Showing papers by "National Institute of Advanced Industrial Science and Technology published in 1995"

Photoassisted hydrogen production from a water-ethanol solution: a comparison of activities of AuTiO2 and PtTiO2

Abstract: A comparison of the photocatalytic activity for H 2 generation between AuTiO 2 and PtTiO 2 has been made. The deposition of Au and Pt was carried out using TiO 2 powders in aqueous suspensions containing HAuCl 4 ·4H 2 O or H 2 PtCl 6 ·6H 2 O by deposition-precipitation (DP), impregnation (IMP), photodeposition (FD) and, in the case of Au, by mixing TiO 2 with colloidal gold suspensions (MIX). The main reaction products obtained from the irradiation of an aqueous 5 M C 2 H 5 OH suspension containing AuTiO 2 or PtTiO 2 were hydrogen, methane, carbon dioxide and acetaldehyde. Small amounts of acetic acid were also detected. The overall activity of Au samples was generally about 30% lower than that of Pt samples. The activity of Au samples strongly depended on the method of preparation and decreased in the order AuTiO 2 -FD>AuTiO 2 -DP>AuTiO 2 -IMP>AuTiO 2 -MIX. The activities of the platinum samples were less sensitive to the preparation method and decreased in the order PtTiO 2 -FD>PtTiO 2 -DP≈PtTiO 2 -IMP. Gold and platinum precursors calcined in air at 573 K showed the highest activity towards H 2 generation, followed by a decline in activity with increasing calcination temperature. The H 2 yield was found to be dependent on the metal content on TiO 2 and showed a maximum in the ranges 0.3–1 wt.% Pt and 1–2 wt.% Au. The exposed surface area of gold had only a small influence on the rate of hydrogen generation. On the other hand, the rate of H 2 production was strongly dependent on the initial pH of the suspension. pH values in the range 4–7 gave better yields, whereas highly acidic and basic suspensions resulted in a considerable decrease in the H 2 yield.

The internal structure of an active sea-floor massive sulphide deposit

Abstract: THE hydrothermal circulation of sea water through permeable ocean crust results in rock–water interactions that lead to the formation of massive sulphide deposits. These are the modern analogues of many ancient ophiolite-hosted deposits1–4, such as those exposed in Cyprus. Here we report results obtained from drilling a series of holes into an actively forming sulphide deposit on the Mid-Atlantic Ridge. A complex assemblage of sulphide–anhydrite–silica breccias provides striking evidence that such hydrothermal mounds do not grow simply by the accumulation of sulphides on the sea floor. Indeed, the deposit grows largely as an in situ breccia pile, as successive episodes of hydrothermal activity each form new hydrothermal precipitates and cement earlier deposits. During inactive periods, the collapse of sulphide chimneys, dissolution of anhydrite, and disruption by faulting cause brecciation of the deposit. The abundance of anhydrite beneath the present region of focused hydrothermal venting reflects the high temperatures ( > 150 °C) currently maintained within the mound, and implies substantial entrainment of cold sea water into the interior of the deposit. These observations demonstrate the important role of anhydrite in the growth of massive sulphide deposits, despite its absence in those preserved on land.

Bending of Polyelectrolyte Membrane-Platinum Composites by Electric Stimuli I. Response Characteristics to Various Waveforms.

Abstract: Bending of Polyelectrolyte Membrane–Platinum Composites by Electric Stimuli I. Response Characteristics to Various Waveforms

Carbon dioxide and carbon monoxide hydrogenation over gold supported on titanium, iron, and zinc oxides

Abstract: Gold deposited on TiO2, Fe2O3, ZnO and ZnFe2O4 with high dispersion was found to be active for the hydrogenation of both carbon dioxide and carbon monoxide at temperatures between 150 and 400°C. Over the above catalysts, methanol was produced more readily from carbon dioxide than from carbon monoxide. In particular, Au/ZnO and Au/ZnFe2O4 showed high methanol selectivities from carbon dioxide, which were comparable to those obtained for copper catalysts. As for methanol synthesis from carbon monoxide, only Au/ZnO gave appreciable yields with similar selectivity as copper catalysts. The comparison between experimental and thermodynamic data proved that over all the catalysts except for Au/TiO2 three reactions, namely between carbon dioxide and methanol, carbon monoxide and methanol, carbon dioxide and carbon monoxide, simultaneously reached equilibria at temperatures above 300°C and that the methanol yield decreased with further increase in temperature. Hydrocarbons were formed at high temperatures and the resulting water was also involved in the above equilibria. As a main hydrocarbon product, methane was obtained much more selectively from carbon dioxide than from carbon monoxide. Ethane and propane were also produced from carbon dioxide and carbon monoxide over gold supported on reduced iron oxides.

