Behavior of hydrated Cr oxide film formed by electrolytic reduction in chromic acid bath investigated by means of tracer technics

The behavior of the hydrated chromium oxide film formed on the steel surface during galvanostatic electrolysis for a few seconds in an electrolyte consisting of 50g/l of chromic acid and 0.5g/l of sulfuric acid was investigated by means of tracer technics using radioactive Cr (51Cr).The results obtained were as follows:1) In the intermittent electrolysis, the film formed in the early stage of electrolysis did not act as intermediate for deposition of metallic chromium.2) The formation simultaneous with dissolution of the film took place during the electrolysis.3) The true quantity of the film linearly increased with the progress of electrolysis time, but its value measured increased exponentially, because a part of the film was exponentially dissolved in the electrolyte.The measured value of the film quantity (m) after galvanostatic electrolysis for t seconds was shown by the following equation:m=A/B(1-e-Bt)where A and B are constantsTherefore, it was suggested that the thickness of the film would develop to a certain limit.