Zairyo-to-Kankyo
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ONLINE ISSN: 1881-9664
PRINT ISSN: 0917-0480

Zairyo-to-Kankyo Vol. 54 (2005), No. 10

  • Degradation and Maintenance of Materials in a Marine Environment-General

    pp. 470-474

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    Port structures in many ports need large-scale rehabilitation measures due to neglected periodic maintenance. Therefore, a knowledge of the causes of degradation and damage, the methods of monitoring, maintenance and repair necessary for the life cycle management is essential. Since the area between MLWL and a point just below LWL is the location where the greater corrosion rate usually occurs, the WG31 proposed that the zone between MLWL and a point approximately 0.5 meters below LWL was LWL zone. The general of the degradation, inspection, maintenance and repair of materials in a marine environment, and the proposed LWL zone are presented in reference to the revision of PIANC PTC-II WG17 report by WG31.
  • Corrosion Sensors to evaluate Corrosiveness of Installation Environment for Electronic Equipment

    pp. 476-482

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    We developed original corrosion sensors, an in-situ measurement type corrosion sensor and an electrical resistance type corrosion sensor, to evaluate the corrosiveness of installation environments for electronic equipment. The in-situ measurement type corrosion sensor measures the approximate corrosion thickness using the difference between a non-corroded metal color and a corrosion film color. The sensor does not require any professional instrumental analysis knowledge. The electrical resistance type corrosion sensor accurately measures the continuous corrosion thickness using electrical resistance change coupled with the metal electrode cross-section. In this paper, we constructed trial corrosion sensors made of silver film used extensively in electronic devices. First, we investigated the corrosion behavior in silver film of corrosion sensors and in the conventional silver coupon. As the silver film was corroded by the same mechanism as the silver coupon was corroded when exposed to a mixed corrosive gas, we can measure corrosion thickness of silver film exposed to a corrosive environment with the corrosion sensors instead of the silver coupon. Next, we used the corrosion sensors to investigate the corrosiveness of the environment in a heavy industrial plant and an office with a computer installed. The in-situ measurement type corrosion sensor is suitable for investigating the corrosiveness of severe corrosive environment, while the electrical resistance type corrosion sensor is suitable for investigating the corrosiveness of weak corrosive environment. We proved that these corrosion sensors are effective for evaluating the corrosiveness of installation environments for electronic equipment.
  • Conditions of Cathodic Polarization for Electrocoating Formation on Carbon Steel in Flowing Tap Water

    pp. 483-487

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    The conditions for electrocoating formation on carbon steel in flowing tap water were investigated. The cathodic polarization tests were carried out galvanostatically. Electrocoating started within one day by giving larger cathodic current than diffusion current of oxygen. The condition for electrocoating formation was also obtained from electrode potential whose value was less than -0.73V vs. SHE. The presence of electrocoating reduced protection current density by a factor of about ten.
  • Sacrificial Anode Cathodic Protection of Steel in Tap Water

    pp. 488-493

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    Recently, cathodic protection is applied to steel in fresh water. This paper discusses the condition which satisfies cathodic protection in practical use.
    A sacrificial anode is zinc. Steel being in contacted with zinc is dipped in Tsukuba-city tap water at 25°C for 780h. Weight loss, potential and cathodic current between zinc and steel are measured.
    Steel does not corrode when the ratio of area [γ=area of steel/(area of steel+area of zinc)] is lower than 0.75. In this case, the cathodic current density to steel is more than 0.12A/m2 and the potential continues to rise. When steel corrodes, the potential attains the steady value of about -400mV (SHE). We propose the protection criterion considering both the potential and the direction of change of potential.
  • Effect of Anions on Initial Stage of Localized Corrosion of Zn-55 mass% Al Alloy Coated Steels by Photon Rupture Method and Anodizing

    pp. 494-500

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    Photon rupture with a focused single pulse of pulsed YAG-laser irradiation was used to investigate abrupt destruction and repair of passive oxide films or localized corrosion on anodized Zn-55 mass% Al coated steels. The specimens were irradiated with a focused pulse of a pulsed Nd-YAG laser beam at a constant potential in borate solutions, pH=9.2, with and without Cl-, NO3-, and SO42- ions and the current transients were monitored. The oxide films were reformed in the borate solution with NO3- and SO42- ions after removal of the oxide film. The oxide film formation kinetics follows the inverse logarithmic law, according to Cabrera-Mott theory at the late stage after t=10ms. As the potential becomes nobler, the current increases. These behaviors can be explained by a preferential dissolution of the metal substrate, which is enhanced at nobler potentials and with the anions. In Cl- containing solutions, localized corrosion of the coated layer occurs at high potentials, while film reformation occurs at low potentials.

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