The mechanical properties of materials often decrease due to corrosion. For example, stress corrosion cracking (SCC) is one of the major issues in this problem, because it is difficult to estimate the remaining life of the materials by SCC. A tarnish film is usually created on the surface of copper during corrosion. SCC for pure copper is attributed to the film. In this study, an attention is paid to the growth of the tarnish film. The specimens used were made of pure copper annealed in a vacuum, and were corroded in 1.0kmol·m-3 NaNO2 solution up to 100ksec. The experiments were conducted by immersing the specimen in the solution under two different conditions: One at free corrosion and another at several electrode potentials. The brightness of specimen surface changed with corrosion. The film was observed by using a CCD camera; the distribution and the extension of the corrosion were examined by using an image processing technique (IPT). A fractal analysis was applied and the applicability of the fractal analysis was investigated. The fractal dimension was effective to evaluate the corrosion stage of pure copper. The results obtained in this study are summarized as follows:
(1) Change in average brightness of images against the immersion time occurred at each point of the more anodic electrode potentials. The brightness values measured by IPT showed the corrosion stage of pure copper.
(2) The extension of the corrosion state of pure copper showed fractal characteristics at every electrode potential in the present experimental conditions. The fractal dimension of Dark OR image measured by Box counting method showed remarkable change at the current density corresponding the range of the repassivation potential.