MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 55 , Issue 8
Showing 1-46 articles out of 46 articles from the selected issue
  • Shin-ichi Orimo, Yumiko Nakamura, Kazuhiro Ishikawa, Hiroyuki Saitoh, ...
    2014 Volume 55 Issue 8 Pages 1113
    Published: August 01, 2014
    Released: July 25, 2014
    JOURNALS FREE ACCESS
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  • Hiroyuki Saitoh, Seiichi Kato, Masahiko Katagiri
    2014 Volume 55 Issue 8 Pages 1114-1116
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: April 18, 2014
    JOURNALS FREE ACCESS
    Anodized aluminum samples with different surface oxide layer thicknesses (approximately 0.3 and 3 µm) were hydrogenated at 9 GPa and 600°C for 24 h. A few large crystals of AlH3, of which average crystal size was 30 µm, were formed when the aluminum sample with the thicker oxide layer was hydrogenated, whereas the sample with the thinner oxide layer was uniformly hydrogenated to form AlH3 crystals 10 µm in particle size. It is likely that the surface oxide layer inhibits not only the hydrogenation reaction of aluminum but also the spontaneous nucleation of AlH3, which causes the difference between the formed crystal sizes.
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  • Toyoto Sato, Shigeyuki Takagi, Motoaki Matsuo, Katsutoshi Aoki, Stefan ...
    2014 Volume 55 Issue 8 Pages 1117-1121
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: May 02, 2014
    JOURNALS FREE ACCESS
    We have studied the vibrational properties of Li4RuH6, consisting of the lightest Li+ metal cation, and the octahedral [RuH6]4− complex anion by Raman and Fourier Transform Infrared (FTIR) spectroscopies and first-principles calculations. The Li+ forms a cubic framework with the [RuH6]4− inside as the local atomic arrangement of Li4RuH6, which is similar to that of a related M2RuH6 with a divalent metal cation M′ (M′ = Mg, Ca, Sr, Ba, and Yb). Comparing the vibrational studies on Li4RuH6 with M′2RuH6, the peak frequencies for the antisymmetric Ru–H stretching mode (νanti-str) showed a reasonable relationship with the Ru–H bond distances (dRu–H) in [RuH6]4−, with higher peak frequencies for shorter bond distances according to the linear relation νanti-str = 10052 − 4990 × (dRu–H).
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  • Koji Tanaka, Hiroyuki T. Takeshita, Ho Shin, Kosuke Kurumatani, Tetsu ...
    2014 Volume 55 Issue 8 Pages 1122-1128
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: May 16, 2014
    JOURNALS FREE ACCESS
    The micro/nano-structural transition and hydrogen absorption mechanism in Mg/Cu super-laminate composites (SLCs) were investigated. Differential scanning calorimetry (DSC) measurements were performed on Mg/Cu SLCs at several heating rate and till several repetition cycles up to twenty cycles, and micro/nano-structures of Mg/Cu SLCs were examined by stereomicroscope, digital-microscope, scanning electron microscope (SEM), and scanning transmission electron microscope (STEM). It is found that the micro/nano-stractures of Mg/Cu SLCs change drastically at early cycles and reach a steady state after around the tenth cycle. The detailed examination of DSC curves, and SEM and STEM observations of Mg/Cu SLCs suggest that the hydrogen absorption process consists of a fast and a slow reaction which shows a sharp exothermic peak around at 610 K and a broad exothermic peak around at 570 K connected with it in DSC profiles, respectively.
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  • Kazutaka Ikeda, Toshiya Otomo, Hidetoshi Ohshita, Naokatsu Kaneko, Mas ...
    2014 Volume 55 Issue 8 Pages 1129-1133
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: May 16, 2014
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    Local structural changes that accompany amorphization during the decomposition of LiAl(ND2)4 were investigated by neutron total scattering measurements. Structure factors before the decomposition were attributed to single-phase LiAl(ND2)4 characterized by isolated [ND2] units. Atomic pair distribution functions after heat treatments at 433 and 673 K showed that LiAl(ND2)4 decomposed to amorphous mixed phases that contain Li3AlN2 and AlN.
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  • Hai-Wen Li, Yigang Yan, Etsuo Akiba, Shin-ichi Orimo
    2014 Volume 55 Issue 8 Pages 1134-1137
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: May 16, 2014
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    The complex hydride LiBH4, with a hydrogen density of 18.5 mass%, has been attracting significant interests for hydrogen storage, while suffers from its high dehydrogenation and rehydrogenation temperature. In this work, we systematically investigated the improvement effects of nanosized Ni on the dehydrogenation and rehydrogenation reactions of LiBH4 using thermogravimetry, quadrupole mass spectrometry and pressure-composition-isotherm analyses. Nanosized Ni was homogeneously dispersed on the surface of LiBH4 after ball milling. The dehydrogenation peak temperature of LiBH4 was reduced from 743 to 696 K with addition of 25 mass% Ni. First, LiBH4 tended to react with Ni to form Ni4B3, which suggests the thermodynamic destabilization effect of Ni. Then, the in-situ formed Ni4B3 was suggested to play a catalytic role on the dehydrogenation of the unreacted LiBH4. Moreover, the rehydrogenation content of LiBH4 was improved from 4.3 to 10.8 mass% by addition of 25 mass% Ni, suggesting the significant improvement effect of Ni4B3 on the rehydrogenation.
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  • Shigehito Isobe, Yudai Ikarashi, Hao Yao, Satoshi Hino, Yongming Wang, ...
    2014 Volume 55 Issue 8 Pages 1138-1140
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: May 23, 2014
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    Recently, LiAlH4 has attracted attention as one of the most promising hydrogen storage materials, because LiAlH4 is able to release large amount of hydrogen (7.9 mass%H2) below 250°C. However, the kinetics of the dehydrogenation reaction of LiAlH4 is too slow for applications to fuel cell vehicles. To improve the dehydrogenation kinetics, the dopant effect of TiCl3 has been investigated in this research. Here, LiAlH4 doped with various ratios (0, 0.1, 0.2, 0.5, 1.0, and 2.0 mol%) of TiCl3 were prepared by ball milling for 30 min under a 1.0 MPa H2 atmosphere. The decomposition of LiAlH4 proceeds via a two-step reaction and the dehydrogenation kinetics of each step were compared to determine the optimum amount of TiCl3 that would assist the process. With increasing of TiCl3 amount, the dehydrogenation temperature for both of the reactions decreased. Activation energies decreased with increasing TiCl3 amount, however the amount of desorbed hydrogen decreased. Considering the kinetics and hydrogen capacity in the both steps, the results suggest that the optimum amount of doped TiCl3 for the dehydrogenation of LiAlH4 is around 0.2 mol%.
