GB880794A - Process for the production of metallic niobium or tantalum by an electrolytic method - Google Patents

Abstract

880,794. Electrodeposition of niobium and tantalum. CIBA Ltd. Aug. 11, 1958 [Aug. 9, 1957], No. 25783/58. Class 41. In a process for the production of metallic niobium or tantalum by the electrolysis of a melt, the vapour of the pentachloride of the metal is introduced into an oxygen-free melt consisting of an alkaline earth metal chloride and/or alkali metal chloride and an alkaline earth metal fluoride or alkali metal fluoride and is electrolysed at an anodic current density below the critical value for occurrence of the anode effect given by the fluoride content in the melt, and the pentachloride vapour is continuously introduced into the melt during electrolysis at a rate stoichiometrically related to the effective current, and during the electrolysis the rate of supply of pentachloride vapour maintains a constant content of metal in the bath and by being related to the fluoride concentration of the melt retains a part of the alkaline earth metal fluoride or alkali earth metal fluoride in the melt as such. Preferably the current density is adjusted to be, at most, equal to the figure given by the formula amps./dm<SP>2</SP>, where e is the base of natural logarithms, A is the percentage of free fluoride in the melt, and T is the temperature in degrees Centigrade. In an example there was used a cell consisting of a graphite crucible which also served as the anode. The cathode was a nickel rod dipping into the middle of the electrolyte in the crucible. The cathode was surrounded by a graphite tube which also served as a conduit for introducing the pentachloride vapour. The cell was externally heated. The electrolyte comprised a fused mixture of sodium chloride, potassium chloride and potassium fluoride maintained at a temperature of 750‹ C. Tantalum pentachloride vapour was introduced into the melt which was electrolysed with a current of 60 amperes. After the electrolysis the space above the electrolyte was scavenged with argon and the cathode was withdrawn. A further example is given of the production of niobium using a similar fused salt melt and a third example refers to the production of tantalum from a melt composed of sodium chloride, potassium chloride and barium fluoride. Specifications 734,094 and 873,844 are referred to.