Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

Copper nanoparticles fabricated onto reduced graphene oxide (Cu NPs/rGO) were successfully synthesized via a one-pot dimethylformamide (DMF) reduction approach with an addition of nominal water. This small amount of water can significantly decrease the degree of GO reduction by DMF. As a result, the remaining oxygen-containing functionality on rGO can still interact with the copper cation precursor leading to the high Cu content fabricated onto the support material, which was evidenced by X-ray photoelectron spectroscopy (XPS). Moreover, small particle sizes and high dispersion of Cu NPs on rGO were confirmed by scanning transmission electron microscopy (STEM). In addition, our Cu NPs/rGO was competent to catalyze the Ullmann-coupling reaction (i.e., arylation of 3,5-dimethylphenol with 86% yield and turnover number 2,642).

DOI： 10.1246/bcsj.20200115

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

N,N-Dimethylformamide-stabilised Pd nanocluster (NC) catalysed cross-coupling reactions of hydrosilane/disilane have been investigated. In this reaction, the coupling reaction proceeds without ligands with low catalyst loading. N,N-Dimethylacetamide is a crucial solvent in these reactions. The solvent effect was considered by various techniques, such as transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The Pd NCs can be recycled five times under both hydrosilane and disilane reaction conditions.

DOI： 10.1039/c9ra02895a

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Ti Pd alloys were investigated as heterogeneous catalysts for hydrogen autotransfer reactions. This is the first reported study of alloys as catalysts for hydrogen-borrowing reactions using alcohols. We improved the catalytic activities of alloys by increasing their specific surface areas via a hydrogenation powdering process. The reactivities and selectivities of hydrogenated Ti Pd alloys [Ti Pd(Hy)] were higher than those of non-hydrogenated alloy catalysts in N-alkylation by hydrogen autotransfer using alcohols. A plausible catalytic cycle is proposed based on control studies and deuterium labelling experiments.

DOI： 10.1002/cctc.201900318

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Ti-Pd alloys have been found to be novel heterogeneous palladium catalysts for organic cross-coupling reactions. Catalyst preactivation is not necessary, resulting in facile recovery and reuse of the catalysts. Palladium is not leached into the reaction solution and the catalysts can be recycled several times without losing their catalytic activity.

DOI： 10.1246/bcsj.20180363

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS & MATERIALS  

Microstructure formation mechanism through competitive reactions during initial hydrogenation in Mg/Cu super-laminate composites (SLCs) was investigated. Mg/Cu SLCs (Mg2Cu composition) were fabricated by accumulative roll bonding (ARB) and composed of laminate structures of Mg and Cu layers with the thickness of few hundreds nm. During the heating process of initial hydrogenation of Mg/Cu SLCs, hydrogenation of Mg and alloying of Mg with Cu followed by hydrogenation of Mg2Cu occurs competitively. It is found that microstructures of Mg/Cu SLCs during initial hydrogenation have changed drastically depending on the order of hydrogenation of Mg and Mg2Cu. The microstructures of Mg/Cu SLCs after initial hydrogenation can be categorized in three types such as (1) MgCu2 network, (2) MgCu2 sheath and (3) MgCu2 layer. Features of differential scanning calorimetry (DSC) profiles of the first cycle were well explained by this microstructure formation mechanism. In order to achieve only MgCu2 network structure, it is important to get fine, even and uniform microstructures in Mg/Cu SLCs. The large number of ARB cycles is inefficient. Changing flow properties such as annealing during ARB, warm-rolling and ultrasonic assisted rolling can be good strategies for that purpose.

DOI： 10.2320/matertrans.MB201807

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DOI： 10.1088/1757-899X/375/1/012032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Highly activated, monodispersed N,N-dimethylformamide (DMF)-stabilized iron-oxide nanoparticles (Fe2O3 NPs) were synthesized by using iron(III) acetylacetonate as a precursor under open-air conditions. The resulting Fe2O3 NPs were characterized by various techniques (e.g., transmission electron microscopy, dynamic light scattering, X-ray diffraction, X-ray photoelectron spectroscopy, FTIR spectroscopy, and X-ray adsorption near-edge structure). The Fe2O3 NPs exhibited efficient catalytic activity for the hydrosilylation of alkenes without the need for further additives. An effective recycling process of the colloidal catalyst by extraction with a hexane/DMF system was developed, and recycling of the catalyst over five cycles did not result in any significant loss in catalytic activity.

