Zairyo-to-Kankyo
Online ISSN : 1881-9664
Print ISSN : 0917-0480
ISSN-L : 0917-0480
Volume 67 , Issue 12
Showing 1-8 articles out of 8 articles from the selected issue
Commentary
Review
Conference Publication
  • Mariko Kadowaki, Izumi Muto, Yu Sugawara, Nobuyoshi Hara
    2018 Volume 67 Issue 12 Pages 497-501
    Published: December 10, 2018
    Released: June 25, 2019
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    A microelectrochemical system equipped with a confocal laser scanning microscopy was applied to the real-time observation of pit initiation in the pearlite structure of carbon steel. By using this system, high-resolution images of pit initiation process could be obtained. It was revealed that the initiation site of pitting was in a ferrite lamella, and the pit propagated along the lamellar structure. The cementite remained in the very early stage of pitting.

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  • Satoru Yamamoto, Eisaku Kojima, Masaru Abe, Kenichi Tashiro
    2018 Volume 67 Issue 12 Pages 502-506
    Published: December 10, 2018
    Released: June 25, 2019
    JOURNALS RESTRICTED ACCESS
    It is important to monitor the corrosion rates of steel in electrolyte environments such as aqueous solution or soil in order to evaluate the integrity of the members of facilities. As a corrosion rate monitoring method, CIPE (Current Interrupted Polarizing Extrapolation) method was developed. By CIPE method the corrosion rate is calculated by the Tafel equation obtained from the polarization curve of the in-situ measurement. In this paper, in order to evaluate accuracy of the method, the measured corrosion rates were compared with the values calculated from mass losses of steel specimens in neutral aqueous solutions of various oxygen supplying conditions. As a result, the actual corrosion mass losses gave good agreement with the values of coulomb amounts which were calculated from the corrosion rates monitored by CIPE. Therefore it is clear that CIPE is an applicable method to real-time monitoring of corrosion rate of steel in aqueous solution. Furthermore, it was found that the corrosion rates which were limited by the oxygen diffusion rates could be measured by CIPE method.
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  • Takatoshi Maeda, Hiroyuki Inoue, Shin-ichiro Adachi, Gen Nakayama, Wat ...
    2018 Volume 67 Issue 12 Pages 507-512
    Published: December 10, 2018
    Released: June 25, 2019
    JOURNALS RESTRICTED ACCESS

    We considered the corrosion of a steel base at the through coating defective of thermal-sprayed aluminum(TAS) would be suppressed by adding Si to an Al spray material. The steel plate specimens that were thermally spray coated with Al-5Si or Al-12Si and were machined a disk-shaped artificial defect down to the base steel were prepared. For the sake of comparison, the specimens coated with the two types of Al with different purities or Al-5Mg were also prepared in a same manner. After subjecting to outdoor exposure in Okinawa, the charge transfer resistance at an interface between the rust layer and the base steel in the defective part was investigated by EIS. The charge transfer resistance at the interface for the specimen coated with the Al-5Si or the Al-12Si was higher than that coated with the Al or the Al-5Mg. It was estimated that the highly protective rust layers were formed by the action of Si and Al leaching from the coatings by atmospheric corrosion. The thermal spray coating of the Al-5Si and the Al-12Si was superior than that of the Al and the Al-5Mg in the respect of the tensile adhesive strength to the base steel.

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Research Paper
  • Hiroyuki Abe, Akio Yasukawa, Rintaro Minamitani, Hiroyuki Saito
    2018 Volume 67 Issue 12 Pages 513-518
    Published: December 10, 2018
    Released: June 25, 2019
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    We studied a highly accelerated corrosion test method for in-vehicle electronic modules. In the module, a circuit board on which the silver wiring was formed was stored in a casing sealed with silicone. SO2, H2S, S8 gas tests were conducted under the condition of 3300 ppm/90℃/80%RH in SO2 test, 60 ppm/90℃/80%RH in H2S test, and 4 ppm/90℃/<10%RH in S8 test. As a result of examining the corrosion rate of the silver wiring, it was found that the S8 gas test has the highest rate of corrosion acceleration. High corrosion rate is presumed to be due to high permeability of S8 gas through silicone, in addition to its high corrosion ability to silver. Based on this result, we propose S8 gas test as a sulfur corrosion accelerated test method.

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  • Toshihiko Ooi, Kuniyasu Araga, Norihito Ikeda, Takeshi Shimizu, Kiyota ...
    2018 Volume 67 Issue 12 Pages 519-526
    Published: December 10, 2018
    Released: June 25, 2019
    JOURNALS RESTRICTED ACCESS

    Since there were not so many reports concerning to the corrosion of painted steel in the indoor environment, we conducted long-term exposure test for Pb free cation electrodeposited painted steel sheet, which was widely used for steel industrialized housing, in the indoor environment. Further, observation and evaluation of blister width, red rust width, ratio of red rust area and the maximum corrosion depth were carried out. From results of evaluation and analysis after exposure test, better correlation between the corrosion on and under the paint film became clear, and the possibility of estimation for corrosion expansion and depth under the paint film by observing appearance of corrosion on the paint film was indicated. On the other hand, among the environmental factors, annual average relative humidity and amount of deposited sea salt are considered to influence in the corrosion behavior under the paint film.

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