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MATERIALS TRANSACTIONS Vol. 53 (2012), No. 7

ISIJ International
belloff
オンライン版ISSN: 1347-5320
冊子版ISSN: 1345-9678
発行機関: The Japan Institute of Metals and Materials

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キーワードランキング

26 Dec. (Last 30 Days)

MATERIALS TRANSACTIONS Vol. 53 (2012), No. 7

Fabrication of Non-Stoichiometric Titanium Dioxide by Spark Plasma Sintering and Its Thermoelectric Properties

Yun Lu, Katsuhiro Sagara, Liang Hao, Ziwu Ji, Hiroyuki Yoshida

pp. 1208-1211

DOI:

10.2320/matertrans.E-M2012808

抄録

To obtain non-stoichiometric titanium dioxide, TiO2 powder was sintered in a graphite die by spark plasma sintering (SPS). The microstructure and the crystal type of the compacts were examined. Thermoelectric properties of the compacts were measured and discussed. The results revealed that TiO2 could be easy to be reduced in the graphite die by SPS to obtain non-stoichiometric titanium dioxide, TiO2−x with uniform composition distribution. Electrical resistivity of the compacts decreased with increase of SPS temperature. Seebeck coefficient also decreased with increase of SPS temperature, but kept large absolute values over 300 µV·K−1. Therefore, the compacts fabricated by SPS showed relatively high thermoelectric performance. The power factor reached 5 × 10−5 W m−1 K−2 at 523 K.

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Effect of the Amount of Vacancies on the Thermoelectric Properties of Cu–Ga–Te Ternary Compounds

Theerayuth Plirdpring, Ken Kurosaki, Atsuko Kosuga, Manabu Ishimaru, Adul Harnwunggmoung, Tohru Sugahara, Yuji Ohishi, Hiroaki Muta, Shinsuke Yamanaka

pp. 1212-1215

DOI:

10.2320/matertrans.E-M2012810

抄録

The Cu–Ga–Te ternary compounds: Cu3Ga5Te9, Cu2Ga4Te7, CuGa3Te5, CuGa5Te8, and CuGaTe2 have zinc-blende or chalcopyrite structure. The compounds except for CuGaTe2 contain vacancies in the cation site due to the valence mismatch between cation and anion, and the vacancy concentration is different between these compounds. Here we investigated the effect of the amount of vacancies on the thermoelectric (TE) properties of the Cu–Ga–Te ternary compounds. At room temperature, the presence of vacancies reduced the Hall mobility (μH) and the lattice thermal conductivity (κlat), showing that the vacancies scattered both carriers and phonons. It was found that the decreasing rate of the μH was larger than that of the κlat. Therefore, the presence of vacancies degraded the TE performance of the Cu–Ga–Te ternary compounds. In other words, CuGaTe2 without vacancies would show the best TE figure of merit. The room temperature ZT values for Cu3Ga5Te9, Cu2Ga4Te7, CuGa3Te5, CuGa5Te8, and CuGaTe2 were 2.0 × 10−2, 2.4 × 10−2, 8.9 × 10−3, 1.3 × 10−2, and 5.6 × 10−3, respectively.

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Effect of Phase Transition on the Thermoelectric Properties of Ag2Te

Do-young Jung, Ken Kurosaki, Yuji Ohishi, Hiroaki Muta, Shinsuke Yamanaka

pp. 1216-1219

DOI:

10.2320/matertrans.E-M2012815

抄録

Ag2Te is well-known as a silver ion conductor. In this compound, a phase transition occurs at around 420 K and silver ions jump to interstitial sites repeatedly at the point of starting the phase transition. We consider that the active movement of silver ions would have influence on the scatterings of both charge carriers and heat carrying phonons in Ag2Te. In order to evaluate the effect of the silver ion conduction on the thermoelectric properties of Ag2Te, the Seebeck coefficient, electrical resistivity, thermal conductivity and Hall coefficient of polycrystalline bulk samples of Ag2Te were examined in the temperature range from room temperature to 650 K. The electrical resistivity and the Seebeck coefficient dramatically changed at around 420 K due to the change of the carrier concentration before and after the phase transition. However, the carrier mobility and the lattice thermal conductivity showed no remarkable change at around the phase transition temperature. These results imply that the thermoelectric transport properties of Ag2Te were affected by the change of the crystal structure rather than the presence or absence of the movement of silver ions.

