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Volume 54, Issue 8
August
Displaying 1-13 of 13 articles from this issue
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Paper
Paper
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Kazuhiro Hasezaki2007 Volume 54 Issue 8 Pages 543-546
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSBi0.5Sb1.5Te3.0+x compounds with varying tellurium content (x=−0.10∼0.10) were prepared using mechanical alloying (MA) and the vertical Bridgman method (VBM), and compared their Hall coefficients, electrical resistivities and Seebeck coefficients at room temperature. In changing the tellurium content, it was possible to change the carrier concentration from 7.99×1024 to 1.52×1026m−3 for −0.10 < x < 0.00. In contrast, the carrier concentration was almost constant at 1.0×1025m−3 for 0.00 < x < 0.10. For samples with the same composition, it was observed that the carrier concentration of the VBM sample was approximately four times higher than that of the MA sample. The Seebeck coefficients for the two methods corresponded well with the relative carrier concentration, although the electrical resistivities of the VBM samples were found to vary because of preferred orientation. The maximum power factors for the MA and VBM samples were 3.52×10−3Wm−1K−2 at 1.23×1025m−3 (x=0.03), and 3.52×10−3Wm−1K−2 at 3.18×1025m−3 (x=0.00135), respectively. These results indicate that the difference in the carrier concentrations for two methods can be explained by the tellurium deficiency in samples prepared using the VBM.View full abstractDownload PDF (341K)
Special Issue:New Trends in Electromagnetic Processing
Summarization
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Yukio Makino2007 Volume 54 Issue 8 Pages 548
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSDownload PDF (117K)
Review
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Hiromi Nakano, Yukio Makino2007 Volume 54 Issue 8 Pages 549-555
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSAlumina prepared by millimeter-wave sintering, compared to that by electric-furnace sintering, was densified at a 250 K lower temperature and exhibited twice the bending strength (800 MPa). However, this alumina showed a 7% lower value of Young's modulus than alumina by electric-furnace sintering. The reasons for these properties were clarified by microstructural analysis using a transmission electron microscope. The lower Young's modulus was caused by the higher porosity. The relationship between bending strength and porosity or grain size showed a lower correlation, but the reduction in pore size corresponded to the increase in bending strength. At the grain boundaries of all of the alumina ceramics, no thin films or impurities were observed, and, therefore, no significant difference in these features among aluminas could be attributed to sintering conditions. However, a difference in the distribution of pores was clearly observed. Many small pores existed in the grains of the alumina by millimeter-wave sintering, while larger pores existed at the grain boundaries of the alumina by electric-furnace sintering. The small pores in the grains contributed to the improved bending strength. This result was caused by the millimeter-wave sintering process, in which the pore velocity was less than the boundary velocity due to the rapid diffusion of atoms.View full abstractDownload PDF (1665K) -
Noboru Yoshikawa2007 Volume 54 Issue 8 Pages 556-559
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSMicrowave interacts with materials. And it is possible to heat various materials, if they are a good microwave absorber. The heating mechanism has been generally understood as the friction of molecules in their rotation under microwave electric field. In this paper, on the other hand, importance of heating effect by microwave magnetic field is pointed out, and microwave heating of metal powders is discussed, especially.
Heating mechanisms of microwave was classified according to its interaction with materials, related to the difference in microwave penetration depth into materials. The heating mechanisms of materials are classified as the dielectric loss, the induction (eddy current) loss and the magnetic loss. Application of microwave heating to materials processing and environmental engineering fields is briefly discussed.View full abstractDownload PDF (446K) -
Kiyoshi Mizuuchi, Kanryu Inoue, Masakazu Kawahara, Hiroshi Asanuma, Ke ...2007 Volume 54 Issue 8 Pages 560-569
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSTi-aluminides reinforced Ti matrix composites were fabricated from 0.04mm-thcik Ti foils with 0.012mm-thick aluminum foils, using pulsed current hot pressing (PCHP) process, and the effect of processing condition on the properties of composites thus fabricated was investigated. Microstructure of the composite fabricated was an alternatively-laminated structure composed of Ti and Ti-aluminides, and the structure of the Ti-aluminides in the composites changed with increasing a holding temperature during PCHP. Tensile tests carried out for the composites at room temperature revealed that the mechanical properties of the composites changed by altering the holding temperature. The tensile strength and the elongation of the composite produced at 1273 K attained to 810 MPa and 3.64%, respectively. Microstructural observations of fractured specimens showed that the Ti layers effectively bridged numerous cracks emanating from the Ti-aluminides in the composites fabricated at less than 1273 K. In the present review, above results are summarized in comparison with the microstructure and mechanical properties of laminate materials fabricated by conventional vacuum hot pressing.View full abstractDownload PDF (1606K) -
Keizo Kobayashi2007 Volume 54 Issue 8 Pages 570-575
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSA pulsed current sintering is a new sintering process that powder in the conductive mold is heated by applying current under a pressure. This new sintering process is able to apply high-speed heating and densification at lower sintering temperature. Therefore, this process is effective for consolidation of nanocrystalline materials.
