The galvanic behavior of an illuminated rutile-type TiO
2 and iron couple and the corrosion mass loss of the iron under the formation of this galvanic cell were investigated as a function of the hydrogen ion concentration in the aqueous solution. The rutile-type TiO
2 with the form of film was formed by a high-temperature oxidation and then was reduced by a high-temperature hydrogen gas. The rest potential of the TiO
2 fell due to the light irradiation. This drop increased with an increase in temperature of hydrogen reduction. The drop of the rest potential with light irradiation for the TiO
2 reduced at 1173 K increased with an increase in solution pH in the aqueous solutions of pH higher than 10. In these solutions, as a result, the rest potential of the TiO
2 was lower than that of the iron. When the illuminated TiO
2 was in contact with the iron in the aqueous solutions of 10∼12 pH, the cathodic current passed for the iron. This current increased with an increase in the solution pH. It was found that this reason was due to that the photo-anodic current for the TiO
2 increased with an increase in the solution pH. The corrosion mass loss of the iron under the formation of galvanic cell with the illuminated TiO
2 was lower than that of the iron under the formation of galvanic cell with no illuminated TiO
2 and that of the no galvanized iron. Further, the corrosion mass loss of the iron under the formation of galvanic cell with the illuminated TiO
2 decreased with an increase in the ratio of surface area of the TiO
2 to the iron.
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