Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Because abnormal grain growth (AGG) degrades mechanical properties of industrial polycrystalline materials such as steel, understanding and controlling AGG are important. In this study, AGG of Al-Nb-microalloyed lowcarbon steel was investigated at 1100 degrees C using in-situ scanning electron microscopy-electron backscatter diffraction (SEM-EBSD). Owing to the pinning particles of AlN and Nb(C,N), fine austenite grains formed initially, and AGG appeared owing to the dissolution of the pinning particles at high temperatures. Relatively large grains invaded the surrounding smaller grains with a size ratio of approximately 0.3, resulting in AGG. We developed the in-situ observation method to investigate the AGG of the carburization process using a diffusion couple of high- and lowcarbon steels. The carbon diffusion into the low-carbon steel from the high-carbon steel enhanced the grain growth of the low-carbon steel. Although the detailed mechanism is still unclear, we clearly showed that carburization can reduce the pinning force. When focusing on the misorientation of the grain boundary, grain boundaries with misorientation angles of 50-59 degrees remained during AGG, which is explained by their lower mobility owing to their lower grain boundary energy. These results suggest that the difference in grain-boundary mobility can induce duplex grain growth with a bimodal distribution, resulting in AGG.

DOI： 10.1016/j.mtla.2020.100985

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Iron and Steel Institute of Japan  

DOI： 10.2355/isijinternational.ISIJINT-2020-403

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

DOI： 10.1016/j.jallcom.2020.156817

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Iron and Steel Institute of Japan  

Effects of fine precipitates on the austenite (gamma) grain structures were investigated in JIS SCM420-based case-hardening steels with several different concentrations of the micro-alloying elements and hot-forging temperatures. Micro-alloyed steels of 18AI (0.018 mass% Al) and 35AI-32Nb (0.035 mass% Al, 0.032 mass% Nb) were forging-simulated at 1 150 degrees C or 1 250 degrees C, normalized at 1 070 degrees C, and carburized at 1 050 degrees C. When the as-received 18AI steel was normalized and carburized without forging-simulated heating, a uniform y grain structure was observed with the distribution of fine AIN precipitates. However, coarsening of AIN occurred when the forging-simulated temperature was 1 150 degrees C and it caused abnormal grain growth during carburization. In 35AI-32Nb steel, the same heating did not induce the abnormal grain growth owing to the AIN-Nb(C,N) combined particles. The size of these particles increase with an increase in the forging-simulated temperature. The high forging-simulated temperature caused the dissolution of the fine precipitates, followed by reformation and coarsening of the precipitates during the subsequent cooling and the normalization heating, which resulted in a decreased pinning force and ygrain coarsening. Furthermore, TEM observations revealed that a considerable amount of Nb(C,N) particles exist near large eutectic MnS particles. Thermodynamic calculations based on the Scheil's condition showed that the formation of these Nb(C,N) particles was due to segregation during solidification. It was suggested that such local concentration of the precipitate particles in the last solidifying region leads to ununiform distribution of the pinning force that may induce the abnormal grain growth.

DOI： 10.2355/isijinternational.isijint-2020-123

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN  

The effects of fine precipitates on the austenite grain refinement of micro-alloyed steel during cyclic heat treatment were investigated under different solution treatments. After three rounds of cyclic heat treatment of A(c3) and A(r3) transformations of the as-received steel rod with rapid heating and cooling, the austenite grain size was 3-10 mu m. On the other hand, three rounds of cyclic heat treatment after solution treatment at 1 300 degrees C reduced the austenite grain size to 2-5 mu m. The as-received sample included AIN-Ti(C,N)-MnS composite particles with a mean diameter of 30 nm and a number density of 11 mu m(-3), and the mean diameter did not change during cyclic heat treatment. Thus, it was considered that the reduction in austenite grain size without solution treatment was caused by the increase in the nucleation site of austenite phase with increasing number of cycles, due to the refinement of the prior austenite grains with martensitic structure during the cyclic heat treatment. When solution-treated at 1 300 degrees C, the AIN-Ti(C,N)-MnS composite particles were solved, and they were precipitated during the cyclic heat treatment with a mean diameter of 12 nm and an increased number density of 85 mu m(-3). Thus, it was considered that the further reduction in austenite grain size with solution treatment was caused by the pinning effect of the fine precipitates, in addition to the increase in the number of austenite phase nucleation sites with increasing number of heat treatment cycles.

DOI： 10.2355/isijinternational.ISIJINT-2019-153

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Ceramic Society of Japan  

DOI： 10.2109/jcersj2.19110

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

The austenite (gamma) structure reversely transformed from martensite in Fe-0.55C mass% C alloy was investigated at high temperatures using in-situ an electron backscatter diffraction (EBSD) method. When the heating rate was varied, a rapidly heating produced fine gamma grains, in contrast, a slow heating induced coarse gamma grains having the same crystal orientations as those of the prior gamma grains; known as "gamma memory". The most likely mechanism for the gamma memory could be variant restrictions owing to cementite (theta). To investigate the effect of theta on the gamma memory, the sample was tempered at 700 degrees C for 24 h and theta was precipitated. The tempered sample exhibited the gamma memory irrespective of the heating rate. To clarify the origin of the gamma memory, we focused on the reversely transformed gamma formed adjacent to the theta and directly observed the orientation relationships (ORs) using the in-situ EBSD. A crystallographic analysis on the between neighboring ferrites (alpha), theta, and gamma revealed the existence of Kurdjumov-Sachs OR between gamma and two alpha (alpha 1 and alpha 2), Isaichev OR between alpha and theta, and Pitsch OR between theta and gamma. In the all possible combinations, the reversely transformed gamma satisfying the K-S OR for two alpha variants was limited to four variants. The theta variant satisfying the Isaichev OR for alpha 1 and alpha 2 was limited to one variant, which was close to one of the four variants by Pitsch OR, which suggests the gamma memory is due to these variant restrictions among alpha-theta-gamma.

DOI： 10.1016/j.mtla.2019.100409

Web of Science

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.4164/sptj.56.267

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/matertrans.MC201810

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

DOI： 10.1111/jace.15947

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

DOI： 10.1002/sia.6549

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Chinese Society of Rare Earths  

Cerium-doped yttrium aluminum garnet (YAG:Ce) as a yellow phosphor for white light-emitting diodes (LEDs) was synthesized via a facile combustion method using Y2O3, CeO2, Al2O3, Al, and NaClO4 as raw materials. The combustion synthesis approach utilizes the strong exothermic oxidation of aluminum to realize a self-sustaining reaction. In this study, we investigated the effects of the ratios of Al2O3 to Al, fluxes, and coprecipitated materials as raw materials on the luminescence properties of the synthesized YAG:Ce phosphors. When the amount of Al2O3 x is varied, the combustion reaction proceeds at x ≤ 1.8, with x = 1.725 being the optimum condition for producing a high-performance product. When 5 wt% BaF2 is added, the luminescence intensity is significantly improved owing to a decrease of YAP (YAlO3) formation with improved uniformity. However, the addition of CaF2 and NaF does not improve the luminescence properties. To suppress the segregation of CeO2, we used the coprecipitated material Y2O3–CeO2 as a raw material. Unlike with separate addition of Y2O3 and CeO2, Ce ions are uniformly distributed in the coprecipitated material, resulting in improved luminescence properties. The combination of BaF2 and coprecipitated material significantly improves the internal quantum efficiency to 83.0%, which is close to that of commercial phosphors.

