Electrochemistry
Online ISSN : 2186-2451
Print ISSN : 1344-3542
ISSN-L : 1344-3542
Volume 67 , Issue 6
Showing 1-36 articles out of 36 articles from the selected issue
Visions
Headline
  • Isao OKADA
    1999 Volume 67 Issue 6 Pages 529-540
    Published: June 05, 1999
    Released: November 15, 2019
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    Molten additive binary systems having a common anion yield much more heuristic information for a better understanding of the mechanism of ionic conduction than pure melts do. In most of such systems the Chemla effect occurs; the mobility isotherms of two cations have a crossing point called the Chemla crossing point. In binary multivalent cation systems, the larger cation is more mobile than the smaller one. An internal mobility u of a monovalent cation is generally expressed by an empirical equation: u = [A/(VmV0)]exp(−E/RT), where Vm is the molar volume; A, V0 and E are constants nearly independent of the kind of the second cation. Deviation from this equation could be interpreted in terms of the agitation effect (positive deviation), and the tranquilization effect or the free space effect (negative deviation). The dynamic dissociation model well accounts for the above-mentioned findings; in other words, the internal mobility is strongly related to the dissociative motion of neighboring cation and anion. The effect of highly polarizable cations on internal mobilities is also discussed.

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Comprehensive Paper
  • Norimasa UMESAKI, Yoshifumi KITA, Katsumi HANDA, Shinji KOHARA, Kentar ...
    1999 Volume 67 Issue 6 Pages 541-546
    Published: June 05, 1999
    Released: November 15, 2019
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    The structures of potassium borate glasses and melts with 10 and 30 mol % K2O have been studied by the use of pulsed neutron total scattering measurement. With an increase in K2O content, the first peak of the experimental radial distribution function corresponding to nearest neighbor B-O correlation spread asymmetrically to the higher bond distance r side, and the coordination number of O atoms around a reference B atom, Nbo, increased from 3.0 to 3.4 reflecting a structural change from BO3 triangle units to BO4 tetrahedral units. It can be concluded from the neutron results that some BO3 units present are converted to BO4 units on the addition of up to 30 mol % K2O to the B2O3 melt in the same way as in K2O-B2O3 glasses. XAFS studies of network modifying cations in alkali borate glasses have made an important contribution to our understanding of the structure of glass. The local structure in K2O-B2O3 glasses has been determined in order to the elucidate the environment of network modifying K+ ions. The average coordination number, NK-O, of oxygen around K+ cations and the mean distance, rK-O, are found to be approximately 6 and 2.83∼2.86 Å, respectively. The XAFS results are in good agreement with X-ray diffraction and MD simulation results.

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Communications
Technical Papers
  • Yasuhiko IWADATE, Kazuko FUKUSHIMA, Ryuzo TAKAGI, Marcelle GAUNE-ESCAR ...
    1999 Volume 67 Issue 6 Pages 553-557
    Published: June 05, 1999
    Released: November 15, 2019
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    The short range structure of Na3ErCl6 melt at 973 K and K3ErCl6 melt at 1053 K was investigated by X-ray diffraction. The nearest neighbor distance of Er3+-Cl and the coordination number of Cl around Er3+ in Na3ErCl6 melt, for instance, were estimated to be 2.61 Å and 5.7, respectively, and the Er3+-Er3+ and Cl-Cl distances 5.15 Å and 3.90 Å, respectively. The ratio of the anion-anion pair distance to the cation-anion pair distance (r−−/r+−) was, therefore, 1.49, being close to 1.41, characteristic of octahedral geometry. These results indicate that the stable ErCl63− octahedra exist in Na3ErCl6 and K3ErCl6 melts. Probably, complex ions such as Er2Cl104− and Er2Cl115− expected to be in the pure ErCl3 melt are little formed at these compositions according to the geometrical calculations of bond lengths and bond angles.