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Effect of Europium Substitution on Thermoelectric Properties of Noble-Metal Silicon Clathrates with Ba8−xEuxCuySi46−y Nominal Compositions

H. Anno, K. Okita, K. Koga, S. Harima, T. Nakabayashi, M. Hokazono, K. Akai

pp. 1220-1225

DOI:

10.2320/matertrans.E-M2012816

抄録

The effect of the substitution of a rare-earth element for a guest element on the electronic and thermoelectric properties is investigated for clathrates with the nominal composition Ba8−xEuxCuySi46−y (x = 0, 1, 2; y = 4, 5, 6). The Seebeck coefficient and the electrical conductivity of the rare-earth-substituted Ba8−xEuxCuySi46−y samples are consistent with n-type conduction and metal-like behavior. The Hall carrier mobility of Ba8−xEuxCu6Si40 at room temperature decreases with increasing Eu substitution. The conduction band effective mass of rare-earth-substituted Ba8−xEuxCu6Si40 (x = 1, 2) is experimentally estimated to be larger than that of Ba8Cu6Si40. On the basis of ab initio electronic structure calculations for Ba6Eu2Cu6Si40 and Ba8Cu6Si40, it is deduced that the conduction band edges of Ba8Cu6Si40 are modified by the substitution of Eu for the guest atom Ba, resulting in an increase in the density-of-states effective mass, which is consistent with the experimental result.

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Electronic Transports for Thermoelectric Applications on IV–VI Semiconductors

Akihiro Ishida, Yutaro Sugiyama, Hirokazu Tatsuoka, Tomoki Ariga, Mikio Koyano, Sadao Takaoka

pp. 1226-1233

DOI:

10.2320/matertrans.E-M2012812

抄録

Seebeck effect, Peltier effect, Thomson effect, electronic thermal conductivity, Hall effect, and Nernst effect are described on the basis of electronic conduction theory, taking account of effective mass anisotropy, nonparabolicity in E–k relation, and temperature dependent band gap. It is shown that the temperature dependence of the band gap does not modify the basic equations for the Seebeck coefficient, thermal conductivity, and Nernst coefficient. In narrow gap semiconductors, existence of minority carriers significantly enhances the electronic thermal conductivity, owing to the multiple carrier transport known as bipolar diffusion. Calibration coefficient γ for the Hall effect (RH = - γ /en) is increased by nonparabolicity in the E–k relation. Nernst coefficient gives useful information on scattering properties of the materials.

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Microstructure and Texture of Al–2Si–xSn (x = 0, 4, 8 mass%) Alloys Processed by Equal Channel Angular Pressing

Gonzalo Gonzalez, Chedly Braham, Jean L. Lebrun, Yvan Chastel, Wilfrid Seiler, Ignacio A. Figueroa

pp. 1234-1239

DOI:

10.2320/matertrans.M2012011

抄録

The influence of Sn on the microstructure, microstrain and grain morphology in Al–2Si–xSn samples processed by ECAP is reported and discussed. The pseudo-binary Al–xSn alloys (where x = 0, 4, 8 mass%) were produced by conventional ingot casting. Samples were characterised by X-ray diffractometry (XRD), transmission electron microscopy (TEM), dynamical mechanical analysis (DMA) and microhardness. Results showed that the initial texture was modified after several ECAP passes and the formation of subgrains were observed. The presence of Sn enhanced the tribological properties of the alloy but, the ECAP capacity for grain refining was reduced. Besides, it was also confirmed that the damping capacity and microhardness behaviour were dependent of the Sn contents.

