NaOH水溶液中での電解着色ステンレス鋼の表面組成と耐食性

概要

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A coloring treatment has been applied to SUS 430 and SUS 304 stainless steels by anodizing in 5kmol m-3 NaOH solution. XPS and AES analysis were used to measure the chemical state of the constituents of the color film and composition-depth profiles of the film. Corrosion resistances were estimated by the interfacial impedance method for the stainless steels colored at 298K in 0.1kmol m-3 H2SO4, and at 353K in 20kmol m-3 NaOH. SEM photographs showed some porous surface structures in SUS 430 and SUS 304 polarized at -0.05V for 1h. XPS analysis showed that Cr on the film surface was depleted with increases in polarization time or in applied potential. Films formed on SUS 430 at the transpassive potential (about -0.25V) were Cr-rich and the film became Cr-deficient at more nobler potentials. It can be explained by an increase in the transpassive reaction rate for the Cr component on the surface with increasing applied potential. Since Ni dose not dissolve readily in alkaline solution, its concentration in films on SUS 304 was high. The time during which high interfacial impedance occurred in 298K, 0.1kmol m-3 H2SO4 a and 353K, 20kmol m-3 NaOH solutions increased with increases in polarization time or potential. This is thought to be during to the thicker surface films, giving rise to a higher corrosion resistance for SUS 430 and SUS 304 stainless steels.
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