Patent GB-791151-A (GB)
Title: Fused salt bath for the electrodeposition of the polyvalent metals titanium, niobium, tantalum and vanadium
IPC: C25C3/26
Filed: 1954-12-10
Abstract: 791,151. Fused salt baths for electrolytic production of titanium, niobium, tantalum and vanadium. HORIZONS TITANIUM CORPORATION. Dec. 10, 1954 [Dec. 14, 1953], No. 35819/54. Class 41. A fused salt bath for the electrolytic production of the polyvalent metals (i.e. metals capable of exhibiting more than one valence) titanium, niobium, tantalum and vanadium is formed by fusing together at least one halide of the alkali or alkaline earth metals with 5-50 per cent by weight of a higher valent halide of the polyvalent metal, introducing into the melt the carbide or carbide-monoxide solid solution of said metal or the metal itself in impure form, and heating until all the halide of the polyvalent metal is reduced to a lower valent form, and separating the fused salt bath from any bath insoluble substances. Preferably the polyvalent metal halide is a double fluoride of an alkali metal, the thermal reaction is effected at 800-1200‹ C. and the resultant fused salt bath is electrolysed with a carbon anode to cathodically deposit the polyvalent metal, the residual salt bath being regenerated with more of the polyvalent metal product. Typically to a salt bath containing 100 parts sodium chloride and 15 parts potassium fluotitanate there is added 10 parts titanium carbide prepared in pellet form as in Specification 778,218 and the mixture is heated under argon to 850‹ C. for 6 hours, cooled to room temperature, the brownishpurplish portion of the salt cake removed and the unreacted carbide lumps separated from the residual salt cake. The salt cake containing the reduced double fluoride is then introduced into a cell which was flushed with argon and then subjected to a pre-electrolysis to remove oxygen impurities as in the abovementioned Specification, followed by electrolysing to deposit titanium using a graphite anode and a steel cathode with a cathode current density of 80 amps./sq. ft. and an applied voltage of 2.2. Alternatively the titanium carbide pellets may be suspended in a graphite basket, the basket with unreacted carbide and free carbon being withdrawn at the end of the heat treatment and the metal electrodeposition being effected with the salt remaining cake in the same container. If the sodium chloride is replaced by a mixture of equal amounts of sodium and potassium chlorides, the electrodeposition bath temperature is 800‹ C. After cooling under argon in a gas-tight chamber in communication with the cell, the titanium deposit is cracked off the cathode, dry mortared and washed with hot dilute hydrogen peroxide solution and decanted repeatedly, wet mortared and repeatedly washed and decanted as before, rinsed in water, covered with concentrated hydrochloric acid, rinsed successively with water and alcohol, air-dried in an oven, and finally melted into an ingot under argon. The fused salt bath is then reacted with further titanium carbide and the cycle of operations is repeated. Succeeding ingots are of lower hardness. Omission of the pre-electrolysis step results in the ingots from the first and second cycles being harder. The same process is applicable to the metals niobium, tantalum and vanadium. Specification 788,295 also is referred to.