DOI： 10.1002/cctc.201800161

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

To identify the reasons why Ti-Pd alloys for hydrogen storage materials show good hydrogenation properties, X-ray photoelectron spectroscopy and the Suzuki-Miyaura cross-coupling reaction were used to investigate a small amount of Pd added Ti-Pd alloys. Pd in or on Ti oxide films is in a valence state of 0 (Pd-0). Catalytic activity was shown by Pd-0 in the Suzuki-Miyaura cross-coupling reaction. Therefore, the enhanced hydrogenation properties of Ti-Pd alloys for hydrogen storage materials is due to Pd-0's catalytic activity in dissociating hydrogen molecules. In addition, the potential catalytic activity of Ti-Pd alloys was shown to be based on a Pd catalyst.

DOI： 10.2320/matertrans.M2018240

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

Competitive reactions and formation mechanism of microstructures in Mg/Cu super-laminate composites (SLCs) during initial hydrogenation were studied. During initial hydrogenation of Mg/Cu SLCs, hydrogenation of Mg and alloying of Mg with Cu followed by hydrogenation of Mg2Cu are competitive. It is found that microstructures of Mg/Cu SLCs during initial hydrogenation have changed drastically depending on the order of hydrogenation of Mg and Mg2Cu. The microstructures of Mg/Cu SLCs after initial hydrogenation can be categorized in 3 types.

DOI： 10.4028/www.scientific.net/MSF.941.1927

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The use of redox active organic compounds as an alternative positive electrode material of rechargeable lithium batteries can be a solution for the resource issues of the current battery system. To satisfy both the high capacity and long cycle life of the batteries using organic active materials, naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) derivatives, which potentially exhibit a four-electron transfer redox reaction, were investigated. While the unsubstituted naphthazarin lithium salt (1), having a high theoretical capacity of up to about 550 mAh g(-1), showed only half the expected capacity and a short cycle life as a positive electrode active material, the chloro-substituted ones (1-Cl-2, 1-Cl-4) exhibited improved properties in both their initial capacity utilization and cycle life. In addition, the high stability of a chloro-substituted naphthazarin salt (1-Cl-4) was supported by a reversible electrochromic behavior during the redox reaction. The substituent effect of the naphthazarin derivatives on the cycle stability was discussed with respect to the battery performance and electrochromic behavior. Also, a guide for designing a new organic active material which shows a high capacity and long cycle life is suggested.

DOI： 10.1007/s10853-017-1368-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The formation mechanism of microstructures in Mg/Cu super-laminates composites (SLCs) fabricated by accumulative roll-bonding (ARB) during initial activation was investigated. It is revealed that Mg2Cu can grow with sufficient growth rate at low temperatures (<453 K) in Mg/Cu SLCs. The growth of Mg2Cu layers for short growth length is diffusion-controlled. The activation energies for layer growth process of Mg2Cu layers in Mg/Cu SLCs are 107 +/- 8 kJmol(-1) with acid cleaning prior to ARB and 103 +/- 12 kJmol(-1) without acid cleaning prior to ARB, respectively, which are about 2/3 of those in Mg-Cu diffusion couples. It is considered that the high density of lattice defects in Mg/Cu SLCs fabricated by ARB contributes the much lower activation energies for layer growth process of Mg2Cu layers in Mg/Cu SLCs than in Mg-Cu diffusion couples. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2017.02.193

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ATLANTIS PRESS  

Titanium (Ti) based hydrogen-storage materials can absorb hydrogen under mild conditions. However, the materials could not absorb hydrogen without initial activation, owing to the formation of surface oxide layer. For mitigate the initial activation conditions, addition of Pd to Ti based materials were conducted. In spite of a tiny content of Pd, the addition was effective. In this study, effect of Pd in Ti oxide layer on initial hydrogenation property was investigated. Ti(1-x) Pdx (x=0, 0.002, 0.005, 0.010) alloys were fabricated with an arc-melting machine in an Ar atmosphere. Turnings-like specimens were obtained by milling the ingots with a milling machine for increase of specific surface. Initial hydrogenation properties were carried out with a Sieverts-type apparatus. Surface property of Ti0.990Pd0.010 before hydrogenation was carried out by X-ray photoelectron spectroscopy. Pd-added Ti alloys rapidly formed Ti hydride compared with pure Ti. Pd in the oxide film existed as valence state of 0 (Pd-0). Because metallic Pd was well-known as catalyst for dissociation of molecular hydrogen, Pd-added Ti alloys can faster absorb hydrogen.

