GB576144A - Improvements relating to the production of nickel or cobalt in the form of flake - Google Patents

Abstract

576,144. Pigments. MOND NICKEL CO., Ltd. April 25, 1944, No. 7731. Convention date, May 17, 1943. Drawings to Specification. [Class 95] [Also in Groups XXII and XXXVI] Nickel and cobalt are deposited electrolytically in a laminated form which can easily be stripped from the cathode and reduced to flakes suitable for use as a pigment. Nickel in the required form is produced by a deposition from an electrolyte containing from 0.2 to 0.31 gram of thiourea per litre. A cobalt bath requires 0.4 to 0.6 gram thiourea per litre. Metals suitable for the cathode are aluminium, tantalum, and nickel-chromium-iron alloys, nickel or chromium or insoluble metals being used for the anode. In an example the electrolyte consists of a solution of nickel sulphate, nickel chloride and boric acid, to each litre of which 0.2 to 0.31 gram of thiourea is added, the deposition taking place at 45 to 65‹C. with a current density of 9 to 30 amps. per square foot. though currents up to 100 amps. per square foot may be employed. The deposited metal may be built up to a thickness of 0.03 inch or more and is readily stripped from the cathode and easily split into thin layers. The thiourea in the electrolyte is destroyed at a rate varying from 0.01 to 0.04 gram per ampre hour and must be replaced as the electrolysis proceeds. Most of the sulphur is plated out with the metal but some is deposited on the anode. The nitrogen goes into solution to form ammonium salts which may be crystallized out. When the bath ceases to produce a satisfactory deposit of nickel it may be purified by the addition of hydrogen peroxide and filtered. Thinner laminations of the deposited metal may be produced by making sudden variations in the current such. as interruptions, reversals and momentary large currents. In order to reduce the deposit to flake form it is stripped from the cathode and subjected to impact for twenty hours or more and then ground in a ball mill for about ninety hours. The thickness of the flakes can be further reduced by treating the laminated deposit with a weak solvent before grinding. Dilute sulphuric acid may be used for this purpose and the treatment may continue for 100 hours. An alternative preliminary treatment consists in heating the metal in a reducing atmosphere at a temperature of 1,100‹F. Before grinding, the metal may be sheared into pieces of 0.75 inch square. The pieces are fed to the ball mill with an equal weight of a petroleum product known as varnolene, 1 per cent, of stearic acid and 1 per cent. of aluminium stearate.