GB925142A - Improvements in metallic compositions and the manufacture of same - Google Patents

Abstract

<PICT:0925142/III/1> In a process of hot pressing inorganic powdered materials such as metals, alloys, oxides, carbides, nitrides, silicides, bromides, phosphides and cermets, or powdered reactants which react to form these materials, the powders are packed in a compressible envelope lined with an inert refractory, the assembly is confined in a die and the powder is then subjected simultaneously to heat and a longitudinally applied pressure of at least 5,000 p.s.i. As shown in Fig. 3 the powder 16 is charged into a ductile metal envelope 10 lined with a refractory 14 which may include getters such as Al or Mg. The envelope is either evacuated or purged with a suitable gas, placed in die assembly 23 and heated electrically to a controlled temperature and subjected to a pressure of 10,000-250,000 p.s.i. Alternatively the powder may be charged into a graphite mould which is supported inside the refractory lined metal envelope (Fig. 5 not shown.) If necessary the powder may be briquetted prior to charging. Some examples of the dense sintered bodies formed by not pressing the respective powders are:- WC/Co; 95% Fe/5% BN; SiC; B4C; Al2O3; 60% Fe/40% SiC; and many metals and alloys (see Group II). Titanium diboride and molybdenum silicide are also produced by hot pressing briquetted mixtures of the constituent powders. Metals and alloys are also formed by a combined exothermic reaction hot pressing process and cermets may also be so formed (see Group II). Hot pressed metal carbides, borides, silicides and phosphide may also be formed in situ by reducing the oxides of Fe, Cu, Ni, Cr, Mo, Ti, W, U, Zr with Mg or Al and simultaneously reacting the metal with C, B, Si or P containing material. B4 C and Si C are also formed by hot pressing a powder mixture of boric oxide or silicon dioxide with carbon and aluminium. High purity crystalline borides ranging from micron size up to 1/4 inch are formed by reacting and hot pressing powder mixtures of boric oxide, the required metal oxide, a reducing agent such as Al, Mg or Ca and an oxide of a solvent metal such as Ni, Co, Fe, Mn, Zn, Cu, Ag. The borides of Ti, Zr, Cr, V, Mo, W, Nb, Hf, U and Th are produced in this way, the borides being separated from the regulus by leaching or electrolysis. In a further example a boron ore is directly reduced to boron by treating a powder mixture of the boron ore and aluminium. The resulting boron-alumina regulus is crushed and separated in a heavy liquid such as acetylene tetra bromide, the separated boron having a purity of at least 90%. According to a further embodiment the process is used for the synthesis and growth of inorganic crystals such as diamonds, precious and semi-precious stones, complex silicates, garnets, olivines, corundum, rutile and zirconia. In this embodiment the powdered charge consists of an organic material such as the mono, di and polysaccharides. The powdered sugar is subjected to a pressure of at least 75,000 p.s.i. and a temperature of less than 1000 DEG C. in the refractory lined metal envelope. The highly corrosive solvents formed dissolve some of the refractory material which is precipitated out on cooling.