Time filter

Source Type

Kondo H.,Yokohama National University | Matsumiya M.,Yokohama National University | Tsunashima K.,Wakayama National College of Technology | Kodama S.,Nippon Chemical Industrial Co.
Electrochimica Acta | Year: 2012

The suitability of triethyl-pentyl-phosphonium bis(trifluoromethyl- sulfonyl)amide ([P 2225][TFSA]), room temperature ionic liquid for the electrodeposition of neodymium has been investigated in this study. From the standpoint of the scientific aspects, the temperature dependence of the reduction behavior for Nd(III) in [P 2225][TFSA] was investigated from the cyclic voltammetry and the diffusion coefficient of Nd(III) was investigated by chronopotentiometry with cylindrically symmetrical diffusion. It was revealed that the over-potential of reduction reaction for Nd(III) was decreasing with elevating the bath temperatures and the diffusion coefficient of Nd(III) was estimated to the order of 10 -11 m 2 s -1 at 100 °C. The activation energy of diffusion for Nd(III) obtained from the temperature dependence was 61 kJ mol -1. On the other hand, the spectroscopic and thermal analyses were also researched and it was revealed that the complex formation of Nd(III) in [P 2225][TFSA] would not be rigid structure. The fusion temperature and the enthalpy of NdTFSA 3 were estimated to be 195 °C and 24 kJ mol -1, respectively. According to the electrochemical, spectroscopic and thermal evaluations, the electrodeposition of neodymium in [P 2225][TFSA] was performed by potentiostatic electrolysis at -3.1 V at 150 °C in order to stimulate the mass transfer and to lower solution viscosity. The current efficiency evaluated from the mass change of the anode was more than 90%. A black electrodeposit on a copper substrate was fine and formed uniformly neodymium particle was observed by SEM. It was also identified that the contents of metallic neodymium in electrodeposits were 48% from the evaluation of EDX. The electrodeposit was composed of most of metallic neodymium and a part of neodymium oxide as identified from XPS. © 2012 Elsevier Ltd. All rights reserved. Source

Yasuhara H.,Ehime University | Neupane D.,Ehime University | Hayashi K.,Wakayama National College of Technology | Okamura M.,Ehime University
Soils and Foundations | Year: 2012

A grouting technique that utilizes precipitated calcium carbonate as a cementing material is presented. The enzyme urease is used to enhance the rate and the magnitude of the calcium carbonate precipitation. Evolutions in the mechanical and the hydraulic properties of treated sand samples are examined through unconfined compression and permeability tests, respectively. The grout is mainly composed of urease, which bio-catalyzes the hydrolysis of urea into carbon dioxide and ammonia, urea, and calcium chloride solutions. This method employs chemical reactions catalyzed by the enzyme, and ultimately acquires precipitated calcium carbonate within soils. The mechanical test results show that even a small percentage of calcium carbonate, precipitated within soils of interest, brings about a drastic improvement in the strength of the soils compared to that of untreated soils - the unconfined compressive strength of the samples treated with < 10 vol% calcium carbonate precipitation against the initial pore volume ranges from ∼400 kPa to 1.6 MPa. Likewise, the hydraulic test results indicate the significant impervious effects of the grouting technique - the permeability of the improved samples shows more than one order of magnitude smaller than that of the untreated soils. Evolutions in the measured hydraulic conductivity and porosity are followed by a flow simulator that accounts for the solute transport process of the injected solutions and the chemical reaction of the calcite precipitation. Predictions of the changes in permeability with time overestimate the test measurements, but those of the changes in porosity show a good agreement with the actual measurements, indicating that such simulations should become a significant supplementary tool when considering real site applications. © 2012 The Japanese Geotechnical Society. Source

Kazama R.,Yokohama National University | Matsumiya M.,Yokohama National University | Tsuda N.,Yokohama National University | Tsunashima K.,Wakayama National College of Technology
Electrochimica Acta | Year: 2013

