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

Zairyo-to-Kankyo Vol. 48 (1999), No. 6

  • Polymer Alloy: Biodegradable Polymer Blends

    pp. 330-337

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    Miscibility, crystallization behavior and morphology of biodegradable aliphatic polyester/poly (vinylidene halide) blends are investigated by differential scanning calorimetry and optical microscopy and obtained results are briefly reviewed. All the blends investigated form miscible mixtures and the crystallization behavior and morphology of the blends are strongly dependent upon the crystallization kinetics. Therefore, it is concluded that the kinetic factors are the most important in controlling the crystallization and the morphology of the biodegradable crystalline polymer blends.
  • The Study on Stray Current Corrosion for These 100 Years and the Activity of Committees

    pp. 338-344

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    This paper introduce stray current corrosion control and the committees related this problem, after described generation mechanism and control.
    Some problems of stray current corrosionarose immediately after construction of electric railway in Japan, in 1895. To solve this problems, the study was started and continued for 100 years up to now. Until the Taisho Era (-1926), major subject of the study was improvement of raiway return circuits, and drainage systems on underground metallic piping were added in the early Showa Era (1926-). After World War II, the study was resumed and plastic cable, coating systems for steel pipes, and impressed current systems for practical use, have been developed until now.
    The Study Committee on Stray Current Corrosion was established in 1933 by academic specialists, engineers of various utilities, and government authorities, and it has been still continuing research activities. The Co-ordinated Committees on Stray Current Corrosion were established in 5 districts. And these committees started research activities to solve problems such as co-ordinated interference.
  • Evaluation of Particle Impact Conditions in a Sand Blast Type Erosion Test Rig

    pp. 349-354

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    For the prediction of actual damage to materials in plant components and in making the erosion mechanisms clear, it is important to define and to control the particles impact condition in a testing facility. A sand blast type erosion test rig, which can achieve the particle impact velocities over 120m/s and a wide range of impact angles has been constructed. A new method was proposed to determine particle velocities in this facility. The key factors in particle impact conditions of impact velocities and impact angles were examined. The theoretical velocity of particle calculated by the equations of particle motion were compared with the experimental results. Impact angles were controlled by using two types of specimen geometry, and erosion tests at an impact angle of three degrees could be conducted soundly. Although some spread particles were observed surrounding the central damage area of the specimen surface, the greatest amount of damage was concentrated in the center. As a result, it was found that particle impact conditions were well controlled in this testing unit.
  • Impact Angle Dependence of Erosion by Solid Particle Impact for Metallic Materials

    pp. 355-361

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    The aim of this paper is to estimate erosion damage under any condition involving impact angle, impact velocity and shape and size of solid particles. Erosion tests were carried out on six metallic materials using angular silica sand, silicon carbide and glass bead particles at impact angles ranging from 3 to 90 degrees and at impact velocities of less than 120m/s in a sand blast type test rig. The dependence of normalized erosion damage, the relative damage to that at normal angle, on impact angle was investigated under the foregoing conditions. The impact angle dependence of normalized erosion damage was hardly affected by both the impact velocity and the particle size. On the other hand, the shape of the particles had a marked effect on the impact angle dependence for the softer materials. Round particles moved the impact angle of maximum erosion rate to higher impact angles than those angular particles did, for aluminium and iron specimens. The impact angle, the shape of particles and material hardness were revealed to be effective factors on the amount of erosion damage. Finally normalized erosion damage curves for tested materials were well simulated with an exponential equation which was expressed as the product of cutting and plastic damage term with the parameters of impact angle and material hardness. Moreover, the two exponential variables of the equation were reasonably related to the material hardness. These results suggested the possibility of estimating erosion damage at given impact angle from that at the normal impact angle.
  • The Effect of Micro Segregation on Pitting Corrosion of SCS14 Austenitic Stainless Steel Castings in Sea Water Environments

    pp. 362-368

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    Austenitic stainless steel castings, such as SCS 13, SCS 14, which consists of δ/γ duplex phase, are extensively used as structural material in seawater environments. It is known that SCS14 involving 2wt% Mo is more resistant to pitting corrosion than SCS 13. In this paper, effects of Mo on the pitting corrosion are discussed in terms of microstructure of the material. The corrosion behavior of the materials with different δ ferrite contents and cleanlinesses have been evaluated by seawater exposure testing, electrochemical polarization, and TEM-EDX analysis. The results indicate that pits mainly nucleate at nonmetallic inclusions such as MnS and δ/γ boundaries, and materials containing δ ferrite above 7vol% have high pitting corrosion resistance. The nucleation at δ/γ boundaries is assumed to be due to the segregation of P. It is considered that because of segregation of Mo along δ/γ boundaries, SCS 14 is much resistant to pitting corrosion than SCS 13.
  • Corrosion Behavior of Carbon Steel in Concentrated LiBr solutions up to 473K

    pp. 369-374

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    In view of demand for raising maximum operation temperature in commercial absorption refrigerator, the corrosion behavior of carbon steel in concentrated LiBr solutions was investigated as a function of LiBr concentration and temperature up to 473K. Carbon steel specimens were exposed in deaerated LiBr solutions for 200h and the changes in weight were measured. The amount of corrosion increased with temperature when the concentration of LiBr was higher than 17mol kg-1, while it decreased slightly with temperature in 10mol kg-1 LiBr solution. Lithium hydroxide (0.1mol kg-1) decreased the amount of corrosion markedly when the LiBr concentration was lower than 10mol kg-1 but it could not inhibit the corrosion at concentrations higher than 17mol kg-1. Among several oxoacid salts tested in this study, molybdate ion worked most effectively as an inhibitor at 473K as well as at lower temperatures. A specimen oxidized in air at 673K almost sustained its passivity during exposure to 17mol kg-1 LiBr+0.1mol kg-1 LiOH solution at 473K.
  • Dynamics of Hydrogen Induced Blistering of a Low Carbon Steel Sheet by Lamb Waves Analysis

    pp. 375-381

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    With the aim of studying the fracture dynamics of environmentally assisted fractures in thin plates, we developed a new source simulation method of the zeroth-order symmetric (or S0-) Lamb wave using the experimental overall-transfer function of the system. The transfer function was determined by the time-domain deconvolution of detected S0-Lamb component by the artificial fracture source of a compression-type PZT element whose vibration kinetics was previously monitored by a laser interferometer. The fracture kinetics was estimated by the iteration so that the S0-waveform computed to the assumed fracture kinetics best represents the S0-waveform detected. Hydrogen induced blistering was found to be caused by the succession of fast Mode-I fracture with source rise times from 0.6 to 1.0μs. The crack volume estimated by the source simulation corresponded to that of fine blistering with an opening displacement of 5μm. As the estimated fracture kinetics of hydrogen blistering coincide with those of delayed fracture of high tension low alloy steel under tensile loading, the kinetics of first and micro-fractures and blistering induced by hydrogen gas precipitation appears to be independent on the hydrogen solubility and strength of steels, the applied stresses and the orientation of cracks.

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