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Platinum Metals Rev., 1959, 3, (1), 8

Platinum Plating of Zirconium

Protection From Corrosion Under Irradiation Conditions

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Studies on the use of zirconium and its alloys for the construction of spherical shells for a homogeneous reactor at Oak Ridge National Laboratory have shown that these materials corrode slowly in uranyl sulphate solutions of pH 1.7 to 2.5 in the temperature range 250 to 350°C under irradiation conditions. It was thought that a platinum cladding would be sufficiently resistant in these conditions and an investigation was therefore carried out at Battelle Memorial Institute. The results of this study are reported by A. B. Tripler, J. G. Beach and C. L. Faust in the U.S. Atomic Energy Report No. BMI-1097.

Mechanical cladding was temporarily ruled out because of the brittle alloy phase which forms at cladding temperatures and electro-deposition was therefore investigated. It was essential that the deposit should be adherent, continuous and impervious, should resist corrosion under irradiation and should not exceed the thermal neutron capture cross section equivalent to 0.25 inch of zirconium.

A diammino-nitrite bath was used, containing 6 g platinum in 750 ml, with platinum foil anodes. Preliminary plating tests on nickel showed a continuous D.C. method to give an unsatisfactory deposit. A periodic reverse technique was therefore employed. After establishing optimum conditions of current density and time cycle, dense lustrous deposits were obtained up to 0.0015 inch in thickness.

With a satisfactory method of deposition established, plating of zirconium was undertaken. Studies were made of duplex plates of 0.0005 to 0.00075 inch platinum over 0.001 inch nickel, diffusion bonded to the zirconium, and of deposits of 0.0005 inch platinum directly on to zirconium. Both types were found to be adherent and resistant to corrosion, but microscopic examination showed that the platinum on nickel deposit was much smoother than the direct platinum deposit.

On the basis of these results a procedure involving periodic reverse platinum plating over diffusion bonded nickel was used for the preparation of specimens sent to Oak Ridge for in-pile testing. If necessary, the thickness of platinum could be increased.

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