Kernforschungsanlage Julich

Kernforschungsanlage Julich Gesellschaft MIT Beschrankter Haftung

Forschungszentrum Julich Gmbh

Kernforschungszentrum Julich Gmbh

Aristides Naoumidis

Erno Gyarmati

Ashok K Gupta

Rudolf Munzer

Hermann Kreutz

Hubertus Nickel

Bernd D Struck

Herbert Neumeister

Hartmut Luhleich

Francisco J Dias

Frank Tietz

Marian Kampel

Arno Schirbach

Dieter Triefenbach

Rudolf Muenzer

Ernoe Gyarmati

Martin Gat-Liquornik

Bernd Gottselig

In an electrode for a fuel cell which has a porous self-supporting layer and another layer with catalytic properties disposed on said self-supporting layer, the self-supporting layer has a thickness several times greater than that of the layer with the catalytic properties and consists of a cermet comprising Al.sub.2 O.sub.3 or TiO.sub.2 to which Ni is admixed.

Electrode substrate for fuel cell

A fuel cell with a solid oxide (SOFC) or a molten carbonate salt electrolyte (MCFC). The anode of the fuel cell, according to the invention, is a CERMET anode which consists of a solid mixture of tungsten carbide and an ion-conducting oxide, such as yttrium-fully stabilized zirconium oxide (YSZ). The fuel cell anode is prepared by a process whereby in order to form the solid mixture of which the anode is formed, a mixture of anion-conducting oxide powder and WC/WC(O), WO.sub.3 or precursor thereof is prepared, and this mixture is converted into a YSZ-WC mixture in a CO/CO.sub.2 atmosphere in a temperature range of 600.degree.-1000.degree. C.

Fuel cells and process for the production of the anode

A layer of titanium carbosilicide Ti.sub.3 SiC.sub.2 on a silicon carbide surface polished for making a joint makes it possible to join silicon carbide bodies together in a hot pressing procedure and obtaining a joint strength comparable to the strength of the silicon carbide material. Such a layer on silicon carbide also makes possible brazed juoints with steel alloy or nickel based alloy parts. The layer may be applied directly by a powder dispersion in a volatile but viscous glycol or by sputtering or else the layer can be made in place from a powder mixture of components, especially TiC.sub.0,8 and Tisi.sub.2 (5:1) or a titanium layer of a thickness in the range of 1 to 3 .mu.m that reacts with the silicon carbide surface. When silicon carbide parts are joined together, the heating up to make the joint also serves to convert a titanium layer into titanium carbosilicide. When silicon carbide is to be joined with metal, a preliminary heating step is necessary to at first convert a powder mixture or a titanium layer on the silicon carbide surface to Ti.sub.3 SiC.sub.2. Alternatively a Ti.sub.3 SiC.sub. 2 surface layer can be formed by a sputtering process. The Ti.sub.3 SiC.sub.2 layer favors brazing of the metal part to the silicon carbide surface as treated. The heating requires reaching a temperature in the region from 1200.degree. to 1600.degree. C. for periods between a half hour to about three hours in the presence of a reducing protective gas.

Method and components for bonding a silicon carbide molded part to

A thin metal foil or an array of fine wires or a graphite web, mat or the ke, having electrical conductivity was interposed between clean polished surfaces of ceramic parts which are to be joined, with application of pressure. A high current electrical discharge with very short duration puts so much energy into the conducting material that it explosively vaporizes and penetrates interacts with the ceramic before the ceramic can absorb an appreciable amount of heat and before the hot material can undesirably react with the surrounding atmosphere, so that an inert atmosphere is not necessary for the process. Metals that form silicides and/or carbides are for e.g. desirable for connecting SiC parts and conducting forms of carbon such as graphite are also suitable. Precoating the surfaces to be joined, with reactive or reaction-promoting material as well as a thermal treatment of the joint may be favorable.

Process for joining ceramic parts with a reactive conducting material

A cathode/membrane assembly for an electrolysis cell capable of producing hydrogen in a cathode compartment, utilizes as the cathode material on a proton-permeable solid-electrolite ion-exchange membrane, a layer of porous graphite in the form of carbonaceous fibers coated with tungsten carbide. The graphite felt can be impregnated with an aqueous solution of para-ammoniumtungstate or with an alcoholic solution of tungsten hexachloride and the tungsten compounds are then converted to the tungsten oxides. The tungsten oxide coated graphite felt is then subjected to carburization at a temperature of 620.degree. to 950.degree. C. in a carburizing atmosphere, preferably a flowing CO/CO.sub.2 mixture.

