Patent GB-653117-A (GB)
Title: Method of forming a metallic plate of accurately predetermined shape
IPC: C25D1/06
Filed: 1948-07-12
Abstract: 653,117. Electrolytic production of plates or films. HENROTEAU, F. C. P. July 12, 1948, No. 18718. [A Specification was laid open to inspection under Sect. 91 of the Acts, Jan. 12, 1949.] [Class 41] A method of forming a metallic plate or film of accurately-predetermined shape comprises forming an interface between two liquids, one of which is a copper electrolyte containing also in ionized form gold or silver, and the other is a heavier liquid immiscible with the electrolyte, and applying to the electrolyte a difference of electric potential by a cathode extending through the interface, and by an anode. The predetermined shape may be produced by rotating the immiscible liquids to form a paraboloidal interface, or by changing the level of the interface at a predetermined rate. In the arrangement shown in Fig. 1, a glass tank 10 is provided with two immiscible liquids 14, 15, the liquid 14 comprising a solution of copper sulphate and containing also gold chloride or silver nitrate. The liquid 15 may be carbon tetrachloride. The tank 10 supports a flanged anode 19 and has a top provided with a disc 17 attached to a cathode 16. The tank 10 is secured to a turntable 24 which is rotated at a constant speed so that the interface 13 between the liquids is of the form shown, current being supplied to the electrodes through brushes 18, 22. A mirror forms along the interface starting outwardly from the cathode, the facing against the lower liquid being of silver or gold and the upper or backing surface being of copper. The mirror when finished is removed on disassembling of the apparatus. The mirror is convex, and a concave mirror may be made therefrom by plating on the convex surface and dissolving away the original mirror. In the arrangement shown in Fig. 2, the tank 26 is fixed and the cathode 30 extends up from the base 28 through the interface 29 into the electrolyte 14, being opposite the anode 31. The anode is surrounded by a glass tube 32, the lower end of which is provided with a dialyzer 34 held in place by an elastic band. A coil of wire 49 is immersed in the lower liquid 15, and wire 52 from the coil is wound on a drum 53 adjusted to be rotated by a synchronous alternating current motor 56. The motor is connected to a source of current by a switching mechanism comprising a drum 57 of electrically-conducting material driven through gearing and an insulating coupling 59 by a synchronous alternating current motor 60. The drum shaft 58 drives through gearing 68 of insulating material a screw 67, by means of which a contact 66 is drawn across the drum 57. Part of the drum is covered with insulating material 70 with a curved edge 71. While the contact 66 engages the uncovered part of the. drum, the circuit is completed for the motor 56 whereby the wire 52 is drawn from the coil 49 and the interface 29 is lowered. The extent to which the interface is lowered is determined by the shape of the curve 71. The drum shaft 58 is connected through an insulating coupling 74 to a drum 76 of conducting material, the surface of which is partly covered with insulating material 77. Brushes 78, 80 bear respectively against the surface of the drum 76 and its shaft, and the brushes are connected to a source of direct current 81 used for the electrolytic process. The arrangement is such that the process is only in operation while the liquids are completely at rest. During the process the electrolyte is filtered by vacuum applied to the top of a vessel 43, the liquid circulating through siphons 48, 39, pipe 41 with air inlet 42, pipe 45, and a filter 46. In a further arrangement, the anode is caused to travel in a spiral path with respect to the vertical axis of the cathode, the anode moving outwardly at a rate corresponding to the outward growth of the cathode. The anode is surrounded by a narrow glass tube so that only the tip of the anode protrudes into the electrolyte. Instead of a wire, a triangular sheet of material, for example, celluloid, is drawn from a coil immersed in the lower liquid, whereby the interface between the liquids is lowered. The resultant metallic plate has a concave reflecting surface. A convex surface could be provided by adding, instead of withdrawing, the wire or triangular sheet to the coil immersed in the lower liquid.