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  • Akihiko KAJINAMI, Osamu SAKAI, Shigehito DEKI
    1999 Volume 67 Issue 6 Pages 558-562
    Published: June 05, 1999
    Released: November 15, 2019
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    Raman spectra were measured for the mixture of alkali metal propionates and water in the composition range of hydrate melt to highly concentrated solution. Band positions and band widths for the C1-C2 stretching, C-O stretching in the propionate anion, and O-H stretching bands in water molecule were investigated for various compositions and temperatures. The dependence of Raman bands on composition, cation, and temperature is discussed in view of ion-ion, ion-water, and water-water interactions, suggesting that the direct interaction between cation and anion increases with decreasing water content.

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  • Yuzuru SATO, Mikio FUKASAWA, Kenji ABE, Tsutomu YAMAMURA
    1999 Volume 67 Issue 6 Pages 563-567
    Published: June 05, 1999
    Released: November 15, 2019
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    Surface tensions of basic NaCl-AlCl3 and LiCl-AlCl3 binary melts were measured by using capillary-rise method up to 1200 K precisely. It was found that the adding very small amount of AlCl3 into NaCl or LiCl decreases the surface tension very steeply to less than half value of NaCl or LiCl. The surface enthalpy and surface entropy also decreases steeply. These phenomena are similar to the action by surface active agent although the phenomena are rare in molten salt systems. This is due to the formation of the compound of NaAlCl4 and LiAlCl4. The compound is considered to be concentrated in surface phase due to their lower coulombic energy, and resulted the decrease of surface tension and surface energy, and furthermore the increase of ordering on surface phase. Based on present results and the thermodynamic consideration, the concentrations of NaAlCl4 and LiAlCl4 in the surface phase were calculated.

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  • Yuzuru SATO, Yutaka MATSUZAKI, Minoru UDA, Akihiro NAGATANI, Tsutomu Y ...
    1999 Volume 67 Issue 6 Pages 568-572
    Published: June 05, 1999
    Released: November 15, 2019
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    Density, viscosity and surface tension of molten aluminum chloride have been measured precisely to understand its unique physicochemical properties by using a float method, a capillary viscometry and a capillary rise method, respectively. The apparatuses used are all made of quartz or Pyrex glass and the melt was sealed in them completely. Density, viscosity and surface tension obtained are considerably lower than those of other conventional molten salts. The temperature corresponding to critical temperature could be estimated from the surface tension. The hypothetical melting temperature by assuming that the molecular solid which consists of Al2Cl6 was estimated to be almost 150 K lower than melting temperature of real ionic crystal of aluminum chloride. These results suggest that the molten aluminum chloride is different in the condition of the study from other typical molten salts, namely it is considerably superheated liquid due to the structural change on melting from ionic crystal to molecular liquid. The lower values measured in this work are attributed to such a superheated state.

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  • Toshihiro TANAKA, Shigeta HARA
    1999 Volume 67 Issue 6 Pages 573-580
    Published: June 05, 1999
    Released: November 15, 2019
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    The thermodynamic model has been discussed for the surface tension of molten salt mixtures in the common ion alkali-halide, carbonate, sulfate and nitrate systems. In addition, the extension of the above model has been investigated to alkaline-earth halide systems and reciprocal alkali-halide systems. Based on the present approach, the thermodynamic databases, which are usually used to the calculation of phase diagrams of salt mixtures, can be applied to the evaluation of the surface tension of molten salt mixtures.

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  • Keiichi TAKASE, Norikazu OHTORI
    1999 Volume 67 Issue 6 Pages 581-586
    Published: June 05, 1999
    Released: November 15, 2019
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    We have investigated the calculation conditions necessary for precise and efficient evaluation of the thermal conductivity of a molten salt based upon the equilibrium Green-Kubo formula by molecular dynamics simulation. The suitable parameters are also presented for the Ewald sums in the calculations of the interionic force and the energy current. The statistical error was estimated at ±10% under the calculation conditions. The dependence of the calculated results was examined on various calculation conditions. The number of time steps of at least 50000, which corresponds to 200 ps, was required in order to obtain a fully converged value of the time integral of the correlation functions. No significant dependence was found on the number of particles used in the simulated system compared with the statistical error. The dependence on the time step, the interval between time origins when the correlation functions were sampled, and the upper integral limit for the correlation functions was negligible compared with the statistical error. The addition of a small velocity vector to the ions, however, significantly influenced the calculated value of the thermal conductivity.

