Patent GB-781941-A (GB)
Title: Metallic halides
IPC: C01G31/04
Filed: 1955-08-26
Abstract: Halides of molybdenum, niobium, tantalum, titanium, tungsten, uranium, vanadium, zirconium and hafnium having a valency lower than that corresponding to their Group in the periodic table are produced by reacting a halide of higher valency with a carbide of one of said metals in the form of particles at least as fine as 200 Tyler mesh in a non-oxidizing atmosphere above the vaporization but below the disproportionation temperature of the resultant lower valent halide. The lower halides may be subsequently dissolved in a fused salt bath comprising a major quantity of alkali metal halide.  Higher valency halides specifically referred to are in the case of titanium, zirconium, hafnium, niobium and tantalum, tetravalent halides, and in the case of molybdenum, tungsten, uranium and vandium penta- and hexa-valent halides.  The carbides used should be free from oxygen, nitrogen, sulphur and other elements and may be purified by heating with 2-5 per cent of graphite in excess of that required to convert the oxide to carbide in a quartz-lined furnace at 2200-2300 DEG  C. in a vacuum or with an inert atmosphere, e.g. of helium or argon. The reaction may also take place in such an apparatus, the vaporous higher halide being passed over or through a mass of carbide, and passing out (if the product is a vapour at the reaction temperature) into a closed condensing system.  The temperature used usually lies within the range 300-1100 DEG  C., and ranges for each metal are given within which lower temperatures favour halides of lowest valency.  Pressure may be increased to permit higher operating temperatures with vaporous lower halides, or reduced to permit lower operating temperatures so as to obtain the lowest valent halide; reference is made to obtaining titanium dichloride by disproportionation of titanium trichloride at pressures of 0.5 and 10-6 mm. of mercury. Examples refer to (1) reduction of titanium tetrachloride to titanium trichloride at 750 DEG  C. and 1 atmosphere with titanium carbide, the product being obtained as a solution by leaching with normal hydrochloric acid; (2) reduction of titanium tetrachloride at 750 DEG  C. and 1 atmosphere with titanium carbide followed by reduction to 10-2 atmospheres and leaching the dichloride/carbon/carbide mixed product with molten sodium chloride/potassium fluoride; (3) reduction of titanium tetrabromide to titanium dibromide and tribromide at 450 DEG  C. with titanium carbide; (4) reduction of zirconium tetrachloride at 800 DEG  C. with zirconium carbide to zirconium dichloride; (5) reduction of molybdenum pentachloride with molybdenum carbide at 700 DEG  C. to give molybdenum dichloride; (6) reduction of titanium tetrachloride to an unspecified chloride at 650 DEG  C. and 1 atmosphere with titanium carbide, followed by disproportionation at 900 DEG  C. and 10-5 atmospheres to give metal; (7) reduction of zirconium tetrabromide with zirconium carbide as in (6) followed by disproportionation to zirconium at 800 DEG  C.ALSO:Molybdenum, niobium, tantalum, titanium, tungsten, uranium, vanadium, zirconium and hafnium and mixtures of or alloys between these metals are obtained by heating, usually at at least 500 DEG C. above the disproportionation temperature, a halide of said metals having a valency lower than that corresponding to their group in the periodic table and produced by reacting a higher valent halide and a carbide of the metal (see Group III abridgment).  By reducing the pressure a lower disproportionation temperature may be used.  By this process the metal is produced without loss of the higher valent halide which may be recirculated with only make-up quantities of this halide. Suitably a vessel lined with silica or dense alkali metal fluoride, or dense or sintered carbide of one of the above metals may be used, but below 800 to 850 DEG C. graphite is suitable.  In examples, (1) titanium tetrachloride is reduced by passage over titanium carbide in a boat in a vacuum-tight silica tube at 650 DEG C. and 1 atmosphere, and after several hours the product which has collected in the cooler parts of the tube is heated at 900 DEG C. and 10-5 atmospheres to give fine particles of titanium.  (2) The same procedure was employed using zirconium tetrabromide and zirconium carbide except that a disproportionation temperature of 800 DEG C. was used.  For mixtures or alloys, the halides of more than one metal and/or the carbides of more than metal are reacted.