DOI： 10.1016/j.jre.2017.06.014

Scopus

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

DOI： 10.1039/C8TA04708A

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

DOI： 10.1016/j.solmat.2018.08.001

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Yellow Ca-alpha-SiAlON:Eu2+ phosphors for white light-emitting diodes (LEDs) were synthesized by a facile combustion synthesis method using CaO, Eu2O3, alpha-Si3N4, Si, and Al as raw materials. Ca concentrations and diluent ratios were optimized to improve their luminescence properties. The lattice constant and luminescence properties improved as x increased from 0.4 to 1.2 in Ca(x)Si(12-(m+n))Al(m+n)OnN(16-n):En(0.06). The optimum value was x = 1.2. Scanning transmission electron microscopy combined with energy dispersive X-ray analysis detected segregation of Ca and Eu at grain boundaries, which decreased luminescence behavior in the x = 1.4 sample. The influence of Si and Si3N4 diluents was investigated by varying the diluent ratio phi = (CaO + Eu2O3 + alpha-Si3N4)/(CaO + Eu2O3 + a-Si3N4 + Al + Si). Changes in temperature and flame propagation speed were measured during combustion synthesis using two thermocouples. When phi, was less than 0.5, the combustion temperature exceeded 1600 degrees C and the synthesized material contained an amount of the high-temperature beta-SiAlON phase. At phi > 0.7, the reaction temperature fell below 1200 degrees C, and unreacted raw materials remained. The optimum value of phi was 0.6. The internal quantum efficiency of the product synthesized at x = 1.2 and (I, = 0.6 was approximately 35% under 450-nm excitation. According to electron probe X-ray microanalysis, composition varied within individual synthesized particles, which may explain the decrease in emission behavior relative to a commercial product.

DOI： 10.1016/j.ceramint.2017.06.106

Web of Science

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

This study investigates the combustion synthesis of AlN fibers using an NH4Cl additive and reports the effects of Al particle size (3, 30, and 180 mu m) and N-2 pressure (0.10, 0.25, and 0.50 MPa) on the purity and morphology of AlN fibers. The combustion temperature was directly measured during the synthesis to elucidate the formation mechanism of the AlN fibers. The phase purity and morphology of the products were studied using X-ray diffraction and scanning electron microscopy, respectively. When the particle size of Al was reduced from 180 to 3 mu m, the purity of the AlN product increased significantly owing to the large reaction area, which increased the combustion temperature. Furthermore, lower N-2 pressures enhanced the formation of AlN nanofibers due to the accelerated gasification of Al. The optimum values of the particle size of Al and the N-2 pressure for the formation of high-purity MN nanofibers were found to be 3 mu m and 0.10 MPa, respectively.

DOI： 10.1016/j.ceramint.2017.04.170

Web of Science

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

Latent heat storage (LHS) technology employing phase change materials (PCMs) has received great attention as an alternative to conventional solid sensible heat storage (SHS) for future high-temperature energy utilisation systems. In this study, we report the synthesis of a core-shell type microencapsulated PCM (MEPCM) consisting of AI-25 wt% Si microspheres (mean diameter of 363 pm and melting temperature of 577 degrees C) as the core (PCM) and Al2O3 as the shell. The MEPCM was prepared in two steps involving (1) the formation of an AlOOH precursor shell on the PCM microspheres by a hydroxide precipitation process in hot water and (2) heat-oxidation treatment in an O-2 atmosphere to form a stable Al2O3 shell. In particular, the effects of heat oxidation temperature on the shell morphology, shell crystal structure, mechanical strength, heat capacity, and cyclic durability of the prepared MEPCMs were examined. The resultant MEPCM is composed of a stable alpha-Al2O3 shell and Al-25 wt% Si core with an effective void inside the core to allow for volume expansion of the PCMs during solid-liquid phase transitions. The heat capacity measured for this material is five times higher than that of conventional solid SHS materials. Additionally, the MEPCM exhibits excellent durability up to 300 heating and cooling cycles under oxygen atmosphere. Consequently, it can potentially be used in the next-generation LHS-based high-temperature thermal energy storage and transportation systems. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.apenergy.2016.11.025

Web of Science

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

We investigated the atomic and local electronic structures of Ca(2)AIMnO(5+delta) to assess its potential as an oxygen storage material. High-angle annular dark-field scanning transmission electron microscopy was used to investigate structural changes in the material during oxygen storage. We found that the AlO4 tetrahedra convert to AlO6 octahedra during such a process. According to the Mn L-edge electron energy-loss near-edge structure (ELNES) measurements, the Mn oxidation state increased from +3 to +4 on oxygen storage. The observed site-resolved oxygen K-ELNES and first-principles electronic structure calculations showed that each nonequivalent oxygen site has different characteristics, corresponding to local chemical bonding and oxygen intake and release. For Ca(2)AIMnO(5), the prepeak intensity was higher at MnO6 octahedral sites, indicating covalent bonding between the oxygen and Mn atoms. After oxygen storage, the ELNES spectra revealed that the Jahn Teller distortion of the Mn sites was suppressed by the increase in the Mn oxidation state; furthermore, the spectra indicate that Mn octahedron shrank in the z-direction, accompanied by an increase in Mn O covalent bonding, thus providing sufficient space to form octahedral AlO6. Consequently, we found that the reversible oxygen storage ability is related to the canceling of the volume changes of the Mn and Al octahedra. The electrons in Mn 3d orbitals play an important role in this structural change.

DOI： 10.1021/acs.chemmater.6b04099

Web of Science

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

A series of surface-doped LiMn2O4 samples modified by a Li2CuO2-Li2NiO2 solid solution were synthesized using a simple and facile sol-gel method to achieve the enhanced cycling performance, especially at elevated temperatures. The corresponding phase structure and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The modified layer on the surface of LiMn2O4 particles, featuring a LiNi delta Mn2-delta O4-like phase, together with a Li2CuO2-Li2NiO2 solid solution, as confirmed by XRD and transmission electron microscopy (TEM), plays a key role in alleviating the dissolution of manganese, thus enhancing the cycling performance and rate capability relative to bare LiMn2O4. The 0.5 wt.%-modified LiMn2O4 sample delivers a discharge capacity of 113 mAh g(-1), and a capacity retention of 93.2% following 300 cycles at 1C and 25 degrees C, which is higher than the values of 96 mAh g(-1) and 81.2% for bare LiMn2O4. In addition, at 55 degrees C, a capacity retention of 81.2% at 1C is obtained for the 0.5 wt.%-modified LiMn2O4 sample after 200 cycles, compared to 70.0% for bare LiMn2O4. Modifying the surface of the latter by a LiNi delta Mn2-delta O4-like phase mixed with a Li2CuO2Li2NiO2 solid solution, is an effective strategy for improving electrochemical properties. (C) 2016 Published by Elsevier Ltd.