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  • Pao-Hwa CHOU, Ryuzo TAKAGI, Isao OKADA
    1999 Volume 67 Issue 6 Pages 587-592
    Published: June 05, 1999
    Released: November 15, 2019
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    The ε values in the internal cation mobilities of (Li, Na, K)(CO3)0.5 of the eutectic composition (43.5-31.5-25.0 mol %) in the temperature range from 773 K to 1023 K have been measured by a countercurrent electromigration method, that is the Klemm method, where ε is defined as (uiuj)/ua; ua is the average internal cation mobility and subscripts i and j refer to any two of three cations. From the present data and the densities and electric conductivities, the internal cation mobilities of uLi, uNa and uK have been calculated. The internal mobility of Li+, uLi, was compared to the empirical equation expressed for binary alkali carbonates. The orders of the internal cation mobilities were uK < uLi < uNa at 773-873 K, uLi < uK < uNa at 923 K, and uLi < uNa < uK above 973 K, although these were broadly equal to one another. These orders could be interpreted in terms of the dynamic dissociation model previously presented.

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  • Toshikatsu KOJIMA, Masahiro YANAGIDA, Kazumi TANIMOTO, Yukiko TAMIYA, ...
    1999 Volume 67 Issue 6 Pages 593-602
    Published: June 05, 1999
    Released: November 15, 2019
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    The surface tension and the density of molten Li2CO3-X2CO3 (X : Na, K, Rb, and Cs) and Na2CO3-Y2CO3 (Y : K, Rb, and Cs) binary carbonate systems were measured using maximum bubble pressure technique. The addition of Rb2CO3 or Cs2CO3 to Li2CO3 or Na2CO3 effectively decreases the surface tension of mixtures. At constant temperature, the relationship between surface tension and composition in all binary carbonate systems was well correlated by the Guggenheim’s Equation for regular solution. The molar volume of Li2CO3-Rb2CO3 and Li2CO3-Cs2CO3 systems shows positive deviation from additivity.

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  • Xinge ZHANG, Paolo CAPOBIANCO, Autora TORAZZA, Biagio PASSALACQUA
    1999 Volume 67 Issue 6 Pages 603-607
    Published: June 05, 1999
    Released: November 15, 2019
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    The solubility of prelithiated NiO and prelithiated cobaltite as cathode materials for MCFC in 62 Li-38 K eutectic carbonate melts was studied with immersion test method. It was found that the solubility of either prelithiated NiO or prelithiated cobaltite was affected by its lithium (Li) content. The higher Li content was, the lower solubility could be in the range of 0∼0.25 mole fraction of Li. With the prelithiated NiO at Li content of 0.2 mole fraction, Ni solubility was reduced to 3∼4 × 10−6 mole fraction, which was only one-third of that of the normal NiO cathode in 30% CO2-70% air at 1 atm. It was obtained that the solubility of prelithiated cobaltite and even LiCoO2 were higher than the prelithiated NiO in the low O2 concentration gas. This suggested that even LiCoO2 was not stable in the O2 depleting condition, and more soluble than NiO.

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  • Choong-Gon LEE, Kohta YAMADA, Yasunari HISAMITSU, Yu ONO, Isamu UCHIDA
    1999 Volume 67 Issue 6 Pages 608-613
    Published: June 05, 1999
    Released: November 15, 2019
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    The electrode kinetics and mechanism of oxygen reduction at gold electrodes in (53 + 47) mol % (Li + Na)CO3, (62 + 38) mol% (Li + K)CO3 and (43.5 + 31.5 + 25) mol % (Li + Na + K)CO3 melts have been investigated under pressurized Air/CO2 oxidant gas conditions in a temperature range of 823-973 K. The total pressure was changed from 1.0 to 5.0 atm with a constant ratio of Air/CO2 = 70/30, 80/20, 90/10 or 95/5. It was observed that the oxygen reduction current in cyclic voltammograms increased with the total pressure, indicating that the concentration of reactive species increased. The analyses of the gas partial pressure dependence on Warburg coefficients, which were obtained by ac impedance measurements, revealed that the reaction process in the tested conditions was dominated by the mixed diffusion of superoxide ion O2 and dissolved CO2.

