津田 哲哉

The electrodeposition of Al-Mo-Mn ternary alloys was examined in the Lewis acidic 66.7-33.3% mole fraction (mol%) aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl3-EtMeImCl) molten salt containing Mo(II) and Mn(II). By adjusting the CMn(II)/CMo(II) concentration ratio in the plating solution and employing different current densities, it was possible to prepare alloys with widely varying compositions and surface morphologies. All Al-Mo-Mn alloys were dense, compact, and adhered well to the copper substrate surface. The addition of small amounts of Mn to the Al-Mo alloy resulted in an improvement in the chloride pitting corrosion resistance and metallic brightness. For example, Al90.1Mo9.9Mn0 and Al89.5Mo9.1Mn1.4 displayed pitting potentials that were 725 and 837 mV more positive than that for Al, respectively. Al-Mo-Mn alloys that contained more than about 10 atom % Mo + Mn exhibited a metallic glass structure. (c) 2005 The Electrochemical Society.

The electrochemistry of Zr(IV) and Zr(II) and the electrodeposition of Al-Zr alloys were examined in the Lewis acidic 66.7-33.3 mol % aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt at 353 K. The electrochemical reduction of Zr(IV) to Zr(IT) is complicated by the precipitation of ZrCl3; however, solutions of Zr(II) can be prepared by reducing Zr(IV) with Al wire. Al-Zr alloys can be electrodeposited from plating baths containing either Zr(IV) or Zr(II), but for a given concentration and current density, baths containing Zr(IV) lead to Al-Zr alloys with the higher Zr content. This result was traced to the diminutive concentration-dependent diffusion coefficient for Zr(II). It was possible to prepare Al-Zr alloys containing up to similar to17% atomic fraction (atom %) Zr. The structure of these deposits depended on the Zr content. Alloys containing less than 5 atom % Zr could be indexed to a disordered face-centered cubic structure similar to pure At, whereas alloys containing similar to17 atom % Zr were completely amorphous (metallic glass). The chloride pitting potentials of alloys with more than 8 atom % Zr were approximately +0.3 V relative to pure Al. (C) 2004 The Electrochemical Society.

The electrodeposition of aluminum-molybdenum alloys was examined at copper rotating disk and wire substrates in the Lewis acidic 66.7-33.3 mol % aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt containing Mo(II) in the form of dissolved (Mo6Cl8) Cl-4. The molybdenum content of the electrodeposits depended on the electrode rotation rate, Mo(II) concentration, and bath temperature. It was possible to produce nonequilibrium alloys containing up to 11 atom % Mo. These alloy deposits were compact and chloride-free. Al-Mo alloys containing more than 8 atom % Mo exhibited a chloride corrosion pitting potential of approximately 1800 mV against pure aluminum. The corrosion resistance of this alloy is superior to that of all the aluminum-transition metal alloys that have been electrodeposited to date from chloroaluminate molten salts. (C) 2004 The Electrochemical Society.

Reaction of some N-alkylimidazolium chlorides with anhydrous hydrogen fluoride (HF) gave nonvolatile room temperature molten salts (room temperature ionic liquids), RMImF.2.3HF where RMIm = 1,3-dimethylimidazolium (DMIm), 1-ethyl-3-methylimidazolium (EMIm), 1-methyl-3-propylimidazolium, 1-butyl-3-methylimidazolium, 1-methyl-3-pentylimidazolium, and 1-hexyl-3-methylimidazolium. Vacuum stable salts at room temperature exhibited similar stoichiometry regardless of the type of cation. In the differential scanning calorimetry (DSC) curve, DMImF.2.3HF exhibited both the freezing and melting on the cooling and heating process, respectively, while EMImF.2.3HF showed the glass transition on the cooling process and devitrification and melting on the heating process. The other salts show only the glass transition on the DSC curves. High specific conductivities, 110 and 100 mS cm(-1), were observed at 298 K for DMImF.2.3HF and EMImF.2.3HF, respectively. Introduction of the longer alkyl side chains to the imidazolium cation increased the viscosity and decreased the conductivity. These salts were stable in air and did not etch a Pyrex glass container at ambient conditions. The dissociation pressures of HF from the salts were negligibly small at ambient condition. The electrochemical windows of these salts was about 3 V. (C) 2003 The Electrochemical Society.

