Online ISSN : 1881-9664
Print ISSN : 0917-0480
ISSN-L : 0917-0480
Volume 67 , Issue 6
Showing 1-6 articles out of 6 articles from the selected issue
Conference Publication
  • Masahiro Sakai, Hironobu Takahashi
    2018 Volume 67 Issue 6 Pages 246-250
    Published: June 15, 2018
    Released: December 05, 2018

    Immersion tests for phosphorous deoxidized copper (PDC) and oxygen-free copper (OFC) tubes were conducted to investigate an ant nest corrosion developed in copper formate and copper acetate solutions. The test solutions with copper formate and copper acetate concentrations of 0.001, 0.01 and 0.1 mol/L were prepared. The copper tubes were taken out from the solutions at 28, 56 and 84 days for optical and scanning electron microscopy on the cross-sectional surface of the specimens. Typical ant nest corrosion with randomly-branched pits occurred in both PDC and OFC tubes immersed in 0.001, 0.01 and 0.1 mol/L copper formate solutions. On the other hand, hemispherical single pit developed in both PDC and OFC tubes immersed in only 0.1 mol/L copper acetate solution. SEM observation revealed that the corrosion pit area developed in both the copper formate and the copper acetate solutions were composed of metallic copper with fine sponge-like pores.

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  • Hirokazu Tamagawa, Koji Kanamori, Kozo Kawano, Yoshihiko Kyo, Yoshiyuk ...
    2018 Volume 67 Issue 6 Pages 251-255
    Published: June 15, 2018
    Released: December 05, 2018

    The susceptibility of copper to stress corrosion cracking is increased by the addition of Zn, P, As, Sb, Si and other elements. Among these, P, As and Sb can lead to substantial increases even when present in extremely small amounts. P is an important additive element used in copper tubes, recently found to enhance resistance to ant-nest corrosion in Cu-P alloys with concentrations increased 10-fold. The problem of stress corrosion cracking in copper heat transfer tubes, typically used in air conditioner heat exchangers, is known rarely phenomenon. But its relationship to high-phosphorus alloys is not yet understood. In this study, the relationship between highphosphorus copper tubes and stress corrosion cracking was analyzed by investigating the effects of P concentration and tube-shape on stress corrosion cracking in hair-pin bending copper tube.

    We confirm that alloys with small amounts of added P (0.027%) were prone to grain boundary corrosion. However, no clear difference in the degree of corrosion progression between Cu-0.027%P and Cu-0.38%P alloys was observed. While the segregation of P to grain boundaries in high-P alloys is a clear cause for concern, no segregation was observed in alloys with concentrations from 0.02% to 0.4% in our FE-EPMA analysis. We conclude that residual stress in hairpin bent copper tubes is a rare phenomenon. Similar results were found for thin-walled copper tubes. But the stress corrosion cracking in Cu-P alloys tended to occur when there were abnormalities in the bending process. As the shape of hairpin bent tubes became non-uniform, stress concentrated around local area, resulting in residual stress and stress corrosion cracking.

    In summary, it was found that while shape defects in hairpin bending process reduce the resistance to stress corrosion cracking in Cu-P alloy tubes, variations in P concentration from 0.02 - 0.4% produced no significant effect on stress corrosion cracking.

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  • Nobuhiro Okada, Makoto Nagasawa, Nobuo Otsuka
    2018 Volume 67 Issue 6 Pages 256-260
    Published: June 15, 2018
    Released: December 05, 2018

    Steel plate painted by inorganic zinc primer has high performance of corrosion protection by zinc particles. However, details of corrosion mechanism are not clear. Numerical analysis model is valid to make clear that of initial corrosion mechanism. We have been developed a numerical analysis model of corrosion phenomena, which can calculate ions movement and chemical reactions. From calculation result, zinc particles were corroded at first by rich dissolved oxygen and corrosion products such as MgCO3 and CaCO3 were precipitated around the zinc particles at the top of the primer. The calculated distributions of MgCO3 and CaCO3 were agreed with the cross section EPMA analysis results of exposed specimen, but the calculated distribution of zinc corrosion products were different from the cross section EPMA analysis results of exposed specimen. After several studies, it was cleared that cathodic current density of the painted steel after exposure test was decreased to 1/8 from that of before exposure. Numerical reanalysis was conducted with 1/8 decreased cathodic current density of the zinc particle, and then corrosion products of zinc were agreed with the EPMA cross section. It indicates that the corrosion products around the zinc particles disturbed oxygen diffusion and its cathodic current density was decreased.

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Research Paper
  • Rintaro Minamitani
    2018 Volume 67 Issue 6 Pages 261-267
    Published: June 15, 2018
    Released: December 05, 2018

    We have developed a visual inspection corrosion sensor to diagnose the corrosivity in installation environments for electronic equipment. The sensor identifies color difference between corroded and non-corroded metal film and shows how the length of discolored area side change over time. The change in length can then be used to determine the amount of metal corrosion by corrosion analysis considering diffusion of corrosive gas and corrosion reaction of metal. Once we know the amount of metal corrosion, we can classify the level of corrosivity in the environment. Silver is sensitive to reduced sulfur that has recently been identified as a primary corrosion risk to electronic equipment. In this paper, we produced trial corrosion sensor made of silver film. We checked on the accuracy of silver corrosion sensor by using mixed flowing gas tests that simulate actual use environments. The amount of corrosion by the corrosion sensor agrees with that by conventional silver coupon with error margin of 20 %. Our proposed sensor is compact, inexpensive, and does not require a power supply, so it can be easily and safety used in any location at which electronic equipment is installed. Moreover, corrosivity in the environment can be visualized on-site, without the need for instrumental analysis.

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