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  • Satoshi IINOU, Naobumi MOTOHIRA, Nobuyuki KAMIYA, Ken-ichiro OTA
    1999 Volume 67 Issue 6 Pages 614-617
    Published: June 05, 1999
    Released: November 15, 2019
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    The formations of Li-doped NiO and LiNiO2 in molten carbonates have been studied in O2 atmospheres from 873 K to 1173 K. NiO was reacted in Li containing molten carbonates; Li2CO3, (Li0.62K0.38)2CO3 and (Li0.52Na0.48)2CO3 melt for 20 h. The rate of lithiation reaction of NiO was measured by TGA and the products were analyzed by XRD. LiNiO2 was formed in O2 atmosphere at higher temperatures. The formation rate of LiNiO2 was the fastest in Li2CO3 and the temperature of LiNiO2 formation in Li/K carbonate and Li/Na carbonate was higher than that in Li2CO3. The Li content in molten carbonate and the oxygen in the atmosphere would have important roles for the lithiation of NiO and the formation of LiNiO2 as well as the reaction temperature.

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  • Kazuaki NAKAGAWA, Toshiyuki OHASHI
    1999 Volume 67 Issue 6 Pages 618-621
    Published: June 05, 1999
    Released: November 15, 2019
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    The stabilities of lithium zirconate (Li2ZrO3) and zirconia in molten carbonates were tested. There are some disputes about the stable zirconium compound in molten carbonates. We considered a possible reversible change between lithium zirconate and zirconia by means of the thermodynamic calculation and experiments. All results suggest that the change not only depends on temperature and CO2 partial pressure but also on the presence of molten carbonates, e.g., alkali carbonate in molar ratio of Li : K = 62 : 38. In the presence of the molten carbonates, the change proceeds reversibly.

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  • Xinge ZHANG, Hajime OKAWA, Satoshi OHARA, Takehisa FUKUI
    1999 Volume 67 Issue 6 Pages 622-627
    Published: June 05, 1999
    Released: November 15, 2019
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    A new way to solve the nickel deposition problem in the matrix of MCFC has been proposed, i.e. by using the matrix of LiAlO2 powder coated with cobalt oxide to decrease the concentration of reducing agents (such as H2) in the matrix through the reaction with in situ oxide agents. The possibility of the co-existence of H2 and O2 at a trace amount in the presence of normal γ-LiAlO2 matrix powder around 650 °C was verified by the gas chromatography analysis. It was found that H2 amount was sharply reduced in the presence of γ-LiAlO2 matrix powder coated with cobalt oxide, that means the cobalt oxide have the catalytic function for the reaction of H2 and O2 even while both H2 and O2 are at a trace amount. Electrochemical measurement showed that the redox potential (Eredox) in the normal matrix was almost the same in the tested distance ratios, and the value was less than −1000 mV. However, the Eredox value in the matrix coated with cobalt oxide increased linearly with the distance ratio from the anode side to the cathode side. According to the nickel deposition potential, it was deduced that Ni deposite zone might be limited within the region near the anode side. Therefore, it was anticipated that the short-circuit time of a cell would be postponed by use of the matrix with cobalt oxide.

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  • Akimasa TASAKA, Hitoshi TAKEBAYASHI, Satoko KONDO, Hideaki TAKEMURA, O ...
    1999 Volume 67 Issue 6 Pages 628-634
    Published: June 05, 1999
    Released: November 15, 2019
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    The effect of nickel oxide such as NiO1+x and LiNiO2 in the Ni based composite anode on the physico-chemical properties of oxidized layer formed on the composite anode prepared by sintering or dispersion coating method was studied. The galvanostatic and potentiostatic polarization behaviors of the Ni, the Ni-NiO, and the Ni-LiNiO2 composite anodes were investigated to elucidate the anodic processes. The electrical conductivity of the oxidized layer formed on the Ni-NiO and the Ni-LiNiO2 composite anodes was large in a well dehydrated melt of NH4F·2HF and its resistance to corrosion during polarization at potentials higher than 4.6 V vs. H2 was high compared with those on the Ni anode, because of the higher content of nickel oxide in the oxidized layer on the anode.

