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

Zairyo-to-Kankyo Vol. 40 (1991), No. 3

  • Corrosion Inhibition of Carbon Steel by Benzotriazole and Lithium Nitrate in Concentrated LiBr-CaCl2 Solution at Elevated Temperature

    pp. 163-168

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    Inhibition of the corrosion of carbon steel in a concentrated LiBr-CaCl2 mixed solution was investigated in a glass sealed-tube at various temperatures. The LiBr-CaCl2 is used as heat storage medium for chemical heat storage in cooling systems. A mixed inhibitor of benzotriazole (BTA) of 0.0017 and lithium nitrate of 0.0015mol/kg-H2O provides excellent inhibition of corrosion in carbon steel when immersed in a mixture of 5.1mol/kg-H2O LiBr and 4.0mol/kg-H2O CaCl2 at 393K. It is assumed that this corrosion inhibition effect, by the mixed inhibitor, is a direct result of the synergestic effect caused by the compact layer composed of Fe3O4 and Fe-BTA which is formed on the surface of carbon steel. The layer formed on carbon steel inhibits the anodic reaction.
  • Effects of Alloying Element and Metallurgical Structure on Semiconducting Characteristics of Oxide Film of Zirconium Alloy

    pp. 169-176

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    Semiconducting characteristics of oxide films formed on pure Zr, Zr-Sn binary alloy and Zr-Sn-X (X: Fe, Ni or Cr) ternary alloys were evaluated by photo-electrochemical method, in order to make clear the effects of alloying elements on oxidation mechanism of Zr alloy in BWR environment. Oxide films of the alloys showed the characteristics of n-type semiconductor. Maximum photocurrent (I max) was generated by an illumination of monochromatic light with the energy of 5-6eV, i.e. the band gap energy of the Zr alloy oxide was 5-6eV. This value is lower by 2-3eV than the theoretical band gap energy (8eV) of stoichiometric ZrO2. These facts suggest that the generation of I max was resulted from an excitation of electrons trapped with anion vacancies (oxygen vacancies) of non-stoichiometric ZrO2-x. Therefore, the value of I max is considered to be proportional to the density of anion vacancy.
    High rorrosion resistant alloys showed lower value of I max. The changes of I max, due to change of chemical composition of alloys and due to the change of metallurgical structure, was able to be explanned by the valence theory of oxide semiconductor, i.e. the decrease of 1 max was considered to be resulted from the decrease of anion vacancies due to the substitution of divalent cations (Ni2+) and trivalent cations (Fe3+, Cr3+) at Zr4+ cation sites. From these results, it was concluded that oxidation rate of Zr alloy depended on the density of oxygen vacancies in oxide film.
  • Determination of the Optimum Cathodic Protection Potentials of Common Use Metals in Seawater by their Polarization Resistances

    pp. 177-182

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    The selection of an optimum potential value for cathodic protection is vital to the achievement of maximum corrosion suppression at minimumpower. In spite of the importance of the appropriate choice of the cathodic protection potential value for each specific case, the selection is usually made empirically, without a firm theoretical basis. Tsuru, Jeon and Haruyama indicated that the optimum cathodic protection potential coincides with the potential at which the faradaic impedance is maximum. The impedance technique can be used for both determining and monitoring the optimum cathodic protection potential, but the technique is a complicated work. The authors have recently developed a new theory of determining method that the optimum cathodic protection potential coincides with the potential at which the polarization resistance is maximum or infinite. This determining method by the new theory is very simple. It can indicate the optimum cathodic protection potential directly by the shape of the external cathodic polarization curve. This study is to verify experimentally the validity of the new theory by mean of the corrosion-loss measurement for carbon steel and brass in natural seawater. It was concluded that the polarization resistance technique is a simple and promising method for determining and monitoring the optimum cathodic protection potential for metal.
  • Influence of Sulfide Inclusions on the Pit Embryo of Stainless Steels

    pp. 183-187

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    Stochastic properties of current fluctuations observed before a stable pit propagation were analyzed in a buffer neutral NaCl solution. Distribution and size of sulfides in a 304 stainless steel were changed by surface remelting and rapid soldification by CO2 laser and following heat treatments. Increase in the concentration of sulfides slightly increase the frequency in occurence of pit embryos, and increase of the size of sulfide decreased it. The volume, life time, peak height and stochastic nature of pit embryos, however, were not affected drastically by the size and distribution of sulfides. Weibull plots of life time revealed that there is a critical size for pit embryo formation.
  • Performance and Reliability of Materilas at Cryogenic Temperatures

    pp. 188-197

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    Cryogenic engineering is one of important high technologies. Research and development of superconducting systems has accelerated the studies on structural materials for low temperature use. Mechanical properties of the materials at liquid helium temperature are unique as well as essential for the design and the reliability of cryogenic machinery. The deformation and fracture behaviors of structural materials in liquid helium are reviewed. Chaotic behaviors in the discontinuous deformation are characteristic of fractal in the distribution of plastic deformation. Dimple pattern on fractured surface has also fractal in the randomness of the distribution. The reliability of the cryogenic machinery and systems depends upon the properties of structural materials. Now, the fundamental research of the materials has been promoted and R & D for new materials and the evaluation has been carried out internationally.
  • Inverse Problem Approaches to the Phenomena Related to Materials

    pp. 198-207

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    Some examples of inverse problem approach of the phenomena related to materials are introduced. What is the inverse problem?, what could be obtained, identified or estimated by an inverse approach? are discussed based on the inverse processing of elastic waves. Some problems and uncectainities involved in inverse processing are also discussed.
  • Degradation of Material Properties in the Space Environment

    pp. 208-213

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    At the development of the space apparatus, successful design requires due consideration of space environmental effects on the materials used. Large space system materials, especially those in geosynchronous earth orbit, will be subjected to vacuum, ultraviolet radiation and charged particle radiation which will influence the performance and functional lifetime of the systems. This paper describes the influence of the space environment on the performance and lifetime of the structural materials for system.
  • Atomospheric Corrosion of Metals for Agricultural Facilities Used Under Influence of Gas and Ash Fallen out From Mt. Sakurajima

    pp. 214-220

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  • Corrosion of Electronic Devices

    pp. 221-221

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