GB931336A - Improvements in or relating to boron phosphide - Google Patents

Abstract

Cubic crystalline boron phosphide is produced by heating together to at least a sintering temperature (a) a metal phosphide or phosphorous alloy and (b) a metal boride, boron alloy or boron carbide. Either or both of the phosphide and boride may be prepared "in situ" from reducible phosphates or borates in conjunction with a reducing agent, e.g. C. Metal phosphides of Al, Mg, Cu, Ti, Cr, Mn, V, Zr, Mo, Ta or Th or ferrophosphorous and metal borides of Al, Mg, Cu, Ti, Zn or V or ferroboron may be used. Reducible borate sources are colemanite, magnesium borate and borax and reducible phosphate sources are calcium phosphate ores, apatite and bone ash. The proportions of boron and phosphorous sources used are variable but in different circumstances equitomic proportions or an eccess of the cheaper material can be used. The introduction of metallic components by the above method and/or by direct addition of metals results in the production of boron phosphide in a molten matrix which consists of one or more metals selected from Ni, Sb, Sn, Pb, Bi and those mentioned above. Alternatively the molten matrix may consist of an inorganic salt, e.g. NaCl, KBr, LiBr, CaCl2, MgCl2, BaCl2, RbCl2, CsCl2 or a mixture thereof and the fluidity of the slag in this case may be increased by the addition of silica sand, Na2, SiO3 or CaSiO3. Preferred embodiments of the process are the preparation of boron phosphide from ferroboron and ferrophosphorous at 2732 DEG -3092 DEG F., from magnesium or aluminium alloys of phosphorous and boron, from crude phosphate and borate ores in a molten NaCl matrix using carbon as the reducing agent and from boron and phosphorous sources in a matrix formed from fused iron one to which a SiO2 slag may or may not have been added. Metal compounds are removed from the crude product by leaching with aqua regia and siliceous material removed by HF or alkali. The crystalline boron phosphide may be shaped by hot pressing, e.g. at 500-20,000 psig and 1000 DEG -6000 DEG F., or cold pressing, may be diffused into metal or ceramic shapes by packing round the shape and heating to 1500 DEG -6000 DEG F., may be applied as a coating of particles by flame spraying, electrophoresis, or from a slurry, or may be slip cast and subsequently fired. In all cases fluxes and bonding agents may be added, e.g. Cr, Fe, Ni, Co, Nb, Ta, Ti, Zr, W, Mo, Hf, Al2O3, ZrO2, HfO2, SiO2, BeO2, TiO2, ThO2, alkali metal borates or phosphates, boron phosphate or sodium silicate. Porosity may be produced by adding naphthalene, cork or asbestos. The shape or coating may be densified and sintered, and may be subsequently subjected to reduction with H2, where metal oxides are present, or oxidation. For slurry coating the boron phosphide is dispersed in water with carboxymethyl cellulose. Examples of applications for the resulting temperature and chemical resistant boron phosphide or composition as an article or coating are:-crucibles, missile nose cones, rocket fuel tanks and pump impellers, jet nozzles, Venturi throats, exhaust deflectors, grinding wheels, shaping tools, turbine blades and nozzles, observation windows for furnaces, nuclear reactors, or space ships, burners, agitators, nuclear reactor shields, semi conductors, strengthened metal wear plates, or radiation meters. Porous material may be used as filters or to provide cooling by passage of liquids. Specification 923,860 also is referred to.ALSO:Cubic crystalline boron phosphide is produced by heating together to at least a sintering temperature (a) a metal phosphide or phosphorus alloy and (b) a metal boride, boron alloy or boron carbide (see Group III). Metal compounds are removed from the crude product by leaching with aqua regia and siliceous material removed by HF or alkali. The crystalline boron phosphide may be shaped by hot pressing e.g. at 500-20,000 p.s.i.g. and 1500-6000 DEG F., may be applied as a coating of particles by flame spraying, electrophoresis, or from a slurry, or may be slip cast and subsequently fired. In all cases fluxes and bonding agents may be added e.g. Cr, Fe, Ni, Co, Nb, Ta, Ti, Zr, W, Mo, Hf, Al2O3, ZrO2, HfO2, SiO2, BeO2, TiO2, ThO2, alkali metal borates or phosphates, boron phosphate or sodium silicate. Porosity may be produced by adding naphthalene, cork or asbestos. The shape or coating may be densified and sintered, and may be subsequently subjected to reduction with H2, where metal oxides are present, or oxidation. For slurry coating the boron phosphide is dispensed in water with carboxymethylcellulose. Examples of applications for the resulting temperature and chemical resistant boron phosphide or composition as an article or coating are:- crucibles, missile nose cones, rocket full tanks and pump impellers, jet nozzles, venturi throats, exhaust deflectors, grinding wheels shaping tools, turbine blades and nozzles, observation windows for furnaces, nuclear reactors, or space ships, burners, agitators, nuclear reactor shields, semi-conductors, strengthened metal wear plates, or radiation meters. Porous material may be used as filters or to provide cooling by passage of liquids. Specification 923,860 also is referred to.