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

Zairyo-to-Kankyo Vol. 51 (2002), No. 4

  • A Nanotechnology in Corrosion Science

    pp. 136-143

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    An ultrathin, regularly arranged, tightly interconnected, strongly adsorbed, and highly water-repellent two-dimensional polymer film is prepared on copper by modification of an alkanethiol self-assembled monolayer with alkyltrichlorosilanes. This film is significantly protective against aqueous and atmospheric corrosion of copper.
  • Effects of Phosphates for Macro-cell Corrosion Inhibitors on Steel in Concrete

    pp. 148-152

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    Effects of phosphates for macro-cell corrosion inhibitors in concrete solution were examined by using corroding bipolar electrode against floated current carrying electrodes. When using CaHPO4 and Ca (H2 PO4)2 for inhibitor, the corrosion electrode open-circuit potential was higher than using CaWO4, CaMoO4 and blank solution, was lower than using Ca (NO2)2. But the reaction resistance of calcium phosphates estimated from AC impedance measurement was higher than the other inhibitor. CaHPO4 and Ca (H2PO4)2 showed good performance as inhibitor in macro-cell environment.
  • Evaluation of Atmospheric Corrosion Behavior of Copper Plates by Means of Environmental Indices

    pp. 153-160

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    Atmospheric corrosion test data for copper plates obtained in various sites in Japan were analyzed. Environmental indices were decided by means of measurement of temperature, humidity, corrosive gas, and sea salt particle in air. The longer the exposed period of time and the higher the environmental indices, the larger the weight loss became. And the correlation among the loss of weight, the exposed period of time and environmental indices was investigated. A simple empirical formula was obtained that showed the loss of weight was approximated by a parabolic function of exposed days, where the coefficients for the square root of exposed days were the functions of environmental indices. The environmental indices are obtainable through the assessment of atmospheric environment and the interactive effect of multiple environmental factors on copper can be taken account, the weight loss of copper plates could easily be estimated.
  • Effect of Luminous Intensity on Open-Circuit Potentials for SUS 304 Stainless Steel in Natural Sea Water

    pp. 161-164

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    It has been well known that the activity of microorganisms in corrosive environment has responsibility for an acceleration of corrosion rate of metallic materials. Therefore, the factors such as illuminous intensity which affects the degree of microorganisms activity can be thought to be associated with corrosion behavior of metallic materials. In this study, the effect of illumination on open-circuit potential (EOCP) of SUS 304 stainless steel in natural sea water was investigated. Experimental results showed that EOCP became ennobled with a decrease in illumination, and the response of EOCP to illumination changes was rather rapid. The maximum range of EOCP change was about 200mV with the illumination varying between 0 lx (dark) and 18000 lx. In addition, it was found that the catholic current on Pt electrode at 0V vs. SSE in natural sea water raised with an increase in illumination. Perturbations of EOCP and catholic current with the luminous intensity were observed at the earliest stage of marine biofilm formation on the surface. It was suggested that the differences in luminous intensity on the stainless steel enhanced the possibility of localized corrosion in natural sea water.
  • Crevice Corrosion of Type 304L and 316L Stainless Steels in Nitric Acid Solutions

    pp. 165-172

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    Crevice corrosion of 304 L- and 316 L-stainless steels has been examined for 7.2 or 1.8Ms in nitric acid solutions with/without RuNO (NO3)3, by measuring the mass loss of the specimen, the amounts of metal ions dissolved, and the galvanic current.
    Specimen surface at/around the crevice corroded more vigorously than that without the crevice, and the tendencies became more remarkable at higher HNO3 concentrations, higher temperatures, and with RuNO (NO3)3. Current flowed from the specimen with crevice to the specimen without crevice through a lead wire, when these connected specimens were immersed in a HNO3 solution containing RuNO (NO3)3. The susceptibility to the crevice corrosion was higher on 316L than on 304L stainless steel.
    A mechanism on the crevice corrosion of stainless steels in HNO3 solutions is discussed in terms of a catalytic action of Fe3+ ions accumulated on the surface at the crevice.
  • Application of Cathodic Protection to Coated Steel in Atmosphere and Corrosion Controll

    pp. 173-177

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    A catholic protection technique in the atmosphere has been applied to organic coated steel. This technique differs from the usual catholic protection because catholic current flows through thin water film layer on the coated steel. The steel plate's coating for this technique consisted of three layers. These were an insulating layer, a conductive layer containing carbon powder and a top coat. The cathodic protection current was applied from the conductive layer to steel. Defects were made on these plates in the size of 1×10mm. Various amount of salt were put on defects. Corrosion test was performed under the condition of wet and dry cycles in applied voltage 5V. During the test period, the current through defect area was meseared. As the amount of salt in the defect increased, the measuring current increased. The sample having the greater current showed more protective appearance. In the case of the smaller amount of salt in the defect, the thickness of electrolyte solution film decreased, and the resistance of the defect area increased, then the cathodic current decreased. However, the defect area of this sample showed protective appearence. It is estimated that the steel under the defect was covered with passivation film which was generated by alkalinity due to catholic reaction.
  • Polarization Behavior of Fe-Cu Alloys in Weakly Alkaline Solutions Containing Chloride Ions

    pp. 178-179

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    The effects of copper on the corrosion resistance of steel have been investigated in order to propose the application of scraps as reinforcing steels in concrete structures. The polarization curves in weakly alkaline solutions containing chloride ions indicated that the addition of copper up to 3 mass% significantly improves the corrosion resistance of steel.
  • Development of Valve Seat Materials (Co-free Seat Materials) for High Temperature and High Pressure Services

    pp. 180-187

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    Cobalt based overlaying materials have been widely used as valve seat materials for high temperature and high pressure services, because of the high corrosion and wearing resistances. In nuclear power plants, however, the cobalt-based alloys would be the potential source of 60Co in the reactor water, thus alternate materials (Co-free materials) have been required and studied, especially for use as the large size valve seats on the feed water and condensate lines. From the results of a screening wearing test (sliding distance: 6mm), some Ni-based alloys were selected as the most promising material. Then sliding tests (sliding distanc: 20mm) and mechanical tests were performed on the selected candidate alloys.
    In conclusion, two Ni-based alloys, that is, A-1 (10Cr-4.5Si-0.2B-40Fe-Bal. Ni) and A-3 (10Cr-4.5Si-0.2 B-40Fe-Bal. Ni) were confirmed to be useful for large size valves for high temperature and high pressure services, and the mechanical properties of both alloys were similar to those of the conventional cobalt based material.

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