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  • Toshiyuki NOHIRA, Yasuhiko ITO
    1999 Volume 67 Issue 6 Pages 635-642
    Published: June 05, 1999
    Released: November 15, 2019
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    A novel SiH4 production method using molten salt electrochemical process has been proposed. In order to examine the possibility of the method, a potential-pH diagram was constructed for the Si-H system in a LiCl-KCl eutectic melt. The electrode behavior of a single crystal Si electrode was investigated by cyclic voltammetry in molten LiCl-KCl-LiH(5 mol %) systems at 673 K. The result showed that a passivation film was formed on the electrode by anodic polarization and that further polarization leads to breakdown of the passivation film. From the IR absorption spectroscopy of the evolved gas, SiH4 production was confirmed. Fluoride ion addition to the melt was found to be effective for promoting the SiH4 production. The current efficiency for the SiH4 evolution was improved to about 20% by using a lower LiH(0.8 mol %) system, which suggests that SiH4 evolution mainly proceeds by the indirect reaction of chlorosilanes.

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  • Huan QIAO, Toshiyuki NOHIRA, Yasuhiko ITO
    1999 Volume 67 Issue 6 Pages 643-648
    Published: June 05, 1999
    Released: November 15, 2019
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    The electrochemical behavior of hydride ion on a nickel electrode in a LiF-NaF-KF eutectic melt at 773 K has been studied by means of gas chromatography, cyclic voltammetry, chronopotentiometry and chronoamperometry. It was found that hydride ion is anodically oxidized at around 0.45 V vs. M+/M (M = alkali metal) and pure hydrogen gas is generated according to the following reaction:

    H → l/2 H2 + e

    This anodic process is a reversible, one-electron reaction governed by diffusion transport. The diffusion coefficient of hydride ion, , was estimated to be around 1 × 10−5 cm2 s−1 at 773 K.

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  • Noriyuki SHIMOMURA, Kazuhiko ICHIKAWA
    1999 Volume 67 Issue 6 Pages 649-654
    Published: June 05, 1999
    Released: November 15, 2019
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    Electrochemical study on redox reactions of polybismuth cations has been carried out in the acidic 1-metyl-3-benzyl imidazolium chloride (MeBzImCl) + 67 mol % AlCl3 melt, where MeBzImCl was synthesized from 1-methyl imidazole and benzyl chloride. The reduction of Bi44+ to Bi82+ (Bi44+ + 3e = 1 / 2 Bi82+) occurs at the cathodic peak around 0.6 V for BiI dissolved into this melt. The number of electron which took part into reduction at the cathodic peak around 0.6 V was determined as 2.8 ± 0.3 by polarography for BiI. For Bi6Cl7 dissolved into this melt, the reductions of Bi3+ to Bi+, Bi53+ to Bi82+ and Bi82+ to Bi metal occur at the cathodic peaks around 0.9, 0.7 and 0.2 V, respectively. The oxidations of Bi53+ to Bi3+ and Bi82+ to Bi3+ occur at the anodic peaks around 1.45 and 1.67 V for both BiI and Bi6Cl7.

