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

Zairyo-to-Kankyo Vol. 47 (1998), No. 7

  • Recycling of Waste Home Appliances

    pp. 422-430

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    From the standpoint of environmental preservation, considerable interest has been generated by the recycling of manufactured goods such as home appliances. In terms of waste home appliances, there is an urgent need for an improvement in recycling rates, and laws pertaining to waste disposal have become even stricter, as well as calls for four items-refrigerators, air-conditioners, washing machines and televisions to be designated as primary specified goods under those laws that encourage the use of recycled materials. On this background, strong calls are made for products to be developed in a way that facilitates recycling activities, as well as for the development of waste disposal techniques. In this paper, the development of products to facilitate recycling and treatment technology for waste home appliances are mentioned.
  • Contents of “Q&A” from the Beginning up to now

    pp. 437-439

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  • Corrosion Inhibition of Mild Steel by Schiff Base Compounds in Various Aqueous Solutions (Part 2)

    pp. 447-453

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    The effects of Schiff base-metallocomplexes on the corrosion of mild steel were investigated by corrosion weight loss measurements, electrochemical measurements and surface analyses in various aqueous solutions such as hydrochloric acid solution and pseudo cooling water. The maximum value of inhibition efficiency on the corrosion of mild steel in 1mol/dm3 hydrochloric acid solution was about 95.8% in the case of Indium (III) {N, N'-bis (salicylaldehyde)-1, 12-diaminododecane} complex. The molecules of Schiff base-metallocomplexes adsorbed on the surfaces of mild steels to depress the corrosion.
  • Optimum Design of Cathodic Protection for Long Pipeline

    pp. 454-459

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    A boundary element method (BEM) is developed for optimizing the locations and impressed currents of electrodes in a catholic protection system for a long underground structure such as a pipeline and an oil well casing. The cattodic protection system has usually been designed on the basis of past experience together with a limited number of empirical formulas applicable for a narrow range of conditions. The optimization is performed by minimizing the electric power necessary to keep the potential on the metal surface below a critical value. A long underground structure is often buried in soil with non-uniform electric conductivity. In this case, direct application of conventional multi-domain method for BEM analysis gives an unrealistic solution. To overcome this problem, the electric conductivity is modeled with a linear function of location. The polarization characteristics are also formulated to express its continuous change. A penalty function is used as a objective function which has a term taking a large value when the protection condition is not satisfied. To minimize the objective function, the Simplex method is employed. In order to demonstrate the usefulness of the method, some example problems are presented.
  • The Synergistic Inhibition Effects of Hard Base and Oxidizing Inhibitors on Pit Initiation and Growth of a Passive Film on Iron

    pp. 460-467

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    The synergistic inhibition effects of a hard base, octylthiopropionate ion C8H17S(CH2)2- COO-(OTP-) and various oxidizing inhibitors on pit nucleation and growth were investigated for a passivated iron electrode in an aerated borate buffer solution (pH 8.49) containing an aggressive anion Cl- by polarization measurements. Because the pitting potential Epit and the repassivation potential Erep were mostly shifted in the positive direction by mixtures of OTP- plus MoO42-, WO42-, NO3-, and NO2-, these inhibitor mixtures suppressed both pit nucleation and growth. Mixtures of OTP- plus CrO42- and VO3- inhibited pit initiation but stimulated pit propagation, resulting in the formation of large pits. The hard bases, OTP- and oxidizing inhibitors suppressed pit nucleation by repairing defects in the passive film with deposits of their salts or complexes. After pit initiation, since oxidizing inhibitors like WO42- and NO3- oxidized the iron substrate surface at the bottom of a pit to change a soft acid to a hard one, they inhibited pit growth by precipitation of oxides within the pit. Inhibition of pit nucleation and growth on the passive iron surface was closely related to the hard and soft acids and bases (HSAB) principle.
  • Corrosion Behavior of Cu and its Welds by Bacteria in Underground Water

    pp. 468-475

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    Corrosions were found at the heat-exchanger made of Cu pipes which the reason why this trouble had estimated may be due to the microbially influenced corrosion (MIC). Laboratory measurements by the use of the same environments were planed. Underground water from the same plant was transferred to laboratory. Bacteria in the test solution was activated by the addition of small nutrients in the underground water. Cu samples were exposed to the test solution. After 2 weeks, a lot of pits occurred on the surface. On the other hand, pitting corrosion was not observed a test solution, which was sterilized by autoclaving. Culturing of bacteria residing in the underground water revealed 7 different species of bacteria. It was became that some 4 species of bacteria were killed by microbicidal activity of Cu ion. The residual 3 species were incubated separately in liquid culture. Next, this liquid culture was used as exposure test solution. Formation of biofilm on the Cu sample surface was observed when the samples were exposed in the test solution with the Staphylococcus sp. Under the biofilm, a lot of pits were occurred. It was became that the Staphylococcus sp. had an ability of proteinaceous fermentation. This fermentation produces ammonia. In conclusion, metallic Cu are corroded by the ammonia in the test solution. Corrosion path of Cu pipe by the underground water are discussed.
  • Effect of Water Adsorption on the Corrosion Rate of Contaminated Aluminium Surfaces

    pp. 476-483

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    The effect of water adsorption on the corrosion rate of aluminum thin film was measured by means of quartz crystal microbalance (QCM). The amount of water adsorbed on the surface was varied by contamination of the surface with varying amount of salt particles and relative humidity. The corrosion rate is closely related to the amount of adsorbed water, but independent of kinds of salt particles (NaCl, MgCl2·6H2O and (NH4)2SO4) used for contamination and temperature of corrosion rate measurements (20-40°C). Increasing difficulty of oxygen dissolution in the water thin film with temperature and inhibition of the anodic reaction by the corrosion products are suggested to be responsible for the present finding of little dependence of corrosion rate on temperature. The aggregation of water molecules is more efficiently taken place over the surfaces covered with the corrosion products than the uncorroded surfaces. This may be due to the changes of surface chemical properties and morphology rather than the hygorscopic effect of the corrosion products. An attempt has been made to quantitatively confirm the schematic relationship between the corrosion rate and the moisture film thickness proposed by Tomashov.

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