GB1134217A - Improved process for the electrodeposition of metals, alloys or compounds thereof from molten electrolytes - Google Patents

Abstract

1,134,217. Electrolytic deposition process using a molten electrolyte. UNION CARBIDE CORP. Dec.2, 1965 [Dec.14, 1964], No.51108/65. Heading C7B. While electrolytically depositing metals, alloys or compounds thereof on a solid cathode using a molten electrolyte, gas above and around the electrolyte surface is heated at least to the liquidus temperature of the electrolyte by heating means separate from the electrolyte heating means. Thereby, temperature differentials within the electrolyte which would normally cause circulation of the electrolyte are minimized and dense, fine grain deposits free from roughness are deposited. Fig. 1 shows resistance heaters 11, 13, a heat shield 12 and thermal insulation 10. Materials which may be deposited are Zr, Hf, V, Nb, Ta, Cr, Mo, W or alloys or compounds thereof, e.g. ZrB 2 . The electrolyte may be an all fluoride melt, other anions being present only as minor impurities. The melt may be composed of a base melt (a) comprising at least one fluoride of K, Rb or Cs and at least one fluoride of other elements higher in the electro-motive series than the metal to be deposited and (b) at least one fluoride of the metal to be deposited. The base melt may be a eutectic composition of LiF, NaF and Kf. The metal fluoride employed may be simple or complex. The electro-deposition is carried out in an inert, non- oxidizing atmosphere such as A, Ne, He, e.g. above or below atmospheric pressure. The cathode may be of stainless steel, graphite, Ni or Cu and may be pre-treated by anodizing. The source of metal to be deposited may be the anode or the electrolyte. Where the anode is the source it may be in the form of rods, plates, rondels or chunks or may be of particulate material in an Ni mesh container. The process may be an electro-winning, electro-refining, electro-plating or electro-forming process. An insoluble, soluble or gaseous anode may be used. Using an insoluble anode, e.g. of graphite, the voltage applied is at least as high as the breakdown potential of the melt but using other anodes, e.g. a gaseous H 2 anode or a soluble anode containing an active metal of Li, Na, K, Mg, Ca or Al the voltage need not be as high. Using an active metal anode the melt may be recirculated through an external station where active metal fluoride formed at the anode is removed and refractory metal fluoride added. Electro-forming may be on an Ni base which is subsequently dissolved in HNO 3 or mechanically removed, on a graphite base which is mechanically removed or on an alloy base which subsequently can be pulled away from the metal. The examples are of plating on to Cu rod: - I Ta, II Nb and III W. Specification 1,007, 930 is referred to.