Large third-order optical nonlinearities in transition-metal oxides

Abstract: ADVANCES in the field of optical computing1–3 will require the development of materials that combine a large nonlinear optical response with a fast response time. For many applications, this translates into a third-order nonlinear optical susceptibility, χ(3), in excess of 10−8 e.s.u., and a response time faster than lO ps (ref. 4). Although a wide range of inorganic5–18 and organic19–21 materials have been found to exhibit a large χ(3), either the response times tend to be far too slow or the materials are not sufficiently stable for device applications. Recently, the transition-metal oxide Fe2O3 was found to have a large χ(3) (ref. 22). Here we show that oxides of several other 3d transition metals show a similarly large nonlinear optical response; moreover, we find that a significant contribution to the overall χ(3) (∼10−8 e.s.u. in the case of V2O5) has a response time of the order of 35 ps.

Preparation of nanometer gold strongly interacted with TiO2 and the structure sensitivity in low-temperature oxidation of CO

Abstract: Gold can be deposited on TiO2 as hemispherical fine particles with diameters smallerthan 4nm by deposition precipitation. Gold hydroxide precipitates with high and homogeneous dispersion on TiO2, most probably on specific surface sites, in the pH range 6 to 10. The calcination of TiO2 with Au(OH)3 in reducing gas atmospheres, such as H2 and CO led to smaller gold particles than in air. In the case of Au/TiO2 samples prepared by deposition precipitation, the catalytic activity for low-temperature CO oxidation was very high and could be observed even at temperatures below 0°C. Physically mixed Au/TiO2 samples though of much lower catalytic activity, showed gradual improvement with increasing calcination temperature. An increase in calcination temperature not only caused particle coagulation but also brought about a stronger interaction with the TiO2 support. The above results therefore indicate that the catalytic activity of Au/TiO2 is sensitive to the structure of the perimeter interface between Au and TiO2.

Photochemical reactions in GeO2-SiO2 glasses induced by ultraviolet irradiation: Comparison between Hg lamp and excimer laser.

Abstract: ${\mathrm{GeO}}_{2\mathrm{\ensuremath{-}}}$${\mathrm{SiO}}_{2}$ glasses prepared by vapor-phase axial deposition were exposed to ultraviolet (uv) radiation from a Hg discharge lamp (4.9 eV) and excimer lasers (KrF laser: 5.0 eV, XeCl laser: 4.0 eV). Two photochemical reaction channels were ascertained: (1) The exposure of the glasses to the Hg lamp radiation (\ensuremath{\sim}16 mW/${\mathrm{cm}}^{2}$) induced Ge E' centers accompanied by bleaching of the absorption band due to oxygen-deficient defects near 5 eV (5-eV band) and the emergence of an intense band near 6.4 eV. (2) The irradiation with KrF and XeCl lasers (power densities of 10 and 90 mJ/${\mathrm{cm}}^{2}$/pulse, respectively, pulse duration of 20 ns) generated two types of paramagnetic defects, electron trapped centers associated with fourfold coordinated Ge ions (GEC) and a self-trapped hole center (STH: bridging oxygen trapping a hole). The former and the latter were considered to be caused via one-photon and two-photon absorption processes, respectively. These alternative reactions proceeded independently depending on the power densities of uv photons. The formation of GEC's was saturated easily by irradiation with KrF laser pulses, and then the conversion of GEC to Ge E' centers was caused by prolonged irradiation.