DOI： 10.2991/ame-17.2017.10

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/2374068X.2016.1247336

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The microstructure and mechanical properties of thermomechanically processed Zr-14Nb alloy with low magnetic susceptibility were investigated in this study. The stress-strain curves of Zr-14Nb alloy were classified as higher or lower work-hardening types depending on the thermomechanical process. Serration was observed in curves of the higher work-hardening type. SEM-EBSD analysis indicated that {332}<113> twinning should form at the hands that appear after tensile testing. On the other hand, no serration appeared in the lower hardening rate curves. The mechanical properties of centrifugally cast Zr-14Nb alloy with a lower work-hardening rate possessed moderate tensile strength and high elongation because of the formation of the isothermal re phase during cooling after centrifugal casting, although the tensile strength was increased and the elongation was decreased with increase of the isothermal w phase formed after aging. The magnetic susceptibilities of thermomechanically processed Zr-14Nb alloys were still one-third lower than those of Ti-6A1-7Nb. Accordingly, the mechanical properties of Zr-14Nb can be controlled by thermomechanical processing while keeping low magnetic susceptibility.

DOI： 10.2320/matertrans.MI201512

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELECTROCHEMICAL SOC INC  

In order to understand the solution chemistry of electrolyte solutions at concentrations far from infinite dilution, the solution density, viscosity and ionic conductivity of Li- and Na-TFSI dissolved in GBL and PC were measured at 0.1 <= C/mol.dm(-3) <= 2.0 and 278 <= T/K <= 328, where TFSI = bis(trifluoromethanesulfonyl) imide, GBL = gamma-butyrolactone and PC = propylene carbonate. The results are compared to those of previously determined perchlorate salts. The partial molar volume of the solute, derived from the density, confirmed that the Na-systems occupy more volume in the solution than the Li-systems. On the other hand, the viscosity and ionic conductivity suggested that the Na-systems are more fluid and conductive than the Li-systems. The relative viscosity vs. the molarity follows a modified empirical Jones-Dole equation. The molar conductivity linearly decreased with respect to the cube-root of the molarity, which was analyzed by the pseudolattice model. The Raman spectroscopy revealed that, while the solvation number is comparable at 1-2 for either the Li- or Na-systems, Li+ is more tightly bound to the solvent molecules than Na+. The higher fluidity and conductivity of the Na-systems than those of the Li-systems result from the less occurrence of the solvent-shared ion pairs in the former than in the latter. (C) 2016 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.0931606jes

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

Mg is hydrogenated as core-shell type hydride in which the surface is covered with MgH2 (shell) and unreacted Mg remains at the internal side (core). Therefore, increase of absorption capacity to the theoretical hydrogen capacity is still one of the most important issues for the hydrogen storage materials, although several treatments were proposed to enhance their absorption capacity. In this study, the procedure of the core-shell structure as well as effect of Al concentration in Mg on the growth MgH2 in Mg were investigated using pure Mg and Mg-(3-9) mass. Al-1 mass%Zn alloys (AZ). MgH2 was formed on the surface as well as inside of unreacted Mg core which was apart from both gaseous H-2 and the surface MgH2 layer. The inside MgH2 was formed in a granular form on Mg grain boundary and its size increased by applying plastic deformation. Thickness of the surface MgH2 and size of the internal MgH2 increased with an increase in hydrogenation time until the hydride surface was completely covered with MgH2. However, the growth of the surface and internal MgH2 came to a halt after the surface was covered with MgH2. The increase in Al concertation in AZ lead to decrease in thickness of the surface MgH2, prolongation of the halt time and increase in the internal MgH2 grain size. From these results, supplying H from metal side was dominantly contributed for growth of the surface and internal MgH2 because diffusion rate of H in Mg was much higher than that in MgH2. In addition, the growth of internal MgH2 as well as control of surface MgH2 can contribute to the promotion of the complete hydrogenation of Mg based hydrogen storage materials.

DOI： 10.2320/jinstmet.JD201603

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

To increase the cycle-stability of rechargeable batteries using an organic positive-electrode material, we synthesized a polymer from a 5,8-dihydroxy-1,4-naphthoquinone (DHNQ) skeleton, which potentially undergoes a four-electron transfer redox reaction. The polymeric material (PDHNQ) was synthesized by the condensation reaction between DHNQ and formaldehyde under acidic media conditions. The initial capacity of the electrode using the monomer (DHNQ), 193 mAh/g, quickly decayed to 56 mAh/g after 100 cycles. On the other hand, the electrode incorporating the prepared PDHNQ showed the higher initial discharge capacity of 256 mAh/g and a longer cycle-life, retaining about 133 mAh/g after 100 cycles. (C) 2016 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2016.05.028

