GB926724A - Electrolytic process for the preparation of pure metals in compact form and an apparatus for carrying out the process - Google Patents

Abstract

926,724. Dense cathode electrodeposits in fused halide electrolysis. EUROPEAN ATOMIC ENERGY COMMUNITY (EURATOM). Dec. 28, 1961 [Dec. 28, 1960], No. 46528/61. Class 41. Pure metals are electrodeposited in compact form from salt melts characterized in that during the electrolytic precipitation, under non- oxidizing conditions, the formation of a dendritic structure is inhibited by repeated application of mechanical pressure to the deposit surface. The mechanical pressure is adjustable and is applied continuously progressively and positively over the whole surface of the exposed cathode and the electrode rotates. As an illustration, Fig. 1 shows anode crucible 1 of graphite containing fused salts 2 and cathode 3 with cathode equipment mounted centrally. The fused electrolyte, e.g. alkali chloride mixture plus fluoride or chloride of metal required, is electrolytically decomposed to deposit the metal on the cathode which should be fabricated from the same metal. For example, tantalum can be deposited on a tantalum cathode from an alkali chloride mixture containing 10-20% of K 2 TaF 7 or TaCl 5 . Cathode 3, immersed in a fixed position relative to the fused salt electrolyte, is reversibly rotated through shaft 5 by reversible motor 4. Coupling shaft 5 has a screw-thread 6 engaging with collar 7 which is continually reversibly driven to and fro up and down the length of the screw thread for the distance required thereon to correspond with the depth of immersion of the cathode. Collar 7 carried levers 9 via supports 8. Pressing rollers 10 which engage the cathode deposit to perform the object of the invention are secured to and controlled by levers 9. The operating pressure can be varied through the agency of hydraulic ram 11. The moving structure and rotating electrode is held rigid by framework 12. A single treatment cycle, namely an upward and downward travel of the rollers 10 should last for not more than from 1-2 minutes depending upon the amperage and cathode surface. The cathode equipment must be of high-temperature and corrosion-resistant alloy steels coated with sprayedon ceramic insulation of alumina, silicates or the like; conveniently the rollers are of highly refractory and insoluble materials such as borides, carbides, nitrides or oxides which also ensure the required electrical insulation. The process and apparatus of the invention can also be used for purifying impure metal, which is introduced anodically by scattering the impure metal, e.g. tantalum, over the base of the graphite crucible to act as soluble anode material. The invention is applicable to metals which are plastically deformable at temperatures below the associated temperature of their electrolytic salt melt such as thorium, plutonium, uranium, titanium, niobium, zirconium, hafnium, beryllium, the rare earth elements and tantalum.