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  • Hiroaki YAMAMOTO, Atsushi KAWAKAMI, Kensuke KURODA, Ryoichi ICHINO, Ma ...
    1999 Volume 67 Issue 6 Pages 655-660
    Published: June 05, 1999
    Released: November 15, 2019
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    A Magnesium-Nickel hydrogen absorption alloy, Mg2Ni, was produced as a film by molten salts electrolysis and diffusion process. Magnesium was electrodeposited on a nickel substrate from a 25 mol % NaCl - 5 mol % KC1 -70 mol % CaCl2 mixture as a supporting electrolyte, and additionally 10 mol % MgCl2 with respect to the supporting electrolyte as magnesium-ion source. The electrodeposition was conducted at 873∼1073 K and with cathodic current densities between 0.02∼0.10 A cm−2 for 3.6∼18 ks. After the electrolysis, the specimens were subjected to X-ray diffraction and EPMA line analysis to identify the phase of compounds and to measure the thickness of the film. As a result, only hydrogen absorption alloy films, Mg2Ni, were obtained with 20 µm and 27 µm thickness from electrodeposition with 0.10 A cm−2 for 3.6 ks at 1023 K and with 0.02 A cm−2 for 18 ks at 873 K, respectively. At 1073 K, the intermetallic compound MgNi2 was also detected between the Mg2Ni layer and the nickel substrate. These specimens were subjected to hydrogen absorption tests in 30 mass % KOH solution at 298 K. It was confirmed that these specimens absorbed hydrogen.

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  • Toshihide TAKENAKA, Takayuki SUZUKI, Masahiro ISHIKAWA, Eiichi FUKASAW ...
    1999 Volume 67 Issue 6 Pages 661-668
    Published: June 05, 1999
    Released: November 15, 2019
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    Direct electrowinning of liquid titanium metal has been investigated by using a DC-ESR (Direct Current Electro Slag Remelting) apparatus. A small scale DC-ESR unit was operated in a DC reverse polarity mode, where a graphite rod was used as anode and a steel or a copper base-plate was used as cathode. The used salt was CaO-CaF2-TiO2 mixture. The distance between the cathode and the anode was essential to the electrolysis. A metal pool was formed on the base-plate and the current efficiency for the reduction was up to 18% with the proper distance between the electrodes. Some amount of titanium was electrodeposited on the base-plate though its state changed with the electrolytic condition. Pure titanium metal pieces were obtained in the solidified salt after the run with the bigger distance. It is concluded that the electrowinning of liquid titanium metal by the present process is possible if sufficient heat to form a metal pool can be supplied at the bigger distance between the electrodes.

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  • Hideya TAKENISHI, Akira KATAGIRI
    1999 Volume 67 Issue 6 Pages 669-676
    Published: June 05, 1999
    Released: November 15, 2019
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    The effect of oxide ion was investigated in the electrodeposition of tungsten in an acidic ZnCl2-NaCl (60-40 mol %) melt at 450 °C. Cyclic voltammetry was performed in melts which contained various tungsten compounds and different amounts of ZnO. In constant potential electrolysis, metallic tungsten was obtained from K2WO4, WO3, WOCl4, and WCl6, but not from KWCl6, K2WCl6, WCl4, K3W2Cl9 and WCl2. When ZnO was added, metallic tungsten deposited from KWCl6, K2WCl6, and WCl4. It seems that the oxide ion or an oxochlorotungsten species participates in the electrodeposition process.

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  • Koichiro KOYAMA, Masao MORISHITA, Takayuki UMEZU
    1999 Volume 67 Issue 6 Pages 677-683
    Published: June 05, 1999
    Released: November 15, 2019
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    This investigation was carried out to find a molten salt which enables a smooth electrodeposition of tungsten. The KF-B2O3-WO3 molten salt was selected on the basis of the acid-base cooperative reaction theory. A composition of KF(67 mol %)-B2O3(26 mol %)-WO3(7 mol %) was selected as the preferred bath composition. Using a tungsten anode, smooth electrodeposits were obtained at 1123 K and at a current density ranging from 250 Am−2 to 550 Am−2 on nickel, copper, stainless steel, and mild steel substrates. When a graphite anode was used, smooth electrodeposits accompanied by dendrites were obtained. The Vickers microhardness number of the electrodeposit was 422 (load 0.49 N). The smooth electrodeposit had tendencies to form the 111 fiber texture or a mixed texture of the 111, 211 and 321 fiber textures.