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  • Guanqiao Li, Motoaki Matsuo, Stefano Deledda, Bjørn C. Hauback, ...
    2014 Volume 55 Issue 8 Pages 1141-1143
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: May 30, 2014
    JOURNALS FREE ACCESS
    The dehydriding property of xNaBH4 + (1 − x) Mg2FeH6 (x = 0.1–0.75) is measured to investigate the effect of combining with complex hydride Mg2FeH6 on reducing dehydriding temperature of metal borohydrides, which has lately been found to be effective for LiBH4. When x = 0.1 and 0.125, a single-step dehydriding reaction is observed, while in the composition range x ≥ 0.25, a multi-step dehydriding reaction is observed. Despite the different dehydriding process, X-ray diffraction measurements confirmed that Mg2FeH6 and NaBH4 began releasing hydrogen simultaneously over the entire composition range. The results also indicate that the dehydriding temperature of NaBH4 is reduced by at least 150 K when combining with Mg2FeH6.
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  • Hyunjeong Kim, Kouji Sakaki, Yumiko Nakamura
    2014 Volume 55 Issue 8 Pages 1144-1148
    Published: August 01, 2014
    Released: July 25, 2014
    JOURNALS FREE ACCESS
    The effect of nitrogen interstitial atoms on the cyclic stability of V0.37Ti0.33Mn0.3 was investigated. V0.37Ti0.33Mn0.3 with and without nitrogen were hydrogenated and dehydrogenated for 100 times. During hydrogen cycling, the hydrogen absorption plateau pressure of both samples decreased significantly but the desorption plateau pressure stayed the same resulting in smaller hysteresis at higher cycle. Their reversible hydrogen storage capacity progressively diminished with increasing cycle number. At the first cycle, V0.37Ti0.33Mn0.3 without nitrogen absorbed more hydrogen than V0.37Ti0.33Mn0.3 with nitrogen but at the 100th cycle the situation was reversed; V0.37Ti0.33Mn0.3 with nitrogen showed a higher reversible hydrogen storage capacity. This result strongly suggests that nitrogen interstitial atoms somehow retard the degradation of the hydrogen storage capacity of V0.37Ti0.33Mn0.3.
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  • Lingjun Wei, Zhengwei Cui, Yunfeng Zhu, Liquan Li
    2014 Volume 55 Issue 8 Pages 1149-1155
    Published: August 01, 2014
    Released: July 25, 2014
    JOURNALS FREE ACCESS
    Multi-wall carbon nanotubes supported nickel (Nano-nickel/MWCNT) is added to the hydriding combustion synthesis (HCS) product of Mg99Ni by mechanical milling to yield a designed composite for improving the hydrogen storage properties of magnesium. It is revealed that there is a synergistic effect of nano-Mg2NiH4 and MWCNT on the hydrogen storage properties of Mg99Ni, which improves the hydrogenation and dehydrogenation performance when compared to adding either nano-Ni or MWCNT alone. The composite requires only 80 s to reach its saturated hydrogen capacity of 6.79 mass% at 373 K and desorbs 97.2% hydrogen within 1800 s at 543 K. The dehydrogenation activation energy of this system is 105 kJ mol−1, which is much lower than that of as-received MgH2 (153 kJ mol−1). In addition, the composite preserves stable hydrogen storage capacity and kinetics in the hydrogenation/dehydrogenation cycles at 423 K.
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  • Jianxin Zou, Sheng Long, Lifu Zhang, Chong Lu, Xi Chen, Xiaoqin Zeng, ...
    2014 Volume 55 Issue 8 Pages 1156-1160
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 11, 2014
    JOURNALS FREE ACCESS
    In the present work, a Fe covered pure Mg ultrafine powder–Mg@Fe- was prepared through electroless plating of Fe on the arc plasma evaporated Mg powder in a FeCl3 n-butyl alcohol solution. The phase components, microstructure and hydrogen sorption behaviors of the Mg@Fe composite powder were investigated using XRD, TEM and PCT techniques. TEM observations revealed that those ultrafine Mg particles were covered by nano α-Fe grains reduced by Mg during electroless plating. The hydrogenation enthalpy of the Mg@Fe composite is determined to be −78 kJ/mol H2 based on PCT measurements. Meanwhile, the hydrogen absorption activation energy of Mg@Fe composite is reduced to 54.6 kJ/mol H2 and the onset desorption temperature of hydrogenated Mg@Fe is lower down to 620 K when compared to those for pure Mg powder. The improved hydrogen sorption kinetic properties of Mg@Fe composite over pure Mg powder can be mainly attributed to the catalytic effects from nano α-Fe covered on the Mg ultrafine particles.
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  • Nobuhiko Takeichi, Yasuhiro Sakaida, Tetsu Kiyobayashi, Hiroyuki T. Ta ...
    2014 Volume 55 Issue 8 Pages 1161-1167
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: May 30, 2014
    JOURNALS FREE ACCESS
    The hydrogen absorption and desorption reactions of pure MgH2 were investigated by pressure-time measurements using a Sieverts’ type instrument in the temperature and pressure ranges of 653–683 K and 0.5–1.7 MPa, respectively. The absorption and desorption behaviors were analyzed using a fraction of the reaction product during the hydrogen absorption and desorption. The fraction was evaluated based on the amount of absorbed and desorbed hydrogen.
    The hydrogen absorption of pure Mg immediately occurs when the thermodynamic condition in which the reaction can proceed is reached at 653–683 K, but the hydrogen desorption does not start immediately when it can thermodynamically proceed at the same temperatures. Incubation periods were observed and had varied values in the range from 0.15 to 1.5 ks under the above-mentioned pressure and temperature conditions.
    In order to clarify the hydrogen desorption mechanism, the data obtained were analyzed by the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation. The obtained values of the Avrami exponents varied from 3 to 0.6 with the increasing fraction of Mg. The hydrogen desorption process was classified into four stages based on the KJMA plots of the hydrogen desorption curves of MgH2 measured in this study. These values indicated that the Mg nuclei generate and three-dimensional grow during the initial stage, then the growth is restricted to a two- or one-dimensional.
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  • Kouji Sakaki, Hyunjeong Kim, Hirotoshi Enoki, Shin-ichi Yoshimura, Shu ...
    2014 Volume 55 Issue 8 Pages 1168-1174
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: June 13, 2014
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    The effect of substitution elements on hysteresis and flatness of the equilibrium pressure plateau in ZrxTi1−xMn0.8V0.2Ni1.0 was investigated and suitable hydrogen storage alloys for a metal hydride (MH) actuator in rehabilitation devices were developed. By changing the Zr/Ti ratio, the equilibrium pressure was tuned for the MH actuator. Al substitution made the hysteresis factor smaller, while Fe and Cu substitution did not. In addition, it was confirmed that ferrovanadium is available in these alloys to reduce not only the material cost but also the hysteresis factor leading to better properties for the MH actuator. The developed Zr0.5Ti0.5Mn0.8V0.2Ni0.9Al0.1 showed no significant reduction of hydrogen capacity and no significant change in the shape of the pressure-composition (P-C) isotherms even after 1000 cycles.
