Method of manufacturing an electrically conductive cermet
AssigneesW.C. Heraeus GmbH, Friatec Aktiengesellschaft
InventorsDavid Francis Lupton, Jorg Schielke, Hans-Joachim Graf, Arno Reckziegel
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Abstract
A method of manufacturing an electrically conductive cermet that includes less than 35% by volume of a precious metal by mixing a powdered refractory ceramic with the powdered metal, molding the mixture into a green, and sintering the green to create a cermet with a dense ceramic phase and a metallic phase in the form of a coherent network. The object is good electric conductivity at a low metal content. The precious metal powder is selected to shrink less and exhibits less sintering tendency as it forms the metallic phase than does the ceramic powder as it forms the ceramic phase.
Claims22
A method of manufacturing an electrically conductive cermet having less than 35% by volume of a precious metal comprising the steps of
- mixing a powdered refractory ceramic with powdered precious metal, the precious metal powder and the ceramic powder being selected such that during sintering, the precious metal powder shrinks less and exhibits less sintering tendency as it creates the metallic phase than the ceramic powder does as it creates the ceramic phase;
- molding the mixture into a green;
- and
- sintering the green to form a cermet with a dense ceramic phase and a metallic phase in the form of a coherent network
- wherein the precious metal powder is platinum or an alloy containing at least 50% platinum and the remainder at least one metal selected from the group consisting of Ir, Ru, Rh or Pd, and
- is selected to have a mean particle size of at least 10 .mu.m and no more than 10% by weight has a particle size of less than 2 .mu.m;
- the refractory ceramic contains Al.sub.2 O.sub.3, MgO, ZrO.sub.2 or oxides of rare earth metals;
- and
- sintering occurs at temperatures between 1500.degree. C. and 1750.degree. C.
A method of manufacturing an electrically conductive cermet having less than 35% by volume of a precious metal comprising the steps of
- mixing a powdered refractory ceramic with powdered precious metal, the precious metal powder and the ceramic powder being selected such that during sintering, the precious metal powder shrinks less and exhibits less sintering tendency as it creates the metallic phase than the ceramic powder does as it creates the ceramic phase;
- molding the mixture into a green;
- and
- sintering the green to form a cermet with a dense ceramic phase and a metallic phase in the form of a coherent network;
- wherein the precious metal powder is selected to have a mean particle size of at least 10 .mu.m and no more than 10% by weight has a particle size of less than 2 .mu.m;
- and
- the ceramic powder is selected to have a specific surface at least 20 times larger than that of the precious metal powder as measured by the BET method.
A method of manufacturing an electrically conductive cermet having less than 35% by volume of a precious metal comprising the steps of
- mixing a powdered refractory ceramic with powdered precious metal, the precious metal powder and the ceramic powder being selected such that during sintering, the precious metal powder shrinks less and exhibits less sintering tendency as it creates the metallic phase than the ceramic powder does as it creates the ceramic phase;
- molding the mixture into a green;
- and
- sintering the green to form a cermet with a dense ceramic phase and a metallic phase in the form of a coherent network;
- wherein the precious metal powder is platinum or an alloy containing at least 50% platinum and the remainder at least one metal selected from the group consisting of Ir, Ru, Rh or Pd, the refractory ceramic contains Al.sub.2 O.sub.3, MgO, ZrO.sub.2 or oxides of rare earth metals and sintering occurs at temperatures between 1500.degree. C. and 1750.degree. C.;
- and
- the precious metal powder and ceramic powder are selected such that the precious metal powder loses at least 5% less volume entering the metal phase as the green is sintered than the volume lost by the ceramic phase.
A method of manufacturing an electrically conductive cermet having less than 35% by volume of a precious metal comprising the steps of
- mixing a powdered refractory ceramic with powdered precious metal, the precious metal powder and the ceramic powder being selected such that during sintering, the precious metal powder shrinks less and exhibits less sintering tendency as it creates the metallic phase than the ceramic powder does as it creates the ceramic phase;
- molding the mixture into a green;
- and
- sintering the green to form a cermet with a dense ceramic phase and a metallic phase in the form of a coherent network;
- wherein the precious metal powder is Ir, Ru, Rh or Pd, or an alloy containing at least 50% Ir, Ru Rh or Pd and the remainder being Ir, Ru, Rh, Pd or Pt or a mixture thereof.
In an electrically conductive cermet of the type formed by sintering a refractory ceramic green wherein a precious metal is dispersed to provide the electric path, wherein the improvement comprises
- said cermet containing approximately 25% to 35% precious metal;
- said cermet having been sintered at temperatures of 1500.degree. to 1750.degree. C. to obtain a high density ceramic;
- and
- a 6 mm thick disk of said cermet, 10 mm in diameter, has an electric resistance of less than 10.OMEGA..
Dependencies are inferred from the claim text.