1971 Volume 22 Issue 8 Pages 404-408
The oxide films formed on aluminum in acids were investigated by means of the apparatus consisting of a potentiostat and a high sensitive recorder.
The results obtained were summarized as follows:
1) When the set potential was maintained at-0.3V vs. S.C.E. in sulfuric acid, two straight lines having different slopes were obtained in the following two periods; from O to 1.5 and from 1.5 to 12sec. The above facts suggested the formation of oxide films by ionic conduction and the film obtained in the latter period was considerably more compact than that in the former period.
2) When the set potential was OV, the formation of oxide film by ionic conduction was continued for 6sec.
The oxide film was soon converted into a compart insulating film and the anode current was increased with the lapse of time, which represented that the dissolution of the oxide film took place.
3) When the set potential was above OV, an electrochemical process virtually similar to 2) was observed.
4) In hydrochloric acid, the anode current rapidly flowed at a potential higher than spontaneous electrode potential.
When hydrochloric acid was used as an electrolyte, the film was not formed at all and aluminum seemed to be dissolved in proportion to the passing of anode current. As for the corrosion, pits were produced over the whole surface.