DOI： 10.1016/j.electacta.2016.12.041

Web of Science

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

We analyzed the spatial distribution of Ca dopants in alpha-SiAlON by using a statistical approach that analyzed a high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) image. By evaluating the image intensity of each atomic column, we found that the intensity deviation of columns with Ca atoms was twice that of other atomic columns. The results of HAADF-STEM image simulation suggested that there was a long-range repulsive interaction along the [0001] direction between pairs of Ca atoms in the same Ca column. Moreover, correlation of image intensities in neighboring Ca columns suggested the existence of a short-range repulsive force between first-nearest-neighbor Ca atoms. The origin of such anisotropic interactions between pairs of Ca atoms will be discussed.

DOI： 10.2320/matertrans.MAW201705

Web of Science

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

In this paper, a novel method is proposed to produce MnO/carbon composites, in which the MnO nanoparticles were embedded into a porous carbon matrix, by a single-step nitrate-cellulose combustion synthesis. The composition, structure and morphology of the composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and scanning/transmission electron microscopy. The composites were used as lithium ion battery anodes to evaluate their electrochemical properties. The MnO/carbon composite with a proper carbon content showed enhanced cycling performance and capacity retention, which delivered a reversible capacity of 561 mAh g(-1) after 90 cycles at 0.2 A g(-1). The easy production and good electrochemical properties enables the composite to be a possible candidate as an anode alternative for high-performance lithium ion battery. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2016.08.054

Web of Science

J-GLOBAL

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

Twin formation in hematite during dehydration was investigated using X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy (TEM). When synthetic goethite was heated at different temperatures between 100 and 800 degrees C, a phase transformation occurred at temperatures above 250 degrees C. The electron diffraction patterns showed that the single-crystalline goethite with a growth direction of [001](G) was transformed into hematite with a growth direction of [100](H). Two non-equivalent structures emerged in hematite after dehydration, with twin boundaries at the interface between the two variants. As the temperature was increased, crystal growth occurred. At 800 degrees C, the majority of the twin boundaries disappeared; however, some hematite particles remained in the twinned variant. The electron diffraction patterns and high-resolution TEM observations indicated that the twin boundaries consisted of crystallographically equivalent prismatic (100) (010), and (10) planes. According to the total energy calculations based on spin-polarized density functional theory, the twin boundary of prismatic (100) screw had small interfacial energy (0.24 J/m(2)). Owing to this low interfacial energy, the prismatic (100) screw interface remained after higher-temperature treatment at 800 degrees C.

DOI： 10.1007/s00269-016-0831-8

Web of Science

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

We investigated the dopant distribution in Ca-doped alpha-SiAlON by using high-angle annular dark-field scanning transmission electron microscopy and a multi-slice image simulation. Our results showed that the electron wave propagated by hopping to adjacent Si(Al) and N(O) columns. The image intensities of the Ca columns had wider dispersions than other columns. To estimate the Ca distribution in the bulk material, we performed a Monte Carlo atomic simulation of the alpha-SiAlON with Ca dopants. A model including a short-range Coulomb-like repulsive force between adjacent Ca atoms reproduced the dispersion of the intensity distribution of the Ca column in the experimental image.

DOI： 10.1093/jmicro/dfw020

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

In this study, Ca-alpha-SiAlON:Eu2+ yellow phosphors for white light-emitting diodes (LEDs) were synthesized via a facile combustion synthesis method by using CaO, Eu2O3, Si, and Al as raw materials, while NaCl and Si3N4 were utilized as diluents to contain the combustion temperature. The concentration of Eu was varied, and the resulting changes in phase purity, photoluminescence properties, and thermal quenching were investigated. We observed that the increase in lattice constant depended on the amount of Al, while the Ca sites were partially substituted by Eu ions. The synthesized Ca-alpha-SiAlON: Eu2+ powders exhibited emission wavelength at 556-560 nm and high thermal stability, revealing high potential for application in white LEDs. (C)2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2016.04.211

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We investigated four catalysts for the dry reforming of methane: three Ni-containing natural iron ores (LN, SN, and NN ores) and one Ni-supported ore (Ni-supported NN ore) to solve the problems about unused high-temperature waste heat and CO2 emission in the steel industry. The CO2 conversion ratio was highest for the LN ore (1.18 wt '% Ni), followed by Ni-supported NN (1.0 wt % Ni), SN (0.30 wt % Ni), and NN (0 wt % Ni) ores. The CO2 conversion ratio of the LN ore was much higher than that of the Ni-supported NN ore, despite the fact that they contained almost the same amount of Ni. This is because the LN ore had a higher surface area and a higher nickel dispersion. Transmission electron microscopy with energy dispersive X-ray spectroscopy revealed that Ni existed quite finely in the LN ore but existed as a larger particle (20 nm) in the Nisupported NN ore. Smaller Ni particles have a higher surface area, resulting in the higher catalytic performance of the LN ore. More CO2 and CH4 reacted and higher amounts of H-2 and CO were produced with the LN ore catalyst compared to the uncatalyzed reaction. The LN ore showed more reduction at higher temperatures, and metallic iron and nickel were produced above 1073 K; reduction did not progress past Fe3O4 at lower temperatures.

DOI： 10.1021/acs.energyfuels.6b00940

Web of Science

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

The surface of spinel LiMn2O4 is modified with different quantities of a Mn4+-rich phase prepared by a facile sol-gel method to improve electrochemical properties at elevated temperatures. Impurity-free and uniform morphologies for the LiMn2O4 particles are demonstrated from the X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The Mn4+-rich phase modified on the surface of the LiMn2O4 alleviates the dissolution of manganese in the electrolyte, thus improving the cycling performance and rate capability relative to the bare LiMn2O4. 1 wt.%-modified LiMn2O4 delivers a capacity retention of 92.7% and a discharge capacity of 113.5 mAh g(-1) after 200 cycles at 1C and 25 degrees C, compared with that of 83.1%, and 100.8 mAh g(-1) for the bare LiMn2O4. In addition, after 100 cycles, a capacity retention of 88.6% at 1C is achieved for 1 wt.%-modified LiMn2O4 at 55 degrees C, which is higher than the 76.0% for the bare LiMn2O4. Furthermore, this sample shows the best rate capability among all samples. The Mn4+-rich phase is an appropriate candidate for modifying surfaces to suppress dissolution of manganese, thereby improving the electrochemical properties of LiMn2O4. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.electacta.2016.05.075