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  • Shigehito Isobe, Ayaka Umeda, Takenobu Wakasugi, Tao Ma, Ryo Yamagami, ...
    2014 Volume 55 Issue 8 Pages 1175-1178
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: June 13, 2014
    JOURNALS FREE ACCESS
    We propose the microstructural change model of magnesium hydride catalyzed by Nb2O5 during hydrogenation. The ball-milled composites, MgH2 and 1 mol% Nb2O5, were dehydrogenated and then rehydrogenated for varied time at room temperature under 0.1 MPa H2 atmosphere. The crystallite size of Mg and MgH2 was evaluated by powder X-ray diffraction (XRD) measurement and confirmed by transmission electron microscopy (TEM) observation. The crystallite size of generated MgH2 was smaller than that of Mg and did not change significantly with increasing time of hydrogenation. It is suggested that the number density of MgH2 crystallites increases during the hydrogenation process.
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  • Kenji Higashi, Yasumasa Chino, Yorinobu Takigawa
    2014 Volume 55 Issue 8 Pages 1179
    Published: August 01, 2014
    Released: July 25, 2014
    JOURNALS FREE ACCESS
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  • Jinbao Lin, Qing Wang, Weijie Ren, Qudong Wang, Lifeng Ma
    2014 Volume 55 Issue 8 Pages 1180-1183
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: June 06, 2014
    JOURNALS FREE ACCESS
    The effects of cyclic extrusion and compression (CEC) on the deformation behavior and failure of ZK60 alloy were examined using in-situ scanning electron microscope (SEM) uniaxial tensile testing at room temperature. Fracture surface was analyzed by SEM. Result shows that the tensile elongation of the extruded ZK60 alloy is obviously increased by CEC deformation. The change in fracture modes has been attributed to the suppression of twinning and the activation of non-basal slips due to the grain refinement and texture modification induced by CEC deformation.
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  • Tomomi Ito, Masafumi Noda, Hisashi Mori, Yoshio Gonda, Yuta Fukuda, Sa ...
    2014 Volume 55 Issue 8 Pages 1184-1189
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: June 13, 2014
    JOURNALS FREE ACCESS
    We investigated the effect of the cooling rate and molten metal temperature on the microstructure and mechanical properties of a sub-rapidly solidified magnesium alloy, Mg–10Al–0.2Mn–1Ca, prepared by antigravity suction casting using a water-cooled steel mold. The microstructure of the antigravity-suction-cast material without water cooling consisted of coarse grains (grain size: 780 µm), with networks of an Al–Ca compound at the grain boundaries. The higher cooling rate of the water-cooled steel mold promoted the formation of the Al–Ca compound and voids in accordance with increases in the internal and external temperature gap and differences in the solidification rate of the mold. The formation of voids and the shrinkage were suppressed, however, by adjusting the cooling rate and decreasing the molten metal temperature. The particle size of the Mg phase was refined to 135 µm and the grain-boundary compounds were finely dispersed in the Mg phase. The as-cast alloy showed an ultimate tensile strength of 166 MPa and an elongation of 8%. The microstructure and mechanical properties of the as-cast alloy were dependent on the cooling rate and molten metal temperature, but they were not dependent on the casting speed.
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  • Yasumasa Chino, Xinsheng Huang, Kazutaka Suzuki, Motohiro Yuasa, Mamor ...
    2014 Volume 55 Issue 8 Pages 1190-1195
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: May 30, 2014
    JOURNALS FREE ACCESS
    The texture formation behaviors of rolled and subsequently annealed Mg–1.5 mass%Zn–0.2 mass%Ce alloy, whose texture was characterized by a split of basal planes in the transverse direction (TD-split texture), were investigated by electron back-scattering diffraction analysis. When the rolling temperature was set to 723 K, the basal poles of the as-rolled specimen exhibited tilted distribution toward the TD, and the TD-split texture appeared more significantly after annealing. Grains with the TD-split texture component were observed to construct some aggregates in the annealed specimen rolled at 723 K. It was observed that the aggregates of the grains with the TD-split texture component in the annealed specimen were created by the subdivision of the matrix grains by the fragments of twins. Activation of non-basal slips such as prismatic < a> slips was suggested to be related to the reorientation of grains with the TD-split texture component. In addition, room temperature formability of rolled Mg–Zn–Ce alloys was investigated by conical cup tests and deep drawing tests. In the conical cup tests, significant conical cup value, which corresponds to aluminum alloys, was obtained in the Mg–1.0Zn–0.2Ce and Mg–2.0–0.2Ce alloys. In the deep drawing tests, the large drawing ratio of 1.8 was obtained in the Mg–1.5Zn–0.2Ce alloy, when the blank holder force, punch speed, punch diameter, die hole diameter, shoulder radius of punch and lubricant was set to 2 kN, 5 mm/min, 33.0 mm, 35.6 mm, 3.0 mm and molybdenum disulfide paste, respectively.
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  • Makoto Hino, Koji Murakami, Takahiro Hori, Teruto Kanadani
    2014 Volume 55 Issue 8 Pages 1196-1201
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: June 27, 2014
    JOURNALS FREE ACCESS
    The effects of two different pretreatments on the anticorrosive performance of AZX911 magnesium alloy containing 1.0 mass% calcium treated with an anodizing from phosphate and ammonium salt solution have been studied. The AZX911 magnesium alloy after anodizing had a lower anticorrosive performance. The lowering of this anticorrosive performance was attributed to the 0.1 mass% calcium in the anodized coating. The anticorrosive performance of the AZX911 magnesium alloy was improved by applying a fluoride salt solution in the pretreatment. This fluoride salt solution treatment made it possible to remove calcium close to the surface of the AZX911 magnesium alloy substrate, the calcium content in an anodized coating being decreased. The anticorrosive performance was improved by the anodizing from phosphate and ammonium salt solution with a sacrificial anticorrosive effect.
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  • Motohiro Yuasa, Xinsheng Huang, Kazutaka Suzuki, Mamoru Mabuchi, Yasum ...
