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

Zairyo-to-Kankyo Vol. 48 (1999), No. 10

  • Application of Quartz Crystal Microbalance to Corrosion Research

    pp. 610-620

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    A quartz crystal microbalance (QCM) is capable of detecting small mass changes in the order of nano-grams from the changes in resonant frequency of a quartz oscillator. This article dealt with the principle of QCM and its application to corrosion research such as atmospheric corrosion and aqueous corrosion of metal thin films.
    The corrosion kinetics and mechanisms of copper and iron thin films were discussed on the basis of typical results obtained by QCM combined with Auger electron spectroscopy and/or electrochemical technique. It was stressed that the heterogeneous corrosion, the stress generated in the film and the changes in the interfacial properties (viscosity and density) have to be taken into consideration as the factors influencing the resonant frequency which would provide the apparent mass changes. Moreover, the attempt to evaluate the vibration states of the quartz oscillator from the analysis of electrical equivalent circuit was introduced with respect to the deliquescence phenomena of salts adhered to the surface.
  • Materials of Lithium Ion Batteries and Their Corrosion

    pp. 621-625

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    Organic and inorganic materials that are used in practical lithium ion batteries have been described from a viewpoint of their stability in the battery system. The lithium ion battery consists of a carbonaceous negative electrode, an organic solution dissolving lithium salt, and a lithiated transition-metal oxide positive electrode. The active material of the positive electrode, LiMn2O4, a promising candidate of the relief for LiCoO2, degrades in organic solutions containing LiPF6 as the electrolyte salt. The partial substitution of Mn by other trivalent metal improves the durability of the material. The Cu current collector of the negative electrode is susceptible to environmental cracking under the charging condition. The Al current collector of the positive electrode is generally stable in LiPF6 solutions with organic solvents, but it is susceptible to pitting corrosion under highly polarized conditions. The lithium salts with sulfonyl groups assist the pitting corrosion of Al.
  • Investigation of Wetting Process of Sea Salt Particles by QCM

    pp. 633-638

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    Wetting processes of sea salt particles were analyzed using an optical microscope combined with a QCM (quartz crystal microbalance). Sea salt particles used were collected at some seashore areas. Resonance frequencies of QCM were measured with every several of relative humidity step. QCM results frequently indicate that the weight gains according to moisture absorption were not observed and frequency change corresponding to weight loss were measured. These phenomena were discussed in comparison with thermodynamic and fluid mechanical calculation. It was found that the oscillation of QCM was attenuated in the water droplets, which were created by moisture absorption of sea salt particles. The weight change indicating the moisture absorption of sea salt particles is difficult to detect by the QCM sensor used in this study, having 10MHz of resonance frequency.
  • Real-Time Spectroscopic Ellipsometry Analysis of Dissolution Process of Fe2O3-Cr2O3 Films Formed by Low Pressure CVD

    pp. 639-646

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    Fe2O3-Cr2O3 thin films were formed on Pt substrates at 623K by low pressure CVD technique using Fe(O2C5H7)3 and Cr(O2C5H7)3 as precursors and O2 as a reaction gas. The dissolution processes of the films under anodic and cathodic polarization in 1kmol·m-3 H2SO4 were examined in-situ by real-time spectroscopic ellipsometry. Spectra of refractive index nfilm and extinction coefficient kfilm of the optical constant of the films, Nfilm (=nfilm-ikfilm), in a wavelength range 470-780nm were measured as a function of dissolution time. When the film with a Cr cationic fraction XCr=0.26 was polarized at a cathodic potential of 0.0V (vs. Ag/AgCl/3.33kmol·m-3 KCl), the value of nfilm in a wavelength range less than 700nm and that of kfilm in the whole wavelength range decreased with time. This suggests that reductive dissolution of Fe2O3 gives rise to an enrichment of Cr2O3 in the film, which is followed by an increase in the void fraction of the film. When the film with XCr=0.61 was polarized at an anodic potential of 1.1V, the value of nfilm first increased and then decreased with time, while that of kfilm monotonously decreased with time. The change in nfilm was prominent in a short wavelength range. These results show that the oxidative dissolution of Cr2O3 causes both an enrichment of Fe2O3 and an increase in a void fraction or surface roughness. The influence of the enrichment of Fe2O3 on nfilm is ascendant in the initial stage of dissolution and that of the increased void fraction or surface roughness is predominant in the subsequent stage of dissolution.
  • Pitting Corrosion of Copper Soft Tubes in Well Water

    pp. 647-653

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    Pitting corrosion of copper soft tubes has been experienced in the pass-through plumbing system using well water. Although the morphology of the pitting was similar to type 1 pitting corrosion of copper tubes, the quality of well water was different from those in plumbing system. The factor of the pitting corrosion has been investigated by field test in actual plumbing system. The free carbon dioxide in well water was 17 to 20ppm. The presence of both carbon film on the copper tubes and free carbon dioxide in well water caused the pitting corrosion. The pitting corrosion of copper tubes occurred under the presence of both residual ferr carbon more than 5mg/m2 and free carbon dioxide more than 15ppm.
  • Improvement of AC Impedance Method for Monitoring Corrosion of Rebar in Concrete Structure by Boundary Element Inverse Analysis

    pp. 654-659

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    A new method based on the boundary element inverse analysis was developed to improve the accuracy and efficiency of AC impedance method for monitoring corrosion of a rebar in a concrete structure. In this method, the potential in the concrete domain is described with the Laplace's equation, the validity of which was verified experimentally by using a concrete block specimen. The potential in the concrete domain is calculated by solving the Laplace's equation using the boundary element method, and an inverse analysis is carried out to estimate the location and the complex impedance of the corroded part on the surface of a rebar from a small number of potential data measured on the surface of a concrete structure. The cost function to be minimized in the inverse analysis is a function of the difference between the measured and calculated values of potential. An example using a prismatic concrete block with an embedded piece of rebar was presented to demonstrate the accuracy and efficiency of the proposed method.
  • Investigation of Limiting Potential of Protection of Stainless Steel in Electrochemical Protection (Part 2)

    pp. 660-663

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    To obtain an orientation for rapid and precise evaluation in a constant load method, a limiting potential of protection of two-phase stainless steel (SUS 329J4L) was investigated at a stress in plastic region. In the tests under this conditions, the limiting potential of protection (-0.85V vs. Ag/AgCl) could be rapidly and precisely determined by using parameters of relative elongation percentage (εr), decreasing percentage of area (A), tensile strength (ST), yield stress (σy), rupturing stress (σr) and total length of cliff (Lc). In particular, parameters, A and σr, were effective in consideration of working efficiency. A rupturing time of steel was able to be determined by a measurement of steady strain rate (Rss), which was an effective parameter in a prediction of rupturing time.

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