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In this study, a Sn-C composite material as anode material for lithium ion batteries was fabricated via MgO template-assisted solution combustion synthesis, in which the starting material was a gel containing Sn(NO3)(2), glycine (C2H5O2N) as the carbon source, and Mg(NO3)(2)center dot 6H(2)O for the template. After the combustion reaction, the generated MgO was removed from the carbon, and the Sn nanoparticles were dispersed into a porous carbon structure during the carbon reduction of SnO2 under calcination in N-2. The effects of ratios of glycine (n) and MgO (m) on the material phase, morphology, carbon content, and electrochemical properties were mainly investigated. At glycine (n) ratios of 2 and 3, the SnO2 phase was not fully reduced to Sn. With n > 3, a composite material of metallic Sn nanoparticles and carbon was synthesized, in which the ratio of carbon increased with increasing n. With increasing m, the porosity of the particles increased, resulting in enhanced cyclic stability owing to the buffer space provided by the porous structure of carbon. The composite material obtained at n = 4 and m = 4 exhibited the highest reversible capacity of 588 mA h/g after 100 discharge/charge cycles at a current rate of 0.5 A/g as compared to the 269 mA h/g observed for n = 4 and m = 2. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

DOI： 10.1016/j.apt.2016.06.004

Web of Science

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

In this study, MnO nanocrystals incorporated in a N-containing carbon matrix were fabricated by the facile thermal decomposition of manganese nitrate-glycine gels. MnO/C composites with different carbon contents were prepared by controlling the initial ratio of manganese to glycine. The composition, phase structure and morphology of the composites were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning and transmission electron microscopy, and thermogravimetric analysis. The results indicated that MnO nanocrystals were uniformly embedded in the N-doped carbon matrix. The carbon matrix could effectively enhance the electrical conductivity of MnO and alleviate the strain arising from the discharge/charge cycling. The composite materials exhibited high discharge/charge capacities, superior cycling performance, and excellent rate capability. A high reversible capacity of 556 mA h g(-1) was obtained after 110 cycles of discharging and charging at a current rate of 0.5 A g(-1). Even at a high current rate of 3 A g(-1), the sample still delivered a capacity of around 286 mA h g(-1). The easy production and superior electrochemical properties enables the composites to be a promising candidate as an anode alternative for high-performance lithium-ion batteries.

DOI： 10.1039/c6ra00571c

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN  

This study optimizes the dehydration temperature of goethite to control pore morphology. The pore morphology was characterized by using transmission electron microscopy and the nitrogen adsorption method. When the goethite was dehydrated at 200-250 degrees C, slit-like pores with a width lesser than 2 nm were formed along the [010] direction. These slit-like pores changed to spherical micropores (300-500 degrees C), and eventually disappeared (600-800 degrees C). Compared to the synthetic goethite, natural goethite has a lower crystallinity and smaller primary particle size of under 100 nm. The natural goethite before dehydration contained 4 nm pores as cracks that remained even after heating to 800 degrees C. In the case of natural goethite, the optimum dehydration temperature for higher surface area and pore volume was 350 degrees C, which was higher than that of 250 degrees C for the synthetic goethite.

DOI： 10.2355/isijinternational.ISIJINT-2016-231

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

In this paper, we describe the glycineenitrate-based solution combustion synthesis of SrTiO3 nanoparticles. The effects of the fuel ratio, 4, and washing treatment by HNO3 on the size, morphology, and crystalline structure of the synthesized particles were investigated. The photocatalytic activity of the final samples was also evaluated by measuring the photodegradation of methylene blue. The samples, which were calcined at 1000 degrees C for 10 h after combustion synthesis, were mainly SrTiO3. When 4 was increased, the number of pores in the sample was increased because of the increase in volume of ejected gas. Additionally, the initial particle size decreased with increasing 4 because glycine functioned not only as a fuel but also as a dispersant and stabilizer. After washing in a HNO3 solution, the porous structure decomposed to particles with high crystalline structure. The photocatalytic activity of SrTiO3 was significantly improved by HNO3 washing owing to the elimination of impurities, the increase in surface area, and the uncovering of the surface that consisted of (100) planes. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2015.08.227

Web of Science

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

Urchin-like CoO and Co3O4 hollow structures with potential use as anodes in lithium ion batteries were synthesized via the facile thermal decomposition of precipitated amorphous cobalt carbonate hydroxide under either Ar or air. The morphology and, consequently, electrochemical properties of the samples were highly dependent on the precipitation temperature. The cobalt oxides, as derived from precursors that were obtained at room temperature, exhibited superior activity to those obtained at 50 degrees C and 80 degrees C because of their unique nanosized architecture. Meanwhile, CoO samples demonstrated much better cyclability and rate capability than Co3O4 samples, as they exhibited much higher coulombic efficiency and lower hysteresis for lithium insertion/extration. The curved, short, and closely entangled nanowires of CoO sample, which was derived from room temperature precursor, yielded excellent electrochemical performance. The sample displayed a high reversible capacity of about 850 mAh g(-1) at a current density of 500 mA g(-1), a good stability through 50 cycles with a high coulombic efficiency of about 98%, and a high rate capability of 610 mAh g(-1) even at a rate of 3000 mA g(-1). (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2015.05.206

Web of Science

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

Solution plasma has been used in a variety of fields such as nanomaterials synthesis, the degradation of harmful substances, and solution analysis. However, as existing methods are ineffective in generating plasma over a large surface area, this study investigated the contact glow discharge electrolysis, in which the plasma was generated on the electrode surface. To clarify the condition of plasma generation, the effect of electrolyte concentration and temperature on plasma formation was studied. The electrical energy needed for plasma generation is higher than that needed to sustain a plasma, and when the electrolyte temperature was increased from 32 to 90 degrees C at 0.01 M NaOH solution, the electric power density for vapor formation decreased from 2005 to 774 W/cm(2). From these results, we determined that pre-warming of the electrolyte is quite effective in generating plasma at lower power density. In addition, lower electrolyte concentrations required higher power density for vapor formation owing to lower solution conductivity. On the basis these results, a method for large-area and flat-plate plasma generation is proposed in which an initial small area of plasma generation is extended. When used with a plate electrode, a concentration of current to the edge of the plate meant that plasma could be formed by covering the edge of the electrode plate. (c) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4926493

Web of Science

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

An amorphous iron oxide-carbon composite has been fabricated through an effective, inexpensive, and scalable method employing solution combustion synthesis. Amorphous iron oxide nanoparticles with diameters of about 5 nm were synthesized and uniformly embedded in a dense carbon matrix. The synthesized composite exhibits enhanced cyclability and rate capability, showing a high reversible capacity of 687 mA h g(1) after 200 discharge/charge cycles at a current rate of 0.5 A g (1), compared to the 400 mA h g (1) observed for Fe2O3 nanoparticles. This enhanced performance was retained despite more demanding conditions, delivering a high capacity of about 525 mA h g (1) and a nearly perfect coulombic efficiency even after 400 cycles at 1 A g (1). The easy production and superior electrochemical properties of this composite suggest that it is a promising material for use as an anode material in high performance lithium ion batteries. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2015.02.043

