抄録
Lead alloy electrode which contains noble metals such as silver is used as the anode for cathodic protection in sea water, but the mechanism of formation of the anti-corrosive film is not known as yet.
In the previous reports, the author studied stationary polarization curves of lead, silver, etc. with a potentiostat in order to investigate the film formed on the anode in relatively short time. However, for fast electrode reaction in which several kinds of surface films are formed at high velocity, detailed study on the film formation can not be made by the stationary polarization measurement method heretofore in use. Therefore, the potential sweep method was adopted to observe the anodic polarization curves of Pb, Sb and Sn in sodium sulfate and sodium chloride solutions, and the mechanism of formation of the anti-corrosive film on the surface of these metals was investigated.
The results obtained are as follows:
(1) The anti-corrosive films formed in sodium sulfate solution are α-PbO2 and β-PbO2 in case of lead, Sb2O3, Sb2O4 and Sb2O5 in case of antimony, and SnO2 in case of tin.
(2) The anti-corrosive films formed in sodium chloride solution are lead chloride in case of lead, antimony oxide in case of antimony, and tin chloride in case of tin.
(3) Chloride film is reduced at less noble potential than the spontaneous potential.
(4) Reduction of chloride film is more difficult than that of oxide film.