The influence of the graphitic structure on the electrochemical characteristics for the anode of secondary lithium batteries

Abstract: Carbon is one of the best candidate materials for the negative electrode of rechargeable lithium batteries; however, the electrochemical characteristics are not fully understood in terms of the structure of the materials. The relationship linking the volume ration of the graphitic structure (P{sub 1}) of mesocarbon microbeads (MCMBS) and the electrochemical characteristics has been examined, and it was found that the capacity in the range between 0 to 0.25 V (vs. Li/Li{sup +}) in 1 mol/dm{sup 3} LiClO{sub 4}/ethylene carbonate (EC) + 1,2-diethoxyethane (DEE) electrolyte increased with an increase of the P{sub 1} of the MCMBs. This result shows that the lithium storage mechanism in this potential range is the lithium-intercalation reaction into the graphitic layers with the AB or ABC stacking. On the other hand, MCMB heat-treatment temperature (HTT) 1,000 C showed much larger capacity in the range between 0.25 to 1.3 V than higher HTT MCMBs, and it is suggested the interaction among each graphite layer is weaker in nongraphitized carbon than that in well-graphitized ones.

Micro catheter system with active guide wire

Abstract: In this paper, we propose a new prototype model of micro-catheter with active guide wire that has two bending degrees of freedom. The design and fabrication methods of this micro active catheters (MAC) are described. Prototype models are 3Fr, 4Fr, 6Fr (1Fr=1/3 mm) in diameter and consist of catheter tube and active guide wire with ionic conducting polymer film actuator on its front end as the servo actuator. The bending characteristics of the MAC have been measured by application of electricity in physiological saline solution. We also modeled this MAC for characteristic evaluation. Experimental results show that the model of the active catheter is reasonable for practical applications. By using simulators (whose conditions are similar to those of a body cavity), we also carried out simulation experiments "in vitro". The experimental results indicate that the proposed MAC is applicable to intracavity operations.

Application of STM Nanometer-Size Oxidation Process to Planar-Type MIM Diode.

Abstract: Ultra fine oxidized titanium (Ti) lines 18 nm wide and 3 nm high have been formed on the surface of a 4 nm Ti layer on a SiO 2 /Si substrate using the scanning tunneling microscope [STM] tip as a selective anodization electrode. The dependence of the size of the oxidized titanium line on the various parameters is investigated. The formed oxidized titanium line has resistivity of 2 × 10 4 ohm cm, which is a value seven orders of magnitude higher than that of the deposited Ti layer. The oxidized Ti line is used in the planar type metal-insulator-metal [MIM] diode, and works as an energy barrier for the electron. The energy barrier height of the oxidized Ti line is found to be δE g = 0.25 eV

Biocompatible whiskers with controlled morphology and stoichiometry

Abstract: Hydroxyapatite whiskers have been prepared by the hydrothermal method. The crystals had diameter, length, and aspect ratio in the range of 1–10 μm, 30–50 μm, and 5–20, respectively. Their Ca/P molar ratio varied from 1.59 to 1.62. The morphology of the crystals can easily be controlled by the concentrations of species in the starting solution, while the Ca/P ratio is almost independent of them. Through the reaction with calcite powder at 600 °C, the Ca/P ratio of the whiskers has been improved even to the stoichiometric value of 1.67. Taking into account morphology and chemical composition of the HAp whiskers, they should not be health hazardous and may find applications as substitutes for asbestos and other fibrous materials which presently have restricted use because of their carcinogenic natures.

Cerium impregnated H-mordenite as a catalyst for shape-selective isopropylation of naphthalene. Selective deactivation of acid sites on the external surface

Abstract: The impregnation of cerium is the effective method for the deactivation of external acid sites of H-mordenite. The selectivity of 2,6-DIPN in the isopropylation of naphthalene was enhanced by the impregnation with such a large amount as 30–50 wt.-% of cerium without significant decrease of catalytic activity. The highest selectivity of 2,6-DIPN was achieved up to 70% over a highly dealuminated H-mordenite, (HM(128); SiO 2 /Al 2 O 3 = 128, with 30 wt.-% of cerium. The enhancement of the selectivity is ascribed to the deactivation of external acid sites judging from the activity of the cracking reaction of 1,3,5-triisopropylbenzene. The effective pore radius was not reduced by the modification. The ceria is highly dispersed only on the external surface of H-mordenite without any formation of new kinds of acid sites. The 129 Xe NMR observation suggfests that cerium is not in the pores, but on the external surfaces. The deactivation of the external acid sites is a characteristic property for cerium. Lanthanum and neodymium inhibited catalytic activity of the isopropylation because the pores were narrowed by their impregnation. A possible reason of the deactivation is ascribed to the amphoteric property of ceria.

