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

Zairyo-to-Kankyo Vol. 52 (2003), No. 5

  • Development of Corrosion Inhibition Technologies in Absorption Chiller Heaters

    pp. 236-243

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    As the highly concentrated LiBr solution has been used as an absorbent in the absorption chiller heaters, the corrosion inhibition of constructing materials was the key technology for developing efficient two stage units. In this paper, the corrosive behavior of metals, especially of carbon steel, inhibiting effects of many inhibitors and their mechanisms are widely reviewed.
  • Regression Analysis for Corrosion Loss, W, of Zinc against Time, t, in Indoor Atmospheres into a Formula of W=atn

    pp. 249-253

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    Literature data for zinc coating in outdoor exposure tests were analyzed into an equation of W=atn where W is a corrosion loss in g/m2 after a period of t years. The coefficient a varies widely from 0.3 to 100g/m2, while the exponent n is found to be close to 0.5 in marine and less corrosive rural environments.
    An indoor corrosion test was carried out sheltered from rain and sunlight. Zinc coated specimens were given 0.1 or 1.0g/m2 of sea salt and 10g/m2 of Kanto loam deposited on each and placed horizontally inside a box with ventilation holes to make the inner condition in temperature and humidity similar to the outer one. This test determined the n value as 0.37-0.39 for zinc coating, which combined with the outdoor exposure data made it moderate to assume the n value to be 0.5.
    The expression of W=at0.5 was applied to several W data after period, t, as long as 30-40 years obtained from galvanized ducts in some buildings. The analyzed values of a are found to depend highly on the amount of chloride ion deposited on each duct and considered as a good characteristic to corrosivity of the environment to which ducts have been exposed.
  • Measurements of Pitting Potential of Moundless Type Pit in Condensed Tap Water

    pp. 254-258

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    The pitting potential of moundless type pit for copper tubes was measured in the condensed tap water. For comparative study, two types of tap water were prepared as test solution; one type of water is “pitting area's water” which causes the moundless type pit and another type is “pitting-free area's water” which never causes the moundless type pits. Both types of water were condensed by heating and evaporating until the electric conductivity showed about 50mS/m. Water-glass scales were observed on the surface of the specimen after the 3 month immersion tests in pitting area's condensed tap water. Pits occurred in the potentiostatic corrosion test at 150, 200 and 300mV (Ag/AgCl) for 200 hours in pitting area's condensed tap water. The appearances of pits occurred in the potentiostatic corrosion tests are similar to the real moundless type pits because the entrances of pits were open. The pitting potential of mondless type pit of 150mV (Ag/AgCl) was determined by the potentiostatic corrosion test in condensed tap water for 200 hours.
  • The Effect of Free Carbon Dioxide on Copper-corrosion Behavior

    pp. 259-266

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    Copper tube is generally used in water supplying systems, however the copper tube rarely suffers from Type I pitting-corrosion. In this study, the effect of free carbon dioxide (CO2 (aq.)) on the copper-corrosion behavior was examined.
    Copper specimens were immersed in simulated tap-waters in atmospheres of 79%N2-21%O2, 78.8%N2-21%O2-0.2%CO2, 77%N2-21%O2-2%CO2 and 59%N2-39%O2-2%CO2 (artificial airs). The concentrations of CO2 (aq.) and dissolved oxygen (DO) in the waters were changed by these methods. After the immersion tests, electrochemical impedance spectroscopy (EIS) measurements were carried out. The electrochemical parameters were determined by curve fitting after EIS.
    The pHs of waters were constant in 78.8%N2-21%O2-0.2%CO2, 77%N2-21%O2-2%CO2 and 59%N2-39%O2-2%CO2 throughout the immersion tests. Generally, H+ is consumed for reduction of DO with oxidation of copper. On the other hand, H+ is supplied by CO2 (aq.) and H2O as follows.
    CO2 (aq.)+H2O↔H2CO3
    H2CO3↔HCO3-+H+
    It is considered that the concentration of CO2 (aq.) and pH are held constant when the partial pressure of CO2 gas is constant. The values of charge-transfer resistance and Warburg impedance decreased with the increasing partial pressure of CO2 gas and/or O2 gas. Consequently, the copper-corrosion rate increased with the concentrations of CO2 (aq.) and/or DO in the water. H+ was supplied by CO2 (aq.) and H2O. H+ might assist the reduction of DO to promote the oxidation of copper as follows.
    O2+4H++4e-→2H2O
  • Electrochemical Evaluation of Adhesion between Photoresist and Invar Alloy for Fine Etching

    pp. 267-274

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    Shadowmasks used for color cathode ray tubes (C-CRT) have electron pass holes formed by photoetching technique. The accuracy of shapes and dimensions of the holes is controlled by the adhesion between photoresist and the substrate alloy. The adhesion is empirically known to be influenced by the pretreatment of substrate before coating the photoresist. The aim of this study is to evaluate quasiquantitatively the effect of conditions of the pretreatment on the adhesion by electrochemical technique. Thin sheets of Invar alloy (Fe-36 mass% Ni) were used as specimens. As factors that influence the adhesion, the concentration of detergent, the drying time and temperature, and the quantity of spread water were selected. The specimens coated with photoresist after different pretreatments, except for etching patterns, were potentiostatically polarized at 0.3V (vs. Ag/AgCl, 3.33kmol·m-3 KCl) in 0.1kmol·m-3 Na2SO4+0.003kmol·m-3 NaCl solution. Time-dependent change in current at 0.3V and the initiation of crevice corrosion at photoresist/substrate interfaces at the same potential were examined. Etching tests were also performed on the specimens coated with photoresist in a FeCl3 solution of sp. gr. 1.485 at 293K.
    In result, it was found that the specimens that showed increasing current during the potentiostatic polarization at 0.3V suffered from crevice corrosion owing to the bad adhesion of photoresist. These specimens that were susceptible to crevice corrosion also showed small etching factors and large errors in the dimension of etching holes.

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