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Volume 62, Issue 12
Displaying 1-16 of 16 articles from this issue
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Nobuyuki Mori, Keisaku Ogi1998 Volume 62 Issue 12 Pages 1109-1116
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTo clarify the solidification mechanism of the faceted 123(YBa2Cu3O7−x) crystals from liquid+primary 211(Y2BaCuO5) phases of the superconductive Y-Ba-Cu-oxides (YBCO), new 2-dimensional numerical simulation method of the growth process of the faceted peritectic crystal is proposed and appreciated with the experimental results. The basic model of peritectic solidification of the 123 phase consists of three sequential primitive processes: (a) growth of faceted peritectic crystals, (b) melting of primary particles in the liquid, and (c) solute diffusion in the liquid. Two-dimensional numerical calculations for peritectic growth of the faceted 123 phase with solute diffusion in the liquid are carried out by the explicit control volume finite difference method (FDM) to calculate distribution of 211 particles in the 123 phase and solute distribution in the liquid from the initial distribution of 211 particles in the liquid. The normal growth rate (R) of a facet plane is given by the following relation, which suggests the screw dislocation mechanism: R=ag·ΔTk2, where ag is a kinetic growth constant, and ΔTk is the kinetic undercooling on the faceted interface. The melting rate of superheated 211-particles in the liquid is also assumed to be given by the above equation with a kinetic melting constant (am). The effects of the ratio (ag⁄am), the diffusion coefficient in the bulk liquid, the interface energy of 211 particles, and the local undercooling caused by non-uniform distribution of 211 particles on the growth process are examined in the calculations. The distributions of residual 211 particles and liquid pools in the faceted 123 crystals are calculated form the experimentally obtained log-normal distributions of 211 particles in the liquid of YBCO quenched during unidirectional solidification, and the calculated distributions agree well with the experimental results.View full abstractDownload PDF (1261K) -
Katuo Saitou1998 Volume 62 Issue 12 Pages 1117-1122
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSProduction of copper ultrafine particles by means of an Ar-H2 arc plasma method was performed using a graphite crucible. The arc voltage and the arc current were taken as the influence factors affecting on the generation rate of ultrafine particles and the effect of these factors on the generation rate was studied. The temperature of the crucible close to the melted sample was measured and the relation between the temperature and the generation rate was investigated.
Experiments were carried out under an Ar-50%H2 mixed gas at atmospheric pressure and the arc generation condition of 25∼40 V and 90∼220 A.
The generation rate of ultrafine particles at constant arc voltage increased with increasing arc current and increased with increasing arc voltage at constant arc current. However, when the generation rate was arranged with an electric power as a product of the voltage and the current, it depended solely on the electric power. These results were discussed from the viewpoint of the velocity of the plasma jet generated from the cathode and an anode heating by electrons.
The temperature of the crucible increased with increasing electric power and had a tendency to approach saturation. The temperature was affected intensively by an average temperature of the melted sample, so that an evaporation enthalpy of copper was obtained as a value of 170-230 kJ/mol using the rate process based on the assumption that the measured temperature is the vaporization temperature of the sample.View full abstractDownload PDF (590K) -
Motoi Hara1998 Volume 62 Issue 12 Pages 1123-1131
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe solution-pH dependence of photo-potentials generated at rest potential for the TiO2 films formed by high-temperature oxidation and then reduced by a high-temperature hydrogen gas was investigated in a Na2SO4 solution. The effects of the oxygen gas contained in the solution and the temperature at the hydrogen reduction on this dependence of the TiO2 films were also investigated. The photo-potentials at rest potential for the TiO2 films were increased in the negative direction with an increase in solution pH. The photo-potentials at rest potential for the TiO2 films in the solution saturated with oxygen gas were larger in the negative direction than those in the solution deaerated by bubbling of hydrogen gas. An increase in temperature for the hydrogen reduction of the TiO2 films tended to increase the photo-potential of the film in the negative direction. Such a solution-pH dependence of photo-potentials at rest potential for the TiO2 film was explained from a change in degree of anodic polarization at rest potential with reference to the flatband potential, that is, the band bending for the TiO2 film on the basis of the energy-band model. The effects of the oxygen gas contained in the solution and the temperature for the hydrogen reduction on the photo-potentials of the films were also discussed.View full abstractDownload PDF (1046K) -