Transformation of C60 fullerenes into a superhard form of carbon at moderate pressure

Abstract: A very hard and conducting form of carbon has been obtained from pure C60 fullerenes, as well as its mixture with aluminium at nonhydrostatic pressures of 2.6–3 GPa and a temperature of 700 °C. The hardness of the material is more than 4000 kg/mm2. Its electrical conductivity is about 100 Ω−1 cm−1 and is weakly dependent on temperature in the range 4.2–300 K. X‐ray diffraction and Raman measurements show lack of the long‐range crystalline order in the transformed material.

Langmuir-Blodgett film of amphiphilic C60 carboxylic acid

Abstract: An amphiphilic C 60 molecule with a substituent having a hydrophilic carboxylic group at the end was found to form a monolayer at the air-water interface and the structure of the Langmuir-Blodgett (LB) film (Z-type) was elucidated. The shortest distance between the C 60 was estimated to be 0.95 nm using a limiting area per molecule of 0.78 nm 2 at the air-water interface, assuming the close packing of the C 60 moiety in two dimensions. Adjacent C 60 moieties have an electronic interaction which was shown in the red-shift of the characteristic bands in the UV/vis absorption spectrum of the LB film compared with that of a solution spectrum. Several lines of evidence suggested that the molecule has an oblique orientation in the LB film and exists in a pairwise manner due to the dimer formation of the carboxylic groups within a monolayer, not between the adjacent monolayers. The AFM observations revealed that the surface of a single-layer LB film, which consists of domains of ca. 0.1 μm in diameter, is rather smooth and that the undulation is ±1 nm for most of the surface except for defects such as vacancy and bilayer regions. The area fractions of the monolayer, the vacancy, and the bilayer regions were estimated to be 88 ± 7, 7 ± 5, 5 ± 3%, respectively. The layer structure was also confirmed using X-ray diffraction analyses which indicate the repeat distance of ca. 2.6 nm along the surface normal of the multilayer LB film.

An Investigation of Anodes for Direct‐Oxidation of Carbon in Solid Oxide Fuel Cells

Abstract: Several transition metal carbides were examined as anodes for the internal direct-oxidation of carbon in solid oxide fuel cells Observed values of open-circuit voltage of carbide anode cells were found to be in the same order as the oxygen potentials calculated for the respective metal carbide/metal oxide equilibrium All the carbide anodes investigated showed higher performance in polarization curves than graphite The chemical stability of anodes under a polarized condition was estimated by thermochemical calculations Based on this calculation and outlet gas analysis from the cells, a VC anode was able to activate carbon, while ZrC and TiC anodes were not able to activate carbon due to the oxidation of carbides The redox reaction of anodes plays an important role for activating carbon in carbide anode cells

An IR study of CO-sensing mechanism on Au/ZnO

Abstract: An FTIR and quadrupole mass study of the adsorption and oxidation of CO on an Au/ZnO sample with 16 O 2 and 18 O 2 is presented. The results indicate that CO adsorbed on gold sites at the perimeter interface with ZnO reacts with surface lattice oxygens at the oxide surface to form carbonate-like intermediates. This reaction and the decomposition of the intermediates can be assumed to be mainly responsible for the conductivity changes of the semiconductive metal oxide caused by CO in air. Oxygen, present in the mixture and adsorbed on gold vicinal sites, makes the nucleophilic attack of surface oxygens on the CO easier as a consequence of an electron-withdrawing effect. This effect produces a positivization of the carbon of adsorbed CO by an inductive effect and activates the reactivity of support lattice oxygens on the CO.

Formation of a Methoxy-Modified Interlayer Surface via the Reaction between Methanol and Layered Perovskite HLaNb2O7·xH2O