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  • Nobuyuki KOURA, Takayuki UMEBAYASHI, Yasushi IDEMOTO, Guoping LING
    1999 Volume 67 Issue 6 Pages 684-689
    Published: June 05, 1999
    Released: November 15, 2019
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    The electrodeposition of the Nb-Sn alloy from the SnCl2–NbCl5–EMIC melt was investigated. From the results of the physical properties and cyclic voltammetry, the possibility of electrodeposition of the Nb-Sn alloy was suggested, which was subsequently obtained from the melt by electrodeposition. However, the Nb content in the deposits was very low. The low Nb content was related to the low limiting current density of Nb. From the results of bath temperature, melt composition and pulse electrolysis for increasing the Nb content in the deposits, the Nb-Sn alloy containing 69.1 wt % Nb was obtained from the 2.8 mol % SnCl2–68.6 mol % NbCl5–28.6 mol % EMIC melt at 200 mA cm−2 with a pulse period of 10 ms, duty ratio of 0.2 at 160 °C.

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  • Yoshikazu KANEKO, Lu CHEN
    1999 Volume 67 Issue 6 Pages 690-694
    Published: June 05, 1999
    Released: November 15, 2019
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    The vanadium bronze films were synthesized onto the ITO electrode by electrolysis in molten dimethylsulphone (DMSO2)-V2O5 and DMSO2-V2O5-LiNO3 systems at the temperature about 150 °C. The obtained film was analyzed by x-ray diffraction. Moreover, the electrochromic (EC) reactions of the vanadium bronze film in room temperature solution of propylene carbonate (PC) or high temperature solution of DMSO2 were investigated. The lithium vanadium bronze film was discussed on the basis for high temperature electrochromic materials.

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  • Mikito UEDA, Kohich IMASAWA, Shoichi KONDA, Takeshi SASAKI, Tatsuo ISH ...
    1999 Volume 67 Issue 6 Pages 695-699
    Published: June 05, 1999
    Released: November 15, 2019
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    To decrease the reaction polarization of the cathodic reaction of Cl2 + 2e → 2Cl in Al-Cl2 electrochemical cell in NaCl-KCl melt at 1023 K, we developed a cell system with a vertically rotating electrode composed of sliced graphite disks which are partially immersed in the melt. The apparent reaction resistance of the cathodic reaction was evaluated from transient potential and current changes of the cell. The reaction resistance decreases with an increase of the number of the graphite disks. The resistance is a function of the rotation rate of the electrode and exhibits the minimum value around a rotation rate of 20 rpm. The dependence on the rotation rate may be explained from Cl2 concentration in a thin melt layer formed on the graphite electrode during exposure to Cl2 gas phase. The rotation may introduce a continuous supply of the thin melt layer with a high concentration of Cl2 to a reaction place at a meniscus part on the graphite electrode. However, if the rotation rate is too high, the exposure time of the thin melt layer to Cl2 gas is not enough to establish an equilibrium concentration of Cl2 in the layer.

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  • Masatsugu MORIMITSU, Morio MATSUNAGA
    1999 Volume 67 Issue 6 Pages 700-705
    Published: June 05, 1999
    Released: November 15, 2019
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    The reaction distributions in not only the circumferential but also the longitudinal directions of the positive electrode of a Na/SeCl4 cell utilizing the basic AlCl3-NaCl melt are discussed. The two-dimensional potential distributions during charge, discharge, and open circuit are measured using tungsten microelectrodes inserted in a dual-mat graphite electrode and the local potentials are compared with the emf of the Na/SeCl4, cell to calculate the radial and axial distributions of the formal oxidation states of selenium. The radial reaction distribution during discharge is uniform independently of current densities, while the axial one is almost homogeneous except at deeper stages of discharge at a high current density. The radial and axial reaction distributions during charge are also uniform until the occurrence of the melt acidification which is confirmed from the result that the local potential becomes nobler than the emf of the cell in the fully charged state. The uniformity of the reaction distribution in the dual-mat graphite electrode, especially in the radial direction, causes a uniform deposition of solid NaCl on the graphite electrode, consequently inducing the enhanced depth of discharge and the improved utilization of tetravalent selenium.

