Introduction of Cu to the inside of the crevice by chelation and its effect on crevice corrosion of Type 316L stainless steel

Aoyama, Takahito; Kato, Chiaki

Corrosion Science, 210(2), p.110850_1 - 110850_10, 2023/01

https://doi.org/10.1016/j.corsci.2022.110850

The chelated complex of Cu: [Cu(EDTA)] was used to introduce Cu from outside to the inside of crevice. The introduced Cu was expected to act as an inhibitor for the crevice corrosion on stainless steels. Crevice corrosion tests, confirmed the introduction of Cu to the inside of the crevice via electromigration of [Cu(EDTA)] was confirmed. Migrated [Cu(EDTA)] reacted with H and inhibited decrease in pH inside the crevice, where Cu was separated from [Cu(EDTA)] and suppressed active dissolution of the stainless steel.

Effect of Sr dissolved solution on corrosion potential of type 316L stainless steel

Aoyama, Takahito; Kato, Chiaki; Sato, Tomonori; Sano, Naruto; Yamashita, Naoki; Ueno, Fumiyoshi

Zairyo To Kankyo, 71(4), p.110 - 115, 2022/04

https://doi.org/10.3323/jcorr.71.110

no abstracts in English

Effect of oxygen concentration on corrosion rate of carbon steel in air/solution alternating condition

Otani, Kyohei; Ueno, Fumiyoshi; Kato, Chiaki

Zairyo To Kankyo, 71(2), p.40 - 45, 2022/02

The purpose of this study is to investigate the effect of oxygen concentration in the air on the corrosion rate of carbon steel in an air/solution alternating environment in the low oxygen concentration range and to clarify the corrosion rate and corrosion mechanism of carbon steel depending on the oxygen concentration in air by the mass change of specimens before and after the corrosion test and observing the iron rust layer formed on the surface of carbon steel. The corrosion rate increases with increasing oxygen concentration in the air, and the gradient of the corrosion rate decreases gradually. The maximum erosion depth increased with increasing oxygen concentration except for the case of 1% oxygen concentration, however, the maximum erosion depth for 1% oxygen concentration was larger than that for 5% air oxygen concentration.

Corrosion of carbon steel in the simulated air/solution interface environment

Otani, Kyohei; Kato, Chiaki

Zairyo To Kankyo, 70(12), p.480 - 486, 2021/12

https://doi.org/10.3323/jcorr.70.480

This is a comprehensive paper of the corrosion of carbon steel in air/solution alternating condition. From cross-sectional observation and analysis of the iron rust layer formed on the surface of carbon steel in the alternating condition, it was found that a multilayered iron rust layer composed of red rust layer (-FeOOH), rust crust layer (FeO), inner crystal (FeO), and inner rust layer was formed on carbon steel. The multi-layered iron rust layer would accelerate the cathodic oxygen reduction reaction, and the reason why the corrosion rate of the carbon steel in the alternating condition was accelerated. The effect of artificial seawater (ASW) composition on the corrosion rate of carbon steel in air/solution alternating condition was investigated. It was found that the corrosion rate increased with increasing concentration from pure water to 200 times diluted ASW, and decreased with increasing concentration from 20 times diluted ASW to no diluted ASW. The Mg and Ca ions in ASW precipitated on the reaction interface and formed a metal cation layer, which inhibited the oxygen reduction reaction, and thus the corrosion of carbon steel was inhibited in the highly concentrated ASW.

Hydrogen absorption mechanism into iron in aqueous solution including metal cations by laser ablation tests and first-principles calculations

Igarashi, Takahiro; Otani, Kyohei; Kato, Chiaki; Sakairi, Masatoshi*; Togashi, Yusuke*; Baba, Kazuhiko*; Takagi, Shusaku*

ISIJ International, 61(4), p.1085 - 1090, 2021/04

https://doi.org/10.2355/isijinternational.ISIJINT-2020-065

In order to clarify the effect of metal cations (Zn, Mg, Na) in aqueous solution on hydrogen permeation into iron, the amount of hydrogen permeation from iron surface was measured by electrochemical tests with a laser ablation. Moreover, in order to obtain the basic mechanism of hydrogen permeation with metal cation, first-principles calculations were used to acquire the adsorption potential of the metal cation and the electronic state around iron surface. By Zn in solution, anodic reaction on ablated surface by laser irradiation was suppressed. Also, by quantum analysis Zn atoms were chemically bonded stronger than Na and Mg atoms to iron surface. It was suggested that the dissolution reaction of iron was suppressed by the formation of the Zn layer, and that lead suppression of hydrogen permeation into iron.

Effect of seawater components on corrosion rate of steel in air/solution alternating condition

Otani, Kyohei; Tsukada, Takashi; Ueno, Fumiyoshi; Kato, Chiaki

Zairyo To Kankyo, 69(9), p.246 - 252, 2020/09

https://doi.org/10.3323/jcorr.69.246

The purpose of this study was to investigate the effect of artificial sea water concentration on the corrosion rate of carbon steel under air/solution alternating condition, and to clarify the corrosion mechanism of carbon steel that changes with artificial seawater concentration. Mass measurements showed that the corrosion rate of carbon steel in the alternating condition accelerates with increasing concentration in the concentration region between deionized water to 200 times diluted artificial seawater (ASW), and the corrosion rate decreases with increasing concentration in the concentration region between 20 times diluted ASW to undiluted ASW. It can be considered that the reason why the carbon steel corrosion was suppressed in highly concentrated artificial seawater would Mg ions and Ca ions in the artificial seawater precipitate and cover on the surface due to the increase in pH near the surface by oxygen reduction reaction.