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Silicon nanoparticles (Si-NPs) were directly synthesized from a Si bar electrode via a solution plasma. In order to produce smaller Si-NPs, the effects of different electrolytes and applied voltages on the product were investigated in the experiments detailed in this paper. The results demonstrated that the use of an acidic solution of 0.1 M HCl or HNO3 produced Si-NPs without SiO2 formation. According to the transmission electron microscopy and electron energy-loss spectroscopy, the obtained Si-NPs contained both amorphous and polycrystalline Si particles, among which the smaller Si-NPs tended to be amorphous. When an alkaline solution of K2CO3 was used instead, amorphous SiO2 particles were synthesized owing to the corrosion of Si in the high-temperature environment. The pH values of KCl and KNO3 increased during electrolysis, and the products were partially oxidized in the alkaline solutions. The particle size increased with an increasing applied voltage because the excitation temperature of the plasma increased.

DOI： 10.1088/0957-4484/26/23/235602

Web of Science

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

A convenient method for coating titanium dioxide (TiO2) by Au nanoparticles (AuNPs) is demonstrated in solution plasma to improve the photocatalytic activity of TiO2. AuNPs from a metallic Au electrode were bonded to the surface of a commercial TiO2 powder, which acted as a catalyst support, with the reaction taking place in an electrolyte solution. The effect of diverse plasma conditions on the size and productivity of the AuNPs was investigated initially to provide a reference in the absence of TiO2. At 290V, "partial plasma" was attained, with only a weak light emission surrounding the Au electrode. Conditions then evolved to "full plasma", with a strong orange emission at 330 V. Partial or full status was maintained for 1 h at 300 and 400 V, respectively. At the transition to full, the AuNP particle size increased from 3.72 to 6.09 nm and the productivity increased dramatically from 0.025 to 0.87mgh(-1)mm(-2). Stronger plasma very efficiently synthesized AuNPs, and therefore, it was adopted for further study. AuNP-TiO2 combinations were formed by applying 400 V to a TiO2-dispersed solution. In these experiments, TiO2 coated with AuNPs was synthesized; these combinations of AuNP-TiO2 had 0.44 mol% of Au. The photocatalytic activity of AuNP-TiO2 was investigated by measuring the degradation of Rhodamine B (RhB). Under UV irradiation, the AuNP-TiO2 particles removed up to 95% of the dye in 70min. Commercial TiO2 achieves values closer to 85%. The results thus raise the possibility that solution plasma methods can be generalized as a means for achieving catalysis-enhancing coatings. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2015.03.075

Web of Science

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

Single-phase, high-purity nanosized LiMn2O4 powders, which are employed as cathode materials for lithium-ion batteries, were produced by solution combustion synthesis using glycine, sucrose, and nitrate, followed by calcination. Phase structure and morphology of the powders were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performance was measured by galvanostatic charge-discharge cycling in a voltage range of 3.2-4.4 V. The analysis of yield, morphology, and electrochemical performance mainly focused on the influence of different glycine/sucrose ratios. Compared to the sample obtained using 100% glycine, the yields of powders obtained by adding sucrose to the fuel were remarkably improved, from around 50% to over 90%. The highest discharge capacity at 1 C was obtained for the sample with 2% added sucrose, which retained a capacity of 116.6 mAh/g after 80 cycles. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

DOI： 10.1016/j.apt.2015.01.019

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Latent heat storage using alloys as phase change materials (PCMs) is an attractive option for high-temperature thermal energy storage. Encapsulation of these PCMs is essential for their successful use. However, so far, technology for producing microencapsulated PCMs (MEPCMs) that can be used above 500 degrees C has not been established. Therefore, in this study, we developed Al-Si alloy microsphere MEPCMs covered by alpha-Al2O3 shells. The MEPCM was prepared in two steps: (1) the formation of an AlOOH shell on the PCM particles using a boehmite treatment, and (2) heat-oxidation treatment in an O-2 atmosphere to form a stable alpha-Al2O3 shell. The MEPCM presented a melting point of 573 degrees C and latent heat of 247 J g(-1). The cycling performance showed good durability. These results indicated the possibility of using MEPCM at high temperatures. The MEPCM developed in this study has great promise in future energy and chemical processes, such as exergy recuperation and process intensification.

DOI： 10.1038/srep09117

Web of Science

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

A series of LiBixLaxMn2-2xO4 (x = 0, 0.002, 0.005, 0.010, 0.020) samples were synthesized by solution combustion synthesis in combination with calcination. The phase structure and morphology of the products were characterized by X-ray diffraction, scanning electron microscopy, and transition electron microscopy. The results demonstrated that a single-phase LiMn2O4 spinel structure was obtained for the LiBixLaxMn2-2xO4 (x = 0, 0.002, 0.005) samples, whereas impurities were observed for the LiBixLaxMn2-2xO4 (x = 0.010, 0.020) samples as a result of the doping limit. The electrochemical properties were investigated by galvanostatic charge-discharge cycling and cycling voltammetry in a voltage range of 3.2-4.4 V. The substitution of Mn3+ by equimolar Bi3+ and La3+ could significantly improve the structural stability and suppress the Jahn-Teller distortion, thereby resulting in improved electrochemical properties for the Bi and La co-doped samples in contrast with the pristine LiMn2O4 sample. In particular, the LiBi0.005La0.005Mn1.99O4 sample delivered a high initial discharge capacity of 130.2 mA h g(-1) at 1C, and following 80 cycles, the capacity retention was as high as 95.0%. Moreover, it also presented the best rate capability among all the samples, in which a high discharge capacity of 98.3 mA h g(-1) was still maintained at a high rate of 7C compared with that of 75.8 mA h g(-1) for the pristine LiMn2O4 sample.

DOI： 10.1039/c5ra13005k

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：HINDAWI LTD  

Over the past few decades, the research field of nanomaterials (NMs) has developed rapidly because of the unique electrical, optical, magnetic, and catalytic properties of these materials. Among the various methods available today for NM synthesis, techniques for plasma generation in liquid are relatively new. Various types of plasma such as arc discharge and glow discharge can be applied to produce metal, alloy, oxide, inorganic, carbonaceous, and composite NMs. Many experimental setups have been reported, in which various parameters such as the liquid, electrode material, electrode configuration, and electric power source are varied. By examining the various electrode configurations and power sources available in the literature, this review classifies all available plasma in liquid setups into four main groups: (i) gas discharge between an electrode and the electrolyte surface, (ii) direct discharge between two electrodes, (iii) contact discharge between an electrode and the surface of surrounding electrolyte, and (iv) radio frequency and microwave plasma in liquid. After discussion of the techniques, NMs of metal, alloy, oxide, silicon, carbon, and composite produced by techniques for plasma generation in liquid are presented, where the source materials, reaction media, and electrode configurations are discussed in detail.