    2014 Volume 55 Issue 8 Pages 1202-1207
    Published: August 01, 2014
    Released: July 25, 2014
    JOURNALS FREE ACCESS
    The effects of precipitate distribution in commercial Mg alloys on the discharge behavior of a Mg–air battery were investigated. Rolled Mg–9 mass%Al–1 mass%Zn (AZ91) alloy sheets were selected as the anode. The discharge behaviors were evaluated by constant current discharge tests, and the corrosion behaviors were estimated by salt immersion tests and potentiodynamic polarization measurements. In the discharge tests, the peak-aged specimens exhibited much shorter discharge time than the solution-treated specimen. In the corrosion tests, the aged specimens exhibited quite a low corrosion rate as compared with the solution-treated specimen. From the potentiodynamic polarization measurements, the aged specimens showed a much lower corrosion current density and higher corrosion potential than the solution-treated specimen. It is suggested that a stable corrosion barrier by densely distributed β-phase precipitates contributed to both the reduction of discharge time and the suppression of corrosion rate for the aged specimens. Microstructural evaluations of the aged specimens revealed that fine β-phase precipitates were densely distributed throughout the specimens and that there was little Al-rich α phase, which would accelerate galvanic corrosion between the α matrix and the β phase. It was confirmed that the finely and homogenously distributed β phase in the aged AZ91 specimens acted as a barrier to the dissolution of the α-Mg matrix because a large Al-rich α phase was not distributed in the AZ91 specimens in this study.
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  • Shigeru Katsuyama, Koji Akai, Hiroaki Anno, Kazuhiro Hasezaki, Kaoru K ...
    2014 Volume 55 Issue 8 Pages 1208
    Published: August 01, 2014
    Released: July 25, 2014
    JOURNALS FREE ACCESS
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  • Hidetoshi Miyazaki, Teruaki Nakano, Manabu Inukai, Kazuo Soda, Yudai I ...
    2014 Volume 55 Issue 8 Pages 1209-1214
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: April 11, 2014
    JOURNALS FREE ACCESS
    We investigated the electronic and local crystal structures of the sintered half-Heusler ZrNiSn alloy by synchrotron radiation photoemission spectroscopy (SR-PES), synchrotron radiation X-ray powder diffraction (SR-XRD) measurements, and electronic band structure calculations to clarify mechanisms leading to improvements in the thermoelectric properties of materials. In contrast to the predicted semiconductor-like electronic structure, the SR-PES results show a pseudo-gap at the Fermi level, and the SR-XRD analysis reveals an interstitial Ni disorder in the half-Heusler structure. An improvement in the thermoelectric properties can be achieved by material design based on the pseudo-gap electronic structure of half-Heusler ZrNiSn-based alloys.
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  • Masaya Kumagai, Ken Kurosaki, Yuji Ohishi, Hiroaki Muta, Shinsuke Yama ...
    2014 Volume 55 Issue 8 Pages 1215-1218
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: May 02, 2014
    JOURNALS FREE ACCESS
    CuGaTe2 has a large thermoelectric (TE) figure of merit (ZT) at high temperatures, i.e., ZT = 1.4 at 950 K. However, at lower temperatures, the ZT values are smaller. One reason for this is that CuGaTe2 has a high lattice thermal conductivity (κlat) at lower temperatures. One known method for reducing κlat is manipulating the microstructure of the bulk material. Therefore, herein, the grain-size effect on the TE properties of CuGaTe2 bulk samples produced by ball milling and hot pressing was investigated. Although κlat decreased with grain size, a simultaneous decrease in the Seebeck coefficient occurred, leading to no overall improvement in ZT.
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  • Xiangning Meng, Takeyuki Fujisaka, Keita O. Ito, Ryosuke O. Suzuki
    2014 Volume 55 Issue 8 Pages 1219-1225
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: June 06, 2014
    JOURNALS FREE ACCESS
    A thermoelectric (TE) module with two different thermal sources for power generation is studied in this work. Here, a conventional Π-type module is tilted in the shape of a parallelogram. A numerical analysis is conducted by using the finite volume method to examine three-dimensional (3-d) flows of heat and electric charge. The module configuration and the shape of the elements determine the distribution of temperature and current density inside the TE module. Further, the shortest path is chosen preferentially as the path of the current, depending on the geometry of the TE elements. Although the distribution of current density depends greatly on the module configuration, the TE output power is not affected by the parallel and symmetrical configurations in the two equivalent modules. Thus, the conventional TE module with Π-type elements is the most favorable, and maximum performance is obtained for a tilting angle of 90° because of the lowest internal electric resistance.
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  • Y. Takagiwa, T. Kamimura, J. T. Okada, K. Kimura
    2014 Volume 55 Issue 8 Pages 1226-1231
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 18, 2014
    JOURNALS FREE ACCESS
    Various compositions of Al–Ga–Pd–Re icosahedral quasicrystals (QCs) were synthesized using arc-melting and annealing methods, and their thermoelectric properties were investigated. With the same trend in the Seebeck coefficient as Al–Pd–Mn and Al–Pd–Re QCs, the Al–Ga–Pd–Re QC has a similar pseudogap electronic structure near the Fermi level. More particularly, we found that a sample with a nominal composition of Al66Ga4Pd21Re9 exhibited a higher Seebeck coefficient of 90 µV K−1 at 373 K, and is thus a highly efficient thermoelectric material. This dense sample, having neither cracks nor pores, shows a 1.5 times higher dimensionless figure of merit ZT of 0.18 compared with sintered Al71Pd20Re9. ZT enhancement through Ga substitution for Al is enabled through an increase in both electrical conductivity and Seebeck coefficient, and a decrease in phonon thermal conductivity. This behavior is discussed in terms of the precipitation of metallic secondary phases and the “weakly bonded rigid heavy clusters (WBRHCs)” scheme applicable to cluster-based solids including quasicrystals.
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  • Guanghe Li, Ken Kurosaki, Yuji Ohishi, Hiroaki Muta, Shinsuke Yamanaka
    2014 Volume 55 Issue 8 Pages 1232-1236
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 11, 2014
    JOURNALS FREE ACCESS
    The high-temperature thermoelectric (TE) properties of group 13 elements (Ga, In, and Tl) triple-filled skutterudites in the nominal compositions of InxGa0.02Tl0.20Co4Sb12 (0 ≤ x ≤ 0.30) were investigated. All samples contained impurity phases in addition to the skutterudite matrix phase, i.e. some of the filler elements added to CoSb3 precipitated as the metal state and antimonides. With increase the starting amount of In, the actual content of In increases while that of Tl decreases. Owing to phonon scattering by rattling of the group 13 elements, low lattice thermal conductivity was achieved, leading to relatively high TE figure of merit (ZT) for all samples. The maximum ZT value was 0.72 at 773 K obtained for the sample in the nominal composition of In0.30Ga0.02Tl0.20Co4Sb12.
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  • L. Daróczi, G. Eszenyi, Zs. Molnár, D. L. Beke, A. B&uum ...