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

Although Mg based hydrogen storage materials absorb hydrogen immediately under appropriate thermodynamic conditions, an obvious incubation period exists for hydrogen desorption. This fact implies that the mechanisms of hydrogen absorption and desorption are different from each other. During hydrogen desorption process, nucleation and growth of Mg are occurring in MgH2. It is considered that free surface is the only nucleation site of Mg in hydrogen desorption process. The nucleation frequency per unit specific surface area should be constant under a fixed temperature and H-2 partial pressure. Therefore, it is estimated that the incubation period is proportional to the inverse of specific surface area.
The relationship between incubation period and specific surface area of MgH2 was investigated in order to understand the mechanism of incubation period on magnesium. hydrogen system. MgH2 with several kinds of specific surface area were manufactured by changing milling time of a planetary ball mill. A primary Gibbs free energy for dehydrogenation was conducted as -1.94 kJ mol(-1) by controlling H-2 pressure for measuring incubation period. The results revealed that the incubation period was proportional to the inverse of specific surface area.

DOI： 10.2320/jinstmet.JD201604

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

A new battery material that is composed of polyglycidol and a redox-active anthraquinone unit (AQ) was prepared and was then used as a positive electrode for lithium ion batteries. Polyglycidol (pGD) is a bio-based polymer that is derived from the waste glycerin that is discarded during bio-diesel processing. The pGD-AQ electrode has a potential plateau at 2.3 V vs. Li+/Li, and a discharge potential that decreased gradually with a capacity of 139 mAh g(-1). The cycle-life stability of pGD-AQ is better than that of chloroanthraquinone, which was used as a reference material. A higher AQ skeleton incorporation rate into pGD leads to a higher battery capacity. These results show that the incorporation of the AQ unit into the polymer is an effective way to improve battery performance in terms of both capacity and cycle-life stability. (C) 2016 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2016.05.027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Formation mechanism of micro/nano-structures through competitive reactions in Mg/Cu super-laminate composites (SLCs) during initial hydrogenation was investigated experimentally. Three types of MgCu2 structures, an open network, a sheathed network and a layer, were observed after initial hydrogenation of Mg/Cu SLCs under the conditions of 573 K, 86.4 ks in H-2 atmosphere of 3.3 MPa. Hydrogenation of Mg (1) and alloying Mg with Cu to form Mg2Cu (2) followed by hydrogenation of Mg2Cu (3) should be competitive. It is proposed that an open network of MgCu2 can be formed when (1) occurs later than (3), a sheathed network when (1) occurs later than (2) and earlier than (3), and a layer when (1) occurs earlier than (2). However, the reaction of MgH2 to Cu under H-2 atmosphere is not known in general. Therefore, in order to prove the existence and the generality of this reaction, pellets of MgH2 and Cu powder were heated under the condition of 673 K, 86.4 ks in H-2 atmosphere of 8.0 MPa. The formation of a layer of MgCu2 was confirmed by SEM observations, EDS analyses and XRD measurements. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2015.01.196

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

We have been proposing that there are competitive two kinds of pathways in the hydrogenation of Mg/Cu super-laminate composites. The one is that Mg reacts with Cu to form Mg2Cu and then Mg2Cu is hydrogenated to form MgH2 and MgCu2. The other is that Mg is hydrogenated and then MgH2 and Cu reacts to form MgCu2 together with H-2 gas, according to a hypothesis that the reaction of MgH2 + 2Cu -> MgCu2 + H-2 occurs. In the present study, the reaction conditions such as pressure and temperature were investigated in order to confirm that the hypothesis is true. Well-mixed MgH2 and Cu powder was compressed to a pellet at 1.73 GPa and then heated at various hydrogen pressures and temperatures. Following results were obtained from the experiments at 673 K. The above-mentioned alloying accompanied by H-2 emission occurs at pressures higher than 6.6MPa of H-2 pressure, which is higher than lower limit for the hydrogenation of Mg2Cu. On the other hand, Mg2Cu is formed at 3.3 MPa which is lower than the limit. The reaction of MgH2 with Cu also occurs at 573K in 3.3 MPa H-2. But it requires very long time such as 691.2 ks, although the existence of MgCu2 is confirmed in 86.1 ks of heating time in the case of Mg/Cu super-laminate composites.

DOI： 10.2320/matertrans.M2014426

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

A variety of microstructures in Mg/Cu super-laminate composites (SLCs) caused by competitive reactions during hydrogenation has been shown experimentally. Two types of MgCu2 structures, three-dimensional (3-D) network and layer, were observed after initial hydrogenation of Mg/Cu SLCs under the conditions of 573K, 86.4ks in H-2 of 3.3MPa. It was proposed that Mg/Cu SLCs could be hydrogenated by two kinds of processes. The one is alloying Mg with Cu to form Mg2Cu followed by hydrogenation of Mg2Cu, leading to the formation of 3-D network of MgCu2. The other is hydrogenation of Mg followed by the reaction of MgH2 to Cu, leading to the formation of layer MgCu2. SEM observations revealed that there existed Mg2Cu nano-crystals at the interface between Mg and Cu in as-rolled Mg/Cu SLCs, and layer MgCu2 at the interface between MgH2 and Cu in pellets of MgH2 powder and Cu powder heated under the conditions of 673K, 86.4ks in H-2 of 8.0 MPa. The existence of Mg2Cu nano-crystals enables alloying Mg with Cu at low temperatures (<473K).