Cathode/membrane assembly and method of making same

Silicon carbon molded parts, whether made of silicon carbide sintered together in the absence of pressure or hot pressed silicon carbide are bonded together at close fitting surfaces by applying a layer not thicker than 1 .mu.m on polished surfaces to be joined, containing at least one carbide and/or silicide forming element from the group Ag, Al, Au, B, Be, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Ni, Pd, Pt, Ta, Ti, V, W and Zr. The surfaces to be joined are than fitted together and heated in an inert or reducing atomosphere at a pressure between 10.sup.-1 and 10.sup.-5 Pa at temperatures in the range 800.degree. to 2200.degree. C. while under a pressure applied which is between 1 and 100 MPa. In particular, the heat treatment range from 1550.degree. C. to 1750.degree. C. under a pressure of 15 to 45 MPa applied pressure in argon at a pressure of from 10.sup.3 to 10.sup.5 Pa argon, for 30 to 60 minutes. Preferably a thin layer is vapor-deposited or sputtered. Cr, Cu, Ni, Pt and/or Pd, and especially Cu and its alloys, have been found particularly effective.

Method of joining molded silicon carbide parts

A method of making shaped bodies of silicon carbide, of graphite coated with silicon carbide or of a graphite-like material with a silicon carbide surface wherein a graphitic body is assembled from preformed parts in the desired shape and is immersed, under a chemically inert atmosphere, in a silicon melt and after penetration of the melt into gaps between abutting surfaces of the body and after reaction of the silicon with the graphite or the graphite-like material to form silicon carbide at the junctions, the body is removed from the melt and is cooled in a chemically inert atmosphere.

Method of making shaped bodies of silicon carbide or of graphite or

A process is disclosed for the production of a tungsten carbide-activated electrode, particularly an electrode which is utilizable as a cathode, and which consists of an electrically-conductive substrate with an active surface layer of tungsten carbide. The tungsten carbide is adhesively bonded through chemical reaction to the surface of a substrate which is constituted of graphite or a graphite-like material. The graphite-like material is a graphite binder mixture, whose binder material components, other than the graphitic filler granules, are only carbonized, and may not be completely graphited.

Process for production of a tungsten carbide-activated electrode

Porous silicon carbide bodies are obtained by starting with a powder of particle size falling within a single sieve mesh range fraction and consisting either entirely of carbon particles or a mixture of carbon and silicon carbide particles of the same mesh fraction is mixed or coated with 15 to 30% by weight of a binder, moulded to shape, warmed in the temperature range from 40.degree. to 200.degree. C. to vaporize volatile material and then coked at a temperature rising to 850.degree. C. Then it is siliconized by raising the temperature to the range from 1650.degree. to 1950.degree. C. with gaseous silicon or impregnated with silicon by dipping the body into a silicon melt and convert it to carbide, with the excess silicon thereafter being removed by vaporizing out or by boiling in lye. Sieve mesh fractions in the region of a few hundred .mu.m are preferred, and the density of the porous body after pressing but before siliconizing should lie in the neighborhood of 0.6 to 0.7 g/cm.sup.3.

Method of making porous silicon carbide bodies

For joining molded parts having silicon carbide surfaces, the surfaces are first roughened to a depth of about 100-500 .mu.m by removal of the free silicon either by vaporization or by etching when treating silicon containing silicon carbide layers containing at least 15% weight of excessive silicon. In the alternative, when no excessive silicon is present, the roughening can be done by laser shots pitting the surface. The pores provided by such a step are then loaded with carbon by (repeated) application of a cokable resin followed by coking, said resin can be soaked into the pores or attached as silicon containing resin wafer of cokable material. The surfaces to be joined are united and are heated, preferably at from 1600.degree. to 1800.degree. C. in the presence of silicon that is either made available at the edges of the joint as a liquid or else has been provided in the joint by a synthetic resin foil in which silicon powder is dispersed.

Method of molding bonded parts with silicon carbide surfaces

Component bodies of silicon carbide base material, at least in their surface layers, are welded together without the provision of a binder at finely polished joining surfaces by virtue of the fact that at least one of the joint surfaces is of a silicon carbide material containing an excess of silicon (SiSiC). The component bodies are kept closely fitted together especially by an additional pressing force of at least 0.1 kg/cm.sup.2 during a heating stage at atmospheric or lower pressure at a temperature in the range from 1500.degree. C. to 1800.degree. C. for 15 to 100 minutes in an inert atmosphere, the excess of silicon at the boundary making it possible for silicon carbide crystal growth to take place across the boundary.

Binderless weld-bonding of preshaped sic-base parts into solid bodies

A significant improvement of the silicon impregnation depth of a carbon precursor body in the siliconizing thereof to make a silicon carbide body is obtained, as well as an accelerated conversion into silicon carbide if activated carbon is used in whole or in part as the carbon powder component of the precursor body. The molding material is preferably 20 to 60% by weight of binder and 20 to 70% activated carbon. This molding material may also usefully contain 10 to 60% by weight of .alpha.-silicon carbide, which may be previously made by siliconizing carbon powder.

Growing community of inventors

Julich, Germany

Aristides Naoumidis