Hideki Ito, Takashi Horita, Souhei Nonaka, Kozo Osamura1998 Volume 62 Issue 12 Pages 1132-1136
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe influence of oxygen partial pressure on the microstructure of Ag/Bi2223 tapes has been investigated in the condition of the powder-in-tube method. When oxygen partial pressure (PO2) was fixed at 7.8 kPa during the heat treatment at temperatures between 1102 and 1103 K, the highest value of critical current density (Jc) was achieved. However, Jc tended to decrease when the heat treatment temperature decreased to 1099 K under oxygen partial pressures between 3.0 and 7.8 kPa. When the volume fraction of 2223 phase increases and the alignment of plate-like 2223 grains becomes parallel each other, the Jc becomes higher.View full abstractDownload PDF (1049K) -
Hiroaki Nakamura, Youichi Ogawa, Akira Kasahara, Toshiaki Kodama1998 Volume 62 Issue 12 Pages 1137-1142
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSElectrical conductivity measurements were made of 95CaS-5Na2S solid solution at 723 K through 1173 K in a sulfur partial pressure range from 10−10∼103 Pa with an alternating current bridge. Sintering of the compacted 95CaS-5Na2S disks were undertaken at the temperature of 1323 K because the sublimation of Na2S became significant above 1373 K.
The conductivity of the 95CaS-5Na2S solid solution was independent of sulfur partial pressure, expressed as
(This article is not displayable. Please see full text pdf.)
\ oindentThe apparent activation energy for electrical conductivity was 5.97 kJ·mol−1.
The electrical resistance change with time was found for potentiostatic electrolysis of 95CaS-5Na2S.
These results lead to a conclusion that the 95CaS-5Na2S solid solution is an ionic conductor.View full abstractDownload PDF (531K) -
Tetsuya Akiyama, Masayoshi Kinoshita, Toshio Terasaki1998 Volume 62 Issue 12 Pages 1143-1150
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe fatigue strength of a specimen with a sharp notch has a tendency to decrease when the mean stress applied to the specimen is increased. To find out some changes of the feature in a fractured surface related to the effect of a mean stress on a fatigue strength, the early second stage of a crack must be observed because the first stage crack can not be affected by the mean stress.
In this report, some changes of the early second stage crack caused by the mean stress in a notched SM400 steel specimen is investigated by using a scanning electron microscopy. The other hand, for the example that there is no effect of a mean stress on a fatigue strength, the fractured surface of the specimen with a large radious notch is additionally observed.
The results obtained are as followed. Under the condition that the stress amplitude is kept at a constant value, the region size of the fractured surface involving with small plane parts is changed by the effect of the mean stress when the mean stress is small. When the mean stress is large, there is no change of the region size. There is no change of the resion size in a specimen with a large radius notch.View full abstractDownload PDF (1523K) -
Kiyoshi Kusabiraki, Yukimichi Nakao, Ken Sakuradani, Shigeoki Saji1998 Volume 62 Issue 12 Pages 1151-1156
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSFe-Ni base alloys form a subscale in the alloy interior by selective oxidation of the elements having a large affinity of oxygen together with the external scale formation on the alloy surface by high-temperature oxidation. Almost of all the previous papers concerning with subscale which consists of both intergranular and intragralular oxides have been on the basis of the two-dimensional observation on the cross-sections of oxidized specimens. However, it is difficult to estimate exactly the three-dimensional morphology development of the subscale because its morphology is peculiar. In order to examine directly the three-dimensional morphology we have developed a metal matrix dissolution technique for the oxidized Fe-Ni alloy without dissolving the metallic oxide phases constituting the subscale by using an organic solvent system solution. In the present study, we report here on the appropriate dissolution of the Fe-36%Ni alloy oxidized in air at high temperatrures under the applied tensile stress conditions in the organic solvent system solution which consists of bromine, tetraethyl ammonium and acetonitrile. The three-dimensional morphology of the intergranular and intragranular oxides formed in the Fe-36%Ni alloy suggests the difference of each growth mechanism.View full abstractDownload PDF (1270K) -