DOI： 10.1088/1757-899X/82/1/012078

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The magnetic susceptibility of cold-rolled Zr-14Nb was evaluated to apply a new metallic medical device used for magnetic resonance imaging (MRI). The magnetic susceptibility of cold-rolled Zr-14Nb decreased up to the reduction ratio of 30%, then gradually decreased up to the ratio of 90%. Transmission electron microscopic observation revealed the strain-induced formation of omega phase after cold rolling at the reduction ratio of 5%, indicating that the initial decrease in magnetic susceptibility was caused by the formation of the omega phase. The omega phase was saturated at the reduction ratio of 30%. The formation of the omega phase could be explained on the basis of the increase in the Young's modulus and Vickers hardness of cold-rolled Zr-14Nb. The effect of texture formation on these properties was not obvious in the cold-rolled Zr-14Nb. Because of the strain-induced formation of the omega phase, the magnetic susceptibility of Zr-14Nb can be reduced by cold rolling to as low as that of as-cast Zr-9Nb, which is one-third that of Ti and Ti alloys. Therefore, cold-workable Zr-14Nb with low magnetic susceptibility could be a promising alloy for medical devices under MRI. 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actbio.2012.10.046

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS & MATERIALS  

We proposed that there are two kinds of competitive processes in the hydrogenation of Mg/Cu super-laminate composites; the one in which alloying (formation of MgCu2 fromMg and Cu) occurs in advance and Mg2Cu is hydrogenated to form MgH2 and MgCu2, and the other in which Mg is hydrogenated and then MgH2 and Cu react to form MgCu2 together with H-2 gas, according to a hypothesis that the reaction of MgH2+2Cu -> MgCu2+H-2 occurs. In order to confirm that the hypothesis is true, we investigated the conditions such as H-2 pressure and temperature at which the above-mentioned reaction proceeds. Well-mixed MgH2 and Cu powder was compacted to form pellet at 1.73 GPa and then heated at various hydrogen pressures and temperatures. Experimental results at 673 K indicated that the above-mentioned reaction occurs at pressures higher than 6.5 MPa, approximately the lower limit for the hydrogenation of Mg2Cu, whereas both Mg2Cu and MgCu2 are formed at 3.3 MPa.

DOI： 10.2320/jinstmet.JC201308

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS PRESS  

Surface modification techniques affect phase transformation which in turn influences strength of zirconia biomaterial. The study aimed at evaluating the tetragonal to monoclinic (t-m) phase transition of zirconia occurring after sandblasting three different ceramic abrasive materials and its subsequent effect on the strength. Zirconia bars (n = 24) were sandblasted using silicon carbide (SiC), alumina (Al2O3) and zirconia (ZrO2) particles. After surface characterization by a scanning electron microscope (SEM) and a laser profilometer, the relative amount of transformed monoclinic (m) phase was analyzed by X-ray diffractometry (XRD) and its corresponding effect on the flexural strength and fatigue strength were determined. Data were analyzed using one-way analysis of variance ANOVA (p < 0.05). Furthermore, Weibull statistics was used to analyze the variability of flexural strength. The highest amount of monoclinic content was found after sandblasting with SiC consequently resulting in an increased flexural strength and fracture resistance under cyclic load conditions. Weibull modulus was reduced in all the groups with SiC blasting showing the least degradation of m values. The strengthening mechanism that is attributed to sandblasting procedure is influenced by the abrasive material used.