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Observation on Isothermal Reactive Diffusion between Solid Fe and Liquid Sn

Masahiro Hida, Masanori Kajihara

pp. 1240-1246

DOI:

10.2320/matertrans.M2012060

抄録

The kinetics of the reactive diffusion between solid Fe and liquid Sn was experimentally examined using Fe/Sn diffusion couples. The diffusion couples were prepared by an isothermal bonding technique and then immediately annealed in the temperature range of T = 703–773 K for various times up to t = 90 ks (25 h). During annealing, a compound layer of FeSn2 is formed at the initial Fe/Sn interface in the diffusion couple and grows mainly into the liquid Sn specimen. At T = 703 K, the compound layer indicates a needle-like microstructure in the early stages but a columnar microstructure in the late stages. On the other hand, at T = 723–773 K, only the columnar microstructure is realized in the compound layer within the experimental annealing times. The mean thickness of the compound layer is proportional to a power function of the annealing time. The exponent n of the power function is mostly close to 0.6. In the early stages at T = 703 K, however, n is equal to unity within experimental uncertainty. If growth of a compound layer with a uniform thickness is controlled by volume diffusion, n is equivalent to 0.5. In contrast, n is equal to unity for longitudinal growth of a needle-like grain, even though volume diffusion is the rate-controlling process. This is the case for the layer growth in the early stages at T = 703 K. Since independent longitudinal growth of each columnar grain contributes to the layer growth governed by volume diffusion, n is slightly greater than 0.5 for the compound layer with the columnar microstructure. Consequently, the discontinuous variation of n corresponds to the transition from the needle-like microstructure to the columnar microstructure.

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First-Principles Calculations on Elasticity and Anisotropy of Tetragonal Tungsten Dinitride under Pressure

Hongcun Zhai, Xiaofeng Li, Junyi Du

pp. 1247-1251

DOI:

10.2320/matertrans.M2011373

抄録

First-principles calculations of the crystal structure and the elastic properties of tetragonal WN2 have been performed with the plane-wave pseudopotential density functional theory method. The calculated structural parameters and elastic constants at zero pressure and temperature are in excellent agreement with the available theoretical results. The dependence of the elastic constants Cij, the aggregate elastic moduli B, G and the anisotropies on pressure have been investigated. WN2 is a brittle system below about 66 GPa, whereas it becomes ductile under high pressure. By the elastic stability criteria, it is predicted that tetragonal WN2 are not stable above 232.1 GPa.

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Microstructure and Mechanical Properties of Hot-Extruded Mg–3Zn–2Sn–0.4Ag–xNd (x = 0, 1 and 3 mass%) Alloys

Byeong Deok Lee, Eun Jeong Kim, Eui Hyuk Kwon, Hyeon Taek Son, Jeong Whan Han

pp. 1252-1257

DOI:

10.2320/matertrans.M2012016

抄録

Mg and Mg alloys are unsuitable for use at temperatures greater than 393 K owing to their poor creep resistance and strength at elevated temperatures. Therefore, it is essential to develop high-strength magnesium alloys for use in elevated-temperature automotive applications. Therefore phase diagrams for Mg–3Zn–2Sn–0.4Ag–xNd alloys were calculated in order to present clear guidelines for Mg alloy development. The results will help in determining solid solutions and aging treatment conditions. The effect of extruded Mg–3Zn–2Sn–0.4Ag–xNd alloys on the microstructure, texture and mechanical properties at room temperature and a high temperature of 423 K were examined.

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Two-Body and Three-Body Types Abrasive Wear Behavior of Hypoeutectic 26 mass% Cr Cast Irons with Molybdenum

Sudsakorn Inthidech, Attasit Chooprajong, Prasonk Sricharoenchai, Yasuhiro Matsubara

pp. 1258-1266

DOI:

10.2320/matertrans.M2012051

抄録

Hypoeutectic 26 mass% Cr cast irons with 0–3 mass% Mo were prepared in order to investigate their abrasive wear behavior. The annealed test pieces were hardened from 1323 K and then tempered at three levels of temperatures between 673 and 823 K for 7.2 ks, the temperature giving the maximum hardness (HTmax), lower temperature than that at HTmax (L-HTmax) and higher temperature than that at HTmax (H-HTmax). The abrasive wear resistance was evaluated using Suga wear test (two-body-type) and Rubber wheel wear test (three-body-type). It was found that hardness and Vγ in the heat-treated specimens varied depending on the Cr and Mo contents. A linear relation was obtained between wear loss and wear distance. The lowest wear rate (RW) was obtained in both the as-hardened and HTmax specimens. The highest RW was mostly obtained in the H-HTmax specimens. Under the same heat treatment condition, the RW in Suga wear test was much greater than that in Rubber wheel wear test. The RW decreased with increasing hardness. The lowest RW obtained in the specimen with a certain amount of retained austenite, 10–15%Vγ. The RW decreased with increasing Mo content in Suga abrasive test and it decreased little by Mo addition in Rubber wheel wear test.

