Online ISSN : 1881-9664
Print ISSN : 0917-0480
ISSN-L : 0917-0480
Volume 58 , Issue 11
Showing 1-3 articles out of 3 articles from the selected issue
Research Paper
  • Misa Sakiya, Ryo Matsuhashi, Tooru Matsuhashi, Akihiko Takahashi
    2009 Volume 58 Issue 11 Pages 378-385
    Published: November 15, 2009
    Released: April 27, 2010
    Potentiostatic tests of stainless steel specimens with crevice between metal and glass were carried out in 460 ppm Cl solution at temperatures of 298 K, 323 K and 353 K in order to clarify effects of potential and temperature on incubation time, tINCU, for crevice corrosion. The test surfaces were polished just before the tests.
    The tINCU increased with the decrease in potential. The charge density, QINCU, which was required for initiation of crevice corrosion, was independent of potential in constant temperature conditions, and it decreased with the increase in temperature. It is considered that hydrolysis reaction rate of dissolved metal ions increases with temperature, and therefore pH of anolyte within crevice can decreases below depassivation pH with few amounts of dissolved metal ions or increase of chemical dissolution of passive film , and the both.
    It is because potential dependence of tINCU is derived from increase of iINCU, average dissolution current density of metal with noble potential. For all kinds of stainless steels tested, tINCU and QINCU decreased with the increase in temperature, and iINCU, on the other hand, increased with temperature. From Arrhenius plotting of these parameters, activation energies of tINCU, iINCU and QINCU for various kinds of stainless steels were obtained, and reactions during crevice corrosion occurrence were presumed.
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  • Manabu Kawasaki, Naoki Taniguchi, Morimasa Naito
    2009 Volume 58 Issue 11 Pages 386-394
    Published: November 15, 2009
    Released: April 27, 2010
    In order to clarify the influence of environmental factors on the corrosion behavior of copper overpacks in oxidizing environment, potentiodynamic and potentiostatic anodic polarization tests were performed in carbonate aqueous solutions at 80°C. As the results, the passivation was promoted and film breakdown was suppressed in higher carbonate concentrations, in lower chloride ion concentrations, and in higher pH conditions. The sulfate ion tended to promote the film breakdown of copper. The effects of the composition of the test solutions on the anodic polarization curve of copper in bentonite/sand mixture were quite smaller than those in simple aqueous solution. By comparison with previous data for lower temperature condition, it was clarified that passivation of copper was promoted in higher temperature condition, but breakdown potential, Eb was independent of temperature. The Eb, was expressed as a function of the ratio of aggressive ion and inhibiting ion such as [Cl]/[HCO3] and [SO42−]/[HCO3], and it was confirmed that the Eb was lowered with increasing the ratio. When the ratio exceeds a certain value, the Eb was no longer able to be determined since the anodic poralization curve becomes active dissolution type. The lower limit of Eb in passive type region was estimated to be about −200 mV vs. SCE. The results of potentiostatic tests showed that pitting corrosion or non-uniform corrosion was observed at the potentials over Eb or second current peak potentials in anodic polarization curve.
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