GB717496A - Improvements in or relating to stabilised platinum group metals and alloys thereof - Google Patents

Abstract

A grain stabilized metal compact consists of a metal of the group platinum, iridium, osmium, palladium, rhodium and ruthenium or an alloy of these metals having silica uniformly distributed through it. The compacts may be used in the production of platinum ware, contact points, furnace heating elements, thermocouple wires and gauze catalysts. In place of silica a mixture of a major proportion of silica with minor amounts of other acidic oxides, e.g. of boron, zirconium, vanadium or titanium may be used. The proportion of silica used may be 0.001-2.5 per cent. by weight of the metal and preferably varies inversely with the specific gravity of the metal. Among the alloys which may be employed are platinum with rhodium up to 50 per cent.; platinum with iridium up to 30 per cent.; platinum with tungsten up to 6 per cent.; platinum with nickel up to 6 per cent. Iron, cobalt, silver and gold may also be constituents of the alloys used. The compact may be made by sintering or by a fusion and casting process. Thus it may be made by incorporating silica in the metal powder, compacting by pressure and sintering at 900 DEG C.-1600 DEG C., the sintered compact being then annealed. Silicic acid sol may be incorporated in finely divided sponge metal powder, the mixture being dehydrated, heated in the range 900 DEG C.-1600 DEG C., fused into moulds and finally annealed. The initial mixture of metal and silica may be made by mixing silicate and syrupy chloroplatinic acid, coprecipitating ammonium chloroplatinate and hydrated silica gel by addition of ammonium chloride, igniting at 450-600 DEG C. to form sponge powder which is compacted, sintered and annealed. Alternatively the precipitate may be ignited at 900 DEG C.-1100 DEG C., compacted, heated at 1400 DEG C.-1600 DEG C., fused, cast and annealed. Rhodium may be added to the mixture of platinum and silica or to the precipitated platinum compound and silica, the resulting mixture being reduced in hydrogen, e.g. at 750-1050 DEG C., prior to fusing or at 200 DEG C.-300 DEG C. prior to sintering. The compact or ingot is annealed for at least 15 minutes at the normal annealing temperature for the metal and may be then hot worked. After further annealing cold working steps may follow with area reduction of 40-99 per cent. with annealing between each step, e.g. at 550-750 DEG C. For producing wire for catalyst gauze a hot rolled rod of platinum-rhodium containing silica is reannealed at 650 DEG C.-750 DEG C., slowly cooled to room temperature, cleaned by chemical pickling and cold worked in two steps, the first being an area reduction of at least 98 per cent. and the second at least 99 per cent. with between anneals at 650 DEG C.-750 DEG C. for at least 3 hours in an oxidizing atmosphere. Chemical pickling may be accomplished by use of a dilute aqua regia solution buffered with ammonium chloride or sodium chloride. The invention is also stated to be applicable to nickel and nickel alloys.