GB811862A - Improvements in the electrolytic production of titanium - Google Patents

Abstract

811,862. Electrolytic production of titanium. NEW JERSEY ZINC CO. April 3, 1956 [May 5, 1955], No. 10143/56. Class 41. In the production of titanium by electrolysis of a fused bath formed of one or more of alkali metal halides, alkaline earth metal fluorides and alkali metal fluotitanates to which is added a decomposable titanium compound, the bath being contained in a two-compartment cell divided by a perforated electrically-conductive structure, the structure is made negative to the anode and the current between is adjusted to deposit titanium on the structure until the degree of permeability required to serve as the porous barrier during cathodic deposition of titanium has been obtained, whereafter the currents flowing between anode, barrier, and cathode are controlled so that titanium is cathodically deposited while maintaining the porous titanium deposit forming the porous barrier. The perforated structure may be a drilled plate or a screen and may be of nickel or its corrosion-resistant base alloys, stainless steel, or molybdenum. A suitable cell comprises a central cylindrical graphite anode within a cup-shaped diaphragm of calendered nickel wire cloth having an impervious nickel sheet bottom and connected at its upper edge to a graphite tube serving as a vent for anodically evolved gas, the cup wall being surrounded by a cylindrical band iron-nickel cathode, all disposed concentrically within a container of the same material as the cathode. The cell is filled to just above the rim of the cup with a eutectic mixture of lithium, potassium, and sodium chlorides and titanium tetrachloride is fed to the cathode compartment. The cell may be operated at 550‹ C. in four stages, in the first of which titanium is deposited on the cup to form the porous barrier, in the second stage the rate of addition of titanium tetrachloride is increased to build up a desired concentration of lower titanium chlorides (e.g. the dichloride) in the catholyte, cathodic deposition of titanium with simultaneous addition of titanium tetrachloride being effected in the third stage while this addition is stopped in the fourth stage to allow stripping of the titanium compounds from the bath. At the end of this the cup and anode assembly and the cathode are raised from the bath to drain off the salt and when the cell has cooled to bring the cathode deposit to 200-250‹ C. the cathode cup and anode are removed from the cell. Typically the bulk of the cathode deposit has a particle size of above 44Á. and an ingot prepared from it has a Rockwell A hardness of 35. In operating the cell the chief guides in the necessary control of the current are the escape of titanium tetrachloride with the anodically evolved chlorine, indicating that the porous barrier is insufficiently impervious to the flow of electrolyte, and the back voltage developed.