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

Zairyo-to-Kankyo Vol. 40 (1991), No. 1

  • Evaluation of Iron Corrosion Rate in Solution Containing Inhibitors by Using Coulostatic Method

    pp. 3-7

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    In order to expand and clear the applicable range of the coulostatic method to measure the metal corrosion rate in solution, the method was tested by measuring the corrosion rate of iron in water containing three types of inhibitor, i.e., potassium chromate, polyphosphate with calcium ion and sodium nitrate, in stagnant state. Though the potential decay curve did not obey the theoretical equation at the initial stage because of the film formation by the inhibitors, the over-potential ηt at t=0 was obtained by extrapolating the linear parts of the log ηt polts to t=0. The corrosion rates obtained by using ηt and other parameters gave good agreement with those obtained by the weight loss method for the same samples. So, from a practical standpoint, the coulostatic method was found to be applicable for iron corrosion rate monitoring in the solution containing above inhibitors.
  • Critical Potentials for Pitting and Crevice Corrosion of Type 304 Stainless Steel in NaCl Solution at 423K

    pp. 8-13

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    Critical potentials for pitting (Epit) and crevicice corrosion (Ecrev) for type 304 stainless steel have been determined from long-term steady polarization tests in deaerated NaCl solutions as a function of NaCl concentration at 423K. Epit and Ecrev were expressed by the conventional form: E=A-B log[Cl-], where A and B in volt vs. SHE were -0.19 and 0.15 for Epit and -0.20 and 0.10 for Ecrev, respectively. The comparison of Epit with pitting potential (Epit) and repassivation potential (ER, pit), which were repeatedly determined from stepwise cyclic polarization tests, showed that ER, pit distributed less nobly than Epit especially at lower NaCl concentrations and that Epit could be described as a lower limit of Weibull's distribution function for Epit. The similar analysis for crevice corrosion showed that the noblest value of ER, crev for its dependency on corrosion extent corresponded to Ecrev but the distribution in Ecrev at different concentrations of NaCl could not be described by the Weibull's function with an identical shape parameter.
  • Corrosion Behavior of the Ti-Pd Coating Using a Vacuum Plasma Spraying System

    pp. 14-18

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    Palladium plating was applied onto the titanium spraying powder, which should be consumed on thermal spraying by using a electroless plating process with sodium hypophosphite as a reducing agent. Then the Pd coated Ti powder was sprayed on the 304 type steel by vacuum plasma spraying system. The coating had a 2.8 mass percent Pd and it's distributed uniformly. The corrosion potential of the Ti-Pd coating in a 1N H2SO4 at 327K indicated the same level potential that Ti passivity zone or an about 0.45V nobler than that of the uncoated Ti sprayed coating, after immersing early stage into the solution. It's corrosion potential was moving to the more noble side slowly with increasing the immersion time. In addition, the anodic polarization characteristics of Ti-Pd coating showed a wide passive state and it's low corrosion current generation, thus showing excellent corrosion resistance.
  • The Use of AC and DC Potential Mapping in the Evaluation of the Effectiveness of Cathodic Protection on Buried Coated Steel Pipelines with Holidays

    pp. 19-25

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    Potential fields formed by the alternating and direct currents flowing into a coating holiday on a buried steel pipeline were analyzed by means of the multi-electrode mapping method. Simulated field experiments demonstrated that the AC potential field analysis permits an accurate trenchless estimation of the location and the size of coating holidays, whereas the DC potential field analysis permits a correct trenchless assessment of the true level of cathodic protection at respective holidays. The effectiveness of the method was also demonstrated on the existing pipelines. Theoretical background and the results of field experiments are given.
  • Analysis Techniques for Surface Contamination

    pp. 32-39

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    Chemical, physical, and morphological methods for the analysis of surface contamination are proposed. A variety of techniques for separtation of contaminants for chemical analysis, the versality and limitations of the instruments for the surface analysis, and the advantages and disadvantages of physical methods in contamination analysis are described.
  • Analyses of Corrosion Products of Metals by Mössbauer Spectrometry

    pp. 40-56

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    The fundamentals and applications of Mössbauer spectrometry, which has been proved to be very useful for the analyses of chemical states of Mössbauer elements such as iron, tin, antimony, europium etc. in solid samples, are described. The typical applications of (CEMS) to the chemical state analyses of corrosion products and chemically coated films deposited on iron, steel and tin, and of magnetic and structural studies of advanced industrial thin films are insroduced.
  • Corrosion Tests for Plastic Packaged LSI

    pp. 57-65

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    Corrosion problems of electronics conponents have been become important in the reliability of the several machines and systems. In this paper, the corrosion mechanism for plastic packaged LSI and its testing methods is discussed. It is shown the materials selection and designing for the plastic packaged LSI are protected from corrosion damage in humidity environments are seemed to actual actions.

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