Solid-state source of atomic oxygen for low-temperature oxidation processes: application to pulsed laser deposition of TiO2:N films

An atomic oxygen (AO) source has been redesigned to coordinate with a pulsed laser deposition system and used to grow nitrogen-doped TiO(2) films by deposition of TiN and simultaneous irradiation of the substrate with AO. The AO source uses an incandescently heated thin tube of zirconia as an oxygen permeation media to generate pure AO of low kinetic energy. The emission flux is calibrated using a silver-coated quartz crystal microbalance. The thin shape of the probe and transverse emission geometry of this emission device allow the emission area to be positioned close to the substrate surface, enhancing the irradiation flux at the substrate. AO irradiation is crucial for formation of TiO(2) phases via oxidation of the deposited TiN laser plume, and is effective for decrease of the substrate temperature for crystallization of anatase phase to as low as around 200 °C.     

Paper-structured catalyst for the steam reforming of biodiesel fuel

Architectonics of the paper-structured catalyst for the application to the biofuel reformer or direct internal reforming SOFC (DIRSOFC) was studied. Inorganic fiber network, “paper”, composed of yttria-stabilized zirconia (YSZ) fiber (Zf), alumina fiber (Af) and inorganic binder (Al₂O₃ sol (As) or ZrO₂ sol (Zs) or CeO₂ sol (Cs)) was prepared by a simple paper-making process. Then, the catalytic activities of the Ni and Ni–MgO loaded papers called “paper-structured catalysts (PSCs)” for the steam reforming of biodiesel fuels (BDFs) were evaluated. Ni–MgO loaded PSC using Cs as an inorganic binder, Ni–MgO/ZfAfCs, exhibited excellent performance over Ru/γAl₂O₃ catalyst beads. Formation of light hydrocarbons, especially C₂H₄, was eliminated and water–gas shift reaction was more promoted compared to the catalyst beads.     

Influence of thermal and flow boundary perturbations on convection heat transfer characteristics: Numerical analysis based on adjoint formulation

A numerical approach based on adjoint formulation of convection heat transfer is proposed to predict the change of heat transfer characteristics for arbitrary thermal and flow boundary perturbations. In order to obtain the adjoint system of the convection heat transfer problem, we formally linearize the governing equations by the perturbation method and then derive the adjoint system for the perturbation system. As a result, it is shown that the numerical solutions of the base and the adjoint problems enable us to predict the changes of heat transfer characteristics, such as the change of total heat transfer rate or the change of temperature at a specific location, when the thermal and flow boundary conditions are perturbed. An application example is presented to demonstrate the proposed method. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(1): 1–12, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10065     

Estimation of flooding in PEMFC gas diffusion layer by differential pressure measurement

The flooding, especially in gas diffusion layer (GDL), is one of the critical issues to put PEMFC to practical use. However, the experimental data of the flooding in GDL is so insufficient that the optimization design related to the water management for GDL has not established. In this study we developed a method to estimate the water saturation, namely the ratio of liquid water to pore volume in GDL. We fabricated a simple interdigitated cell where the supply gas is enforced to flow under rib. This structure enables to estimate the liquid water ratio in GDL by the measurement of differential pressure through the cell. We operated the cell and measured the differential pressure, and succeeded in estimating the water saturation, which changed largely with changing cell operation condition. In addition to this deferential pressure measurement, we measured the ionic resistance in polymer electrolyte membrane by ac impedance method. We evaluated and discussed the influence of the water saturation on cell voltage.     

Inelastic stress-strain response for notched specimen of Cr-1Mo steel at 600°C

Following a series of cooperative studies A-I and A-II (phase III) concerning the inelastic behaviour of high temperature materials under uniform state of stress, finite element analyses were carried out on circumferential notched cylinders subjected to plasticity-creep interaction conditions. Using an electric capacitance type extensometer “Strain-Pecker”, which is capable of measuring a local strain response with a gauge length of 0.5 mm under high temperature conditions, stress-strain responses for both global and local regions near the notch root were evaluated. Ten kinds of inelastic constitutive model were introduced into a finite element code, and the responses for four kinds of loading pattern were examined for two types of notch shape.     

IR study of reaction of 2‐butene adsorbed on deuterated ZSM‐5 and mordenite

The dehydrogenation of ethylbenzene to styrene was studied over single-crystalline iron oxide model catalyst films grown epitaxially onto Pt(111) substrates. The role of the iron oxide stoichiometry and of atomic surface defects for the catalytic activity was investigated by preparing single-phased Fe₃O₄(111) and α-Fe₂O₃(0001) films with defined surface structures and varying concentrations of atomic surface defects. The structure and composition of the iron oxide films were controlled by low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES), the surface defect concentrations were determined from the diffuse background intensities in the LEED patterns. These ultrahigh vacuum experiments were combined with batch reactor experiments performed in water–ethylbenzene mixtures with a total gas pressure of 0.6 mbar. No styrene formation is observed on the Fe₃O₄ films. The α-Fe₂O₃ films are catalytically active, and the styrene formation rate increases with increasing surface defect concentration on these films. This reveals atomic surface defects as active sites for the ethylbenzene dehydrogenation over unpromoted α-Fe₂O₃. After 30 min reaction time, the films were deactivated by hydrocarbon surface deposits. The deactivation process was monitored by imaging the surface deposits with a photoelectron emission microscope (PEEM). It starts at extended defects and exhibits a pattern formation after further growth. This indicates that the deactivation is a site-selective process. Post-reaction LEED and AES analysis reveals partly reduced Fe₂O₃ films, which shows that a reduction process takes place during the reaction which also deactivates the Fe₂O₃ films.     