DOI： 10.3233/BME-2012-0727

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The effects of the microstructures and phases of Zr-rich Mo alloys on their magnetic susceptibilities and mechanical properties were investigated in order to develop a Zr alloy with low magnetic susceptibility for use in magnetic resonance imaging (MRI). The magnetic susceptibility was measured with a magnetic susceptibility balance, while mechanical properties were evaluated by a tensile test. The microstructure was evaluated with an X-ray diffractometer, an optical microscope, and a transmission electron microscope. Evaluation of the microstructures revealed that the alpha' phase was the dominant form at less than 2% Mo content in the as-cast alloy. The omega phase was formed in as-cast Zr-3Mo but disappeared with aging at 973 K. Magnetic susceptibility was reflected in the phase constitution: the susceptibility showed a local minimum at Zr-(0.5-1)Mo with mostly alpha' phase and a minimum at Zr-3Mo with mostly beta and omega phases. The magnetic susceptibility of as-cast Zr-3Mo increased at 973 K due to disappearance of the omega phase. However, the susceptibility was still as low as that of as-cast Zr-1Mo. The ultimate tensile strength of alpha'-based Zr-Mo alloys was tailored from 674 to 970 MPa, and the corresponding elongation varied from 11.1% to 2.9%. Because Zr-Mo alloys containing omega phase were found, through tensile tests, to be brittle this phase should be avoided, irrespective of the low magnetic susceptibility, in order to maintain mechanical reliability. Elongation of the Zr-3Mo alloy was dramatically improved when the phase constitution was changed to alpha and beta phases by aging at 973 K for 86.4 ks. The magnetic susceptibilities of the alpha'-based Zr-Mo alloys are one-third those of Ti-6Al-4V and Ti-6Al-7Nb, and thus these Zr alloys are useful for medical devices under MRI. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actbio.2011.07.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

On the basis of the microstructures and mechanical properties of as-cast Zr-(0-24)Nb alloys the effects of phase constitution on the mechanical properties and magnetic susceptibility are discussed in order to develop Zr alloys for use in magnetic resonance imaging (MRI). The microstructures were evaluated using an X-ray diffractometer, an optical microscope, and a transmission electron microscope; the mechanical properties were evaluated by a tensile test. The alpha' phase was dominantly formed with less than 6 mass% Nb content. The omega phase was formed in Zr-(6-20)Nb alloys, but disappeared from Zr-22Nb. The beta phase dominantly existed in Zr-(9-24)Nb alloys. The mechanical properties as well as the magnetic susceptibility of the Zr-Nb alloys varied depending on the phase constitution. The Zr-Nb alloys consisting of mainly alpha' phase showed high strength, moderate ductility, and a high Young's modulus, retaining low magnetic susceptibility. Zr-Nb alloys containing a larger volume of omega phase were found to be brittle and, thus, should be avoided, despite their low magnetic susceptibility. When the Zr-Nb alloys consisted primarily of beta phase the effect of omega phase weakened the mechanical properties, thereby leading to an increase in ductility, even with an increase in magnetic susceptibility. The minimum value of Young's modulus was obtained for Zr-20Nb, because this composition was the phase boundary between the beta and omega phases. However, the magnetic susceptibility of the alloy was half that of Ti-6Al-4V alloys. Zr-Nb alloys consisting of alpha' or beta phase have excellent mechanical properties with low magnetic susceptibility and, thus, these alloys could be useful for medical devices used in MRI. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actbio.2011.07.020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The effects of Pt and Pd addition to a Zr-20Nb alloy on its microstructure and mechanical property, as well as the elution of metals from the alloys in lactic acid solution, were investigated. The microstructure was characterized with an X-ray diffractometer (XRD), an optical microscope (OM), and a transmission electron microscope (TEM). The mechanical properties were evaluated by a tensile test. The beta phase is dominantly observed in the Zr-20Nb as well as in the Pt-added and Pd-added Zr-20Nb alloys. Needle-like microstructures are observed in equiaxed grains in all alloys. Pd addition to the Zr-20Nb alloy suppresses omega phase formation more than Pt addition does. The 0.2% offset yield strength and the ultimate tensile strength of the Pt-added and Pd-added Zr-20Nb alloys increase with the Pt and Pd concentrations. XRD analysis revealed that the lattice parameter of beta-Zr in the Pt-added and Pd-added Zr-20Nb alloys decreases with the Pt and Pd concentrations. Pt and Pd solute in beta-Zr as a substitutional element and contribute to the increase in the strength by solid solution hardening. The addition of 2Pt and 2Pd to the Zr-20Nb alloy also improves metal elution from the alloys in lactic acid solution. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msec.2011.02.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The microstructures and magnetic susceptibilities of Zr-Mo alloys were investigated to develop a Zr alloy with a low magnetic susceptibility for magnetic resonance imaging (MRI) The microstructure was evaluated with an X-ray diffractometer (XRD), an optical microscope (OM) and a transmission electron microscope (TEM), and the magnetic susceptibility was measured with a magnetic Susceptibility balance. The alpha' phase with acicular structure was dominant in Zr-1Mo alloys. while the omega and beta phases with the equiaxed and relatively flat (no acicular) microstructure was dominant in Zr-3Mo. The mixed microstructural features of Zr-1Mo and Zr-3Mo were observed in Zr-2Mo, which consists of the alpha', omega and beta phases. The beta phase is stabilized when the Mo content exceeds over 3 mass% Mo As-cast Zr-Mo alloys showed a minimum Value of magnetic susceptibility at 3 mass% Mo. and the value abruptly increased up to 10% Mo before remaining stable up to 15 mass% Mo XRD, OM and TEM revealed that the minimum value of the susceptibility was closely related to the appearance of the athermal omega phase in the beta phase As the Mo content decreases from 3 mass%, the alpha' phase appears with the omega and beta phases Oil the other hand, as the Mo content increases from 3 mass%, the beta phase increases and the omega phase decreases Thus the appearance of the alpha and beta phase leads to an increase in magnetic Susceptibility The magnetic susceptibility of as-cast Zr-3Mo alloy was almost one-third that of Ti-6AI-4V, which is commonly used for medical implant devices. Zr-Mo alloys are useful for medical devices used under MRI (C) 2009 Acta Materialia Inc Published by Elsevier Ltd. All rights reserved

