Stock material or miscellaneous articles – Metal continuous phase interengaged with nonmetal continuous...
Patent
1989-02-15
1990-08-14
Lechert, Jr., Stephen J.
Stock material or miscellaneous articles
Metal continuous phase interengaged with nonmetal continuous...
75232, 75234, 75235, 419 19, 419 20, 419 21, 419 22, 419 45, B32B 700
Patent
active
049486764
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to ceramic/metal composite materials having at least one ceramic phase and at least one metallic phase. This invention further relates to a body of the ceramic/metal composite material and to a method of its manufacture.
BACKGROUND ART
Composite materials comprising ceramic and metallic phases, generally referred to as cermets, are known from numerous publications. Such materials are used in a wide variety of applications and their specific composition, structure and other physical and chemical properties may be adapted to the specific intended use.
Among the known types of cermets are those which comprise metal oxides as ceramic phase with a different metal or the same metal as the metallic phase. An example is given in EP-A-0 072 043 which describes a cermet comprising alumina and aluminum. This cermet is proposed for use as a component covered with molten aluminum in fused salt aluminum electrowinning cells. This reference also mentions (page 5, line 30) that the alumina phase may include further oxides which do not readily react with aluminum. The metallic phase may either be pure aluminum or an alloy of aluminum with other metals such as mentioned on page 3, lines 5-32.
It has already been proposed to include cerium compounds in ceramic materials used as components in aluminum production cells. Such developments are described e.g. in EP-A-0 115 689, which discloses a ceramic body fabricated by reaction sintering CrO.sub.3 and CeB.sub.2 to yield a mixture of ceria and CrB.sub.2.
U.S Pat. Nos. 4,454,015 and 4,584,172 have subsequently disclosed various reaction-sintered cermets such as Fe/Ni oxide as ceramic phase with iron, nickel or an iron
ickel alloy as the metallic phase. These cermets were proposed for dimensionally stable anodes in molten salt electrowinning.
EP-A-0 114 085 discloses aluminum electrowinning with a cerium compound dissolved in the molten cryolite electrolyte so that during electrolysis a protective coating of a fluorine-containing oxycompound of cerium referred to as "cerium oxyfluoride" is produced on the anode surface. The anode substrate to be plated with the cerium oxyfluoride was for example SnO.sub.2, but other substrates were also proposed such as electrically conductive and essentially corrosion resistant materials which, in addition, may contain or be precoated with cerium as metal, alloy or intermetallic compound with at least one other metal, or as compound. The substrate may in particular be a conductive ceramic, cermet, metal, alloy or an intermetallic compound.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a new type of cermet material comprising cerium and a cerium-containing oxide.
It is also an object of the present invention to provide a ceramic/metal composite material capable of being plated with a cerium oxyfluoride coating during electrolysis of alumina dissolved in molten cryolite containing small amounts of cerium ions.
It is another object of the present invention to provide a substrate for an anode for a molten salt aluminum electrowinning cell which provides sufficient electrical conductivity to economically operate the electrowinning cell and which, once coated with cerium oxyfluoride, is dimensionally stable during long periods of operation.
It is a further object of the present invention to provide an electrically conductive ceramic/metal composite material which may be used as a component in a molten salt aluminum electrowinning cell and which does not produce harmful corrosion products that contaminate the electrowon aluminum.
It is a still further object of the present invention to provide a material which, when coated with cerium oxyfluoride, provides s self-healing effect for this coating subsequent to damage or the occurence of imperfections.
SUMMARY OF INVENTION
The above and other objectives of the present invention are attained with a ceramic/metal composite material of at least one ceramic phase and at least one metallic phase, comprising mixed oxides
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Darracq Dominique
Duruz Jean-Jacques
Freer John J.
Lechert Jr. Stephen J.
Mai Ngoclan T.
Moltech Invent S.A.
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