抄録
The incorporation of sulfate radical into the hydrated Cr oxide film formed on the steel surface during the galvanostatic electrolysis for a few seconds in the electrolyte, being composed of 50g/l of chromic acid and a small amount of sulfuric acid, was investigated by the tracer technics using radioactive sulfur (35S).
The results obtained were as follows:
(1) The incorporation of sulfate radical into the hydrated Cr oxide film and its dissolution concurrently occurred during the electrolysis in the same way as the behavior of the hydrated Cr oxide film.
(2) The amount of sulfate radical (m) measured in the hydrated Cr oxide film after t sec. of galvanostatic electrolysis was shown by the following equation:
m=A′/B′(1-e-B′t)
Where A′: Rate constant of the incorporation of sulfate radical
B′: Rate constant of its dissolution
(3) The amount of sulfate radical in the hydrated Cr oxide film increased with the increases in the applied current density and the concentration of sulfate ion in the electrolyte. The drop of the electrolyte temperature led to increase of sulfate radical incorporated in the hydrated Cr oxide film.
(4) Most (90-95%) of sulfate radical incorporated in the hydrated Cr oxide film was present as water soluble.
(5) Molar ratio (oxide Cr/SO4-2) in the hydrated Cr oxide film slightly decreased with the time of electrolysis, and then, became almost constant (3-5) after 10-20sec. of electrolysis.
(6) The conditions of electrolysis for obtaining higher current efficiency in metallic Cr deposition almost corresponded with those for the formation of thicker hydrated Cr oxide film and the incorporation of much greater amount of sulfate radical in the hydrated Cr oxide film.