    2014 Volume 55 Issue 8 Pages 1237-1242
    Published: August 01, 2014
    Released: July 25, 2014
    JOURNALS FREE ACCESS
    Probability frequency spectra of the peak area, energy and width of the Barkhausen noise (BN) signals have been measured versus induction in a narrow induction window during traversing the magnetization loop from negative to positive saturation (and reverse) in Fe(75)Si(15)Nb(3)B(6)Cu(1) amorphous metallic glasses. It was obtained, that the noise power, as the function of the induction, B, showed a wide minimum at B = 0 and two sharp peaks around the knees of the magnetization loop. This can be a quite general feature of soft magnetic materials and can be related to the fact that at around the knees a mechanism, different from the domain motion in a random pinning field operates: new domains are created or existing domains are destroyed. Furthermore, it is also shown that the probability frequency of the duration, area and energy of the peaks are described by power function even far from the B = 0 point, but with higher exponents belonging to the stationary values obtained around B = 0.
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  • H. F. Huang, D. H. Li, J. J. Li, R. D. Liu, G. H. Lei, S. X. He, Q. Hu ...
    2014 Volume 55 Issue 8 Pages 1243-1247
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 11, 2014
    JOURNALS FREE ACCESS
    A nickel-base high-temperature alloy (Ni-17Mo-7Cr) has been characterized by nanoindentation and transmission electron microscopy to determine the changes of nanoindentation hardness and microstructural evolution under ion irradiation. Ion irradiation experiments for bulk and thin-foil specimens of Ni-17Mo-7Cr alloy were carried out at room temperature, up to 6.6 dpa, by 7 MeV Xe26+ and 1 MeV Xe20+ ions, respectively. The continuous stiffness measurement (CSM) with a diamond Berkovich indent was used to measure the depth profile of hardness. Nanoindentation results for bulk specimens showed an evident ion irradiation induced hardening phenomenon, and the nanoindentation hardness increases with increasing ion dose. High number density of nano-scale black spots and linear-like defects were observed in thin-foil specimens irradiated at 0.33 and 6.6 dpa, respectively. High-resolution transmission electron microscopy images revealed that the black spots were nano-scale solute clusters and dislocation loops, while the linear-like defects were found to be Ni, Mo and Cr-enrichment regions by using the high-angle annular dark field-scanning transmission electron microscope. The ion irradiation induced defects can be responsible for the hardening of Ni-17Mo-7Cr alloys.
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  • M. Asato, C. Liu, K. Kawakami, N. Fujima, T. Hoshino
    2014 Volume 55 Issue 8 Pages 1248-1256
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 04, 2014
    JOURNALS FREE ACCESS
    We present the ab-initio calculations for the lattice distortion effect of substitutional single impurities, I (= Sc ∼ Ge, Sn), and substitutional two impurities, I–I and I–Sn, in bcc-Fe. Sn is a perturbed-angular-correlation (PAC) probe. The calculations are based on the generalized-gradient-approximation in the density-functional formalism and the full-potential Korringa-Kohn-Rostoker (FPKKR) Green’s function method. For single impurities, we show that the available experimental results, such as lattice distortion around the impurities and the atomic volume changes per impurity, are reproduced very well by the present calculations. For two impurities, we clarify the lattice distortion effect on 1st-nearest neighbor (NN) interaction energies of I–I and I–Sn pairs in Fe, being a difference between the distortion energies with two impurities located on the infinitely separated sites and on the neighboring sites. We initially show that the lattice distortion effect is very low for the interaction energies between two impurities with a small size-misfit, compared with the host atom, although it becomes high for the interaction energies of two impurities with a large size-misfit. The lattice distortion effect on the I–I (I = Cr ∼ Zn) interaction energies is less than 0.02 eV, while the lattice distortion effect on the I–Sn (I = Sc, Ge) interaction energies is greater than 0.2 eV. Secondly, we show that we can improve the agreement with the experimental results for the interaction energies of I–Sn pairs in bcc-Fe, by taking into account the lattice distortion. Finally, we show that the magnetic interaction is important for the lattice distortion of the I–Sn (I = Cr, Mn) pairs. The high lattice distortion for I–Sn pairs (I = Cr, Mn) is partly caused by the antiferromagnetic interaction of impurities I with the 1st-NN host atom on the opposite site of the Sn impurity, resulting in the high energy gain (0.13 eV, 0.06 eV) of I–Sn interaction.
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  • Yasuo Takaki, Tetsuya Masuda, Equo Kobayashi, Tatsuo Sato
    2014 Volume 55 Issue 8 Pages 1257-1265
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 11, 2014
    JOURNALS FREE ACCESS
    In the present paper, the effects of natural aging on the bake hardening behavior of four Al–Mg–Si alloys, i.e., Alloy A (Al–0.6Mg–0.6Si) (mass%), Alloy B (Al–0.6Mg–1.0Si), Alloy C (Al–1.0Mg–0.6Si) and Alloy D (Al–1.0Mg–1.0Si), were investigated by means of Vickers hardness test, tensile test, differential scanning calorimetry analysis (DSC) and transmission electron microscopy (TEM). Two kinds of nanoclusters, i.e., Cluster(1) and Cluster(2) were controlled with the multi-step aging process. As the results, it was found that Cluster(1) formed during natural aging caused the decreased bake hardening response even though the pre-aging was conducted before natural aging. The decrease of the bake hardening response with increasing the natural aging time was markedly higher in the later stage of bake hardening than in the early stage. Exothermic peaks of Peak 2 and Peak 2′ were observed in all of four alloys pre-aged at 343 and 363 K. Peak 2′ became larger with the natural aging time. The size distribution of the β″ precipitates became wider with the natural aging time for Alloy A heated up to the temperature of Peak 2′. This is well understood by the following model. The transition from Cluster(2) formed during pre-aging to β″ occurs preferentially at the early stage of bake hardening or during heating up to the temperature of Peak 2. Then the growth of β″ is inhibited by the presence of Cluster(1) at the later stage of bake hardening. The secondary nucleation of β″ occurs just after the dissolution of Cluster(1) into the matrix during heating up to the temperature of Peak 2′. The combined formation of Cluster(1) and Cluster(2) by the multi-step aging essentially affects the BH response and the β″ precipitates in Al–Mg–Si alloys.