Kyu-Sang Cho, Hiroshi Takamatsu, Hiroshi Honda1998 Volume 62 Issue 12 Pages 1157-1162
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effect of water temperature on the shape, cooling characteristics and non-crystallinity of FeSi7.5B15 (at%) wires produced by the In-Rotating-Water Spinning Method was examined experimentally. The nozzle diameter was 0.25 mm and the incidence angle of molten metal jet to the water surface was 60°. The drum rotational velocity vd ranged from 5.8 to 8.5 m/s and the jet velocity vj from 5.9 to 9.5 m/s. The water temperature Tw was set at 283, 303 and 323 K. The wire produced at Tw≈283 K showed a smooth surface. At Tw≈303 K, a structure like a string of beads appeared partly on the wire surface. At Tw≈323 K, the wire looked like a string of beads. A straight wire was obtained for vj⁄vd≤ 1. The wire became meanderous with increasing vj⁄vd for vj⁄vd>1. The jet temperature decreased almost linearly with the distance from the point of incidence and it’s value was higher for higher vj. The average cooling rate of the wire in the temperature range of 1470 to 1200 K was lower for higher Tw. It decreased gradually with decreasing vd and increasing vj. For a constant Tw, the heat of crystallization ΔH, which is a parameter expressing the degree of non-crystallinity of the wire, was uniquely dependent on the vj⁄vd ratio. For 0.7<vj⁄vd<0.97, ΔH showed a high value which was almost independent of Tw. For 0.97<vj⁄vd, ΔH decreased with increasing vj⁄vd and the decrease was more significant for higher Tw. However, a definite correlation was not observed between the measured cooling rate and ΔH. Discussion was made of the factors that affected the non-crystallinity of the wire.View full abstractDownload PDF (571K) -
Shin-ichi Hasegawa, Takeshi Kobayashi, Ryosuke Hasegawa1998 Volume 62 Issue 12 Pages 1163-1167
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSDirect determination procedure of trace aluminum in iron and steel samples by graphite furnace atomic absorption spectrometry (GF-AAS) has been studied. A rapid analytical method to determine acid-soluble Al and total Al separately was established. Atomization of the analyte was carried out by the stabilized temperature platform furnace (STPF) method using a L’vov platform. Sample solutions were prepared by dissolving iron and steel samples in nitric acid. In the analysis of acid-soluble Al, the supernatant liquid of the centrifuged sample solution was used. While, in the analysis of total Al, the sample solution was fed onto the graphite furnace by means of an ultrasonic slurry sampler. The detection limit (3σ of blank value) was 0.08 ppm when the weight of the sample was 1 g. The use of centrifugal separation and ultrasonic dispersion as the method of pretreatment reduced the blank value due to contamination from the environment and shortened analytical time significantly. The identical working curve for calibration is usable to determine both acid-soluble Al and total Al. The standard samples are not required.View full abstractDownload PDF (488K) -
Kazutaka Okamoto, Takahiko Kato, Akira Yoshinari, Junya Kaneda, Yasuhi ...1998 Volume 62 Issue 12 Pages 1168-1176
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe single crystal austenitic stainless steels Type 316L and 304L were grown in order to improve the resistance to stress corrosion cracking (SCC) using a unidirectional solidification method which can provide the large size single crystals. The mechanical properties and the chemical properties were examined. The orientation and temperature dependence of tensile properties of the single crystals were measured. The yield stress of the single crystal steels are lower than those of the conventional polycrystal steels because of the grain boundary strength cannot be expected in the single crystal steels. The tensile properties of the single crystal austenitic stainless steel Type 316L depend strongly on the orientation. The tensile strength in ⟨111⟩ orientation are about 200 MPa higher than those in the ⟨100⟩ and ⟨110⟩ orientations. The microstructure of the single crystal consists of a mixture of the continuous γ-austenitic single crystal matrix and the δ-ferrite phase so that the effects of the γ⁄δ boundaries on the chemical properties were studied. The effects of the δ-ferrite phases and the γ⁄δ boundaries on the resistance to SCC were examined by the creviced bent beam test (CBB test). No crack is observed in all the CBB test specimens of the single crystals, even at the γ⁄δ boundaries. The behavior of the radiation induced segregation (RIS) at the γ⁄δ boundaries in the single crystal austenitic stainless steel Type 316L was evaluated by the electron irradiation test in the high voltage electron microscope (HVEM). The depletion of oversized solute chromium at the γ⁄δ boundary in the single crystal austenitic stainless steel Type 316L is remarkably lower than that at the grain boundary in the polycrystalline-type 316L.View full abstractDownload PDF (1830K) -
