GB938546A - Improvements in or relating to metalliferous compositions - Google Patents

Abstract

Fe, Co, Ni, Cu, Mo, W, Re and alloys of these metals with each other and with other metals having an oxide which is stable up to 300 DEG C. and has a free energy of formation at 27 DEG C. in the range 30-70 kilocalories per gm.-atom of oxygen, e.g. Cd, Tl, Ge, Sn, Pb, Sb, Bi, In, have their elevated temperature properties improved by first forming a particulate dispersion, the metallic particles having uniformly dispersed therein submicron sized particles of one or more refractory metal oxides and subsequently compacting by conventional means. The refractory oxides are those having a free energy of formation at 1000 DEG C. above 60 kilocalories per gm.-atom of oxygen and their average particle size is in the range 5-1000 millimicrons. Suitable oxides are those of Y, Ca, La, Be, Th, Mg, V, Hf, Ce, Al, Zr, Ba, Ti, Si, Ta, V, Nb, Cr, while mixed oxides such as Mg Al2O4, aluminates, silicates, titanates and complex silicates such as sodium aluminium silicate, may also be employed. The dispersion has a surface area of less than 10 square metres per gram, and the average size of the grains of metal is less than 10 microns. Ratio of oxide: metal may be as high as 1 : 1 by volume, but are generally 0.05-30% of oxide by volume. The composition is made by bringing oxygen-containing compounds of the metal or metals to be improved into intimate contact with discrete particles of either the desired refractory oxide(s) or a compound which on heating to constant weight at 1500 DEG C. is converted thereto, decomposing said compound if necessary, reducing the oxygen-containing compound to metal at a temperature below the sintering temperature of the metal, and subsequently sintering the reduced product below its melting point until its surface area is less than 10 sq. m. per gm. The oxygen-containing compound of the metal or metals may be precipitated from a soluble salt by addition of an alkaline solution on the refractory oxide which may be in the form of an aquasol, followed by washing, drying and reduction in a stream of reducing gas. Alternatively an oxygen-containing compound of the metal(s) to be improved and an oxygen-containing compound of the refractory metal whose oxide is to be dispersed therein are fused together in air to decompose the compounds to oxides, quenching the melt, finely dividing the mass and reducing as before.