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Konishi, Hiroyuki; Yamashita, Masato*; Uchida, Hitoshi*; Mizuki, Junichiro
Materials Transactions, 46(2), p.329 - 336, 2005/02
Times Cited Count：28 Percentile：80.32(Materials Science, Multidisciplinary)Chloride in atmosphere considerably reduces the corrosion resistance of conventional weathering steel containing a small amount of Cr. Ni is an effective anticorrosive element for improving the corrosion resistance of steel in a Cl-rich environment. In order to clarify the structure of the protective rust layer of weathering steel, Cl and Fe K-edge X-ray absorption near edge structure (XANES) spectra of atmospheric corrosion products (rust) formed on Fe, Fe-Ni and Fe-Cr alloys exposed to Cl-rich atmosphere were measured. The Fe K-XANES measurements enable the characterization of a mixture of iron oxides such as rust. The chemical composition of the rust was determined by performing pattern fitting of the measured spectra. All the rust is composed mainly of goethite, akagan
ite, lepidocrocite and magnetite. Among these iron oxides, akaganite in particular is the major component in the rust. Additionally, the amount of akaganite in the rust of Fe-Ni alloy is much greater than that in rust of Fe-Cr alloy. Akaganite is generally considered to facilitate the corrosion of steel, but our results indicate that akaganite in the rust of Fe-Ni alloy is quantitatively different from that in rust of Fe-Cr alloy and does not facilitate the corrosion of steel. The shoulder peak observed in Cl K-XANES spectra reveals that the rust contains a chloride other than akaganite. The energy of the shoulder peak does not correspond to that of any well-known chlorides. In the measured spectra, there is no proof that Cl, by combining with the alloying element, inhibits the alloying element from acting in corrosion resistance. The shoulder peak appears only when the content of the alloying element is lower than a certain value. This suggests that the generation of the unidentified chloride is related to the corrosion rate of steel.
Konishi, Hiroyuki; Yamashita, Masato*; Uchida, Hitoshi*; Mizuki, Junichiro
Materials Transactions, 45(12), p.3356 - 3359, 2004/12
Times Cited Count：10 Percentile：53.05(Materials Science, Multidisciplinary)Cl K-edge XANES measurements of atmospheric corrosion products (rust) formed on Fe, Fe-Ni and Fe-Cr alloys in chloride pollution have been performed using synchrotron radiation in order to clarify roles of anticorrosive alloying elements and of Cl in the corrosion resistance of weathering steel. The spectra of binary alloys show a shoulder structure near the absorption edge. The intensity of the shoulder peak depends on the kind and amount of the alloying element, whereas the energy position is invariant. This indicates that Cl is not combined directly with alloying elements in the rust.
Otani, Kyohei; Tsukada, Takashi; Terakado, Hiroshi*; Ebata, Koei*; Ueno, Fumiyoshi
no journal, ,
Inner components of the primary containment vessels (PCVs) in Fukushima Daiichi Nuclear Power Station was observed by remote-controlled robots and the observation showed that carbon steels of the PCVs wall above the contaminated water level was exposed to an air-solution alternating condition. Previous studies have reported that the corrosion rate of carbon steel is accelerated in case of the steel with thin water film exposed in air under the dry/wet condition. This suggests that the corrosion rate of carbon steel will be accelerated in the air-solution alternating condition. However, the corrosion rate of the steel on the corrosion tests which simulated the air-solution alternating condition has not been clarified. In the present study, a novel corrosion test of carbon steel which simulated the air-solution alternating condition was carried out. In order to simulate the alternating condition in the novel corrosion test, the carbon steel was alternately exposed to air and solution by rotating in a water tank which was not completely filled with solution. The surface observations showed that the rust layer formed on the steel after the tests in the alternating condition was thicker than that of the steel rotated always in solution. The mass loss measurements showed that the corrosion rate of carbon steel in the alternating condition was more than three times larger than that of the steel rotated always in solution. A thin water film was confirmed on the steel when the specimen exposed to the air during the tests. It has been reported that the mass transfer of dissolved oxygen to the carbon steel surface is accelerated in case of the carbon steel covered by a thin water film and corrosion of carbon steel is accelerated by the acceleration of oxygen reduction reaction (cathodic reaction). This suggests that the accelerated corrosion of the steel in the alternating condition would be caused by the thin water film on the steel during the tests.
