GB575449A - Improvements in and relating to refractory metal compositions - Google Patents

Abstract

A metal composition for making electrical contacts, welding electrodes and dies, current-carrying bearings or bushings, valve seats, &c., consists of particles of conductive refractory metals or their compounds coated with a platinum group metal and bonded with copper, silver or gold or an alloy of two or all of these. The refractory metal may be tungsten or molybdenum or their carbides or borides. The coating metal may comprise platinum, palladium, or rhodium and amount to 0.01 to 90 per cent of the coated particles. The bonding metal may amount to 1 to 95 per cent of the final product. The coating may be applied by electroplating, cathode sputtering, spraying, sublimation, chemical deposition, or by applying the metal as powder with or after an adhesive and then heating. The coated particles may be pressed and sintered at 1200 DEG C. and then heated in a reducing atmosphere in contact with the bonding metal. In a modification, the coated particles are mixed with powdered bonding metal and pressed and sintered at 950 DEG C. In another modification, powdered bonding metal is mixed with the coated powder and pressed in a die. The product is then sintered at 1250 DEG C. and impregnated with additional bonding metal. The coated powder may also be sintered before pressing. Small proportions of other materials may be added, e.g. up to 10 per cent of carbon or boron or 1 to 30 per cent of nickel, cobalt, iron, manganese, or silicon. An electric contact consisting of equal parts of tungsten carbide coated with rhodium, and silver may be used with a contact comprising silver 90 per cent and cadmium oxide 10 per cent. U.S.A. Specification 2,145,690 is referred to.