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Ion Exchange Capacity of Sr2+ onto Calcined Biological Hydroxyapatite and Implications for Use in Permeable Reactive Barriers

Keiko Sasaki, Shoichi Tsuruyama, Sayo Moriyama, Stephanie Handley-Sidhu, Joanna C. Renshaw, Lynne E. Macaskie

pp. 1267-1272

DOI:

10.2320/matertrans.M-M2012813

抄録

With the recent Fukushima incident, there is an urgent need to find cost effective and workable permeable reactive barrier (PRBs) for the remediation/retardation of problematic radionuclides. Catfish bones were calcined at various temperatures (400–1100°C) to remove the organic matter (87.1 mg·g−1) and to change the structural properties of the hydroxyapatite (HAP). Increasing temperatures increased the HAP crystallinity as indicated by a decrease in lattice strain (0.0098 to 0.00135) and an increase in crystallite sizes (5.0 × 10−8 to 7.7 × 10−8 m). There was also an observed decrease in specific surface areas (98.9 to 0.99 m2·g−1) and increase in particle sizes (50 to 1000 nm). The sorption densities of Sr2+ decreased with increasing calcination temperatures, from 0.34 to 0.05 mmol·g−1. However, once normalized for surface area, the sorption densities increased from 1.8 to 5.9 mmol·m−2. Overall, this research has important implications for the design of hydroxyapatite PRBs with higher calcination temperatures producing a more reactive material with larger particle sizes for increased permeability. Lower calcination temperatures produced amorphous HAP material, which released more aqueous PO43− and resulted in the precipitation of strontium phosphates, ultimately reducing the permeability of PRBs.

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Statistical Thermodynamic Analysis for Hydrogen Absorption Behaviour in a Four Monolayers (4 ML) Thick bcc Vanadium (110) Superlattice Being in Contact with Molybdenum Layer

Nobumitsu Shohoji

pp. 1273-1277

DOI:

10.2320/matertrans.M2012071

抄録

Hydrogen (H) absorption performance in a four monolayers (4 ML) thick body centered cubic (bcc) vanadium (110) interface layer being in contact with non-H absorbing molybdenum layer (Mo/V (110) superlattice) reported by Öhrmalm et al. was analyzed in terms of statistical thermodynamics. Number θ of the available interstitial sites for occupation by H atoms per V atom was determined to be 0.45 in the 4ML bcc V (110) superlattice while θ was evaluated to be 0.55 for poly-crystalline bulk bcc V lattice. With this choice of θ value, nearest neighbor H–H interaction energy E(H–H) in the 4ML bcc V (110) superlattice was evaluated to be zero and the extent Q of stabilization of H atom in the bcc V (110) superlattice was evaluated to be comparable to that in the bulk bcc V lattice. The evaluated reduction of θ for the 4ML bcc Mo/V (110) superlattice to 0.45 from 0.55 for the bulk bcc V lattice was concluded to be the consequence of modulation of electronic structure in the bcc V lattice in the vicinity of non-H absorbing Mo layer.

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Effects of Alkali Corrosion Preprocessing on the Growth of Aligned Silver Nanorods Array and Its Improvement for Surface-Enhanced Raman Scattering

Zhengcao Li, Ye Yang, Xian Zhang, Zhengjun Zhang

pp. 1278-1281

DOI:

10.2320/matertrans.M2012015

抄録

Silicon wafers were corroded by NaOH aqueous with a high concentration as a substrate preprocessing. These corroded Si wafers with rougher surfaces could provide some initial small discontinuous ‘islands’ for the deposition of silver via glancing angle deposition technique. It turned out that this pretreatment could help to improve the separation of Ag nanorods and result in an enhancement on the Raman intensity, with an increase of 223% at most compared with the one without alkali corrosion. This preprocessing is considered to be a simple, practical and effective way to prepare better SERS-active substrates and improve the sensitivity of trace amount detection using SERS in the future.

