Abstract
The change of the surface state of iron during corrosion in sulfuric acid solution was investigated by using an ellipsometer in the presence and absence of stannous ions.
No optically stationary state of surface was observed for corroding iron in the solution. To obtain reproducibility, electropolishing followed by electrochemical polarization appeared to be the best surface treatment for the optical investigation.
Results of ellipsometric measurements indicate that during immersion of iron in the solution an absorbing film was formed on the surface without appreciable change of the electrode potential. In 1hour immersion the film grew up to about 150Å, which was assumed to be a kind of precipitated solid film.
When stannous ions were added, the surface state of iron changed slowly to the optically reverse direction and reached a steady state, while the potential initially rose rapidly to a noble value and then fell gradually. This can be explained by assuming some structural change of the film resulting in the formation of an iron-tin compound leading to the inhibition of iron corrosion.