DOI： 10.1016/j.actbio.2009.09.013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The magnetic susceptibilities and microstructures of Zr-Nb binary alloys were investigated to develop a new metallic biomaterial with a low magnetic susceptibility for magnetic resonance imaging (MRI). The magnetic susceptibility was measured with a magnetic susceptibility balance, and the microstructure was evaluated with an X-ray diffractometer (XRD), an optical microscope (OM), and a transmission electron microscope (TEM). Zr-Nb alloys as-cast showed a minimum value of magnetic susceptibility between 3 and 9 mass% Nb, and the value abruptly increased up to 20 mass% Nb, followed by a gradual increase with the increase of the Nb content. XRD, OM, and TEM revealed that the minimum value of the susceptibility was closely related to the appearance of the athermal omega phase in the beta phase. Since the magnetic susceptibility of Zr-3Nb alloy consisting of an alpha' phase was as low as that of Zr-9Nb alloy consisting of the beta and omega phases, that of the omega phase was lower than that of the alpha' and beta phases. When Zr-16Nb alloy was heat-treated, the isothermal omega phase appeared, and, simultaneously, the magnetic susceptibility decreased. Therefore, the omega phase contributes to the decrease of the magnetic susceptibility, independently of the formation process of the omega phase. The magnetic susceptibility of the Zr-3Nb alloy as-cast was almost one-third that of Ti-6Al-4V alloy, which is commonly used for medical implant devices. Zr-Nb alloys are useful for medical devices used under MRI. [doi:10.2320/matertrans.M2009187]

DOI： 10.2320/matertrans.M2009187

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Language：Japanese   Publisher：Japan Institute of Metals (JIM)  

Mg is hydrogenated as core-shell type hydride in which the surface is covered with MgH2 (shell) and unreacted Mg remains at the internal side (core). Therefore, increase of absorption capacity to the theoretical hydrogen capacity is still one of the most important issues for the hydrogen storage materials, although several treatments were proposed to enhance their absorption capacity. In this study, the procedure of the core-shell structure as well as effect of Al concentration in Mg on the growth MgH2 in Mg were investigated using pure Mg and Mg-(3-9)mass-Al-1 mass-Zn alloys (AZ). MgH2 was formed on the surface as well as inside of unreacted Mg core which was apart from both gaseous H2 and the surface MgH2 layer. The inside MgH2 was formed in a granular form on Mg grain boundary and its size increased by applying plastic deformation. Thickness of the surface MgH2 and size of the internal MgH2 increased with an increase in hydrogenation time until the hydride surface was completely covered with MgH2. However, the growth of the surface and internal MgH2 came to a halt after the surface was covered with MgH2. The increase in Al concertation in AZ lead to decrease in thickness of the surface MgH2, prolongation of the halt time and increase in the internal MgH2 grain size. From these results, supplying H from metal side was dominantly contributed for growth of the surface and internal MgH2 because diffusion rate of H in Mg was much higher than that in MgH2. In addition, the growth of internal MgH2 as well as control of surface MgH2 can contribute to the promotion of the complete hydrogenation of Mg based hydrogen storage materials.

