GB178422A - Process of rust-proofing by coating with cadmium - Google Patents

Abstract

178,422. Udylite Process Co., (Assignees of Wissler, W. A., and Humphries, C. H.). April 9, 1921, [Convention date]. Cadmium, depositing; treating after deposition. -Wires, rods, spring strips and other articles of iron, steel or other metal are provided with a rust-resisting coating of cadmium by electrolysis of a basic or neutral solution of the cvanide using an anode of graphite, carbon or other insoluble and non-polarizing material. The articles are then washed and baked for some hours at a temperature of 150‹ C. to 200‹ C., or up to 250‹ C. if embedded in calcium hydroxide. They may be further plated with another metal such as nickel, after being cleaned with dilute sulphuric acid or cyanide solution. The electrolyte may contain from 1.25 to 15 per cent of cadmium and from 1 to 25 per cent of sodium cyanide. It is preferably prepared by first dissolving 25 gms. of metallic cadmium in hydrochloric acid to form a neutral solution or a corresponding quantity of the sulphate or chloride in water. If nitric acid is used to dissolve the cadmium, the solution is evaporated to dryness with hydrochloric acid. A solution of sodium or potassium hydroxide is added to the neutral solution until all the cadmium is precipitated and the solution is red to phenol phthalein. Sodium or potassium cyanide is then added until the cadmium hydroxide is redissolved. A slight excess of free cyanide is allowable. The solution is then diluted to the litre. The strength of the solution is maintained constant by adding cadmium hydrate. With an electrolyte containing 10.5 per cent of cadmium, current densities of 25 to 290 amperes per sq. ft. may be used. The articles may be pickled in single or mixed acids, washed, and scratchbrushed, before plating.