DOI： 10.1155/2015/123696

Web of Science

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

Excitation temperature of a solution plasma was investigated by spectroscopic measurements to control the nanoparticle synthesis. In the experiments, the effects of edge shielding, applied voltage, and electrode material on the plasma were investigated. When the edge of the Ni electrode wire was shielded by a quartz glass tube, the plasma was uniformly generated together with metallic Ni nanoparticles. The emission spectrum of this electrode contained OH, H-alpha, H-beta, Na, O, and Ni lines. Without an edge-shielded electrode, the continuous infrared radiation emitted at the edge created a high temperature on the electrode surface, producing oxidized coarse particles as a result. The excitation temperature was estimated from the Boltzmann plot. When the voltages were varied at the edge-shielded electrode with low average surface temperature by using different electrolyte concentrations, the excitation temperature of current-concentration spots increased with an increase in the voltage. The size of the Ni nanoparticles decreased at high excitation temperatures. Although the formation of nanoparticles via melting and solidification of the electrode surface has been considered in the past, vaporization of the electrode surface could occur at a high excitation temperature to produce small particles. Moreover, we studied the effects of electrodes of Ti, Fe, Ni, Cu, Zn, Zr, Nb, Mo, Pd, Ag, W, Pt, Au, and various alloys of stainless steel and Cu-Ni alloys. With the exception of Ti, the excitation temperatures ranged from 3500 to 5500 K and the particle size depended on both the excitation temperature and electrode-material properties. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4894156

Web of Science

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

This work investigates the optimum experimental conditions required for the synthesis of Sn nanopartides (Sn-NPs) via surfactant-free direct-current electrolysis using KCl as the electrolyte. Metallic Sn wire was used as a cathode, which was melted by the local concentration of current upon the application of a direct-current voltage. The effect of electrolyte concentration was analyzed by varying the concentration from 0.01 to 1.0 M, under constant electric power of 40W. Results indicated that the applied voltage required for plasma generation increased with a decrease in the electrolyte concentration and the particle size decreased at high applied voltage with low electrolyte concentration; particles with a mean diameter of 258.5 nm formed at 0.05 M. However, coarse Sn6O4(OH)(4) crystals were precipitated at a concentration of 0.01 M. Therefore, the optimum concentration required for the formation of smaller particles was determined to be 0.05 M. Subsequently, the effect of voltage was analyzed by varying the applied voltage from 70 to 190 V. As a result, the effective production energy of 45 W h/g was obtained at voltages ranging from 110 to 130 V. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

DOI： 10.1016/j.apt.2014.02.003

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

This paper describes the facile solution plasma synthesis of bimetallic nanoparticles, including solid solution alloys (Ni-Cu and Ni-Cr system), eutectic alloys of Sn-Pb, and intermetallic alloys (SnSb and Ni3Sn), by using metallic alloy wire as the cathode and Pt wire as the anode. In the typical process, the cathode was melted by the local-concentration of current, upon applying a DC voltage between the two electrodes immersed in the electrolyte. The solid solution alloys of Ni-Cu and Ni-Cr prepared in this study have a uniform distribution of composition. On the other hand, the uniformity in the composition of the eutectic Sn-Pb alloy depends on the microstructure of the electrode. The use of quenched electrode with small crystal grains favors the formation of Sn-Pb alloy nanoparticles, in which the Sn-rich and Pb-rich phases coexist in each particle. The formation of intermetallic SnSb and Ni3Sn alloy nanoparticles is accompanied by the formation of colloidal oxide. These results demonstrate that the solution plasma technique is applicable not only for the synthesis of pure metals but can also be used for the synthesis of various alloy nanoparticles.

DOI： 10.1088/0957-4484/25/13/135603

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Carbon deposited by tar decomposition within pores of iron ore exhibited a high reactivity during the reduction reaction. The structure of porous low-grade ore was investigated in detail using transmission electron microscopy (TEM); a layered structure with 3 nm diameter pores was observed after dehydration, because of the removal of the hydroxide (OH) group from FeOOH. This pore size was deemed to be appropriate for tar decomposition and resultant carbon deposition. However, it was found that not all pores were filled with carbon. The TEM image showed that some of the deposited carbon partially blocks the pores, which negatively affects the carbon deposition process. In addition to the ore structure, the type of carbon deposited was also successfully evaluated using Raman spectroscopy and found to consist of two main peaks, G and D. The position of the G peak was found to shift slightly, indicating that the sp(3) content was reduced at elevated temperatures because of a greater degree of graphitization. The carbon deposited by integrated pyrolysis-tar decomposition over low-grade ore was categorized as amorphous carbon (a-C), with a sp(3) content of 19-21%. These results can also be explained by high reactivity of the deposited carbon, which was improved by not only nanoscale contact between iron and carbon but also specific molecule bonding and arrangement of amorphous carbon.

DOI： 10.1021/ef500201m

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

This study demonstrates the synthesis of nonstoichiometric titanium oxide (TiO2-delta) nanoparticles using plasma discharge. We have primarily investigated the effect of electrolyte concentration and edge shielding of electrode on the morphology, and oxygen defects of the final product. As a precursor for nanoparticle synthesis, titanium wire was utilized as a cathode, which was immersed in an HCl electrolyte in the concentration range of 0.1-5.0 M. The electrode edge was shielded to maintain uniform distribution of electric current. For comparison, we also used an electrode without edge shielding. Systematic studies indicate that the as-prepared products were spherical titanium oxide nanoparticles, the size of which decreased with decrease in electrolyte concentration. The edge shielding of the electrode was found to affect the size distribution and oxidation degree of the products. In case of the edge-shielded electrode, the oxidation of the product was suppressed, resulting in a product composition of TiO1.72. In contrast, in case of the electrode without edge shielding, the oxidation of the products was favored, resulting in formation of TiO1.90. This could be attributed to the concentration of electric current at the electrode edge, in which the heating-up of the electrode edge enhanced the oxidation of the product. These results confirm the possibility of synthesizing nonstoichiometric oxide nanoparticles with controllable oxygen defects by using plasma discharge in HCl solution. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4869126

Web of Science

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

We have adopted a solution plasma synthesis for preparing Sn nanoparticles (Sn-NPs) directly from metallic Sn electrode. The Sn-NPs were synthesized in the presence of the surfactant, cetyltrimethylammonium bromide (CTAB), and the effect of the concentration of CTAB on the Sn-NPs was investigated. Without CTAB addition, SnO plates were precipitated. Sn-NPs with less than 200 nm were synthesized at a high concentration of 200 x 10(-6) g ml(-1) of CTAB. Electrochemical properties of SnO plates and Sn-NPs were analyzed for use as an anode material in Li-ion batteries. A composite of Sn-NPs and graphite enhanced the cyclic stability owing to the buffer space provided by the graphite for volume expansion. In the case of the 30 wt% loaded Sn-NPs, the capacity was measured to be 414 mA h g(-1) after 20 cycles. (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