In this study, we focus attention on the pressure during the pulsed current sintering of varied functional materials. In the ordinary pulsed current sintering process, the powder in the graphite die was consolidated under a pressure of about 30 MPa. The mechanically alloyed Fe-48at%Cr powder was consolidated in this process without brittle phase. In addition, the Fe-48at%Cr compact with a complex shape was able to be formed.
The pulsed current sintering under a pressure of less than 10 MPa was effective to prepare the homogeneous porous materials. The porous material prepared by this process from copper fiber can be applied to heat sink for cooling CPU. The pulsed current sintering with a pressure of more than 500 MPa was effective to consolidate amorphous powder and to obtain a bulk nanocrystalline compact at s sintering temperature more than crystallized temperature of the amorphous powder. The nanocrystalline Ti-2at%Fe-10at%Si compact had high strength and was applied to the mold for consolidation of NaCl powder.View full abstractDownload PDF (1556K) -
Koji Akai, Tatsuro Kumise, Terumitsu Tanaka, Hiroki Kurisu, Setsuo Yam ...2007 Volume 54 Issue 8 Pages 576-583
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSWe study the thermoelectric properties of some candidates of high performance thermoelectric materials that are fabricated by the spark plasma sintering technique. The first topic is concerned with preparation of higher density samples of zinc antimony compound Zn4Sb3 for which it is known that fabrication of high density samples is a key point to improve the thermoelectric performance. The second topic is concerned with reducing of grain sizes of sintered samples to decrease the thermal conductivity. The third topic is concerned with the new approach combining the experiment and the theory for magnesium silicide Mg2Si. It is one of a good thermoelectric material with the simple crystal structure. Therefore the material is the appropriate material as a test bed of the theoretical method based on the ab-initio electronic structure method.View full abstractDownload PDF (1489K)
Paper
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Tasaburo Saji, Mitsuhiro Isumi, Junji Morimoto, Yukio Makino, Shoji Mi ...2007 Volume 54 Issue 8 Pages 584-589
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESS24GHz Millimeter Wave oscillated by Gyrotron system was radiated to Fe2O3 Powder in atmospheric air. The samples were heated at 1000°C, 1100°C and 1200°C by millimeter wave. The elevating temperature rate was controlled at 10°C/min and 30°C/min. While the temperature was elevating, the temperature of sample raised suddenly at about 550°C. It seemed that Fe2O3 was changed to be a very high dielectric loss material. The lattice constant of all samples became shorter than the lattice constant of raw materials, after heating by millimeter wave radiation. This indicates oxygen goes out of Fe2O3. In other words, the samples are deoxidized by millimeter wave, even in atmospheric air. The lattice constants of samples which were heated on elevating temperature a rate of 30°C/min were shorter than those of sample heated at 10°C/min. Therefore, it seemed higher electric field accelerated the deoxidization. When the focused millimeter wave was radiated to the sample, the oxygen composition was reduced from 58.1at% to 37.8at%. Fe2O3 was deoxidized strongly by strong electric field of millimeter wave.View full abstractDownload PDF (1160K) -
Sadatsugu Takayama, Guido Link, Manfred Thumm, Akihiro Matsubara, Moto ...2007 Volume 54 Issue 8 Pages 590-594
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSNagata and coworkers of the Tokyo Institute of Technology have been working on the development of unique ultra high purity iron refinement technology based on an ancient Japanese iron refinement called "Tatara" method. Their findings during microwave sintering of powder metals led to the idea that rapid refinement of iron should be possible by application of 2.45 GHz microwaves instead of relying on burning of carbon for heat production. While joint experiments at the National Institute on Fusion Science (NIFS) proved that high purity iron (1% carbon concentration) with less than 10% of impurities as compared to irons from modern blast furnaces could be produced in a short time, while reducing the carbon consumption to 1/2.