In this study, the solubility, diffusion coefficient, and nucleation behavior of rare-earth metal complexes in a phosphonium-based ionic liquid (IL) were investigated in order to analyze the electrodeposition mechanism of the Dy metal. For the solubility of Dy(TFSA)3 and Nd(TFSA)3 in an IL, the temperature dependence was also evaluated from 340 to 470 K using ultraviolet-visible spectroscopy. The solubility curves obtained for Dy(III) and Nd(III) have similar tendencies and show a relatively good fit with the modified Apelblat equation. A series of thermodynamic parameters (ΔsolG∞, ΔsolH ∞, and ΔsolS∞) were also estimated, and the results reveal that the dissolution process of rare-earth metal salts in polar ILs is controlled by enthalpy. For electrochemical analyses, cyclic voltammetric measurements reveal that the reduction process of Dy(III) proceeds in two steps by way of Dy(II) [Dy(III) + e- → Dy(II), Dy(II) + 2e- → Dy(0)], when the IL contains a small amount of water (<100 ppm). The number of electrons transferred in the first cathodic reaction at -2.45 V was 0.99 ± 0.01, as evaluated by the EMF method, and a divalent dysprosium complex was found to exist in the IL using Raman and fluorescence spectroscopic analyses. The diffusion coefficients of Dy(II) and Dy(III) in an IL were measured from 318 to 378 K using a semi-integral analysis. The diffusion coefficients of Dy(II) were larger than those of Dy(III) in the entire range of temperatures measured, and the activation energies for diffusion of Dy(II) and Dy(III) were 28.0 and 53.4 kJ mol-1, respectively. In addition, the nucleation and growth processes of Dy(0) were evaluated from chronoamperometry. These results indicate that the nucleation mechanism of Dy(0) changes from instantaneous nucleation to progressive nucleation when the applied overpotential becomes more negative than the deposition peak potential of Dy(0), as estimated from a voltammogram. Furthermore, electrowinning of the Dy metal from 0.1 mol dm-3 Dy(III) in an IL was carried out using a three-electrode system. The surface morphology of the electrodeposits showed accumulated round particles with 0.8-0.9 μm diameter, as observed by a scanning electron microscope. Most of the Dy electrodeposits were in the metallic state, while a part of their top surface was in the oxidation state, as evaluated from the EDX, XPS, and XRD analyses. © 2013 Elsevier Ltd. All rights reserved. Source

Tsunashima K.,Wakayama National College of Technology | Kodama S.,Nippon Chemical Industrial Co. | Sugiya M.,Nippon Chemical Industrial Co. | Kunugi Y.,Tokai University
Electrochimica Acta | Year: 2010

The physicochemical and electrochemical properties of room temperature ionic liquids based on quaternary phosphonium cations together with a dicyanamide anion are presented in this report. The most dicyanamide-based phosphonium ionic liquids prepared were hydrophilic, except ionic liquids containing a long alkyl chain in the phosohonium cation. It was found that asymmetric phosphonium cations gave low-melting salts in combination with a dicyanamide anion. The dicyanamide-based phosphonium ionic liquids exhibited relatively low viscosities and high conductivities when compared to those of the corresponding ammonium ionic liquids. Particularly, the ionic liquids containing a methoxy group in the phosphonium cations indicated very low viscosities. Comparatively good electrochemical stability of the dicyanamide-based phosphonium ionic liquids was confirmed by voltammetric measurements. The thermogravimetric analysis suggested that the dicyanamide-based phosphonium ionic liquids showed higher thermal stability than those of the corresponding ammonium ionic liquids, indicating an improving effect of the phosphonium cations on the thermal stability. © 2010 Elsevier Ltd. All rights reserved. Source

Murayama T.,Wakayama National College of Technology
2013 IEEE/SICE International Symposium on System Integration, SII 2013 | Year: 2013

In this paper we focus on keeping network conne tivity and collision avoidance of multi-vehicle systems. Becau a multi-hop wireless network between vehicles is often used order to share informations, keeping the network connectivi is important concern. Vehicles need to get close when the desire stable communication, but on the other hand, vehicl may collide when they get too close. Here we propose online trajectory planning method based on a receding horizo control, and this method fixes keeping connectivity and collisio avoidance simultaneously. We describe a formulation of th system and the problem, the trajectory planning method w proposed, and show a computer simulation result. © 2013 IEEE. Source

Discover hidden collaborations