Kazunori Sato

Cr Poisoning Suppression in Solid Oxide Fuel Cells Using LaNi ( Fe ) O3 Electrodes

We have investigated the effect of Cr poisoning on various cells which consist of either LaNi 0 . 6 Fe 0 . 4 O 3 (LNF) or La 0 . 8 Sr 0 . 2 MnO 3 (LSM) as a cathode and either yttria-stabilized zirconia (YSZ) or alumina-dopedscandia stabilized zirconia (SASZ) as the electrolyte. It was found that the cathodic overvoltage was almost the same for cells with LNF cathodes, either in the presence or absence of Cr-containing alloy (Inconel 600). LSM cathodes in the presence of Inconel 600 exhibited a very steep increase in voltage curves after applying the current. These results indicate that the LNF cathode is electrochemically stable for Cr poisoning compared with the LSM cathode.

Modulated structure and magnetic properties of age-hardenable Fe-Mn-Al-C alloys

Microstructural changes in the age-hardenable Fe-(30 to 34) wt pct Mn-(8 to 11) wt pct Al-(0.9 to 1.0) wt pct C alloys during aging in the temperature range between 773 and 823 K have been investigated by means of transmission electron microscopy (TEM) and X-ray diffraction. The wavelength of the modulated structure was found to be nearly constant for short aging times and then to increase on further aging, whereas the compositional modulation amplitude was found to increase rapidly from the beginning of aging. The growth of a spinodally modulated structure along the orthogonal «100» directions results in a periodic arrangement of the κ-carbide precipitates, (Fe, Mn)3AlCx, in the austenite matrix. The increases in hardness and residual and saturation inductions in the early stage of aging were in accord with the increase in the amplitude.

Properties of photocatalysts with tunnel structures: formation of a surface lattice O− radical by the UV irradiation of BaTi4O9 with a pentagonal-prism tunnel structure

Abstract The UV irradiation of barium tetratitanate, BaTi 4 O 9 , with a unique pentagonal-prism tunnel structure, produced an EPR signal with g =2.018 and g =2.004 at 77 K: the signal had a short lifetime in vacuum, whereas it was stable in the presence of gaseous molecules (O 2 , H 2 , He, Ar) independently of the kinds of gases. The radical reacted with gaseous oxygen and formed O 3 − at room temperature. The species is assigned to an O − radical resulting from lattice oxygen at the surface, and its formation is closely related to the distorted TiO 6 octahedra forming the tunnel.

Photocatalytic activity for water decomposition of RuO2-combined M2Ti6O13 (M = Na, K, Rb, Cs)

Abstract A series of hexatitanates, M2Ti6O13 (M = Na, K, and Rb), with rectangular tunnel structures and Cs2Ti6O13 with a layer structure were employed to reveal the role of metal oxide structures in photocatalysis. The photocatalytic activity for water decomposition of RuO2-supporting M2Ti6O13 was compared with the efficiency for the production of photoexcited charges (electrons and holes) which was evaluated by the intensity of ESR peaks. The hexatitanates with the tunnel structures showed high photocatalytic activities and photoexcited radical formation, thus indicating a close relationship between the photocatalytic activity and the efficiency of photoexcited charge formation. The role of distorted TiO6 octahedra in the tunnel structures is discussed.

Spinodal decomposition and mechanical properties of an austenitic Fe-30wt.%Mn-9wt.%Al-0.9wt.%C alloy

Abstract The microstructure and mechanical properties of an austenitic Fe-30wt.%Mn-9wt.%Al-0.9wt.%C alloy after aging in the temperature range between 743 and 873 K have been investigated. The occurrence of spinodal decomposition was confirmed by transmission electron microscopy observation of a modulated structure with superlattice reflections and identification of the X-ray sidebands. The rapid increase in the yield stress in the early stage of aging was proportional to the increase in the modulation amplitude and independent of the wavelength. The observed hardening has been examined using a theory dealing with the coherency strain produced by the spinodal decomposition.

Age hardening of an Fe-30Mn-9Al-0.9C alloy by spinodal decomposition

Analyse par diffraction de rayons X, microscopie electronique en transmission de la microstructure de lacier 29,5 Mn-9,2 Al-0,94 C vieilli a 823 K. influence de la structure modulee sur le durcissement par vieillissement

Long-term chemical stability of LaNi(Fe)O3 as a cathode material in solid oxide fuel cells

