GB436282A - Method of removing galvanic or electrolytic deposits of metal from a cathode - Google Patents

Abstract

436,282. Removing electrolytic deposits. EVANS, W. E., 27, Chancery Lane, London.-(Kelaen Special Sheet Holding Soc. Anon.; 33, Konigring, Luxemburg) Jan. 9, 1934, No. 22321 /33. [A Specification was laid open to inspection under Sect. 91 of the Acts, Feb. 10, 1934.] [Class 41] Electrolytic deposits of metal are loosened from cathodes by dissolving the metal on particular surfaces or along particular lines as desired, the solvent selected being one which reacts with the deposit but does not attack the cathode, for example, an acidic oxidizing agent or an acid. The cathode may be made of material passive in the presence of acidic oxidizing agents. For example, chromium steels, and steels which in addition to chromium contain nickel, may be used as cathodes, and copper deposited thereon can be removed with dilute nitric acid or sulphuric acid. Metal films soluble in dilute sulphuric acid can be removed from lead, zinc films on iron can be removed by alkaline solutions, or rare metals such as platinum or carbon or substances containing carbon can be used as cathode material when solvents to which they are resistant are employed. Only those parts of the cathode from which the deposit is to be loosened need be formed of the resistant material. In depositing the metal, means may be used to ensure that the deposit is thinner at the places where loosening is to be effected. For example, a cathode may be arranged between two parallel anodes, the form of the cathode being such, by reason of being tapered towards or provided with channels or recesses at the edges where the deposit is to be dissolved, that the distance from the anodes is greater at these places and the deposits correspondingly thinner. Alternatively, screens may be used to ensure thinner deposits at the edges of the cathode. If steels passive in the presence of acidic oxidizing agents such as mixtures of nitric and sulphuric acids are used as base materials, it is unnecessary to keep on supplying fresh oxidizing agents. Thus instead of nitric acid or a mixture of sulphuric and nitric acids, a mixture of sulphuric acid and sodium nitrate may be used, only the sulphuric acid being renewed and the sodium sulphate removed by crystallization. The method can be used with or without the provision of separating sheets between the cathode base and the deposit.