Compositions pseudo-métalliques et leur préparation

摘要

A particulate metal analog consisting of the carbide of boron or silicon, silicon borides, or the borides, silicides, or carbides of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten, or mixtures thereof, has an average particle size of from 1 to 250 millimicrons, and an X-ray diffraction line broadening coefficient, k1, of from 9 X 10-2 to 3,6 X 10-4 as calculated from the expression where b is the pure angular breadth in radians of a powder reflection, lambda is the wavelength in ngstrom units of monochromatized CuKa radiation X-rays, and 2#q is the angle of deviation of the diffracted beam. The metal analogs may also contain a weight percentage of chemically combined oxygen of from to 25 where D is the average particle size in millimicrons and r is the density of the metal analog in grams per ml. The percentage of oxygen can be as low as 0,015%, i.e. when D = 250 and r =10. To produce the metal analogs, suitably selected reactants are dispersed with agitation in a fused salt bath at 200-1200 DEG C. under reducing conditions, and in an inert atmosphere, for example, argon. The reactants contain the essential elements of the required metal analog, and are so chosen that each contains a different essential element of the metal analog being produced, these reactants being present in proportions such that the atomic ratio of the essential elements in the separate reactants is that of the desired metal analog, and at least one of the reactants contains an essential element in a positive valency state. The reactants may be oxides, halides, carbides, borides, borates, borohydrides, silicides, silicates, or molybdates, and either reactant may be the element itself. The reducing conditions are provided by the presence of an alklai metal or alkaline earth metal, e.g. sodium or calcium, in the stoichiometric amount required to reduce to its zerovalent state whichever of the elements is in a positive valency state in the reactant. The fused salt can be any salt, or a mixture of salts, which does not decompose at the reaction temperature. For temperatures above 600 DEG C. SiCl, NaCl, and CaCl, are preferred, while from 300-600 DEG C. mixtures of AlCl3 with LiCl or NaCl are preferred. is continued until the metal analog particles become flocculated. The metal analog may be isolated under anhydrous, non-oxidizing conditions, either by filtration from the molten salt-bath followed by washing with a molten volatile halide (e.g. TiCl4) and finally distilling off such halide from the metal analog product, or by filtration followed by removing last traces of salt with an anhydrous organic solvent, e.g. ethylene glycol. If desired, the products can be exposed to an oxygen-containing environment, e.g. water or free oxygen, from which they pick up the required percentage of oxygen, aqueous extraction, for example, being carried out at 0-10 DEG C. and pH 4-10 to prevent excessive attack on the metal analogs. The metal analogs may be dispersed in water to form aquasols, or in organic liquids, e.g. methanol, ethylene glycol, to form organosols. Sols of high stability can be obtained if traces of soluble salts are completely removed by dialysis or treatment with ion exchangers. All compounds which may be prepared by the process are listed and a number of specific examples are given.