Abstract: The reactions between methanol (CH{sub 3}OH, CH{sub 3}OD, CD{sub 3}OD, {sup 13}CH{sub 3}OH) and layered HLaNb{sub 2}O{sub 7}{center_dot}xH{sub 2}O were investigated. X-ray powder diffraction (XRD) analysis showed that a peak corresponding to the basal spacing of HLaNb{sub 2}O{sub 7}{center_dot}xH{sub 2}O (1.05 nm) disappeared and a new peak appeared at 1.18 nm. Carbon-13 NMR spectra revealed the presence of two environments of the methyl group; the broad 67 ppm signal is ascribed to the rigid species located in the interlayer space, and the 50 ppm signal is ascribed to mobile methanol on the external surface. The amount of the latter species was negligibly small. Deuterium NMR spectra revealed the presence of a Pake doublet with an effective quadrupole coupling constant (QCC) of 47 kHz and an asymmetry factor ({eta}) of zero, indicating that the CD{sub 3}O group was rigidly bound to the interlayer surface. In addition, when both CD{sub 3}OD and CH{sub 3}OD were used, no signal corresponding to the OD group was observed. Hence, although XRD results can be interpreted as intercalation of methanol, the {sup 2}H NMR results indicate that methanol was dissociatively adsorbed to the interlayer surface. The observed very high thermal stability of the methyl group ismore » consistent with methoxy formation. The structure of the product is discussed on the basis of the results with larger n-alcohols.« less

Spin Correlation in High-Tc Cuprate HgBa2Ca2Cu3O8+δ with Tc=133 K—An Origin of Tc-Enhancement Evidenced by 63Cu-NMR Study

Abstract: The Knight shift, the nuclear spin-lattice relaxation rate, 1/ T 1 , and the transverse relaxation rate, 1/ T 2G , of 63 Cu have been separately measured for the square and the pyramidal CuO 2 planes in HgBa 2 Ca 2 Cu 3 O 8+δ (Hg1223) with the highest transition temperature, T c =133 K to date. From the quantitative analysis of 1/ T 1 and 1/ T 2G , it is shown that the product of the staggered susceptibility and the characteristic energy of spin fluctuations around a zone boundary, χ Q Γ Q , for the square CuO 2 plane site is larger than that for YBa 2 Cu 3 O 7 (YBCO 7 ), although that for the pyramidal CuO 2 plane site is almost the same. This enhancement of χ Q Γ Q for the square site is considered to be responsible for the higher T c in Hg1223 than in YBCO 7 .

Two-Dimensional Dynamic Patterns in Illuminated Langmuir Monolayers

Abstract: Purely light-driven spatiotemporal pattern formation has been found to take place in a liquid-crystalline Langmuir monolayer consisting of an amphiphilic azobenzene derivative, undergoing the trans ↔ cis photoisomerizations. The Langmuir monolayer is in a smectic-C-like liquid crystal phase, whose two-dimensional orientation is easily perturbed by slight conformation changes in the constituent molecules. On illumination with a linearly polarized light, a collective and global in-plane reorientation of the azobenzene chromophores is induced over an existing static stripe texture, which finally yields polarization-dependent steady state orientational patterns. Prolonged photoexcitation generates sustained traveling and solitary waves, associated with variations in molecular tilt directions. The liquid crystallinity of the monolayer allows these orientational responses to occur even at an extremely weak light power at least 2 orders of magnitude smaller than that known in previous photoreorientation studies of azobenzene chromophores.

Optical CO detection by use of CuO/Au composite films

Abstract: Composite films consisting of a thin CuO layer and ultrafine Au particles have been found to be usable for the optical detection of CO in air. The optical absorption of CuO/Au composite films increases due to CO and recovers reversibly in air free of CO. The largest absorbance change due to CO is in the 700-800 nm wavelength region, with the absorbance change enhanced by increasing temperature or increasing CO concentration. We assume that the absorbance change of the CuO/Au film occurs due to the change in the electronic structure of the ultrafine Au particles as a result of their interactions with atmospheric gas.

Excitonic emissions from CuInSe2 on GaAs(001) grown by molecular beam epitaxy

Abstract: CuInSe2 epitaxial films grown on (001)‐oriented GaAs substrates by molecular beam epitaxy have been characterized by means of low temperature photoluminescence spectroscopy at T=2–102 K. Distinct emission lines were observed near the band gap, and have been investigated further with varying sample temperature. An emission at 1.0386 eV (EX1) became broader with increasing sample temperature, and still remained up to T=102 K. A distinct, sharp emission at 1.0311 eV (IX1) which disappeared at a significantly lower temperature than the other peaks was observed only in films with weak donor‐related emissions. We attribute such emissions to the ground‐state free exciton [FEn=1] and exciton bound to neutral acceptor [A0,X], respectively. The band gap of CuInSe2 epitaxial films was also determined to be Eg=1.046 eV at 2 K using the reported exciton binding energy of Eex=7 meV.