GB959442A - Improvements in or relating to metalliferous compositions - Google Patents

Abstract

Metals or alloys having a melting point greater than 50 DEG C. and improved mechanical properties are produced by dispersing in the molten metal or alloy sub-micron sized particles of at least one refractory metal oxide insoluble therein, the particles having a surface area in sq.m./gm. of 12/D-1200/D when the melting point of the composition is 50-70 DEG C. and 6/D-1200/D when the melting point is greater than 720 DEG C., there being also present an active metal which prevents the separation out of the particles, this metal exceeding 4 mol. per cent based on the refractory particles when the melting point of the composition exceeds 720 DEG C., and casting the metal. The active metal is one the oxide of which is not reduced by hydrogen below 1000 DEG C. and has a free energy of formation at 27 DEG C. of at least 88 k.cal. per gm, atom of oxygen. Suitable metals listed are Be, Mg, Al, Si, V, Ti, Ta, Y, Zr, Hf, Nb, rare earth metals, Li, Na, Ca, Ba, Sr. The basis metals are those the oxides of which are reduced by hydrogen below 1000 DEG C. and have a free energy of formation at 27 DEG C. of less than 88 k.cal. Exemplified are Fe, Co, Ni, Mo, W. Cr. Cu, Ag, Au, Cd, Pb, Sn, Bi and In. The refractory oxides used are those having melting points in excess of 1000 DEG C. and having a particles size of 5-500 millimicrons and a free energy of formation at 1000 DEG C. greater than 60 k.cal. when the melting point of the composition is between 50 DEG C. and 720 DEG C. and greater than 90 k.cal. when the said melting point exceeds 720 DEG C. Particular oxides listed are those of Y, Ca, La, Be, Th, Mg, U, Hf, Ce, Al, Zr, Ba, Ti, Si, Ta, V, Nb, Cr, but mixed oxides or compounds such as aluminates, silicates, titanates, vanadites, chromites, or zirconites may be used. Volume loadings of up to 50% of oxide may be employed in compositions having a melting point between 50 and 720 DEG C., and up to 30% when the melting point exceeds 720 DEG C. The compositions may be prepared by direct addition of oxide particles to the molten metallic phase, or incorporation may be facilitated by first vapour depositing the active metal on to the oxide. The presence of oxygen during addition is also advantageous. Alternatively a dispersion of oxide in basis metal may be prepared by partial reduction of mixed oxides and subsequently added to molten metal. There may be also prepared a dispersion of refractory oxide in active metal which is then added to the basis metal. Specification 667,154 is referred to.