The chemical and electrochemical behavior of titanium was examined in the Lewis acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl3-EtMeImCl) molten salt at 353.2 K. Dissolved Ti(II), as TiCl2, was stable in the 66.7-33.3% mole fraction (m/o) composition of this melt, but slowly disproportionated in the 60.0-40.0 m/o melt. At low current densities, the anodic oxidation of Ti(0) did not lead to dissolved Ti(II), but to an insoluble passivating film of TiCl3. At high current densities or very positive potentials, Ti(0) was oxidized directly to Ti(IV); however, the electrogenerated Ti(IV) vaporized from the melt as TiCl4(g). As found by other researchers working in Lewis acidic AlCl3-NaCl, Ti(II) tended to form polymers as its concentration in the AlCl3-EtMeImCl melt was increased. The electrodeposition of Al-Ti alloys was investigated at Cu rotating disk and wire electrodes. Al-Ti alloys containing up to similar to19% atomic fraction (a/o) titanium could be electrodeposited from saturated solutions of Ti(II) in the 66.7-33.3 m/o melt at low current densities, but the titanium content of these alloys decreased as the reduction current density was increased. The pitting potentials of these electrodeposited Al-Ti alloys exhibited a positive shift with increasing titanium content comparable to that observed for alloys prepared by sputter deposition. (C) 2003 The Electrochemical Society.

The electrodeposition of Al-V alloys was investigated in the VCl2-saturated 66.7-33.3 mole percent aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt at 353 K. Because the reduction of V(11) occurs at potentials considerably negative of the Al(III)/Al electrode reaction, Al-V alloys cannot be electrodeposited from this melt without the use of the additive, 1-ethyl-3-methylimidazolium tetrafluoroborate. In the presence of this additive, the vanadium content of electrodeposited alloys increased with increasing cathodic current density or more negative applied potentials. X-ray analysis of Al-V alloys that were electrodeposited on a rotating copper wire substrate indicated that these alloys did not form or contain an intermetallic compound, but were nonequilibrium or metastable solid solutions. The chloride-pitting corrosion properties of these alloys were examined in N-2-saturated aqueous NaCl by using a potentiodynamic polarization technique. Alloys containing similar to10 a/o vanadium exhibited a pitting potential that was +0.3 V positive of that for pure aluminum. However, this pitting potential was inferior to that measured for aged Al-V alloys that were prepared by sputter deposition.

A highly conductive composite electrolyte consisting of poly-2-hydroxyethyl methacrylate and a room temperature molten fluorohydrogenates, EtMeIm(HF)(n)F (EtMeIm: 1-ethyl-3-methylimidazolium, the averaged number n of the oligomeric anions in the vacuum stable salt is 2.3), has been obtained by a radical reaction method. A transparent gel composite electrolyte is formed when the molar fraction of EtMelm(HF)(n)F, N, is in the range of 0.20-0.60. The conductivity of the electrolyte increases as the N increases. The maximum conductivity of 2.3 x 10(-2) S cm(-1) is obtained for N=0.60 at 300 K. Like the original salt, this composite electrolyte exhibits an excellent stability in air and does not etch the Pyrex glass. The electrochemical window of the neat salt, similar to3.2 V, is extended to similar to3.5 V for the composite electrolyte. (C) 2002 Elsevier Science B.V. All rights reserved.

The cathodic polarization curve on a tungsten disk electrode was measured in a LaCl3-saturated AICl(3)-EtMeImCl [1-ethyl-3-methylimidazolium chloride] melt (N = 0.667: N is molar fraction of AlCl3) at 298 K. The deposition overpotential of aluminum increases compared with the curve obtained before adding LaCl3. It was found that the nucleation/growth process is instantaneous nucleation from chronoamperometric data. When galvanostatic electrolysis was performed in the LaCl3-saturated melt, the strong ;orientation of (200) for the electrodeposits is observed at low current densities (less than or equal to 7.5 mA cm(-2)). On the other hand, the normalized integrated intensity of XRD for (200) and (220) reflections has similar strength at high current densities ( greater than or equal to 10.0 mA cm(-2)). The electodeposits become denser than those obtained in the original melt. In particular, very smooth surface is obtained in the case of 15.0 mA cm(-2) with stirring the bath. (C) 2002 Elsevier Science Ltd. All rights reserved.