Nobuya Shinozaki, Hirotaka Mizuguchi, Kusuhiro Mukai1998 Volume 62 Issue 12 Pages 1177-1182
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe Wettability of ZrO2-CaO and ZrO2-Y2O3 substrates with the molten iron of low oxygen content was examined at 1873 K by the use of the sessile drop method. The effect of substrate composition on wettability was made clear, that was, the contact angle was decreased once and increased afterwards with increasing CaO content on using the ZrO2-CaO substrates and low contact angles of about 115 deg were obtained for the ZrO2-Y2O3 substrates. Only minor amount of iron transferred from the molten iron into substrate particles and the grains of substrate grew at the rate of 2 μm/h or less. Neither the transfer of iron nor the grain growth influenced the contact angle. From the work of adhesion it was presumed that the inter-molecular force was predominant at the molten iron-zirconia interface and the chemical interaction also would contribute to the interfacial bonding.View full abstractDownload PDF (564K) -
Hiroyuki Masuda1998 Volume 62 Issue 12 Pages 1183-1188
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSPrevious AFM observation showed that small water droplets and water film were observed on the surface when pure water or aqueous solution was poured on graphite or mica. However, when the specimen surface was dirty and too rough to observe very thin water film like roughly polished metal surface, we cannot decide whether the water film exists or not. The possibility of measurement of water film distribution by surface potential measurement was studied. As the result, it is proved that surface potential becomes low when the water film exists and the thin water film which cannot be distinguished from the surface shape can be observed by measuring the surface potential distribution.View full abstractDownload PDF (1425K) -
Byung-Nam Kim, Teruo Kishi1998 Volume 62 Issue 12 Pages 1189-1196
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe driving force for grain boundary migration and the pinning stress due to a particle are evaluated by three models (the Zener model, the modified Zener model and the sweep model), during the interaction between a curved grain boundary and a spherical particle simulated by the axi-symmetric finite element method. While the pinning stress is determined only by the contacting angle of grain boundary to particle surface in the Zener model, the effect of the change in boundary shape during Zener pinning is considered in the other two models. The variation of the pinning stress and the contacting angle at the maximum pinning stress evaluated by the three models show some differences, and are dependent on the particle size. The maximum pinning stress is linearly dependent on the particle size. When the grain boundary escapes from the particle, the driving force of the Zener model becomes zero because the particle becomes free from the grain boundary. However, in the sweep model, the driving force increases because of the locally increased curvature around the particle prior to escape, which is consistent with the simulation. The evaluation of the macroscopic movement of the grain boundary during Zener pinning is also carried out. The evaluated migration behavior by the sweep model when the grain boundary returns to the steady state agrees well with the simulation. It is found that the Zener model overestimates the pinning stress.View full abstractDownload PDF (864K) -
Takao Yamaguchi, Masaaki Yamamura, Imao Nagasaka, Naoyuki Ohnishi, Dai ...1998 Volume 62 Issue 12 Pages 1197-1203
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn the present paper, the values of the spectral emissivity of color metals i.e. gold and copper, and copper heated in oxidizing atmospheres are measured at the temperature of 1000°C, just below their melting points, and within the wavelength region from 0.38 to 0.94 μm. Also the values of the spectral reflectance of gold and copper are measured at room temperature. And the spectral emissivity calculated from this spectral reflectance.
Then, experimental results are analyzed by the dispersion formula concerning the free electrons and bound electrons. Thus, the formula can be applied whether wavelength dependency of the spectral emissivity is negative and variable (gold and copper), or positive and nearly constant in the case of copper heated in oxidizing atmosphere.View full abstractDownload PDF (791K) -
Takahiro Suwa, Katuhisa Nagayama, Toshio Suzuki1998 Volume 62 Issue 12 Pages 1204-1205
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSDownload PDF (257K) -
Goroh Itoh, Akihiko Nojima1998 Volume 62 Issue 12 Pages 1206-1207
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSDownload PDF (193K)
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