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

Zairyo-to-Kankyo Vol. 40 (1991), No. 2

  • Process and Prevention of Intergranular Corrosion of Aluminium Brass Condenser Tube Surfaces Infested with Barnacles

    pp. 89-95

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    The process of and prevention method for intergranular corrosion beneath attached barnacles on aluminium brass condenser tubes have been studied. Experiments were conducted to find when the corrosion starts and ends by using pieces of the tube with barnacles killed by freezing. The corrosion proceeded rapidly during the first two weeks after death, then lasted slowly or ended afterward. Depth of the corroded portion was deeper in barnacles of greater shell length. S was detected in basis and just beneath Fe coat at high levels by EPMA from the cross section through the blackened barnacle basis to the aluminium brass body. Whitish scale under some blackish scales appeared after 45 days only, indicating that the whitish scale were formed in aerobic condition following recovery after breakdown of the anaerobic condition. Mechanical removal test of barnacles also conducted with ordinary cleaning balls in the laboratory. The sponge and the carborundum ball were effective for smaller than 1mm size and 2 to 3mm size barnacles, respectively. However removal of 5mm size barnacles or larger could not be accomplished by these balls. Three times of a sponge ball-per-tube operation should be applied more than twice a week during the settling season to prevent the corrosion due to barnacles.
  • Forms of Corrosion of Sintered Silicon Nitride Ceramics in Aqueous Environment at High-Temperatures and Pressures

    pp. 96-102

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    Pressureless-sintered Si3N4 with additives (Y2O3-Al2O3 and MgO) prepared with imide decomposed Si3N4 powder was severely corroded in water at high-temperature and pressure (300°C and 8.6MPa), resulting in weight loss and formation of corrosion product layer. The purpose of this work is to correlate the formation of corrosion product to the formation of pits and discuss on an aqueous corrosion pit as the fracture origin. After removal of corrosion product by ultrasonic cleaning in water bath, pits up to about 100μm in diameter were found distributed over the Si3N4 surface. Pit features in these sintered Si3N4 are different depending on the species of oxide additives; Si3N4 with Y2O3-Al2O3 forms deep pits with a thin protective corrosion product layer and that with MgO forms shallow pits with a thick non-protective corrosion product layer. This result in higher corrosion resistance for the former than the latter. Based on these results, schematic model for pitting corrosion of Si3N4 was proposed. The results also suggest that aqueous corrosion attack is practically important because it can lead to a strength degradation of engineering ceramics.
  • The Effect of Salt Composition on the Corrosion of 18Cr12Ni2Mo Stainless Steel in Molten Carbonate

    pp. 103-109

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    The effect of salt composition on the corrosion rate of 18Cr12Ni2Mo stainless steel has been investigated by corrosion test maintained at constant potential (vs. O2/CO2/Au) and electrochemical measurements in molten carbonate at 650°C under fuel gas atmosphere. The obtained results are as follows; 1) The corrosion rate of 18Cr12Ni2Mo steel in salt is affected by the applied potential. But the corrosion rates of 18Cr12Ni2Mo steel maintained at various potentials are nearly proportional to the one-half power of time. 2) The increase of K2CO3 in binary salt (Li2CO3/K2CO3) accelerates the corrosion rate. 3) The results obtained from electrochemical measurements are consistent with the tendency of the penetration depth obtained by corrosion test maintained at constant potential. Therefore, electrochemical measurement is effective to evaluate the corrosion rate of 18Cr12Ni2Mo steel in molten carbonate.
  • E-pO2- Diagrams of Metals in NaCl-KCl and Na2CO3-K2CO3 Eutectic Melts

    pp. 110-114

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    The potential (E) pO2- diagrams for Fe, Ni, Cr, Zr, Co, Ti, Cu and Mo in NaCl-KCl eutectic melt and Fe, Ni, Co and Cu in Na2CO3-K2CO3 eutectic melt at 1023K have been made from thermodynamical data. The diagrams show that the materials of sintered Ni and NiO are well stable under the positive and negative electrodes condition of Molten Salt Fuel Cells. Further thermodynamic calculations offer the promising tool for selecting materials of fuel cell components.
  • Organic Solvent Cleaning and Prevention of Environmental Contamination

    pp. 122-133

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    As you know well, the kinds of organic solvent cleaning are various available and petroleum solvent cleaning, non-petroleum solvent cleaning, finger print removing and vapour degreasing are very popular methods. But, recently environmental contamination is very severe for restriction due to destroy of ozone by fron, etc. Therefore, this is mentioned for details of kinds for organic solvent cleaning and prevention of environmental contaminations.
  • Recent Studies of Pre-filming Technique for Light Water Reactor Materials

    pp. 134-140

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    Reduction of radiation exposure is one of the most important subjects of light water reactor (LWR) plants as well as improvements of reliability and availability. Several methods, for supressing corrosion and deposition of radioactive ions, have been proposed and applied to some actual plants. The following recent studies of the pre-filming technique for LWR materials are presented in this paper. (1) Zinc and Aluminum ion injection methods. (2) Oxidation treatment in high temperature dissolved oxygen controlled water. (3) Palladium coating treatment. (4) Pre-oxidation treatment by RCT method. (5) Pre-oxidation treatment in air or steam atmosphere. (6) Pre-oxidation treatments in low-oxygen potential atmosphere.
  • フロンの回収, 分解

    pp. 144-145

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