In the title complex, (C6H11N2)(3) [LaCl6], centrosymmetric octahedral hexachlorolanthanate anions are located at the corners and face-centers of the monoclinic unit cell. The ring H atoms of the cations interact with the Cl atoms of the anions via hydrogen bonding, and bifurcation of the hydrogen bonding is observed. Cation-cation interactions via hydrogen bonding between the ring H atoms and pi-electrons of aromatic rings are also observed as in other imidazolium salts.

The structures of a series of XF (.) 2.3HF (X = 1-methylimidazolium, 1-ethyl-3-methylimidazolium (EMI), 1-butyl-3-methylimidazolium, 1-hexyl-3-methyl-imidazolium (HMI)) room temperature molten salts have been investigated by the high-energy synchrotron X-ray diffraction technique. The correlation peaks appearing in the total correlation function are mainly ascribed to an intra-molecular correlation of alkylimidazolium cations. However, it is suggested that the peak near 3.6 Angstrom is ascribed not only to intra-molecular but also inter-molecular correlations of the cation. The contribution of the latter is also supported by the first sharp diffraction peak of the total structure factor found at almost the same position as that of a Bragg peak in the simulated X-ray diffraction pattern of solid EMIF (.) HF with a layered structure, corresponding to the layer separation. (C) 2002 Elsevier Science B.V. All rights reserved.

EMIF.HF, 1-ethyl-3-methylimidazolium bifluoride, has been obtained by eliminating HF from a room temperature molten salt EM1F.2.3HF at around 400 K. EM1F.HF crystallizes in space group P2(1)/m with a = 7.281(1) Angstrom, b = 6.762(1) Angstrom, c = 8.403(1) Angstrom, beta = 107.26(1)degrees, V = 395.09(18) Angstrom(3), Z = 2 at room temperature. The cations are stacked in pillars via the hydrogen bonding between the C4 proton and the ring pi-electrons of the adjacent cation. The cations and the anions coupled by strong hydrogen bondings are co-planar. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

The chemical and electrochemical behavior of titanium was examined in the Lewis acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl3-EtMeImCl) molten salt at 353.2 K. Dissolved Ti(II), as TiCl2, is stable in the 66.7-33.3 m/o composition of this melt, but shows a slight tendency to disproportionate in the 60.0-40.0 m/o melt. At low current densities, the anodic oxidation of Ti(0) does not lead to dissolved Ti(II), but to an insoluble passivating film of TiCl3. At high current densities or very positive potentials, Ti(0) is oxidized to Ti(IV); however, the electrogenerated Ti(IV) vaporizes from the melt as TiCl4(g). The electrodeposition of Ti-Al alloys was investigated at Cu rotating wire electrodes. Ti-Al alloys containing up to similar to19 a/o titanium could be electrodeposited from saturated solutions of Ti(II) in the 66.7-33.3 m/o melt at low current densities, but the titanium content of these alloys decreased as the reduction current density was increased. The pitting potentials of these electrodeposited Ti-Al alloys exhibited a positive shift with increasing titanium content comparable to that observed for alloys prepared by sputter deposition.

Reaction of some N-alkylimidazolium chloride with anhydrous hydrogen fluoride (HF) gives involatile room temperature molten salt, RR'ImF(.)2.3HF where RR'Im = 1,3-dimethylimidazolium (DMIm), 1-ethyl-3-methylimidazolium (EMIm), 1-methyl-3-propylimidazolium (PrMIm), 1-butyl-3-methylimidazolium (BMIm), 1-methyl-3-pentyl imidazolium (PeMIm), 1-hexyl-3-methylimidazolium (HMIm). Vacuum stable salts at room temperature exhibit the same composition regardless the type of the cation. High specific conductivities, I 10 and 100 mScm(-1), are observed at 298 K for DMhnF(.)2.3HF and EMImF(.)2.3HF, respectively. Substitution of the proton or the longer alkyl side chains for the ethyl group of the imidazolium cation decreases the conductivity. These salts are stable in air and do not etch a Pyrex glass container at ambient conditions. Electrochemical windows of these salts range around 3V. Elongation of the alkyl side chain on the cation tends to extend the cathode limit. These salts act as good Lewis bases against binary fluorides of some main group elements and transition metals to give ionic salts without involatile byproducts.

