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Platinum Metals Rev., 1958, 2, (2), 60

Iridium Electrodeposits from a Molten Salt Bath

High Temperature Oxidation Resistance

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The high temperature strength of molybdenum would make it a most attractive constructional material for a number of components in jet engines and missiles were it not for the very severe oxidation which occurs when this metal is heated in air; the search for a reliable method of protecting molybdenum from oxidation has therefore become one of the most vigorously pursued of metallurgical studies.

An unusual approach to this problem was reported to the American Electroplaters’ Society Convention held last year in Montreal and is now published in the Society’s Forty-fourth Annual Technical Proceedings. This paper, presented by James C. Withers and Dr. Paul E. Ritt of Melspar Inc., Falls Church, Virginia, under the title “Iridium Plating and its High Temperature Oxidation Resistance”, describes a study of the electrodeposition of iridium from a molten mixture of sodium and potassium cyanides. Iridium complexes, probably K2Ir(CN)6 and Na2Ir(CN)6, were first formed in the bath by electrolysis at 500°C with alternating current, and plating was then carried out with direct current at 600°C. An iridium concentration of 400 to 500 mg per 100 gm of fused salt gave good fine grained deposits at current densities of 10 to 20 amp./sq. ft.

Iridium deposits only 0.0005 inch in thickness were found to give a considerable degree of protection from oxidation to molybdenum exposed at 1000°C for 30 minutes. This leads the authors to conclude that thicker deposits of iridium might well offer complete protection to molybdenum at high temperatures.

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