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

Zairyo-to-Kankyo Vol. 43 (1994), No. 5

  • Relationship between Atmospheric Corrosion of Carbon Steel and Air Quality

    pp. 250-257

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    Relationship of corrosion rate of low carbon steel exposed to the open air and chemical and meteorological parameters including SO2, NOx suspended particulate matter, temperature, relative humidity, wind velocity, precipitation have been studied in Tokyo for these twenty years. In the late 1960s and early 1970s, the levels of SO2, SO42- and suspended particulate matter in the air were considerably high, but their levels had rapidly declined until the late 1970s. According to the trends of air pollution condition, corrosion rates of low carbon steel in the air have decreased in the same tendency. Yearly recent corrosion rates at Chiyoda, commercial and urban area were about 0.033mm/year, Funado, industrial area were about 0.04mm/year, Takao; rural and mountaneous area were 0.02-0.04mm/year, and Ichinose; mountaneous and remote area were 0.005-0.01mm/year respectively. Their difference of corrosion rates almost coincided with concentration of air pollutants, such as SO2, suspended particulate matter, NOx and sea salt. The relationship between corrosion rate and the air pollutant concentrations were confirmed by using statistical analysis of multiple regrresion and correlation. The most effective atmospheric factors to the corrosion rates were concentration of rain components such as H+, SO42-, NO3- and NH4+.
  • On the Requirements for a Reasonable Extreme Value Prediction of Maximum Pits on Hot-water Supply Copper Tubes

    pp. 258-264

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    The application of extreme-value statistics to the problem of predicting the growth of Type II pits on hot water pipes is described. Optimum combinations of the size and number of unit samples required for reasonable extreme-value prediction were studied by using sets of pit depth data on pipes removed after seven years of field service, covering return periods of up to 1670. Based on the results of the analysis, the following conclusions can be drawn concerning the optimum conditions for obtaining a reasonable extreme-value prediction.
    (1) The number and size of unit samples for the extreme-value survey should be determined so that the variance of error of extreme-value estimates is minimized within specific distribution parameters, while the standard deviation of the estimates is limited to one-third of the mode of distribution.
    (2) To improve the accuracy of the estimates, increasing the unit sample size may be more effective than increasing the sample number.
    (3) As a practical guideline, extreme-value analysis of a sample amounting to 3% of the whole, with a return period of less than 500, is taken to be necessary in order to increase the reliability of extreme-value prediction.
  • Effect of Fluoride Ion on the Pitting Corrosion of Type 304 Stainless Steel in Neutral NaCl Solution

    pp. 265-271

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    Effect of fluoride ions on the pitting behavior of type 304 stainless steel has been studied in neutral chloride solutions at 303K. It has been confirmed by means of potentiodynamic polarization measurements that fluoride ions inhibit the chloride ion-induced pitting corrosion and promote the uniform dissolution of the steel. A linear relationship was found to exist between the logarithm of the minimum F- concentration required to inhibit pitting and the logarithm of the Cl- concentration. For a given F- concentration, the critical Cl- concentration required to induce pitting is given by the following equation:
    log[Cl-]=1.36log[F-]-0.08 [molarity]
    This equation suggests that there are Cl-and F-ions competitively adsorb on the surface, which can be described by Freundlich's adsorption isotherm.
  • Effect of Formic Acid on Iron Corrosion in an Anhydrous Methanol Solution

    pp. 272-275

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    Such a protic acid as formic acid is possible to react with anhydrous methanol. Effect of the formic acid reaction with methanol on the corrosion rate of iron in an anhydrous methanol solution of 0.1M NaClO4 was investigated by cyclic voltammetry and impedance measurement. The corrosion rate was lowered as the concentration of formic acid decreased with an increase in the immersion time. The fomation of methyl formate and water by the reaction complicates the process of iron corrosion in the methanol solution.
  • Adhesion of Highpolymer Materials

    pp. 281-289

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    There are various adhesives developed in pursuit of an optimization of mechanical properties of adhesive joints. Especially, the structural adhesives have been applied to many fields, large scale vessels for corrosion type, automobile, archtectural structure, etc. Then, new development of an adhesive was accelerated with each passing day. In the design of an adhesive joint, stress uniformity in the adhesive layer is important in practical application. Therefore, we must consider the elastic properties of an adhesive because the stress distribution in adhesive layer of an adhesive joint is depended on elastic modulus of the adhesive. Consequently, the problem of elastisity of adhesive should be investigated in detail to make the uniform stress distribution in adhesive joint layer. By the way, the structural adhesive curing at shorter time suits for practical usage. For this fact, a newly designed adhesive has been developed. In this paper, the adhesives of elasitic type and short time curing type have been shown as new ones in structural application. These adhesives were converted into soft ones, and new adhesion technique of such adhesives was developed during structural use.
  • Rust Formation on 304 Stainless Steel in Outdoor Atmosphere

    pp. 290-291

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