GB893424A - Improvements in or relating to the manufacture of sintered metallic compositions - Google Patents

Abstract

A sintered composition consisting of a matrix metal or alloy such as Ni, Co, Fe, Cu, W, Mo, Pb or Ag which form easily reducible oxides, and a dispersed phase of one or more refractory oxides such as Al2O3, SiO2, MgO or BeO is formed by precipitating from a solution of a salt of the matrix metal a compound which on heating forms the metal oxide, and also precipitating from a solution of a salt of the metal of the refractory oxide a compound which forms the refractory oxide on heating, mixing the precipitates, heating to form the respective oxides, heating in a reducing atmosphere to form the matrix metal and refractory oxide and then compacting and sintering the mixture. The sintered composition contains less than 1% by weight of the refractory oxide and the precipitation from aqueous solutions of the respective metal salts is effected by the addition of alkali metal hydroxides, ammonia, alkali metal carbonates, alkali metal oxalates, oxalic acid, alkali metal formates and formic acid. The mixed precipitates are ground to minus 300 mesh B.S.S. and the decomposition and reduction of the precipitate may be effected in a single operation by heating in a reducing atmosphere. In an example basic copper sulphate and basic aluminium sulphate are separately precipitated from aqueous solutions of copper sulphate and aluminium sulphate with aqueous ammonia. After mixing, filtering and drying, the mixed precipitates are heated in air at 850 DEG C.-900 DEG C. to form the oxides, crushed to minus 300 mesh B.S.S., reduced in hydrogen at 300 DEG C. and then compacted at 35-50 times p.s.i. and finally intered in hydrogen or vacuum at 1040 DEG C. Specification 893,425 is referred to.