GB348919A - Improvements in and relating to the electro deposition of metals and alloys of the platinum group - Google Patents

Abstract

348,919. Electrolysis. TRIGGS, W. W., 57, Lincoln's Inn Fields, London.- (Baker & Co., Inc. ; 54, Austin Street, Newark, New Jersey, U.S.A.) June 13, 1930, No. 18147. [Class 41.] Platinum, palladium and rhodium and their alloys with one another are deposited from solutions of their ammino-nitrites, rendered alkaline by excess of ammonia. The electrolyte may be prepared by adding excess of sodium nitrite to a solution of a suitable salt such as chloro-platinic acid, palladous chloride or rhodium trichloride and heating until a colour change takes place after which ammonia is added to the hot solution. When dilute solutions are employed the amminonitrate remains in solution probably as tetramminonitrate. When concentrated solutions are employed a diammino-nitrate is precipitated; this is filtered off, washed and dried, and may be dissolved in hot dilute ammonia. A solution prepared in either way may be used as electrolyte, but in the latter case the addition of a conducting salt such as ammonium nitrate or ammonium sulphate is necessary. In the former case the spent electrolyte should be regenerated by addition of the precipitated salt to prevent excessive accumulation of alkali metal chloride. Detailed examples of the preparation of a platinum bath in both ways are given and also of a bath for depositing an alloy containing 90 per cent. platinum and 10 per cent rhodium. Deposition is effected from a hot solution using a voltage of 2-6. Insoluble anodes of platinum or other precious metal or of graphite are employed. The electrolyte may contain ¢-10 oz. of plating salt per gallon.