Online ISSN : 1881-9664
Print ISSN : 0917-0480
ISSN-L : 0917-0480
Volume 60 , Issue 6
Showing 1-5 articles out of 5 articles from the selected issue
Research Paper
  • Hidenori Fujii, Yasuyuki Takatani, Yoshiaki Matsuo, Yosohiro Sugie
    2011 Volume 60 Issue 6 Pages 290-295
    Published: June 15, 2011
    Released: December 07, 2011
    The characterization of passivation on austenitic and duplex stainless steels in soy sauce at 333 K were investigated by using electrochemical impedance spectroscopy (EIS). The soy sauce solution contained 18.4 mass% sodium chloride, 3.00 mass% organic acid, 6.80 mass% protein and 2.50 mass% ethyl alcohol at pH 4.9. These impedance spectra of stainless steels could been simulated the equivalent circuit model with four parameters, oxide capacitance, oxide resistance, charge-transfer reaction resistance and double layer capacitance. The thickness of passive films (reciprocal capacitance of films) were proportional to the resistance of films and charge transfer resistance.
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  • Kiyoshi Sawada, Genta Kanno, Masayuki Iino, Keiichi Satoh
    2011 Volume 60 Issue 6 Pages 296-303
    Published: June 15, 2011
    Released: December 07, 2011
    The phenomena of scale formation of calcium carbonates on the solid plate surfaces (metals, glasses, plastics) in supersaturated solution was investigated at 25.0°C. Except for particular case, the most stable polymorph calcite was adhered and grown on the plate surface. The unstable polymorph vaterite was formed on some metal surfaces under the conditions that the metal plate was inserted in the solution just after the precipitation of CaCO3. The surface density of the number of calcite crystals on the plastic surfaces were very high compared with that on metal surfaces. Roughness of the plastic surface promotes the increase in the surface density of adhered crystals
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  • Kazuhiro Toba, Koji Kawano, Kotaro Tanaka, Hirohito Iwawaki, Jun'ichi ...
    2011 Volume 60 Issue 6 Pages 304-311
    Published: June 15, 2011
    Released: December 07, 2011
    Highly concentrated NH4HS causes significant corrosion. In high pressure plants such as hydrodesulfurization units operated under NH4HS environments, leakage caused by corrosion could result in catastrophic disaster. Therefore, in the design phase, corrosion prevention techniques should be considered. In this study, based on the severe NH4HS corrosion observed selectively in the vapor phase inside air cooled heat exchanger tubes, the NH4HS concentrating model was developed to discern the difference in NH4HS concentration between the vapor phase and the liquid phase. We elucidated that NH4HS concentration in the condensed area in the vapor phase can be much higher than the liquid phase due to the difference of the heat transfer coefficient. This result quantitatively demonstrated the cause of corrosion observed in the air cooled heat exchanger tubes. In addition, this study indicated that the design of the air cooled heat exchanger tube where NH4HS corrosion shall be concerned should consider a flow regime, air temperature or predicted NH4HS concentration in the condensed area in the vapor phase.
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