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  • Misako Nakayama, Masanori Kajihara
    2014 Volume 55 Issue 8 Pages 1266-1273
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 04, 2014
    JOURNALS FREE ACCESS
    The kinetics of the solid-state reactive diffusion between Sn–Ni alloys and pure Cu was experimentally observed to examine effects of addition of Ni into Sn on the growth behavior of compounds at the interconnection between the Sn-base solder and the multilayer Au/Ni/Cu conductor during energization heating. In this experiment, sandwich (Sn–Ni)/Cu/(Sn–Ni) diffusion couples with Ni concentrations of y = 0.01 and 0.03 were isothermally annealed in the temperature range of 433–473 K for various periods up to 1152 h, where y is the mol fraction of Ni. After annealing, a compound layer consisting of Cu6Sn5 and Cu3Sn was recognized between the Sn–Ni alloy and the Cu specimen in the diffusion couple. Here, the thickness of the Cu3Sn layer is smaller than that of the Cu6Sn5 layer. The (Cu,Ni)6Sn5 grains were transformed from the Ni3Sn4 grains in the Sn–Ni alloy in the neighborhood of the Cu6Sn5 layer, and then adhered to the Cu6Sn5 layer. The overall growth of the compound layer including the (Cu,Ni)6Sn5 grains is remarkably accelerated by the adhesion, but that of the compound layer excluding the (Cu,Ni)6Sn5 grains is slightly decelerated by the adhesion. The mean thickness of each layer increases in proportion to a power function of the annealing time. For annealing at 433–473 K, the ratio between the thicknesses of the Cu6Sn5 and Cu3Sn layers is hardly affected by the addition of Ni into Sn up to y = 0.03.
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  • Su Zhao, Donglai Wei, Rongbin Li, Li Zhang
    2014 Volume 55 Issue 8 Pages 1274-1279
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 04, 2014
    JOURNALS FREE ACCESS
    The cooling rate is a key factor of controlling the slab surface microstructures during continuous casting of steel. The effect of cooling rate on phase transformation and microstructure of Nb–Ti microalloyed steel was investigated by a confocal laser scanning microscopy and a Gleeble-3800 thermal simulation machine. The process of phase transformation can be analyzed through in situ observation. A critical cooling rate of 5 K·s−1 was revealed, below which the proeutectoid ferrite along austenite grain boundaries and widmanstatten structures were observed, and carbonitrides precipitated were also observed in the proeutectoid ferrite. With the increase of cooling rate, the quantity of the precipitates decreases while the width of the proeutectoid ferrite becomes smaller. The carbonitrides precipitated along the austenite grain boundary result in the decrease of the carbon concentration near the grain boundary, which is more favorable to form the proeutectoid ferrite as well as to change its width. When the cooling rate was greater than or equal to 5 K·s−1, the precipitates were dispersed uniformly in the grain, and the bainite was observed mainly.
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  • Teng-Shih Shih, Tin-Hou Lee, Ying-Jhe Jhou
    2014 Volume 55 Issue 8 Pages 1280-1285
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 11, 2014
    JOURNALS FREE ACCESS
    The fatigue behaviors of 7075-T73 alloy with/without anodization/sealing treatment were investigated in this study. The microstructure of different samples was analyzed by electron microscopy. As the experiments, the microstructure were observed from the anodized/sealed samples to indicate that precipitates trapped at subsurface near film/metal (f/m) interface would partly dissolved and the deformed matrix existed high fractions of high angle grain boundaries. The bare 7075-T73 alloy samples achieved fatigue strength of 225 MPa and the anodized/sealed samples enhanced their fatigue strength at 107 life cycles with 10–20 µm film thickness. The fractured anodized/sealed sample showed fine striation spacing than bare sample after subjected to low stress amplitude.
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  • Akihide Hosokawa, Hideyuki Ohtsuka, Tiantian Li, Seiichiro Ii, Koichi ...
    2014 Volume 55 Issue 8 Pages 1286-1291
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 18, 2014
    JOURNALS FREE ACCESS
    The microstructure and magnetic properties of nanostructured pure iron, FeCo and FeNi3 produced by high-pressure torsion (HPT) were investigated. Electron backscattered diffraction (EBSD) technique was used to study the evolutions in microstructure and crystallographic texture during HPT, revealing that a weak deformation texture with an orientation of < 110> bcc being parallel to the disc normal for pure iron and FeCo while < 110> fcc was found to be parallel to the hoop direction of the HPT disc in FeNi3. The grain size of the HPTed materials was characterized by means of EBSD and transmission electron microscopy (TEM), and its influence on the coercivity was investigated. The other highlight of this paper is the use of a focused ion beam (FIB)-SEM dual beam instrument. This enabled us to obtain quite high image quality (IQ) values for the EBSD measurements even for the highly deformed microstructure in the current ferromagnetic intermetallics.
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  • Michael C. Faudree, Yoshitake Nishi, Michael Gruskiewicz
    2014 Volume 55 Issue 8 Pages 1292-1298
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: June 27, 2014
    JOURNALS FREE ACCESS
    Up to now, increasing modulus of fiber reinforced polymers (FRPs) by shortening fibers has not been reported however, shortening fiber length from commercial 6.4 to 0.44 mm by additional mixing of paste prior to injection molding was found to increase initial and maximum tensile modulus 5 to 25% in a 3-phase system of highly CaCO3 filled 20 mass% E-glass fiber reinforced thermoset polyester/styrene-butadiene polymer bulk-molding compound (GFRP-BMC). The increased number of spaces between fibers appears to allow for action of coefficient of thermal expansion (CTE) difference between fibers and matrix to increase thermal compressive residual stress sites during shrink and cool-down. A novel “fiber-spacing” model incorporating the “rule of mixtures” is constructed based on physical meaning to predict effect of fiber length (lf), fiber volume fraction (Vf), filled-matrix modulus (Em) fiber modulus (Ef), and nominal fiber diameter (d), valid for fiber orientation parameter (0.43 < ηo < 0.54) on tensile modulus (dσ/dε)o to be useful in BMC composite design. The “fiber-spacing” model exhibited a good fit with the experimental data of 20 mass% fiber composite and predictions were made for 10, 30, and 40 mass% fiber composite agreeing with data in the literature.
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  • Jianxun Song, Qiuyu Wang, Xiaobo Zhu, Jungang Hou, Shuqiang Jiao, Hong ...
    2014 Volume 55 Issue 8 Pages 1299-1303
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: June 20, 2014
    JOURNALS FREE ACCESS
    NaCl–KCl–TiClx was prepared via using titanium sponge to reduce titanium tetrachloride in a NaCl–KCl melt under a negative pressure at 1023 K. The relationship between titanium valence states and [F]/[Ti] molar ratios was investigated with successive adding potassium fluoride in the pre-prepared NaCl–KCl–TiClx. It was found that the average valence of titanium ions tended to be stable around 3.0 when [F]/[Ti] molar ratio was greater than 1.80. The equilibrium redox potentials, ETi3 + /Ti2 + , ETi4 + /Ti3 + , ETi3 + /Ti and ETi2 + /Ti, were also calculated through the obtained concentration of equilibrium titanium ions with different molar ratios of [F]/[Ti]. Meanwhile, the influence of the fluoride anion on over-potential and characteristics of titanium electrodeposition were investigated through changing the molar ratio of [F]/[Ti]. The results showed that, with the increasing of [F]/[Ti] molar ratios, the grain size of electrodeposition products became smaller, while the over-potential was higher.