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Tensile Properties of Optical Fiber Irradiated by Low Voltage Electron Beam Homogeneously

Yoshitake Nishi, Hiroaki Takei, Hideki Kawazu, Yuu Nakahara

pp. 1282-1287

DOI:

10.2320/matertrans.M2011353

抄録

Homogeneous low voltage electron beam irradiation (HLEBI) with small dose of 0.30 to 1.17 MGy enhanced the elasticity indicated by the initial and maximum slope values of stress–strain curves ((dσ/dε)i and (dσ/dε)max) of 250 µm diameter optical fiber (OF), which was constructed with both core (10 µm diameter) and clad (125 µm diameter) silica glasses covered with acryl-urethane sheath (62.5 µm thickness). The highest (dσ/dε)i and (dσ/dε)max values of 5.3 and 5.9 GPa, which were about 10 and 20% higher than those (4.8 and 4.9 GPa) before irradiation, were found at 0.104 MGy, respectively. Moreover, remarkable effects of HLEBI of 0.65 MGy on both tensile strength (σf) and fracture strain (εf) of OF were obtained at each fracture probability (Pf) value. Since HLEBI also enhanced the density of dangling bonds of each material of OF, effects of compressive stress on pull-out resistance and elasticity enhancements of fiber and sheath probably occurred. Thus, 0.64 MGy-HLEBI enhanced the (dσ/dε)i and (dσ/dε)max as well as εf, resulting in enhancement of σf of OF.

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Charpy Impact of Sandwich Structural Composites (CFRP/PC/CFRP) of Polycarbonate (PC) Cores Covered with Carbon Fiber Cross Textile Reinforced Epoxy Polymer (CFRP) Thin Sheets as a Function of Temperature

Yoshitake Nishi, Naoya Tsuchikura, Shinichiro Nanba, Tatsuya Yamamoto, Michael C. Faudree

pp. 1288-1294

DOI:

10.2320/matertrans.M2011357

抄録

The purpose of this study is to investigate a lighter, cheaper and possibly stronger alternative to CFRP, by obtaining the Charpy impact values (auc) of a sandwich structural composite (CFRP/PC/CFRP) constructed of a polycarbonate (PC) core between two thin plies of carbon cross textile fiber/epoxy (CFRP) within the temperature range of aircraft operation, from 200 to 403 K below the glass transition temperature of PC (Tg = 422 K). The auc of CFRP/PC/CFRP were compared with a 2.0 mm thick 12-ply CFRP laminate. Results showed overall, the CFRP/PC/CFRP had higher auc than the CFRP at each fracture probability (Pf) from 300 to 373 K except at 200 K with low Pf and 403 K with high Pf. Specifically, although the volume fraction of carbon fiber (12%) of CFRP/PC/CFRP was much smaller than that (60%) of the CFRP, the auc at room temperature (300 K) of CFRP/PC/CFRP was approximately 64% higher than that of CFRP at mid-fracture probability (Pf) of 0.50. Fracture modes of CFRP/PC/CFRP were explained by delamination between PC core and the CFRP thin sheet surfaces, bending plastic deformation, and CFRP fracture. The highest Weibull coefficient (n) was obtained at 323 K. Based on the 3-parameter Weibull equation, the limiting impact value (as) also exhibited the highest value at 323 K. In addition, the cost of CFRP/PC/CFRP was 40% lower than that of CFRP at the time of this study. Since the use of PC resin as the core enhanced the safety design at low cost, practical use of sandwich structural composites of CFRP/PC/CFRP is possible.

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Elimination of Rotational Domain in AlN Layers Grown from Ga–Al Flux and Effects of Growth Temperature on the Layers

Masayoshi Adachi, Masashi Sugiyama, Akikazu Tanaka, Hiroyuki Fukuyama

pp. 1295-1300

DOI:

10.2320/matertrans.MBW201112

抄録

We have been investigating crystal growth of AlN on nitrided sapphire substrates, and have grown c-axis oriented AlN layers using liquid phase epitaxy (LPE) with Ga–Al fluxes. However, rotational domains having 1-deg difference around the c-axis exist in the AlN layers. One of the purposes of this study is to eliminate the rotational domains. To do so, an annealing process at elevated temperatures was attempted before the LPE process. Then, its effectiveness was discussed. The origin of the rotational domain was explained using distortion of O2− ions arrangement in (0002) sapphire surface. The mechanism of the eliminating the domains was discussed using the lattice vibration of the sapphire at elevated temperatures. Secondly, effects of growth temperature on the AlN layers were investigated in terms of the growth rate, surface morphology and crystal quality. The growth rate of the LPE AlN layer increased concomitantly with increasing growth temperature at 1373–1673 K. The growth rate attained at 1673 K was 0.52 µm·h−1. Crystal quality is almost independent of the growth temperature in that temperature range.

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Controlling the Percolation Threshold of Conductor-Insulator Composites in a 2D Triangular Lattice by Introducing Binary Size Distributions of Conductor Particles

Kazuhito Shida, Ryoji Sahara, Hiroshi Mizuseki, Yoshiyuki Kawazoe

pp. 1301-1304

DOI:

10.2320/matertrans.M2012029

抄録

When one attempts to modulate and control the characteristics of composite materials, the mathematical threshold of the percolation transition dictates the modulation limit. Using a series of computer simulations, we have been investigating the dependence of the percolation threshold on particle size distributions. However, one of the other factors that can deeply affect percolation behavior, the design of lattice, is always fixed to simple square or cubic lattices. This report presents the first calculation of a percolation threshold in a 2D triangular lattice with binary size distributions of conductor particles. Although a small quantitative difference was found, the results qualitatively matched to the results already reported for 2D square lattices, thus confirming our previous finding: the introduction of large conductor particles increases the percolation threshold in 2D.

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Channelrhodopsin as a Noble Biomaterial Useful for the Operation and Performance Test of the Ionchannel Devices

Hidetaka Uno, Zhi-hong Wang, Noriko Takada, Toru Ishizuka, Hiromu Yawo, Tsuneo Urisu

pp. 1305-1309

DOI:

10.2320/matertrans.N-M2012814

抄録

The light-gated ion-channel protein is expected to be able to improve the performance of ionchannel devices for the multi-point screening and neural network devices based on the planar patch clamp. However, no studies with light-gated ion channels on a planar patch clamp have been reported. We constructed an incubation type of planar patch clamp biosensor using silicon-on-insulator substrates with a 1–2 µm micropore in them. Channelrhodopsin 2-expressing C2C12 cells and channelrhodopsin/wide receiver-expressing HEK293 cells were seeded on the surface of the sensor chip and incubated to almost complete confluence. A laser beam (473 nm wavelength) was radiated on the cells adsorbing to the sensor chip’s micropore and the light-gated channel currents of the voltage clamp and action potentials of the current clamp modes were observed. Good signal to noise ratios were obtained, although the seal resistance was not so large, 10–30 MΩ. The observed pulse shape of the ion-channel currents also qualitatively resembled reported results measured with a pipette patch clamp. These results strongly suggest that the light-gated ion channel proteins are useful biomaterials for ionchannel devices.

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Hardness and Wear Properties of Al–4.5%Cu/Al3Mg2 Nanocomposite Prepared by Mechanical Alloying

Narguess Nemati, Massoud Emamy, Ali Reza Emami, Mashhood Mashhoodi

pp. 1310-1317

DOI:

10.2320/matertrans.M2011377

抄録

Al–Mg alloys close to β-Al3Mg2 intermetallic phase were processed by neutral gas coverage melting process of pure elemental Al and Mg with the composition of Al–40 mass% Mg. Mechanical milling was applied in order to convert the pre-alloyed ingots to nanocrystalline or amorphous alloy. X-ray diffraction and transmission electron microscopy (TEM) tests were carried out to investigate the formation of Al3Mg2 single phase nanoparticle. Having prepared the single phase intermetallic, it was added to the pre-alloyed matrix powder of Al–4.5 mass% Cu, in different contents. The effect of the reinforcing agent on the microhardness and wear behavior of the nanocopmosites were studied thoroughly with the aid of press-sinter methodology and quantitative data recorders via pin-on-disk wear test. The results of microhardness tests revealed that the hardness of nanocomposites is significantly improved with increasing reinforcement content with in the matrix. The coexisted wear mechanisms, mainly delamination and abrasive, of the consolidated nanocopmosites were investigated through scanning electron microscopy (SEM) and TEM observations.

