermetallic phase may be aluminides of nickel, titanium or copper, titanium nickelides, titanium ferrites or cobalt titanides, and the metallic phase may include aluminium, copper, nickel, iron or cobalt. The final product, which has ceramic grains in an intermetallic and/or metallic matrix, has a density of at least about 95% of the theoretical density obtained by the application of pressure. Interconnected porosity is not obtained, nor does the process control porosity. Because the pressure is applied uniaxially, it is not possible to produce a net-shaped article, i.e. whose final shape and dimensions may be largely or even completely achieved in the manufacturing process, and for which no or only minor post manufacturing processing such as grinding are required. Also, the required application of pressure prevents high production rates. Moreover, materials produced by the described method but without the application of pressure are weak and have a porosity of about 45 to 48%, which makes them unsuitable as electrodes for aluminium production.
PCT patent application WO/13977 describes the production of ceramic or ceramic-metal electrodes for electrochemical processes, in particular for aluminium production, by combustion synthesis of particulate or fibrous reactants with particulate or fibrous fillers and binders. T
REFERENCES:
patent: 5310476 (1994-05-01), Sekhar et al.
patent: 5378327 (1995-01-01), Sekhar et al.
Sekhar Jainagesh A.
Zhang Hao
MOLTECH Invent S. A.
Valentine Donald R.
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