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Platinum Metals Rev., 1971, 15, (2), 57

The Electrodeposition of Rhodium on Titanium

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The protection of titanium by a thin coating of platinum is well known in chemical technology but, although platinised titanium anodes are commonly used for industrial electrochemical purposes, little attention has been given to titanium coated with other platinum group metals.

A recent paper by K. P. Batashev and V. P. Zverev (Tr. Leningrad. Politekh. Inst., 1970, (304), 130–134) now reports on studies by the polarisation curve method of the electrodeposition of rhodium on titanium and indicates the feasibility of such plating. It can produce both protective and decorative coatings and also insoluble rhodium/titanium anodes. The features of rhodium for these purposes are its lesser density and greater hardness than platinum.

Titanium alloys were degreased chemically and then were etched in sulphuric acid solution at 60 to 90°C before plating in a bath containing 1.2 to 2.0 g/l rhodium and 40 to 50 g/l sulphuric acid at current densities between 0.1 and 1.5 A/dm2 and at temperatures between 20 and 75°C. Insoluble anodes of platinum and rhodium-plated titanium were used and efficiency increased with lower current density and higher bath temperature.

The rhodium coatings obtained at low current density adhered well and were satisfactory as regards hardness, reflectivity (brightness) and corrosion resistance. Tests were carried out to determine the properties, strength and optimum thickness of rhodium coatings on insoluble titanium anodes.

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