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Microstructural Evolution and Mechanical Properties under High Strain Rate Testing of W–3.99Ni–1.71Fe Sintered by a Two-Stage Sintering Process

Woei-Shyan Lee, Tien-Yin Chan

pp. 1318-1323

DOI:

10.2320/matertrans.M2012027

抄録

A two-stage sintering practice was applied to W–3.99Ni–1.71Fe (mass%) to control its microstructural evolution and, accordingly, mechanical properties under high strain rates. Unlike the traditional one-stage liquid phase sintering, the alloy was first solid-state-sintered to close to full densification, and then liquid-phase-sintered by induction heating where the cooling rate was fast. With the two-stage sintering, the growth of tungsten grains and the contiguity of tungsten grains could be closely tailored, and a high dissolved tungsten concentration in the matrix phase could be maintained. All of these microstructural characteristics led to enhanced mechanical properties of this alloy tested under high strain rates.

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Effect of NaCl on Cr(VI) Reduction by Granular Zero Valent Iron (ZVI) in Aqueous Solutions

Hyangsig Ahn, Ho Young Jo, Geon-Young Kim, Yong-Kwon Koh

pp. 1324-1329

DOI:

10.2320/matertrans.M2011375

抄録

This study examined the effect of NaCl on the removal of Cr(VI) by ZVI in aqueous solutions and proposes a potential mechanism of Cr(VI) removal by ZVI in aqueous solutions with NaCl. A series of batch tests was conducted on ZVI using 100 mg/L Cr(VI) solutions at an initial pH of 3 at various NaCl concentrations. The NaCl in aqueous solutions improved the removal efficiency for Cr(VI) by ZVI. Fe(III)–Cr(III) (oxy)hydroxides were precipitated both on the ZVI surface and in the solution via the reduction reactions of Cr(VI) to Cr(III) in the presence of NaCl. The increase in the Cr(VI) removal efficiency in the solutions with NaCl was attributed to the Cl− ions, which accumulate at the anodic sites of ZVI, thereby enhancing ZVI oxidation and colloidal particle formation. In the NaCl solutions, small grains were initially precipitated on the ZVI surface, via relatively fast reactions. The subsequent slowing of these reactions resulted in the precipitation of large grains on the ZVI surface and colloidal particles in the solutions.

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Lorentz Microscopy of Magnetic Domain-Wall Pinning on Artificially Introduced Holes in Electrical Steel Sheets

Yoshikatsu Inada, Zentaro Akase, Daisuke Shindo, Akira Taniyama

pp. 1330-1333

DOI:

10.2320/matertrans.M2012099

抄録

To investigate the interaction between magnetic domain walls and defects in an electrical steel sheet by transmission electron microscopy, size-controlled holes were artificially introduced into specimens by a focused ion beam. By applying an external magnetic field in a transmission electron microscope, the magnetic domain structures around the holes were dynamically observed by Lorentz microscopy. Similar magnetic domain structures were observed around the holes, but the domain-wall pinning strength was found to depend on the hole size. Micromagnetic analysis was performed to ascertain the magnetic domain structures around the holes and to investigate the change in the magnetic energy during domain-wall pinning.

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Influence of Precipitated Phase Formation on Recrystallization Behavior of Superalloy 718

Hwa-Teng Lee, Wen-Hsin Hou

pp. 1334-1342

DOI:

10.2320/matertrans.M2012090

抄録

Post heat treatment fails to refine the grain structure of superalloy 718. Thus, for components with demanding grain size requirements, the forging process should be performed within an extremely limited temperature region just below the δ solvus temperature, yet higher than that required to induce dynamic recrystallization. The grain size of superalloy 718 is generally controlled during manufacturing by inducing full dynamic recrystallization through means of a carefully-controlled hot forming process performed in a powerful and precise forging machine. This work presents an alternative method for obtaining a fine and uniform grain structure through means of static recrystallization and a proper control of the δ phase formation. In the proposed method, the component is cooled in water immediately after forging to suppress δ phase precipitation and preserve the internal strain energy produced by the hot deformation process. The component is then heated to a temperature 30°C lower than the δ solvus temperature 1030°C; resulting in a continuous recrystallization of the microstructure. Experimental results indicate that γ′′ phase precipitation and δ phase precipitation dominate the dynamic and static recrystallization behaviors observed in the conventional and proposed grain refinement methods, respectively. Our results further demonstrate that the proposed static recrystallization method yields a fine microstructure with an average grain size of ASTM No. 7 (31.8 µm). Thus, the proposed method provides an inexpensive and technically straightforward alternative to the conventional hot forming grain refinement method.