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  • Nobuyuki KOURA, Kazutaka IIZUKA, Yasushi IDEMOTO, Koichi UI
    1999 Volume 67 Issue 6 Pages 706-712
    Published: June 05, 1999
    Released: November 15, 2019
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    An AlCl3-1-ethyl-3-methylimidazolium chloride (EMIC) melt has a wide electrochemical window, and it is nonflammable with no ignition. We have developed the rocking chair type lithium secondary battery with an AlCl3-EMIC melt containing excess LiCl with a saturated solubility as the nonflammable electrolyte. In this paper, when LiCl was added in the acidic melt (AlCl3 > 50 mol %), the solubility of the LiCl and the changes in the physical properties were measured. Moreover, SOCl2 or Li metal was treated to completely remove any small amounts of Al2Cl7, which was the ionic species for deposited Al, that remained in the melt. As a result, it was confirmed that Al2Cl7 was completely removed based on a cyclic voltammogram (C.V.) using a W electrode. The reversible deposition and dissolution behavior of lithium was indicated from the C.V. for a Li electrode in the SOCl2 containing melt, and it was found that a Li metal would perform as the negative electrode active material.

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  • Ying Sing FUNG, Ruqi ZHOU
    1999 Volume 67 Issue 6 Pages 713-717
    Published: June 05, 1999
    Released: November 15, 2019
    JOURNALS OPEN ACCESS

    Room Temperature Molten Salt (RTMS) based on 1-methyl-3-ethylimidazolium chloride/AlCl3/LiAlCl4 is recently shown to provide a promising medium for lithium battery due to its high current capability and inertness towards active material. In the present work, the electrochemical properties of a LixMn2O4 electrode in RTMS, the most commonly used positive electrode material, were investigated by cyclic voltammetry, coulometric titration and constant current cycling. From cyclic voltammetric studies, the LixMn2O4 electrode in RTMS was found to exhibit the same electrochemical behavior as in other non-aqueous electrolytes. However, a new and very large irreversible anodic peak was found due to the insertion of AlCl4 into the carbon current collector. During coulometric studies, coulombic efficiencies greater than 96% were obtained at composition close to x = 1 in LixMn2O4. However, for Range I (0 < x < l), a rapid decrease in coulombic efficiency was observed at x less than 0.6. For Range II (1 < x < 2), close to 86% of the electrode material could be used. Thus, Range II was selected for battery application. For cycling at Range I, greater than 95% cycling efficiencies were obtained up to insertion/extraction capacities of 60 mAh/g, whereas at Range II, 98% cycling efficiencies at the first 20 cycles were obtained up to 120 mAh/g. The difference was attributed to the irreversible insertion of AlCl4 anions into the carbon current collector at high anodic potential and hence less lithium was extracted from the LixMn2O4 electrode in 0 < x < 1. The electrochemical performance of the LiMn2O4 electrode as positive electrode material for secondary lithium battery at different lithium insertion in RTMS was discussed in the light of the results obtained.

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Technological Report
  • Yutaka TAKASAWA, Takeshi ONOUE, Yasushi HOSHINO, Naoki TERAMAE, Sumio ...
    1999 Volume 67 Issue 6 Pages 718-725
    Published: June 05, 1999
    Released: November 15, 2019
    JOURNALS OPEN ACCESS

    The effects of current density and temperature on the current efficiency for uranium metal deposition were investigated by electrolysis at the cathodic current densities of 1.34∼22 A/cm2 in the fluoride salts in the temperature range of 1150∼1200 °C. The electrolyte consisted of 74 wt. % BaF2, 11 wt. % LiF, and 15 wt. % UF4. On the basis of the theoretical assumption, the factors affecting the current efficiency were discussed. The current efficiency for uranium deposition increased with increasing current density. A neutral hearth type of electrode in a small cell or a horizontal type of electrode with cathode studs in a large cell enabled to conduct electrolysis at a high cathodic current density. From these results, it is found that the current efficiencies for uranium deposition in both cells were high compared with those reported previously.

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