In order to investigate the effect of microwave frequency, the joint experiments with and Forschungszentrum Karlsruhe (FZK) have done using the samples of magnetite powder mixed with carbon powder. As a result, high quality pig iron could be made from powder samples of mixed magnetite and carbon by 30 GHz mm-waves heating in air. However, in case of heating by 2.45 GHz at similar conditions, mainly FeO was produced. Therefore, we expect that there is frequency dependence in the reduction reaction. This paper describes experimental results obtained by millimeter-wave processing.View full abstractDownload PDF (1276K) -
Toshiyuki Ueno, Takashi Yoshioka, Kiminori Sato, Yukio Makino, Morinob ...2007 Volume 54 Issue 8 Pages 595-600
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSAl-VGCF binary and Al-CF-VGCF ternary composites were fabricated by pulsed electric current sintering. The content of VGCF in the Al-VGCF composites were 0, 15 and 30mass%. The Al-VGCF composites achieved a controlled coefficient of thermal expansion (CTE) ranging 13 to 20×10−6 /K and a thermal conductivity of 100 to 120 W/(m·K). The Al-CF-VGCF composites had a structure of unidirectional aligned CF filled with the Al-VGCF matrix. They attained a high thermal conductivity up to 600 W/(m·K) and a controlled CTE around 18×10−6 /K in the perpendicular direction to the CF.View full abstractDownload PDF (1139K) -
Takaya Endo, Shingo Nakane, Masaki Kato, Ken Hirota, Toshiyuki Nishimu ...2007 Volume 54 Issue 8 Pages 601-605
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSDense zirconium boride (ZrB2)-based materials with and without tungsten (W) have been fabricated directly from mixtures of constituent elemental powders (Zr, B and W) by spark plasma sintering (SPS) at 1800°C for 10 min under 30 MPa in a vacuum. Formation processes of monolithic, W-doped ZrB2 solid solutions ZrB2 (ss) [(Zr1-xWx)B2 (0<x≤0.12)], and composites consisting of ZrB2 (ss) and WB2 were investigated. Their mechanical properties of bending strength (σb), Vickers hardness (Hv) and fracture toughness (KIC) at room temperature were evaluated. Solid solution and composite materials gave higher Hv (∼20 GPa), KIC (∼4.4 MPam1/2), and σb (∼600 and 690 MPa for the former and the latter, respectively) than those (14.1 GPa, 3.21 MPam1/2, and ∼500 MPa) of the monolithic ZrB2 ceramics fabricated under the same conditions.View full abstractDownload PDF (1061K) -
Tadateru Shibata, Masaki Kato, Ken Hirota, Toshiyuki Nishimura, Kiyosh ...2007 Volume 54 Issue 8 Pages 606-611
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSCarbon nanofibers (CNFs: ∼150 nmφ and 4∼5 μml) added SiAlON (Si4Al2O2N6) composites were fabricated directly from mixtures of Si3N4, Al2O3, AlN, and CNF by spark plasma sintering (SPS) at 1700°C for 10 min under 30 MPa in a vacuum. Dispersion of CNFs up to ∼5 vol% into SiAlON matrix introduced the enhancement of densification and diminution of matrix grains, resulted in improvement of mechanical properties, such as bending strength σb (450→600 MPa) and fracture toughness KIC (4.1→4.5 MPa·m1/2); however, Vickers hardness Hv decreased monotonously from 17.7 to 12.2 GPa with increasing CNF content. In addition, homogeneous CNFs dispersion brought a drastic change in electric conductivity; insulative SiAlON ceramics changed into conductive materials with improved mechanical properties by a small amount of CNFs with more than ∼3 vol%.View full abstractDownload PDF (935K) -
Satoshi Sunada, Yasuaki Ueyoshi, Yukio Makino, Kazuhiko Majima2007 Volume 54 Issue 8 Pages 612-618
Published: 2007
Released on J-STAGE: February 19, 2008
JOURNAL OPEN ACCESSThe corrosion behavior of SUS304 specimen produced by spark plasma sintering (SPS) has been studied through electrochemical tests such as polarization curve measurement, electrochemical reactivation ratio measurement and electrochemical impedance spectroscopy (EIS), compared to those of specimens produced by the conventional ingot metallurgy process (I/M) and the powder metallurgy process (P/M).
The corrosion current density (icorr) of the SPS specimen has a tendency increasing with a decrease in electrochemical corrosion potential (Ecorr). The corrosion resistant of the SPS specimen was inferior to that of the I/M specimen because of carbon diffusion from a graphite punch rod while it was improved by removing the surface file through polishing.
The electrochemical reactivation ratio of the SPS specimen without polishing was 27.4%, which was significantly higher compared to 0.13% for the I/M specimen because of its poor passivation film.
The Rct value of the SPS specimen without polishing was 0.09 times as large as that of the I/M specimen, while it became 0.63 times for the SPS specimen with polishing. This result well agrees with the icorr value obtained by the electrochemical polarization test.View full abstractDownload PDF (1274K)
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