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The reaction of copper-gold alloys in aqueous ammonia under oxygen pressure Fisher, James Irwin

Abstract

An investigation was conducted of the corrosion of copper-gold alloys in ammonia solutions under oxygen pressure. The reaction, which took place in an autoclave, was followed by sampling and analysis of the solutions. It was found that only copper was dissolved from the alloys, the gold being left behind in a film on the surface of the corroding specimen. The reaction of pure copper as well as of four alloys ranging in gold content from 2 to 15 atomic percent were studied. Other variables examined include the concentrations of NH₃ and NH⁺₄ in the solution, the oxygen pressure and the temperature. It was found that while the rate curves for the dissolution of pure copper were linear, those for the alloys were generally parabolic in shape. The rate of dissolution of copper from the alloys appears to be determined by the transport of reactants and products through the gold rich films. Some copper oxide may also be precipitated in the pores of the film or in the region between the film and the underlying metal, further impeding the transport processes and contributing to the lowering of the rate.

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