Chemical reactivity of LaNi 0.6 Fe 0.4 O 3 (LNF) with Cr 2 O 3 has been investigated in order to examine the long-term stability of the LNF phase at 1073 K, which shows a high performance as the cathode of intermediate-temperature solid oxide fuel cells (IT-SOFCs). The chemical stability of LNF was compared with that of La 0.8 Sr 0.2 MnO 3 (LSM) under the existence of Cr 2 O 3 . The LNF powder, a powder mixture of LNF and Cr 2 O 3 , and a powder mixture of LSM and Cr 2 O 3 were, respectively, heated at 1073 K, and they are analyzed by X-ray powder diffraction with the Rietveld refinement. We found that the LNF phase maintains the hexagonal crystal system heated in air up to 1000 h. In the LNF-Cr 2 O 3 mixture, the LNF phase kept its pristine crystal structure while a new phase, NiCr 2 O 4 , was detected, which was produced by the reaction between Cr 2 O 3 and the residual NiO contained in the starting LNF powder. In the LSM-Cr 2 O 3 mixture, LSM reacted with Cr 2 O 3 and produced a significant amount of MnCr 2 O 4 . LNF showed a much better chemical stability against Cr 2 O 3 than LSM. LNF can serve as a long-life cathode in the IT-SOFC system.

Effects of RuO2 dispersion on photocatalytic activity for water decomposition of BaTi4O9 with a pentagonal prism tunnel and K2Ti4O9 with a zigzag layer structure

Effects of RuO2 dispersion on the photocatalytic activity for water decomposition of BaTi4O9 n (BTO) with a pentagonal prism tunnel structure and K2Ti4O9 (KTO) with a zigzag layer structure were studied. These titanates were impregnated with either a RuCl3 aqueous solution or a Ru3(CO)12 complex in THF and were n subjected to oxidation at high temperatures. In comparison with the chloride, the employment of n Ru3(CO)12 complex gave rise to the higher photocatalytic activity of BTO and a significant improvement of photocatalytic performance of KTO. High resolution transmission electron microscopic observation showed that n the carbonyl complex led to the formation of uniformly distributed small RuO2 particles (average particle size, ρav, was 1.8 nm for BTO and 5.1 nm for KTO) than did the chloride (ρav was 2.7 for BTO and 15 nm for KTO). The tunnel structure of BTO is shown to have the high capability to disperse RuO2 as small particles, n compared to the zigzag layer. The photoexcited charge formation of KTO with UV irradiation was examined by electron paramagentic resonance (EPR) measurements. A correlation between the photocatalytic activity and the n ability of surface lattice O− formation is established for these n titanates with different structures. The size effects of RuO2 particles on photocatalysis are discussed.

LaNi0.6Fe0.4O3–Ceria Composite Cathode for SOFCs Operating at Intermediate Temperatures

We fabricated single cells with a LaNi 0.6 Fe 0.4 O 3 (LNF) cathode and a scandia alumina-doped zirconia electrolyte. Cells with a cathode consisting of a current collecting LNF layer and an active layer were also fabricated by using a screen-printing technique. The active layer contained Ce 0.8 Sm 0.2 O 1.9 (SDC) or Ce 0.9 Gd 0.1 O 1.95 and LNF particles. The influence of the sintering temperature and particle size of LNF and SDC on the cathode properties was investigated. LNF cathodes with this active layer exhibited good levels of performance, including cathode potential, and interface resistance from the start of the operation at 800°C. This configuration also improved the adhesiveness between the cathode and the zirconia electrolyte. We found that the active layer is functional when the ceria particle size is equal to or smaller than that of the LNF. Scanning electron microscope observations of the active layer showed that a high sintering temperature tends to break weak bonds around the triple phase boundary and create strongly connected bonds of LNF and ceria particles in the active layer. AC impedance measurements revealed that this microstructural change reduced the interface resistance and ohmic resistance of the cathode. The reactivity of LNF and SDC in the sintering process was also investigated by X-ray diffraction analysis.

Surface acoustic wave method for in situ determination of the amounts of enzyme–substrate complex formed on immobilized glucose oxidase during catalytic reaction

Surface acoustic waves (SAWs) have been applied to the in situ determination of the amounts of an enzyme–substrate complex formed on an immobilized enzyme surface during the catalytic reaction. The input and output interdigital transducer (IDT) electrodes were photolithographically fabricated on a LiNbO3 crystal for the generation of Rayleigh SAWs and on LiTaO3 crystals for shear horizontal SAWs. The characteristics of propagation of these SAWs in contact with liquid phases were examined. Glucose oxidase (GOX) was immobilized between two IDT electrodes by silane coupling, The functionalization of which was characterized by X-ray photoelectron spectroscopy. The simultaneous determination of the reaction rates and of the adsorbed amounts of glucose was performed by combining an electrochemical method with the SAW method. When the concentration of glucose in the solution was changed, the amount of the GOX–glucose complex formed varied in rough proportion to the reaction rate, which gives experimental evidence for the establishment of pseudo-equilibrium between the adsorbed glucose and glucose in the solution and hence for the validity of the Michaelis–Menten equation. The reaction rate per enzyme–substrate complex was nearly constant, independent of the amount of glucose adsorbed. The formation of the enzyme–substrate complex showed a bell-shaped change with increase in pH, having a maximum at pH 7, which is quite similar to that observed for the dependence of reaction rate on pH. The catalytic functions of the immobilized active GOX were concluded to be almost equivalent.