Study on the Stainless Steel with Photo Induced Self Healing Ability

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Photo electrochemical response has been applied as a poweful in-situ characterization technique for the passive film on the metals and alloys. However, the effect of the light exposure on the corrosion behavior has been open to discussion. In this study, Type304 stainless steel immersed in 3.5% NaCl was exposed with ultra-violet light to improve pitting corrosion resistance in the same media. uv light of 325 nm in wave-length generated by He-Cd laser was used as light source with output power of 35 mW and the exposure area of 6 mm in diameter. The pitting potential, which is an index for pitting corrosion resistance, was shifted for about 80 mV after uv light exposure during film formation period prior to pitting corrosion test. The improvement of pitting corrosion resistance depends on the light intensity. In the range of the light available in this study, a most suitable intensity was observed.The pitting corrosion induction period at a constant applied potential was also measured and analyzed with the birth and death stochastic probability process for various applied potentials to obtain the generation and repassivation rate of pitting corrosion. The generation rate, gamma, was lowered by a factor about 6 after exposure of uv light during passivation. On the other hand, the uv exposure during pitting corrosion generation period leads to almost no change on mu, the repassivation rate. The exposure during pitting corrosion generation affects only very small improvement on lambda and mu.The X-ray photo electron spectroscopy revealed that the chromium in the passive film, which is known to improve the corrosion resistant of stainless steels, is enriched after an exposure of uv light. Therefore the uv exposure was confirmed to improve the self healing ability of stainless steel, which is obtained by chromium enrichment in the film.