DOI： 10.2320/jinstmet.JD201603

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Language：Japanese   Publisher：Kansai University  

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Other Link： http://hdl.handle.net/10112/8014

Language：Japanese   Publisher：関西大学  

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Language：Japanese   Publisher：公益社団法人 日本金属学会  

DOI： 10.2320/materia.52.582

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We proposed that there are two kinds of competitive processes in the hydrogenation of Mg/Cu super-laminate composites: the one in which alloying (formation of MgCu2 from Mg and Cu) occurs in advance and Mg 2Cu is hydrogenated to form MgH2 and MgCu2, and the other in which Mg is hydrogenated and then MgH2 and Cu react to form MgCu2 together with H2 gas, according to a hypothesis that the reaction of MgH2 + 2Cu-MgCu2 + H2 occurs. In order to confirm that the hypothesis is true, we investigated the conditions such as H2 pressure and temperature at which the above-mentioned reaction proceeds. Well-mixed MgH2 and Cu powder was compacted to form pellet at 1.73 GPa and then heated at various hydrogen pressures and temperatures. Experimental results at 673 K indicated that the above-mentioned reaction occurs at pressures higher than 6.5 MPa, approximately the lower limit for the hydrogenation of Mg2Cu, whereas both Mg 2Cu and MgCu2 are formed at 3.3 MPa. © 2013 The Japan Institute of Metals and Matenals.

DOI： 10.2320/jinstmet.JC201308

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Language：Japanese   Publisher：一般社団法人日本歯科理工学会  

Mechanical properties of Zr/Ag composite wires were evaluated using Vickers hardness and tensile tests. The hardness of Zr increased by swaging while that of Ag did not significantly change. The 0.2% proof strengths of Zr/Ag composite wires decreased with increasing vol.% of Ag and they are higher than the estimated them based on the rule of mixture. Work hardening of Zr may contribute to the increase of the strength. On the other hand, young's modulus of Zr/Ag composite wires was lower than the estimated one, which may be caused by preferential crystallographic orientation of Zr and Ag during swaging.

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Language：Japanese   Publisher：一般社団法人日本歯科理工学会  

The aim of this study was to design an abutment of dental implants with good esthetic and mechanical properties. Zirconia layer was formed on a Zr-Nb alloy by thermal oxidation in air. The heating temperatures employed in this study were 700-1000℃; the heating time were 30-180 min. An optimal white colored and condensed oxidation layer was formed on the alloy. The thickness of oxide layer increased with temperature and time.

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Language：Japanese   Publisher：一般社団法人日本歯科理工学会  

The Zr/Ag composites were fabricated through swaging process, and their magnetic susceptibilities were evaluated using an magnetic balance. The magnetic susceptibilities of the composites decreased with increasing vol.% of Ag. In particular, the magnetic susceptibility of the composite containing 81 vol.% of Ag (1.88 x 10^<-5>) was about one-tenth as low as that of Ti (18.0 x 10^<-5>). The magnetic susceptibilities of the swaged Zr/Ag composites were slightly higher than those of the estimated values based on the rule of mixture. XRD analyses revealed preferred crystallographic orientation for the both swaged Zr and Ag, which may cause the higher magnetic susceptibility than those of the estimated values.

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Language：Japanese   Publisher：一般社団法人日本歯科理工学会  

Microstructure and magnetic susceptibility of Zr-Sn alloys were investigated to develop a novel Zr alloys with a low magnetic susceptibility for magnetic resonance imaging (MRI). The α-Zr(hcp) was observed in Zr-(0-17)Sn alloys. The magnetic susceptibility of Zr-(0-17)Sn alloys decreased with the increase of Sn concentration. The decreasing rate of the magnetic susceptibility indicates that Sn in Zr-Sn alloy may behave as a diamagnetic metal. In addition, Zr-17Sn alloy possesses high proof strength (about 900 MPa) and low magnetic susceptibility (0.86 x 10^<-6> g^<-1> cm^3).

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Microstructure and mechanical properties of Zr-Nb alloys were investigated to develop novel Zr alloys with a low magnetic susceptibility for magnetic resonance imaging (MRI). The Zr-Nb alloys consisting of ω phase show low tensile strength brittle fracture, while the magnetic susceptibility is lowest in the alloy. On the other hand, Zr-Nb alloys consisting of α' phase show high tensile strength and moderate ductility. Since the magnetic susceptibility of the α' phase is lower than that of the β phase, the Zr-Nb alloys consisting of α' phase possess promising properties to prevent artifacts in MRI.

DOI： 10.14832/gsjsdmd.2010s.0.42.0

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Language：Japanese   Publisher：The Japanese Society for Dental Materials and Devices  

MRI診断において, 磁化率の高い金属製インプラントを観察するとアーチファクトを生じ, 診断の妨げとなる. Zr-Nb合金は磁化率が低いとされるTiの半分以下の磁化率を有しており, アーチファクト防止型歯科用インプラントとして期待される. インプラントは製造過程で大きな塑性変形を伴うため, 高い靭性を有していることが求められる. そこで本研究では, Zr-Nb合金の組織と機械的性質について調べた.

DOI： 10.14832/gsjsdmd.2010s.0.42.0

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