GB923860A - Crystalline boron phosphides and production thereof - Google Patents

Abstract

Macro-, or micro-, crystalline boron phosphide of empirical formula B5P to B7P, particularly B6P, is produced by thermal decomposition of BP or by reaction of a source of B with a source of P. The reaction is effected at 800-1947 DEG C., preferably 1000-1600 DEG C. and the partial pressure of P during formation of the phosphide must be less than the decomposition pressure of BP at the temperature prevailing. Micro-crystalline may be converted to macro-crystalline by heating at 2000 DEG C. for 12 hrs. B6P is prepared by heating BP or BP and 5 atomic proportions of B in intimate admixture. An intimate mixture of B and P may be heated or B may be reacted with PH3. Alternatively, boron halide, hydride, or alkyl may be reacted phosphorus or phosphorus halide and H2, or phosphorus hydride. The reaction may also be effected in an inorganic matrix by heating phosphides of Al, Mg, Cu, Ti, Fe, Cr, Mn, V, Zr, Mo, Ta, or Th, or calcium phosphate and carbon, with a boride of Mg, Al, Fe, Cu, Ti, Zr, or V, boron carbide, or crude boron ore, e.g. Ca, Mg, or Na borate so that the reaction occurs in a molten matrix of the one or more metals added as part of the P. or B sources. Thus ferroboron may be reacted with ferrophosphorus. Alternatively, the reactants may be introduced into a molten metal. Shaped articles may be formed in the course of reaction thus BP and B mixture may be shaped and heated, or B may be shaped and converted to BP by treatment with P or PH3 with subsequent conversion by heat to B6P. Alternatively, aluminium phosphide may be shaped and reacted with BCl3 and H2, or B may be added to B6P, shaped and phosphorized. Inert gas, e.g. N2, He, or A, pressure may be applied during the reaction. Coatings of B6P on shaped forms of, e.g. graphite, Mo, W, steel, ceramic, or Al, may be produced by vapour phase deposition from the reaction of a boron halide, hydride, or alkyl with phosphorus and H2, or phosphorus halide, or PH3. Examples refer to products B5.8P, B6.5P, and B7P. The product phosphides may be shaped by moulding and sintering, by hot pressing at 540-3315 DEG C. with possible addition of metals, p oxides, borates or phosphates (many specified) as bonding agents, or of transition temperature change controllers, e.g. SiC, or ZnO, or by cold pressing, with or without metal or oxide additives, and subsequently sintering, reducing, or partially oxidizing. Naphthalene, cork, or asbestos, may be included to develop porosity. Coatings of the phosphides may be obtained by packing round metal or ceramic parts and heating to 815-3315 DEG C. to effect pack diffusion, by flame spraying, by electrophoresis from aqueous suspensions with subsequent densification and sintering or by slurry coating with subsequent densification and sintering. Shaping may alternatively be effected by slip casting and firing. In all cases metals or oxides may be also incorporated. The B6P may be used as abrasive, semiconductor, or dispersion hardeners for metals or alloys in which case they may be produced in situ by the matrix method. Specified uses are: vessels, liners, radiation shields for absorbing neutrons, steam turbine baffles, wear plates, bearings and impellers for pumps, filter elements in rocket and missile fuel systems, and nose cones, tail sections, turbine blades, combustion and fuel tank liners, and elevators for missiles, rockets, and jet planes.