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  • Yoshitake Nishi, Réda Ourahmoune, Masae Kanda, Junhua Quan, Mic ...
    2014 Volume 55 Issue 8 Pages 1304-1310
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: June 20, 2014
    JOURNALS FREE ACCESS
    In short carbon fiber reinforced polyetheretherketone (SCFRP-PEEK) composites, carbon fibers and PEEK matrix typically exhibit a weak adhesive force at the interface. However, applying 0.43 MGy dose of homogeneous low-voltage electron beam irradiation (HLEBI) was apparently shown to improve not only the bending modulus (Ef) 65.5% at the median-ranked cumulative probability evaluated as a distribution function (PE = 0.50) from 6.7 to 11.1 GPa, but also Charpy impact fracture value (auc) 17.5% at median-ranked cumulative probability (Pf = 0.50) from 16.6 to 19.5 kJ m−2. The 0.43 MGy HLEBI dose also remarkably improved the statistically lowest Charpy impact value as at Pf = 0 calculated by 3-parameter Weibull equation 80.0% from 8.0 to 14.4 kJ m−2. Penetration depth, Dp of the HLEBI was calculated to be 153 to 226 µm (3–11%) into both side surfaces. SEM results of the HLEBI-treated Charpy impact sample fracture surfaces show more matrix sticking to the fibers and more matrix being held between fibers than the untreated increasing pullout resistance. The HLEBI appears to assist in strengthening the typically weak bonding between the carbon fiber and PEEK matrix improving mechanical properties.
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  • Kazuki Tabata, Hisato Fujii, Naka Sato, Motoi Hara
    2014 Volume 55 Issue 8 Pages 1311-1318
    Published: August 01, 2014
    Released: July 25, 2014
    JOURNALS FREE ACCESS
    The preparation of a coating consisting of Ni aluminide containing a small amount of Hf was carried out by the electrodeposition of Ni using an aqueous solution and the electrodeposition of Hf and Al using a molten salt. Furthermore, in order to change the depth of the layer containing Hf in the coating, a four-step electrodeposition of Ni, Hf, Ni and Al was carried out, and the times of the first and third Ni electrodepositions were changed. As a result, coatings consisting of Ni aluminide, which contained different depths of the Hf-containig layer, were formed. The cyclic-oxidation resistance of these specimens was evaluated in air at 1423 K. For the specimen with a shallow Hf-containing layer in the coating, the specimen mass reduction due to spallation of the scale was observed, whereas for the specimen with a deep Hf-containing layer, the specimen mass reduction was only slightly observed and a high-cyclic oxidation resistance was obtained. Among the specimens with a deep Hf-containing layer, the specimen prepared by Hf deposition for 0.6 ks showed the highest cyclic-oxidation resistance. For this specimen, the scale formed on the coating after the oxidation test consisted of Al2O3. This scale was adhesive, and locally entered the metal substrate.
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  • Ma Jiaocheng, Liu Jun, Yang Qiang, Chen Liangyu
    2014 Volume 55 Issue 8 Pages 1319-1323
    Published: August 01, 2014
    Released: July 25, 2014
    JOURNALS FREE ACCESS
    In the continuous casting process, the internal temperature of billet is difficult to be measured and the surface temperature of billet is also difficult to be measured accurately. The steady-state heat transfer models can only be used for simulating the steady-state casting operations in off-line. For better control over the whole continuous casting cycle, recently more attention have been paid to developing real-time heat transfer models which are valid under casting condition varying frequently. Considering the heat transfer coefficient is the precondition of solving the model, and it is difficult to be measured directly. An identification method of heat transfer coefficient based on genetic algorithm was developed. According to the measured temperature and shell thickness, the heat transfer coefficient of each spray zone was determined. In order to test the dynamic performance of the real-time heat transfer model, the surface temperature was measured using the CCD (charge coupled device) temperature measurement system, which can effectively eliminate the impact of the scales on the billet surface and keep the fluctuation of the measured surface temperature within the range of ±10°C. The temperature field measurement of billet was realized by the multi-information fusion of CCD temperature measurement system, measured shell thickness and data acquisition system. This provides the possibility to improve the existing cooling system based on the feed-back control considering the measured surface temperature.
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  • Wen Long Zhao, Qing Xian Ma, Shi Li Zha
    2014 Volume 55 Issue 8 Pages 1324-1331
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 18, 2014
    JOURNALS FREE ACCESS
    Non-metallic inclusions are considered undesired, yet unavoidable components of all steels and are prone to act as sources of stress that play a predominant role in crack initiation. Experiments conducted during the forging process of 30Cr2Ni4MoV steel revealed that cracks mainly originate from compound inclusions, especially intensive plastic inclusions or sliced brittle inclusions containing particles in their interior. The deformation behavior of these two types of compound inclusions was then simulated. It has been shown that the intensive plastic inclusions parallel to the applied stress result in two effects that cause additional stress and produce strain concentration, which are key factors of the union of inclusions and the origins of cracks. Tensile stress that can also lead to cracking certainly exists among intensive plastic inclusions distributed perpendicular to the applied stress. In a compound brittle inclusion, as the amount of deformation increases, areas of strain concentration first develop and then conical cracks are initiated on both sides of the interior particle. When multiple particles are distributed within a small distance, the adjacent conical cracks tend to be connected under the maximum shear stress and finally sever the sliced brittle inclusion at an angle of 45°.
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  • Kouta Sakamoto, Kento Yokoi, Aki Saito, Naofumi Ohtsu
    2014 Volume 55 Issue 8 Pages 1332-1336
    Published: August 01, 2014
    Released: July 25, 2014
    JOURNALS FREE ACCESS
    In the present study, we attempted to prepare a photocatalytic titanium dioxide (TiO2) layer on nickel-titanium (NiTi) alloy surface through a simple thermal oxidation process in air. At 723 K, an amorphous TiO2 layer including a slight amount of Ni was formed on the surface. Above 873 K, the TiO2 layer crystallized into a rutile phase. At 1023 K, a complex oxide of NiTiO3 was also formed. The methylene blue degradation test for evaluating photocatalytic activity showed that the formed TiO2 layers act as photocatalyst under ultraviolet (UV) light illumination, and its activity is superior to that of the surface layer formed by oxidizing a pure Ti substrate. The adhesion strength of the surface layers formed at 723 K on NiTi alloy was higher than that of a commercially available TiO2-coating. We conclude that thermal oxidation as a surface modification technique is expected to make NiTi alloys give photocatalytic activity.
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  • Liying Qiao, Yong Wang, Weilang Wang, Marta Mohedano, Caihua Gong, Jia ...