DOI： 10.1016/j.apt.2013.11.001

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The direct-current discharge plasma during nanoparticles formation was observed using a high-speed camera. Metallic plates of Au, Ni, Ti, and Zn were used as a cathode, and a Pt wire was used as an anode. Both electrodes were immersed in a 0.1M NaOH solution. The solution plasma with light emission was generated via the vapor layer surrounding the cathode by applying 190 V. The current concentration occurred at a certain point of the electrode surface, in which the electrode surface was partially melted to produce nanoparticles. According to the high-speed observation, many light-emitting points appeared on the metallic plate and immediately disappeared when a certain point was strongly heated to produce nanoparticles. Additionally, light emission points moved in a chain reaction; after the first emission point was generated, the next emission point tended to be generated in the space surrounding the first emission point. During electrolysis, holes were generated on the cathode. The current concentration strongly heated certain spots on the electrode, and the electrode momentarily melted or vaporized, resulting in the formation of nanoparticles. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4865498

Web of Science

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

In this work, fine powders of spinel-type LiMn2O4 as cathode materials for lithium ion batteries (LIBs) were produced by a facile solution combustion synthesis using glycine as fuel and metal nitrates as oxidizers. Single phase of LiMn2O4 products were successfully prepared by SCS with a subsequent calcination treatment at 600-1000 degrees C. The structure and morphology of the powders were studied in detail by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrochemical properties were characterized by galvanostatic charge-discharge cycling and cyclic voltammetry. The crystallinity, morphology, and size of the products were greatly influenced by the calcination temperature. The sample calcined at 900 C had good crystallinity and particle sizes between 500 and 1000 nm. It showed the best performance with an initial discharge capacity of 115.6 mAh g(-1) and a capacity retention of 93% after 50 cycles at a 1 C rate. In comparison, the LiMn2O4 sample prepared by the solid-state reaction showed a lower capacity of around 80 mAh g(-1). (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

DOI： 10.1016/j.apt.2013.05.015

Web of Science

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

ZnO nanoflowers, amorphous ZnO nanospheres and metallic Zn particles have been controllably synthesized using solution plasma technique at different reaction temperatures and agitation. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that ZnO nanoflowers were synthesized at a high electrolyte temperature in a static system (no agitation). On the other hand, the use of agitation led to both amorphous ZnO nanospheres and spherical metallic zinc particles. The excitation temperature of plasma was 4000 K from the light emission using spectrometer. From these result, melting and vaporization of the Zn electrode produced particles. ZnO nanoflowers grew on the surface of spherical particles by precipitation from Zn(OH)(4)(2-) ions. Photoluminescence (PL) measurement indicated that as-synthesized ZnO flowers and amorphous ZnO nanospheres showed strong green emissions, which was attributable to their surface defect structure. Furthermore, the annealing at 700 degrees C led to a reduction in green emissions, attributable to a decrease in the number of surface defects. Photocatalytic activity of ZnO nanoflowers was increased by the annealing. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2013.11.097

Web of Science

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

A simple, highly efficient method of synthesizing β-SiAlON:Eu2+ phosphors for white light-emitting diodes was reported. The new route was carried out via a combustion synthesis method using Si, SiO2, and Al raw materials, and NaCl as a diluent under nitrogen pressure. The phase purity, photoluminescence properties, and thermal quenching of the phosphors were investigated. The results revealed that the synthesized β-SiAlON:Eu2+ powders, which comprised rodlike crystals, exhibited high thermal stability: The emission intensity at 160 ±C was 84% of that measured at room temperature, which indicates that the synthesized β-SiAlON:Eu2+ phosphors have high potential for application to white LEDs. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.6.042105

Scopus

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

This paper presents a new CaCO3-template synthesis of highly nanoporous manganese oxide hollow structures and their transformation to high-performance LiMn2O4 cathodes for lithium-ion batteries via the facile coprecipitation of Mn-Ca-carbonates and temperature-controlled decomposition of MnCO3 and CaCO3, followed by the selective removal of the carbonates by washing with HCl. The as-prepared Mn2O3 nanostructures showed very high specific surface area with their subunit particle size of <30 nm, as compared with conventional processes with subunits of >100 nm. The transformation to uniformly porous LiMn2O4 hollow structures was successfully achieved by the facile impregnation of LiOH into the porous Mn2O3 hollow precursors, followed by a conventional solid-state reaction. The LiMn2O4 hollow structures deliver a discharge capacity of about 120 mA h g(-1) at a 1 C rate and 115 mA h g(-1) at a 10 C rate with excellent cycling stability. The capacity retention approached 94% after up to 800 cycles of charging-discharging at a 10 C rate.

DOI： 10.1039/c3ta11066d

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

This paper describes the surface morphology of a glow discharge electrode in a solution. In the experiments detailed in the paper, the effects of electrolysis time, solution temperature, voltage, electrolyte concentration, and surface area on the size of nanoparticles formed and their amount of nanoparticles produced were examined to study the surface morphologies of the electrodes. The results demonstrated that the amount of nanoparticles produced increased proportionally with the electrolysis time and current. When the voltages were below 140 V, surfaces with nanoparticles attached, called "Particles" type surfaces, were formed on the electrode. These surfaces changed and displayed ripples, turning into "Ripple" type surfaces, and the nanoparticle sizes increased with an increase in the amount of nanoparticles produced. In contrast, at voltages over 160 V, the surfaces of the electrodes were either "Random" or "Hole" type and the particle sizes were constant at different amount of nanoparticles produced. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4732076]

DOI： 10.1063/1.4732076

Web of Science

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

Single-crystalline tin oxide (SnO) plates were synthesized by a solution plasma technique using an Sn wire. In the experiments, we applied a voltage of 400 V in a 0.001 M K2CO3 solution. The effects on the products of the solution temperature, the use of surfactants, and the cooling rate were investigated. A solution temperature above 95.0 degrees C was effective for producing single-crystal SnO plates. The addition of poly(vinyl alcohol) (PVA) significantly stabilized the Sn6O4(OH)(4) octahedrons. In the case of cetyltrimethylarnmonium bromide (CTAB) addition, SnO and Sn crystals with plate crystal, particle, and rod morphologies were formed. Quenching the solution affected the product size. Faster cooling rates reduced the size of the SnO plates. SnO plates with (001) plane faces precipitated from Sn(OH)(3)(-) ions to form plate-like crystals as a result of the difference in the growth rates at each plane.