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Biomechanical Evaluation of Amorphous Calcium Phosphate Coated TNTZ Implants Prepared Using a Radiofrequency Magnetron Sputtering System

Naru Shiraishi, Rong Tu, Risa Uzuka, Takahisa Anada, Takayuki Narushima, Takashi Goto, Mitsuo Niinomi, Keiichi Sasaki, Osamu Suzuki

pp. 1343-1348

DOI:

10.2320/matertrans.M2012078

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Ti–29Nb–13Ta–4.6Zr alloy (TNTZ), a new β-type Ti alloy, has excellent advantages as a biomaterial, such as low Young’s modulus and cytotoxicity, and the absence of allergens. However, it is unclear whether TNTZ can achieve sufficient osseointegration for it to be used as a dental implant. The effectiveness of surface modification of TNTZ implants by radiofrequency (RF) magnetron sputtering is also unclear. We investigated the biomechanical behaviors of TNTZ implants in vivo, using cylindrical implants of four types: pure Ti, TNTZ, and pure Ti and TNTZ coated with amorphous calcium phosphate (ACP). The implants were inserted in rat femurs, and the femurs were subjected to biomechanical analyses after various time intervals. The results suggest that TNTZ implants can achieve osseointegration similar to that of pure Ti, and that surface modification with ACP by RF magnetron sputtering improves osseointegration, especially in the later stages of healing.

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Enhancement of Chrysotile Carbonation in Alkali Solution

Kyoung Won Ryu, Young Nam Jang, Myung Gyu Lee

pp. 1349-1352

DOI:

10.2320/matertrans.M2012059

抄録

The carbonation of chrysotile [Mg3Si2O5(OH)4] was studied at various temperatures in order to examine the carbonation rate and Mg leaching properties in an alkali solution and distilled water using the direct method. For the efficient carbonation reaction, the chrysotile was converted to metachrysotile by heating at 630°C for 2 h. The carbonation rate was found to increase with the reaction temperature: 5 and 31% at 100°C and 45 and 53% at 260°C in distilled water and alkali solution, respectively. The carbonation in the alkali solution was faster producing well-faceted rhombohedral magnesite (MgCO3) in comparision to the case in the distilled water. Highly crystalline magnesite could be obtained after the carbonation for 1 h at 260°C under a CO2 pressure of 3 MPa in the alkali solution.
The additional object of this study was to convert the fibrous chrysotile to a non-hazardous material. During carbonation, the magnesite exhibited the typical rhombohedral morphology while the unreacted chrysotile changed primarily to aggregations of chrysotile crystals. This result has an important implication for the elimination of toxicity through the transformation of chrysotile asbestos into a non-hazardous material.

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Chestnut Bur-Like ZnO Crystals Synthesized by Solar Thermal Evaporation Technique

Min-Sung Kim, Geun-Hyoung Lee

pp. 1353-1355

DOI:

10.2320/matertrans.M2012091

抄録

Chestnut bur-like zinc oxide crystals were synthesized by the thermal evaporation of zinc sulfide powder without the use of any catalyst. A magnifying lens was used to heat up the zinc sulfide powder. Thermal solar energy was concentrated on the zinc sulfide powder by the magnifying lens. Then the zinc sulfide powder was heated and evaporated within a relatively short time. The zinc sulfide vapor was oxidized in air and the chestnut bur-like zinc oxide crystals were formed. EDX spectrum revealed that the zinc oxide crystals had wurtzite hexagonal structure. A strong green emission was observed in cathodoluminescence spectrum. The thermal evaporation technique using solar energy is one of the techniques to reduce the energy consumption and costs.

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