Zairyo-to-Kankyo
Online ISSN : 1881-9664
Print ISSN : 0917-0480
ISSN-L : 0917-0480
Volume 67 , Issue 3
Showing 1-7 articles out of 7 articles from the selected issue
Commentary
Review
Conference Publication
  • Shota Ohki, Shingo Mineta, Mamoru Mizunuma, Yasuhiro Higashi, Osamu Ka ...
    2018 Volume 67 Issue 3 Pages 118-120
    Published: March 15, 2018
    Released: September 27, 2018
    JOURNALS FREE ACCESS

    Soil corrosion of metal is a complicated phenomenon because various environmental factors are related with each other, and the effect of these environmental factors on corrosion rate of metal is still unclear. In this study, the effects of soil particle size and water content on the corrosion rate were investigated. The AC impedance method was used for measuring the corrosion rates of carbon steel buried in soil whose grains were coarse and fine, respectively. The corrosion rate of carbon steel in the fine-grain soil showed a maximum value at lower water content than in the coarse-grain soil. This can be explained by supposing a balance between water-dissolved oxygen diffusion distance and wet area of the carbon steel surface. In the fine-grain soil, the wet area and thin moisture layer on the carbon steel might be preserved even at the lower water content.

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Technical Report
  • Gen Nakayama, Ippei Shinozaki, Yohei Sakakibara, Wataru Oshikawa
    2018 Volume 67 Issue 3 Pages 121-126
    Published: March 15, 2018
    Released: September 27, 2018
    JOURNALS FREE ACCESS

    Thermal sprayed aluminum coated steels were exposed to subtropical climate at the University of the Ryukyus, Okinawa. They were found to exhibit good corrosion resistance even after 25 years. The results of the present study indicate that the thickness of the thermal sprayed aluminum film need not necessarily decrease, rather it may increase with the duration of exposure, but the porosity clearly increased. Furthermore, a film of alumina was formed on the rust where damaged steel was exposed to the atmospheric environment. Therefore, the thermal sprayed aluminum film is believed to provide 1) environment interception and 2) electrolytic protection.

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Research Paper
  • Matsuho Miyasaka
    2018 Volume 67 Issue 3 Pages 127-131
    Published: March 15, 2018
    Released: September 27, 2018
    JOURNALS FREE ACCESS

    In seawater, the corrosion rate of iron increases as the flow velocity increases. If a flow velocity distribution exists, a macro-cell is formed due to the differential flow velocity, by which corrosion in low flow velocity areas is promoted, while it is suppressed in high flow velocity areas. As a result, the corrosion rate of the former may be higher than that of the latter. This phenomenon is called “differential flow velocity cell corrosion”, and is regarded as a form of “differential aeration cell corrosion”(“differential oxygen concentration cell corrosion”). The author considered the mechanism of “differential flow velocity cell corrosion” by examining the flow velocity dependency of the internal anodic polarization curve. A corrosion test on cast iron was conducted in seawater by changing the flow velocity and potential, to obtain an internal anodic polarization curve based on the corrosion rate. It was confirmed that the internal anodic polarization curve moved to the noble side (low current density side) as the flow velocity increased. Consequently, we experimentally verified a hypothesis developed to explain the mechanism of “differential aeration cell corrosion” and “differential flow velocity cell corrosion” of cast iron and steel.

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