Reaction of 1-ethyl-3-methylimidazolium chloride (EMICl) and anhydrous hydrogen fluoride gives a nonvolatile, room temperature molten salt, EMIF .2.3HF. The elemental analysis, vibrational, and nuclear magnetic resonance spectroscopy suggests the presence of oligomeric anions, (HF)(n)F(-) in the salt. The liquid is stable in air and able to be handled in a Pyrex glass vessel. The specific conductivity is 100 mS cm(-1) at 298 K, which is extremely high compared with other salts of this kind. The high conductivity is realized by its low viscosity (4.85 cP at 298 K). The liquid temperature ranges from 180 to 350 K, and electrochemical window is about 3.2 V when a vitreous carbon is used for the electrode material. (C) 2001 The Electrochemical Society.

The solubility of LaCl3 in acidic AlCl3-1-ethyl-3-methylimidazolium chloride (AlCl3-EMICl) ambient temperature melts at 298 K increases as the acidity of the melts increases. When LaCl3 was dissolved in the melt (molar fraction of AlCl3, N = 0.667), Raman spectra of AlCl4- and Al2Cl7- anion were observed. From these results, the dissolution reaction in the acidic melts is thought to be: 3Al(2)Cl(7)(-) + LaCl3 reversible arrow La(III)+ 6AlCl(4)(-). Electrochemical measurements and potentiostatic electrolysis were performed in various LaCl3 saturated AlCl3-EMICl melts. The electrodeposits obtained at more negative potential than - 0.18 V versus Al(III)/Al in a LaCl3 saturated acidic melt (N = 0.667) were pure aluminum metal. It was suggested that lanthanum metal electrodeposits at around - 1.95 V in the LaCl3 saturated melt (N = 0.667) after addition of excessive LiCl and 50 mmol kg (-1) of SOCl2. (C) 2001 Elsevier Science Ltd. All rights reserved.

The effect of the viscosity of room temperature molten salt (RTMS) electrolyte has been investigated on the performance of dye-sensitized solar cell (DSSC). Both the short circuit photocurrent and conversion efficiency are increased with decreasing the viscosity of RTMS as in the case of conventional electrolytes. The conversion efficiency of 2.1% observed for the cell of EMIm-F.2.3HF is the highest value reported for all the DSSC consisted of RTMS.

Reaction of some N-alkylimidazolium chloride or N-alkylimidazole with anhydrous hydrogen fluoride (HF) gives involatile room temperature molten salt, XF(.)2.3HF where X = 1-ethyl-3-methylimidazolium (EMI), 1-methylimidazolium (MeIm), 1-butyl-3-methyl-imidazolium (BMI), 1-hexyl-3-methylimidazolium (HMI). The highest specific conductivity at 298 K, 10(2) mScm(-1), is observed for EMIF(.)2.3HF. Substitution of the proton. or the longer alkyl groups for the ethyl group of the cation decreases the conductivity. These salts are stable in air and do not etch a Pyrex glass container at ambient conditions. EMIF(.)2.3HF does not freeze above -90degreesC or lose HF below 100degreesC. The low viscosity of the salts (4.85 cP at 298 K for EMIF(.)2.3HF) is essential to the high ionic conductivity of these salts.

The solubility of lanthanum chloride (LaCl3) is dominated by the amount of Al2Cl7- anion in the aluminum chloride (AlCl3)-1-ethyl-3-methylimidazolium chloride (EMIC) room temperature molten salt systems. Electrochemical experiments have been performed in LaCl3 saturated AlCl3-EMIC (N = 0.667) melts. Aluminum-lanthanum alloy which is thought to be in coexisting aluminum and alpha-Al11La3 phase state or in the unidentified metastable / nonequilibrium state is formed at around -0.58 V vs. AI(III)I Al in the melt. From an analysis of the chronoamperometric transients it is suggested that the electrodeposition of this aluminum-lanthanum alloy on tungsten disk electrode involves instantaneous three-dimensional nucleation with mixed diffusion and kinetic controlled growth of the nuclei. In a LaCl3 saturated melt (N = 0.667) with excessive lithium chloride (LiCl) and small quantities of thionyl chloride (SOCl2) added, lanthanum metal is electrodeposited at around -1.95 V vs. Al(III)/ Al. The electrodeposited lanthanum metal does not undergo complete stripping from the electrode surface during anodic polarization.

Reaction of 1-ethyl-3-methyl imidazolium chloride (EMIC) and hydrogen fluoride gives an yellow, involatile liquid, EMIF.2.3HF. The liquid is stable in air and able to be stored in a glass container. The specific conductivity was about 12 S m(-1) at 298 K. (C) 1999 Elsevier Science S.A. All rights reserved.