The electrical conductivity of the M2(WO4)3 (M = Rare Earth, In, Al) solid electrolyte series amounts to 3.2×10−6-6.5×10−5Ω−1cm−1 with corresponding activation energies of 44.1-91.0 kJ/mol. These electrical properties can be individually improved, as is exemplary shown for the case of Sc2(WO4)3 and A12(WO4)3, by the formation of mixed cationic tungstates of the type (Sc1−xMx)2(WO4)3 (M = In, Lu, Dy, Gd) and (Al1−xScx)2(WO4)3 solid solutions, respectively. The larger cations (rM3+>rsc3+ and rsc3+>rAl3+) act to expand the host lattice for an easier migration of the Sc3+ and Al3+ cations, respectively. Maximum enhanced conductivities of about 5 times (Sc3+ conductors) and 6 times (Al3+ conductors) have been observed. The trivalent cations (M) were quantitatively and qualitatively identified as mobile charge carrying species with a cationic transference number of t+> 0.99. Scandium cations have been identified in (Scl−xMx(WO4)3 (M = In, Dy, Gd) as main charge carrying species, whereas in (Scl−xLux)2(WO4)3 and (Al1−xScx)2(WO4)3 the predominant charge carrier changes in dependence on the composition. The experimental procedure for the characterization of M2(WO4)3 and (Sc1−xMx)2(WO4)3 as trivalent cationic conducting solid electrolytes is also given.
The new measurement method of Surface Photovoltage (SPV) technique was applied to the fabrication of a novel type cholinesterase-based biosensor. Cholinesterases (butyrylcholine esterase (BuChE) and acetylcholine esterase (AChE)) have been immobilized directly onto the semiconductor surface to measure the concentration of enzyme substrates, via pH changes. The detection limits of the substrates were 9.0×10−7 M, 2.7×10−6 M and 4.1×10−6 M for butyrylthiocholine iodide, acetylcholine iodide and acetylcholine chloride, respectively. The analytical possibilities were examined from the results of the inhibiting actions exerted in the presence of alkaloids such as physostigmine sulfate and neostigmine bromide on BuChE.
Zinc oxide films containing small amounts of Ti oxide were prepared by heat treatment of Ti sheets with a Zn plated overlayer. Long term photoelectrochemical corrosion tests of the film at a constant potential of 1 V vs. Ag | AgCl was carried out. It was found that Zn2+ ions initially dissolved into the electrolyte solution but that dissolution then stopped. This behavior can be explained by an increase in the surface concentration of Ti. After some dissolution of Zn, the increased Ti concentration enables the surface to withstand further photoelectrochemical corrosion. This Ti containing oxide film showed a much better photoresponse than that of Ti oxide alone in the long wavelength region and would be a good candidate for photo anodes in aqueous electrolytes.
Electrical conductivity of the perovskite-type solid-solution system (Ba1−xLax)(In1−xGax)O3−δ was investigated from a viewpoint of crystal chemistry. XRD showed that the brownmillerite-type orthorhombic phase (x=0.0) gradually approached to cubic phase with increase in x, resulting in the cubic perovskite phase at x≧0.15. A sharp transition temperature (Td) (930°C) of the electrical conductivity observed for x=0.0 shifted to lower temperature with increase in x, at the same time, the electrical conductivity above the Tddecreased. The shift of Tdwas explained by disordering of oxygen vacancy. On the other hand, it was found that the electrical conductivity was strongly affected by the unit cell lattice volume rather than oxygen vacancy.
Well-crystallized LiSb(OH)6 powders with a hexagonal structure were prepared by chemical bath deposition. The thermal decomposition of as-prepared samples was examined and the exchange behavior of lithium ion in LiSbO3 powders was studied. In order to obtain LiSb(OH)6 powders, it was essential to prepare under the following condition; obtaining precipitates of LiSb(OH)6 from a SbCl5 aqueous solution containing tartaric acid by adding LiOH above pH 9. From the results of XRD and FT-IR measurements, it was found that LiSbO3 powders with an orthorhombic structure were obtained by heating LiSb(OH)6 at 800°C. The release rate of lithium ion from LiSbO3 increased with the increase of refluxing temperature and time, and also concentration of nitric acid. The maximum value of exchange rate showed 94% when LiSbO3 powders dispersing in the nitric acid with a concentration above 1.0 mol dm−3 were refluxed at 30°C for 60 min. The insertion rate of lithium ion in HSbO3 also increased, of which behavior was similar to that of the release of lithium ion from LiSbO3. The maximum value of exchange rate was found to attain 87% by refluxing at 70°C for 360 min with the LiOH solution above the concentration of 0.1 mol dm−3.
It is well known that the leakage current decreases at a constant anodizing potential during the anodic oxide formation on aluminum. To elucidate this phenomenon, chronopotentiometric responses to short current pulses during anodic oxidation at a constant potential have been measured and analyzed. We found that the breakdown voltage of the anodic oxide film changed together with the increment of the potential overshoot during the chronopotentiometric responses to the short current pulse during anodic oxidation at a constant potential. The insulating breakdown voltage increment indicated that it is possible to distinguish between the anodizing potential and the insulating breakdown voltage which is in good agreement with the high electric field mechanism for anodic oxide film formation. The dependence of the potential overshoot of the anodizing current has been analyzed by applying programmed current chronopotentiometry, and we found that the potential overshoot may be closely related to the defects in the anodic oxide film.
The application of microelectrode technique to aluminum anodic oxide film formation in ammonium adipate solution has been carried out. The non-Faradaic current and the ohmic drop due to solution resistance can be reduced drastically by microelectrode technique. The use of 25 micrometer alminum thin wire as an microelectrode enabled us to measure the rapid cyclic voltammetry (~1000 V S−1) of alminum anodic oxide formation process at the very large current density range such as 104 A m−2 and larger than it. This current density corrensponds to the 1000 times larger than that of the ordinary electrode.
Nitric oxide dissolved in buffer solutions has been detected by the electrochemical oxidation reaction on a glassy carbon (GC) electrode coated with Nafion film doped with various iron (III) porphyrins. The electrochemical detection was carried out by using different methods, such as normal pulse voltammetry (NPV), differential pulse voltammetry (DPV) and amperometry. All iron (III) porphyrins examined showed a catalytic activity for the electrolytic oxidation of nitric oxide. In the result, tetrakis-(pentafluorophenyl) porphyrin iron (III) chloride (Fe(TPFPP)Cl) showed the most prominent electrocatalytic activity. Amperometric detection of nitric oxide was successfully performed on the GC electrode coated with a Nafion film doped with Fe(TPFPP)CI. In the amperometry with an injection of NO solution, the lower detection limit was found to be about 10 nM.
Ni-YSZ cermet as a substrate of the fuel-electrode-supported-cell was evaluated. The shrinkage of the cermet during the annealing (1050°C, 1000 hours in H2) was 0.15%. Its gas permeability and its mean pore size after the annealing were 6×10−4 cm4 g−1 S−1 and 0.43 μm, respectively. The performance of the cell with 1 cm2 electrodes which consists of the cermet as a fuel-electrode-support, electrolyte and air-electrode was tested using 80% H2O-H2 gas as a fuel and air as an oxidant at 1000°C. The cell was operated without serious concentration overvoltage at the current density lower than 0.7 A cm−2. The anodic concentration overvoltage evaluated from the observed limiting current density was almost equal to the measured one. And the cell voltage at the current density 1.0 A cm−2 revealed no degradation during 1000 hours operation.