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

Zairyo-to-Kankyo Vol. 70 (2021), No. 5

  • Restructuring in the COVID-19 pandemic

    pp. 143-144

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    DOI:10.3323/jcorr.70.143

  • Effect of Pulse Potential Mode on the Electropolishing of Niobium in a Sulfuric Acid Solution

    pp. 145-149

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    DOI:10.3323/jcorr.70.145

    The electropolishing behavior of Nb in a 30 wt% sulfuric acid solution was investigated by controlling the potential of Nb using a three-electrode cell. The Electropolishing was performed with various combinations of cathodic pulse potential (Ec) and anodic one (Ea). Almost completely mirrored surface was obtained after 120 minutes under the condition of Ec=-3.0 V and Ea=+10 V with both pulse periods of 2.0 ms. The mirrored surface was also obtained within 60 minutes by shortening anodic pulse time (ta) to 1.0 ms at Ec=-3.0 V and Ea=+10 V. This is due to the fact that anodic current decays so quickly at Ea=+10 V that anodic pulse time can be shortened to 0.25 ms with no change in anodic charge in one pulse. Thus the total number of cycles in a given time can be increased by shortening ta, which leads to faster electropolising rate: 0.92μm min-1 at ta=2.0 ms and 1.52μm min-1 at ta=0.25 ms.
  • Analyzing the Film Formation Process of Paint Applied in a Wet Surface

    pp. 150-154

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    DOI:10.3323/jcorr.70.150

    The electrochemical impedance spectroscopy (EIS) was examined as the method for analyzing the film formation of an amine cured epoxy paint applied in a wet surface. The impedance characteristics of the models with the epoxy resin and amine curing agent which different affinity for water were analyzed. It was found that the hydrophobic paint film was less affected by the wet environment than the hydrophilic paint film, and the resistance develops in a short time. In addition, from the results of adhesive strength, it was estimated that the water film at the substrate/coating film interface was eliminated in the very early stage. The EIS method was found to be useful for analyzing the coating film formation process in a wet surface.
  • Degradation Characteristics of GFRP using Unsaturated Polyester as Matrix in Weak Alkaline Aqueous Solution

    pp. 155-160

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    DOI:10.3323/jcorr.70.155

    In order to verify the applicability of glass-fiber reinforced plastics with an unsaturated polyester matrix in manhole environments, degradation characteristics in a weak alkaline aqueous solution were evaluated based on solution immersion test. The decrease in flexural strength after immersion test at 313 K fitted well to the logarithmic approximation. Based on Arrhenius equation, we estimated the deterioration behavior under 288 K conditions, which corresponded to a manhole environment. However, since a problem in applying the logarithmic approximation became clear, a more appropriate estimation method is required.
  • Evaluation of Crevice Corrosion Propagation by Continuous Current Step Method for Various Stainless Steels in Artificial Seawater

    pp. 161-169

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    DOI:10.3323/jcorr.70.161

    The new evaluation test method, CCS (Continuous Current Step) method, for crevice corrosion propagation of stainless steels was proposed. This CCS method is based on the crevice corrosion propagation mechanism of stainless steels in natural seawater. The steady state potential (EOUT) is measured galvanostatically on CCS test. The data sets of EOUTi were obtained for various stainless steels. It was considered that this EOUT reflected the state of active corrosion in anolyte of inside crevice under the constant current density.The EOUTi data was analyzed by the exponential decay curve. When the current density i was under 1× 10-5 A cm-2( ≈0.1 mm/y), the obtained potential EOUT was considered as the repassivation potential called ER(CCS) in this test. The crevice corrosion propagation was regarded as stop at less noble potential of ER(CCS).The effects of Cr, Ni, Mo and Cu on the EOUTi relations were tested in artificial seawater. ER(CCS) related to the metal composition and was described as one equation by using the new index, CCR(Crevice Corrosion Propagation Resistance Index).CCR=[Cr]+0.95[Ni]+0.74[Mo]+2.03[Cu]ER(CCS)=-317+13.75 CCR(mV vs.SHE)This new index, CCR, succeeded in unification of the crevice corrosion propagation (ER(CCS)) for various stainless steels.
  • Evaluation of Corrosion Prevention of Zinc-Iron Compound Phases and Iron-Zinc Solid Solution on Galvannealed Steel Sheets

    pp. 170-176

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    DOI:10.3323/jcorr.70.170

    The corrosion resistance of the δ1 phase (Zn-Fe compound) coated on galvannealed steel sheets (GA) and the Γ phase (Zn-Fe compound), α solid solution (Fe-Zn solid solution), which were formed by heating GA, was investigated using combined cyclic corrosion test, polarization measurements and structure analyses. The results suggest that the α solid solution, Γ and δ1 phases have relatively good corrosion resistance in order, and these coating phases have sacrificial corrosion protection against base steel. It was also considered that the corrosion prevention of α solid solution will decrease when the exposed area of the base steel becomes large.

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