Patent GB-778344-A (GB)
Title: A process for producing a transition metal and carbon tetrafluoride
IPC: C22B60/02
Filed: 1955-08-04
Abstract: Carbon tetrafluoride is produced by effecting contact between carbon, carbon-contaminated transition metal (Ti, Zr, Hf, V, Nb, Ta, U, Mo, W, Cr), or a carbide of said metal, with a molten metal double fluoride of said metal at a temperature of at least 1800 DEG  C., preferably up to 2500 DEG  C.  The double fluoride may be in commercial or pure form, it may be mixed with an alkali metal halide, and it should be present in an excess of the stoichiometric amount. The carbon or carbide may be added to the double fluoride either in finely divided form, or formed into electrodes to supply the necessary heat.  Alternatively, the latter may be provided externally, or by using the bath as a resistance element.ALSO:In the production of transition metals free from carbon by effecting contact between carbon, a carbon-contaminated transition metal (Ti, Zr, Hf, V, Nb, Ta, U, Mo, W, Cr), or a carbide of said metal, and a molten alkali metal double fluoride of said metal at a temperature of at least 1800 DEG C., the carbon-tetrafluoride also formed may be used to produce the transition metal tetrafluoride by (a) passing it through or over a body of the transition metal carbide in finely divided form at a temperature of 900-1200 DEG C., preferably in the presence of about 2 per cent elemental chlorine, or (b) reacting it with an oxide of the transition metal at a temperature of 1000-1400 DEG C.  The transition metal tetrafluoride may then be dissolved in dilute aqueous hydrofluoric acid, and alkali metal fluoride added to form alkali metal-transition metal double fluoride which can be recovered by crystallization or salting out.  Alternatively, the alkali metal-transition metal double fluoride may be produced by passing the carbon tetrafluoride into molten alkali metal hydroxide and the resulting alkali metal fluoride added to a mixture or solution of a dioxide or other compound of the transition metal in the presence of dilute aqueous hydrofluoric acid.ALSO:Substantially carbon-free-transition metal (Ti, Zr, Hf, V, Nb, Ta, U, Mo, W, Cr), is produced by effecting contact between carbon, carbon-contaminated transition metal or a carbide of said metal, with a molten alkali metal double fluoride of said metal at a temperature of at least 1800 DEG C., preferably up to 2500 DEG C.  The double fluoride may be in commercial or pure form, it may be mixed with an alkali metal halide, and it should be present in an excess of the stoichiometric amount. Should an excess of carbon produce a carbon-contaminated transition metal, the latter may be used as a solid anode to be electrolyzed in a fused salt bath to deposit the transition metal on a cathode. Should the transition metal be contaminated by an excess of transition metal carbide, it may be brought in finely divided form into contact with a molten mass of the same transition metal-alkali metal double fluoride at a temperature of 800-1200 DEG C., whereupon the transition metal component of the carbide will be transformed to one or more lower valent transition metal fluorides which are removed from the residual carbide-free transition metal product as by leaching or volatilization.  The carbon or carbide may be added to the double fluoride either in finely divided form, or formed into electrodes to supply the necessary heat.  Alternatively, the latter may be provided externally, or by using the bath as a resistance element. The reaction vessel is preferably in the form of a water-cooled metal shell.  The carbon tetrafluoride produced serves as a protective atmosphere for the metal as it is formed, and this protection may be increased by admitting an inert gas such as pure, dry argon or helium, or a reducing atmosphere containing hydrogen, or by maintaining on the molten bath a fresh charge of the double fluoride in granular form.  An alloy of the transition metal may be obtained by incorporating one or more other metals in the reaction mass.