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

Zairyo-to-Kankyo Vol. 43 (1994), No. 6

  • In-situ Measurement of Oxidation Ability of Thiobacillus ferrooxidans by QCM

    pp. 316-321

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    It is essential to evaluate the activity of bacteria for the prediction of bacterial corrosion rate. Thiobacillus ferrooxidans is a kind of iron oxidizing bacteria and oxidizes Fe2+ to Fe3+ in acid water. T. ferrooxidans plays an important role in microbiologically influenced corrosion. The object of this work is to evaluate the activity of T. ferrooxidans, that is, the oxidation rate of Fe2+. Fe3+ is an oxidizer and can ionize solid Cu. It is, therefore, possible to calculate the oxidation rate by measuring the mass loss of solid Cu. Quartz Crystal Micro balance method (QCM) was used to measure the mass loss of Cu in this experiment. L-ascorbic acid or elemental Fe was necessary to be dosed into bacterial solution in order to reduce excessive Fe3+. As a result of these procedures, it became possible to fix the oxidation rate of Fe2+ by T. ferrooxidans. The oxidation rates were 0.5×10-7, 1.7×10-7 and 4.1×10-7mol Fe·dm-3·s-1 after 90, 120 and 150h from the inoculation, respectively.
  • CO2 Reducing Reaction Induced by the Corrosion of Iron

    pp. 322-330

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    Corrosion reaction has been applied to the reduction of carbon dioxide which is considered to cause the greenhouse warming problem. A batchwise study using Pyrex glass ampules has been carried out by saturating carbon dioxide in the solution suspended with iron powder. Experimental parameters employed are the amount of iron powder, the reaction temperature and the leaving time between opening the ampule and determining the products. The gaseous reaction products containing carbon have been identified as carbon monoxide and hydrocarbons of small molecular weight. The following results obtained are considered to be very interesting: (1) methane has been produced more predominantly than other gaseous products; (2) the amount of saturated hydrocarbon produced has been in the order of methane, ethylene, propane and n-butane; (3) with respect to the product in the ampule opened and left still for 23 hours, the yield of all hydrocarbons but methane has considerably increased, compared with that determined immediately after opening. The results have been interpreted by depicting the formation of a metastable conjugate complex among unsaturated hydrocarbons and corrosion products of iron.
  • Anodic Polarization Behavior of Fe, Ni, Cr, Ni-Cr Alloy and Type 304 Stainless Steel in Aqueous Solutions Containing Fluoride Ion

    pp. 331-335

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    Polarization curves of Fe, Ni, Cr, Ni-18 mass% Cr alloy and Type 304 stainless steel were measured in aqueous fluoride solutions of various pH values from 1.9 to 11.7 at 303K. The concentration of fluoride ion was fixed at 0.2kmol·m-3 for all the solutions. Fe shows the very large current density of 101 to 102 A·m-2 beyond -500mVAg/AgCl at pH≤8.2 and beyond -100mV Ag/AgCl at pH 11.7. Ni shows the large current density beyond -200mV Ag/AgCl at pH≤3.2. However, two peaks appear in the curves at pH 5.8 and 8.2, and a passive region has the very small current density of 10-1 to 10-2 A·m-2 at pH 11.7. Cr does not show any active region but a passive region with the very small current density at any pH values. Ni-18 mass% Cr alloy shows that the current density increases with increasing potential at pH≤8.2, and that a passive region with very small current density appears at pH 11.7. Type 304 stainless steel behaves similarly as Cr such that they have very small current densities in the passive region at any pH values. No localized corrosion such as pit was found for all the materials.
  • Unusual Corrosion in CO2 Removal Plants Operated with 65wt% Diglycolamine Aqueous Solution

    pp. 336-339

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    The high amine concentration treating plants which used 65wt% aqueous solution of diglycolamine were newly constructed by Teikoku Oil Co., Ltd. to remove carbon dioxide from the natural gas produced in Nagaoka, Niigata prefecture, Japan. SUS 304 stainless steel was used to places at which aggressive corrosion was suspected. On the inspection on the inside of the plants after one year operation, aggressive uniform corrosion of stainless steel was observed to occur on the pall rings installed in the bottom of the absorber, on the inside of the heat exchanger tube and of the upper part of the stripper, and so on. All the places which aggressive uniform corrosion occured were where contacted with the amine solution absorbing high concentration of carbon dioxide. The article introduces an anomalous, aggressive uniform corrosion of stainless steel found in the high amine-concentration treating plans for raw natural gas.
  • Degradation of Polymers-Causes and Methods for Its Estimation

    pp. 340-346

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    Polymers are widely used in our daily life. However, polymers degradate, The degradation takes different forms, such as fracturing, crucking, and chalking, depending on the nature of polymers, and often involves complex, overlapping and mutually interacting processes. Here, the degradation processes of polymers are reviewed briefly by examples. The methods, currently being used for estimating extents of degradation of polymers, are also included. It is shown that the degradation processes of polymers depend not only on the environments in which they are practically used, but also on their fabrication processes.

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