Extractive Metallurgy of Zirconium by the Electrolysis of Fused Salts

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Abstract
Radioactive cobalt and lead ions in solution have been used to study the distribution of local cathodes on aluminum alloy specimens which were actively pitting, and to study the processes of film breakdown and repair on aluminum alloy specimens after introducing them into a corrosive environment. In the study of pitting, radioactive ions were introduced into the solution after pitting of the sample had proceeded for a predetermined length of time. The tracer was then permitted to plate out onto local cathodes, and, after washing and drying, autoradiographs of the surface were prepared. Results indicate that after a pit is a few hours old it is surrounded by a ring of cathodic surface and outside this is an annular ring of passive surface which prevents lateral expansion of the corrosive attack, the remainder of the surface being cathodic. In the study of the mechanism of film breakdown and repair, samples with different surface treatments were placed in the solution and radioactive ions were introduced after various predetermined times, exchange permitted to take place, samples washed and dried, and autoradiographs prepared of the surface. Results indicate that, on contact with the solution, the surface oxide film breaks down and is then repaired by reaction with the solution.

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