DOI： 10.1021/cg300083k

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We investigated ripple formation on a nickel electrode during a glow discharge in a solution. A nickel wire was partially melted to produce nanoparticles during glow discharge electrolysis. When the electrolysis time was over 30 min, a ripple pattern was formed on the electrode surface, and particle size increased. In this study, we investigated the relationship between the ripple formation and crystal orientation of the electrode. As a result, the ripple patterns were formed on all planes, except (111)- and (100)-oriented planes; their direction was [001]. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709491]

DOI： 10.1063/1.4709491

Web of Science

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

Because of the easy massproduction, synthesis of metallic nanoparticles from a solution plasma is an attractive method. However, a solution plasma produces a highly inhomogeneous electric field via transition to full-plasma, and the products are partially oxidized and agglomerated, with a wide size-distribution. Here, we show a simple method of suppressing oxidation of products. An electrode tip was shield by a glass tube and a voltage of up to 180 V was applied with the electrolyte of 0.1 M NaOH solution. Significantly, the edge-shield was quite effective for maintaining partially glow discharge. The results were (1) surface temperature of the electrode less than 100 degrees C, (2) main phase of metallic nickel evaluated by XRD, and (3) nanoparticles of an average size of 220 nm. These results showed the potential for an application to the production of nanoparticles.

DOI： 10.1007/s11090-011-9313-4

Web of Science

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

We synthesized ZnO nanoflowers using a solution plasma. We examined the effects of the applied voltage and the concentration of the electrolyte on the morphology of the products. In the experiments, the zinc wire (cathode) was immersed in an electrolysis solution of K2CO3 (concentration: 0.01-5.00 M) and was electrically melted by a glow discharge at different voltages ranging from 42 to 200 V. The results revealed that the products were nanoflowers having many nanorods (size: <100 nm). The ZnO nanoflowers had a wurtzite structure with the [0 0 0 1] orientation in the growth direction. The product morphology changed with a change in the concentration of the electrolyte, C, and the applied voltage, V; that is, nanoflowers were generated under the limited conditions of (C, V) = (1.0 M, 66 V), (0.5 M, 80 V), and (0.1 M, 105 V). (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matchemphys.2011.05.084

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

This paper describes the synthesis of copper/copper oxide nanoparticles via a solution plasma, in which the effect of the electrolyte and electrolysis time on the morphology of the products was mainly examined. In the experiments, a copper wire as a cathode was immersed in an electrolysis solution of a K(2)CO(3) with the concentration from 0.001 to 0.50 M or a citrate buffer (pH = 4.8), and was melted by the local-concentration of current. The results demonstrated that by using the K(2)CO(3) solution, we obtained CuO nanoflowers with many sharp nanorods, the size of which decreased with decreasing the concentration of the solution. Spherical particles of copper with/without pores formed when the citrate buffer was used. The pores in the copper nanoparticles appeared when the applied voltage changed from 105 V to 130 V, due to the dissolution of Cu(2)O. (C) 2011 American Institute of Physics. [doi:10.1063/1.3610496]

DOI： 10.1063/1.3610496

Web of Science

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

We report the size control of Ni nanoparticles generated via solution glow discharge and focus on the effect of electrolyte concentration on Ni nanoparticles. In our experiments, voltage was applied to generate a plasma in NaOH electrolytes with concentrations ranging from 1.0 to 0.001 kmol m(-3). The applied voltage strongly depended on the electrolyte concentration, and interestingly, product size decreased with electrolyte concentration; for example, (mean diameter, applied voltage, electrolyte concentration) = (148 nm, 90 V, 0.5 kmol m(-3)), and (70 nm, 590 V, 0.001 kmol m(-3)). These results suggested the possibility of using plasma electrolysis for synthesizing size-controlled nanoparticles by changing only electrolyte concentration.

DOI： 10.1143/JPSJ.79.083501

Web of Science

Event date： 2023.9

Language：English   Presentation type：Poster presentation  

Venue：BEXCO, Busan   Country：Korea, Republic of  

Event date： 2023.9

Language：English   Presentation type：Poster presentation  

Venue：BEXCO, Busan   Country：Korea, Republic of  

Event date： 2023.9

Language：English   Presentation type：Poster presentation  

Venue：BEXCO, Busan   Country：Korea, Republic of  

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2021.9

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Event date： 2021.9

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Event date： 2021.6

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Event date： 2019.9

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Event date： 2018.5

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Event date： 2017.12

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Event date： 2017.8

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Event date： 2017.5

Language：Japanese   Presentation type：Poster presentation  

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Language：Japanese   Presentation type：Poster presentation  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Poster presentation  

Venue：名古屋大学東山キャンパス  

Language：Japanese   Presentation type：Poster presentation  

Language：Japanese   Presentation type：Poster presentation  

Language：English   Presentation type：Oral presentation (general)  

Venue：北海道大学 札幌キャンパス  

Language：Japanese   Presentation type：Poster presentation  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：Japanese   Presentation type：Poster presentation  

Language：English   Presentation type：Oral presentation (general)  

Venue：名古屋大学東山キャンパス  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：English   Presentation type：Poster presentation  

Language：English   Presentation type：Poster presentation  

Language：English   Presentation type：Poster presentation  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：Japanese   Presentation type：Oral presentation (general)  

Language：Japanese   Presentation type：Oral presentation (general)  

Presentation type：Poster presentation  

Venue：Waikoloa Beach, Hawaii  

Presentation type：Oral presentation (general)  

Venue：北海道大学  

Presentation type：Oral presentation (general)  

Venue：京大会館 京都府  

Presentation type：Poster presentation  

Venue：Matrix, Biopolis, Singapore  

Presentation type：Oral presentation (general)  

Venue：Kualalumpur Malaysia  

Presentation type：Oral presentation (general)  

Venue：Haward International House, Taipei  

Presentation type：Oral presentation (general)  

Venue：連合会館, 東京都千代田区駿河台  

Presentation type：Oral presentation (general)  

Venue：東京都 東京ビックサイト 会議棟  

Presentation type：Oral presentation (general)  

Venue：神奈川工科大学 神奈川県厚木市  

Presentation type：Poster presentation  

Venue：愛媛大学  

Presentation type：Oral presentation (general)  

Venue：早稲田大学 早稲田キャンパス  

Presentation type：Poster presentation  

Venue：北海道大学・学術交流会館  

Presentation type：Poster presentation  

Venue：北海道大学 札幌キャンパス  

Presentation type：Oral presentation (general)  

Venue：金沢大学 角間キャンパス  

Presentation type：Oral presentation (general)  

Venue：連合会館, 東京都千代田区駿河台  

Presentation type：Poster presentation  

Venue：東京工業大学大岡山キャンパス  

Presentation type：Oral presentation (general)  

Venue：北海道大学  

Presentation type：Poster presentation  

Venue：北海道大学・学術交流会館  

Presentation type：Oral presentation (general)  

Venue：筑波大学  

Presentation type：Poster presentation  

Venue：京都大学吉田キャンパス  

Presentation type：Oral presentation (general)  

Venue：京都大学吉田キャンパス