Molecular orbital study of pyrolytic carbons based on small cluster models

Molecular orbital calculations are applied to the Raman scattering and ESR of pyrolytic carbons on the basis of small cluster models. The E_2g and A_1g modes of C-C stretching vibrations of coronene, hexabenzocoronene, and circumcoronene, which belong to D_6h carbon clusters, are shown to appear around the 1550 cm⁻¹ and 1360 cm⁻¹ bands, respectively. The unpaired electrons observed in pyrolytic carbons are attributed to the bond-alternation defects on odd-numbered carbon clusters that are more easily mobile than those of trans-polyacetylene.     

Rising behavior of air bubbles in superposed liquid layers

An air bubble that passes through a horizontal interface from a lower layer of Freon-113 to an upper layer of aqueous glycerol forms a two-phase bubble in the upper layer as a result of entrainment of a certain volume of Freon-113 from the lower layer. The volume of entrained Freon-113 and the rise velocity of such a two-phase bubble have been measured. The former increases with an increase of the bubble size irrespective of the viscosity of the upper liquid. The latter is somewhat lower than that of a normal air bubble of the same size.     

Physicochemical properties of Ba(Zr,Ce)O3-δ-based proton-conducting electrolytes for solid oxide fuel cells in terms of chemical stability and electrochemical performance

To enhance the power generation efficiency of solid oxide fuel cells (SOFCs), the use of proton-conducting solid solutions of doped BaCeO₃ and doped BaZrO₃, with formulas of the Ba(Zr_0.1Ce_0.7Y_0.1X_0.1)O_3-δ (X = Ga, Sc, In, Yb, Gd), was investigated as SOFCs electrolyte materials with respect to both chemical stability and electrical conductivity. Regarding chemical stability, the weight changes of each material were measured under a CO₂ atmosphere in a temperature range of 1200 °C–600 °C.Higher chemical stability was observed for dopant ions with smaller radii. Regarding conductivity, the dependences of the total conductivities on the oxygen partial pressure and temperature were measured in the temperature range of 600 °C–900 °C. In each material, the total conductivity was proportional to the oxygen partial pressure to the 1/4 power at high oxygen partial pressures, as previously observed for accepter-doped proton-conducting perovskite-type oxides. The derived conductivities for each type of charge carrier showed that the hole conductivity increased with the ionic conductivity. Based on the measured data, the leakage current densities were calculated for SOFCs with each of the investigated electrolyte materials and an area-specific resistance of 0.383 Ωcm². BZCYSc showed the minimum leakage current density, with a value of 3.7% of the external current density at 600 °C. Therefore, this study indicates that BZCYSc is the most desirable among the materials investigated for use as SOFCs electrolyte. However, for BZCYSc to be used as SOFCs electrolyte material, a protective layer is needed to ensure its chemical stability.     

Module shuffling of a family F/10 xylanase: replacement of modules M4 and M5 of the FXYN of Streptomyces olivaceoviridis E-86 with those of the Cex of Cellulomonas fimi

To facilitate an understanding of structure–function relationships,chimeric xylanases were constructed by module shuffling betweenthe catalytic domains of the FXYN from Streptomyces olivaceoviridisE-86 and the Cex from Cellulomonas fimi. In the family F/10xylanases, the modules M4 and M5 relate to substrate bindingso that modules M4 and M5 of the FXYN were replaced with thoseof the Cex and the chimeric enzymes denoted FCF-C4, FCF-C5 andFCF-C4,5 were constructed. The k_cat value of FCF-C5 for p-nitrophenyl-ß-D-cellobiosidewas similar to that of the FXYN (2.2 s^–1); however, thek_cat value of FCF-C4 for p-nitrophenyl-ß-D-cellobiosidewas significantly higher (7.0 s^–1). The loss of the hydrogenbond between E46 and S22 or the presence of the I49W mutationwould be expected to change the position of Q88, which playsa pivotal role in discriminating between glucose and xylose,resulting in the increased k_cat value observed for FCF-C4 actingon p-nitrophenyl-ß-D-cellobioside since module M4directly interacts with Q88. To investigate the synergisticeffects of the different modules, module M10 of the FCF-C4 chimerawas replaced with that of the Cex. The effects of replacementof module M4 and M10 were almost additive with regard to theK_m and k_cat values.