    2014 Volume 55 Issue 8 Pages 1337-1343
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 11, 2014
    JOURNALS FREE ACCESS
    Self-assembled monolayers (SAMs) of stearic acid (SA) film were developed on pure magnesium with heat-pretreatment in order to improve both the corrosion resistance and the bioactivity of pure magnesium. A new method using a high concentration of SA solution (10−1 mol/L) is proposed to reduce the process time of the conventional SAMs methods. The effect of ultrasonic cleaning treatment on SAMs was investigated. Contact angle measurements were employed to evaluate the hydrophobic properties of the SAMs. The corrosion resistance and the bioactivity of the specimens were evaluated under biological conditions (simulated body fluid, 37°C) using potentiodynamic polarization method and long term immersion test. Surface morphology, composition and structure analysis of samples were characterized by the scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) after immersion test. The results showed the corrosion resistance of pure Mg was improved by stearic acid-SAMs and the MgO layer made by heat-pretreatment, the SAMs made in high concentration (10−1 mol/L) of stearic acid solution just for 1.5 h showed better properties than conventional SAMs. Furthermore, ultrasonic cleaning treatment led to the formation of more dense and orderly SAMs and improved the anticorrosion property of SAMs prepared in high concentration of SA solution. Moreover, SAMs-Mg had better bioactivity than untreated magnesium.
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  • Junhyun Choi, Jeongsik Hong, Kyuhyeong Park, Gahee Kim, Yosep Han, Seu ...
    2014 Volume 55 Issue 8 Pages 1344-1349
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 11, 2014
    JOURNALS FREE ACCESS
    In this study, we investigated the adsorption isotherms of cationic surfactants (i.e., distearyl dimethyl ammonium chloride (DDAC), behenyl trimethyl ammonium chloride (BTAC), and stearyl trimethyl ammonium chloride (STAC)) onto silica surface and the corresponding silica floatability according to chain type and length of cationic surfactants. The results for the adsorption isotherms of cationic surfactants showed that the adsorptive amounts increased with increasing surfactant concentration, but differences in the position of the adsorption isotherms existed between DDAC, BTAC, and STAC. Specifically, in the high range of initial surfactant concentrations (i.e., 10−5–10−3 M), the adsorptive amounts increased with increasing hydrocarbon chain length. In addition, in the presence of DDAC, the adsorptive amounts were much greater than those in the presence of BTAC and STAC. The results were attributed to the fact that the increase in the hydrocarbon chain group of surfactants decreased the Gibbs free energy of the system, resulting in a shift of hemimicelle concentration toward lower concentration. Meanwhile, in the low range of initial surfactant concentrations (i.e., 5 × 10−7–5 × 10−6 M), the adsorptive amounts were comparable regardless of surfactant type, which was due to the fact that the interaction between the cationic surfactants and the silica surface was mainly governed by electrostatic attractive force. The results from silica flotation and hydrophobicity tests showed that silica floatability increased with increasing hydrocarbon chain group of surfactants (i.e., floatability was in the order of DDAC > BTAC > STAC) under the conditions where the adsorptive amounts of the surfactants were comparable and that floatability results were consistent with those for the hydrophobicity of silica surface. Overall, the findings from the present study suggested that the hydrocarbon chain length and type of cationic surfactants play a significant role in both the adsorption behavior of surfactants and the silica floatability.
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  • Azusa Ooi, Yoshinao Hoshi, Eiji Tada, Atsushi Nishikata
    2014 Volume 55 Issue 8 Pages 1350-1355
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 11, 2014
    JOURNALS FREE ACCESS
    The selective dissolution of cobalt and the consequent surface enrichment of platinum in Pt–Co binary alloys immersed in 0.5 mmol·m−3 H2SO4 at 298 K were investigated. Four different Pt–Co alloy thin films with various Pt contents, deposited on glassy carbon sheets by physical vapor deposition, were investigated: 51 at% Pt (Pt51–Co49), 43 at% Pt (Pt43–Co57), 28 at% Pt (Pt28–Co72), and 24 at% Pt (Pt24–Co76). When the thin films were immersed for 24 h in a 0.5 mmol·m−3 H2SO4 solution, a Pt-enriched layer was formed on the surface of all the alloys due to Co-selective dissolution. The enriched layer formed in the higher-Pt alloys (Pt51–Co49 and Pt43–Co57) significantly suppressed further dissolution, whereas the lower-Pt alloys (Pt28–Co72 and Pt24–Co76) exhibited more extensive selective dissolution and roughened surfaces. In this study, the selective dissolution and surface morphology of the Pt–Co alloys are discussed on the basis of these experimental results.
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  • Joon-Phil Choi, Geon-Yong Lee, Jun-Il Song, Joon-Chul Yun, Jai-Sung Le ...
    2014 Volume 55 Issue 8 Pages 1356-1362
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: July 11, 2014
    JOURNALS FREE ACCESS
    The present investigation focuses on the improvements in chemical homogeneity and related powder properties of partially alloyed Fe–1.50Cu–1.75Ni–0.50Mo powder by using a nanopowder process. The nanosized oxide powders of CuO–NiO–MoO3 were prepared by ball-milling for the alloying elements and blended with iron powders. The powder mixture was annealed in a reducing atmosphere, in order to reduce the oxide powders and thereafter partially alloyed with the iron powder. The produced powder was used to evaluate the microstructure, chemical composition, compressibility, and sinterability. It was found that the powder had a uniform distribution of alloying elements with high compositional homogeneity. The fine alloying elements were mostly located in the grooves of the iron powder surface, yielding morphological change, which effectively improved the flow, packing and compaction properties of the powder. The nanopowder process also promoted a diffusion reaction during sintering at 1200°C for 2 h with a homogeneous microstructure and chemical composition.
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  • In-Jin Shon, Hanjung Kwon, Hyoung-Gon Jo
    2014 Volume 55 Issue 8 Pages 1363-1366
    Published: August 01, 2014
    Released: July 25, 2014
    [Advance publication] Released: June 27, 2014
    JOURNALS FREE ACCESS
    For the formation of composite structures, Co or Ni is added as a binder, in the case of cemented TiC. However, the high cost of Co or Ni, and the low corrosion resistance of TiC–Co or TiC–Ni cermet have generated interest in recent years to find alternative binder phases. It has been reported that aluminides show higher oxidation resistance and hardness, and cheaper materials, compared to Co or Ni. Using a high-frequency induction heated sintering (HFIHS) method, the densification of TiC and TiC–TiAl hard materials was accomplished within 3 min. The advantages of this process are the prohibition of grain growth in nano-structured materials, and the rapid densification to near theoretical density. Highly dense TiC–TiAl hard materials with a relative packing density of up to 100% were obtained by HFIHS, under a pressure of 80 MPa. The average grain size of the TiC was lower than 100 nm. The addition of TiAl to TiC significantly improves the fracture toughness of cemented TiC, without greatly decreasing the hardness.
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