Modelling of intergranular corrosion using cellular automata, 1; Characteristics and corrosion rates of stainless steels in modified nuclear reprocessing solution

Yamamoto, Masahiro; Irisawa, Eriko; Igarashi, Takahiro; Komatsu, Atsushi; Kato, Chiaki; Ueno, Fumiyoshi

Proceedings of Annual Congress of the European Federation of Corrosion (EUROCORR 2019), 5 Pages, 2019/09

Intergranular corrosion phenomena were analysed using modified reprocessing solution. The data indicated that corrosion rates increased with time at the initial stage, and these stayed at constant value. Intergranular corrosion propagated at grain boundary in the initial stage and then attacked whole grain boundary causing drop out of grains. Corrosion rates of steady state were sum of intergranular corrosion amounts and weight losses of dropped grains. Surface appearances and cross sections of corroded samples were analyzed. The results indicated that the initial stage of intergranular corrosion was characterized by the ratio of corrosion rates between grain boundary and matrix. These ratios differed from individual grain boundaries. Total corrosion rates were affected by the distribution of these ratios. These data were based on the numerical modelling of intergranular corrosion using cellular automata. And also, calculated results were compared with these analytical data.

In situ electrochemical study on crevice environment of stainless steel in high temperature water

Soma, Yasutaka; Kato, Chiaki; Ueno, Fumiyoshi

Proceedings of the 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, Vol.2, p.509 - 521, 2018/00

https://doi.org/10.1007/978-3-030-04639-2_116

In-situ electrochemical measurement within crevice of stainless steel in 288C water has been conducted to analyze crevice water chemistry. Small sensors ( 250m) measured local solution electrical conductivity, , polarization resistance, and electrochemical corrosion potential. Real-time response of the as functions of bulk water conductivity, dissolved oxygen (DO) concentration has been quantitatively analyzed. The effect of geometrical factors on the crevice environment was also studied. The differ more than an order of magnitude depending on the oxygen potential inside the crevice. The increased by small amount of bulk DO (e.g. 30 ppb). Maximum was observed with DO of 32000 ppb and became more than 100 times higher than that of bulk water. Crevice geometry affected significantly on the water chemistry inside.

Development of metal corrosion testing method simulating equipment of reprocessing of spent nuclear fuels

Matsueda, Makoto; Irisawa, Eriko; Kato, Chiaki; Matsui, Hiroki

Proceedings of 54th Annual Meeting of Hot Laboratories and Remote Handling (HOTLAB 2017) (Internet), 4 Pages, 2017/00

http://hotlab.sckcen.be/proceedings

In the PUREX method, spent fuels are dissolved with nitric acid media. The reprocessing solution containing Fission Products derived from spent fuels is very corrosive to metal materials, the corrosion problem often appears on the surface stainless steel devices. The oxidizing metal ions such as Ruthenium (Ru) and Neptunium (Np) in the process solution is the key reason for severe corrosion of stainless steel. In order to obtain the corrosion rate of stainless steel, we installed the corrosion test apparatus inside an airtight concrete cell in a hot laboratory (the WAste Safety TEsting Facility (WASTEF) of the Japan Atomic Energy Agency), and performed the corrosion tests of stainless steel in the heated nitric acid solution containing Np. The corrosion tests were performed in the temperature range from room temperature to boiling point for 500 hours per batch. The results show that the presence of Np accelerate the stainless steel corrosion in the nitric acid solution.

The Effect of crystal textures on the anodic oxidization of zirconium in a boiling nitric acid solution

Kato, Chiaki; Ishijima, Yasuhiro; Ueno, Fumiyoshi; Yamamoto, Masahiro

Journal of Nuclear Science and Technology, 53(9), p.1371 - 1379, 2016/09

AA2015-0626.pdf:1.2MB

https://doi.org/10.1080/00223131.2015.1110506

The effects of crystal textures and the potentials in the anodic oxidation of zirconium in a boiling nitric acid solution were investigated to study the stress corrosion cracking of zirconium in nitric acid solutions. The growth of the zirconium oxide film dramatically changed depending on the applied potential at a closed depassivation potential (1.47 V vs. SSE). At 1.5 V, the zirconium oxide film rapidly grows, and its growth exhibits cyclic oxidation kinetics in accordance with a nearly cubic rate law. The zirconium oxide film grows according to the quantity of electric charge, and the growth rate does not depend on the crystal texture in the pretransition region before the cyclic oxidation kinetics. However, the growth and cracking under the thick oxide film depend on the crystal texture in the transition region. On the normal direction side, the oxide film thickness decreases on average since some areas of the thick oxide film are separated from the specimen surface owing to the cracks in the thick oxide. On the rolling direction side, cracks are found under the thick oxide film, which deeply propagate along the RD without an external stress. The cracks under the thick oxide film propagate to the center of the oxide layer. The cracks in the oxide layer propagate in the (0002)Zr plane in the zirconium matrix. The oxide layer consists of string-like zirconium oxide and zirconium hydride. The string-like zirconium oxide contains orthorhombic ZrO in addition to monoclinic ZrO. As one assumption for the mechanism of crack initiation and propagation without an external stress, it is considered that the oxidizing zirconium hydrides precipitate in the (0002)Zr and then the phase transformation from orthorhombic ZrO to monoclinic ZrO in the oxide layer causes the crack propagation in the (0002) plane.