Hiroshi Komiyama

The hydrogenation of carbon monoxide by amorphous ribbons

Abstract Fifteen amorphous Fe-Ni base alloys containing P and/or B as additives were studied to determine their catalytic activity for the hydrogenation of CO to produce mainly C1 to C3 hydrocarbons. The amorphous state is catalytically stable, if the reaction temperature is maintained considerably below the crystallization point of the amorphous alloy. With the exception of only one composition, the stable activity of the amorphous state is from several to several hundred times higher than the thermodynamically stable crystalline state of the same composition. Both the amorphous and the crystalline catalysts exhibit an activation energy of 100 ± 4 kJ/mol and a rate law −dP CO dt = kP H 2 1.0 P CO 0 . These results suggest that the active sites are of similar nature but different in number for the different structures and compositions of the catalysts.

Comprehensive comparison of efficiency and CO2 emissions between biomass energy conversion technologies - position of supercritical water gasification in biomass technologies.

Abstract Efficiency and CO 2 emissions between various methods of biomass energy conversion are compared from the viewpoint of life-cycle evaluation. As for electricity generation, efficient processes are thermal gasification combined cycle, supercritical water gasification combined cycle, and direct combustion in order of efficiency for low moisture content biomass. Supercritical water gasification combined cycle is the most efficient for high moisture content biomass. Battery electric vehicle, gasoline hybrid electric vehicle, and gas full cell vehicle (FCV) show high efficiency in automobiles. Biomass FCV shows high efficiency in the vehicles utilizing biomass. Biogas combustion is the most efficient for heat utilization. Then, the position of supercritical water gasification in various technologies of energy conversion is examined by modeling an overall energy system. The tradeoff between CO 2 emissions and total cost of technologies is analyzed so that the most cost-effective technology can be determined for different CO 2 emissions constraints. Computed results show that biomass is mainly consumed for electricity and heat generation so as to utilize finite biomass resources efficiently. Transportation fuels are generally made from fossil fuels. Cost-effective processes for CO 2 reduction are thermal gasification and reforming when the present efficiency and prices are assumed. Supercritical water gasification is also one of the optimal processes when the relative cost to fuel cell decreases. Improving heat exchange efficiency also contributes toward enhancing the position of supercritical water gasification in biomass technologies.

Comprehensive perspective on the mechanism of preferred orientation in reactive-sputter-deposited nitrides

Texture control of sputter-deposited nitride films has provoked a great deal of interest due to its technological importance. Despite extensive research, however, the reported results are scattered and discussions about the origin of preferred orientation (PO) are sometimes conflicting, and therefore controversial. The aim of this study is to acquire a clear perspective in order to discuss the origin of PO of sputter-deposited nitrides. Among nitrides, we focus on titanium nitride (TiN), aluminum nitride (AlN), and tantalum nitride (TaN), which are three commonly used nitrides. First, we collected reported experimental results about the relation between operating conditions and PO, because PO is considered to be determined by film formation processes, such as surface diffusion or grain growth, which is affected by operating conditions. We also collected reported results about such PO-determining processes. Then, we categorized the PO-determining processes into an initial stage and a growth stage of film d...

Wind-wave driven circulation on the coral reef at Bora Bay, Miyako Island

Abstract Current records from three surveys at Bora Bay, Miyako Island, all showed strong unidirectional flows. Ocean water entered the lagoon over the shallower western half of the reef flat and exited the lagoon through a channel on the eastern side. Fourier transform of one of the survey data sets showed that this unidirectional flow is modulated on a cycle with a period half as long as the dominant M2 tidal cycle. The prominent features of the observed time-series current profiles were well reproduced using a numerical simulation that includes a depth dependent formulation of the wind-wave forced cross-reef water flow. The water residence times of the lagoon varied from 1.5 h to 3.7 h when calculated directly from the modeled current field, and from 2.0 h to 9.3 h when calculated as the time required for modeled particles to exit the lagoon. These residence times are surprisingly short and may help to explain how this reef supports high net organic production. Furthermore, the short particle residence times show the importance of analyzing currents on time scales smaller than the dominant tidal cycle to understand the fate of organic material produced in coral reefs.

Initial growth and texture formation during reactive magnetron sputtering of TiN on Si(111).

The initial growth and texture formation mechanism of titanium nitride (TiN) films were investigated by depositing TiN films on (111) silicon substrates by using reactive magnetron sputtering of a Ti metallic target under a N2/Ar atmosphere, and then analyzing the films in detail by using transmission electron microscopy (TEM) and x-ray diffraction (XRD). Two power sources for the sputtering, dc and rf, were compared. At the initial growth stage, a continuous amorphous film containing randomly oriented nuclei was observed when the film thickness was about 3 nm. The nuclei grew and formed a polycrystalline layer when the film thickness was about 6 nm. As the film grew further, its orientation changed depending on the deposition conditions. For dc sputtering, the appearance of (111) or (200)-preferred orientations depended on the N2 partial pressure, and the intensity of the preferred orientation increased with increasing film thickness. For rf sputtering, however, when the film thickness was small (for ins...

IN SITU OBSERVATION OF OXIDATION AND REDUCTION OF SMALL SUPPORTED COPPER PARTICLES USING OPTICAL ABSORPTION AND X-RAY DIFFRACTION

Abstract Oxidation and reduction of small copper particles on supports has been studied at temperatures between 298 and 673 K, using in situ observation of optical absorption and X-ray diffraction. The change in chemical composition with time was traced by observing the change in optical absorption spectra at wavelengths between 300 and 800 nm and in X-ray diffraction peak intensity for Cu(111), Cu 2 O(111) and CuO(111) when the ambient gas was alternated between 5% H 2 /He and 1% O 2 /He. We found that the oxidation of small supported copper particles involves a fast reaction of Cu to CuO x ( x ~ 0.67) with Cu 2 O structure and a slow reaction of CuO x ( x ~ 0.67) to CuO x ( x ~ 1). The activation energy of the CuO x ( x ~ 0.67) to CuO x ( x ~ 1) reaction is found to b

Enhanced optical properties of metal‐coated nanoparticles

Metal‐coated, nanometer‐size particles are modeled with a realistic distribution of coating thicknesses. General expressions are given for the local‐field enhancement, absorption, and nonlinear optical response. In addition, heuristic arguments are used to determine the effects of a diffuse, rather than a sharp interface. The linear and nonlinear optical properties are discussed within the context of the effective medium theory for small volume fractions. An efficient method of solution is used with the flexibility to handle an arbitrary number of coatings.

Electrical conductivity of a pure C60 single crystal

The temperature dependence of the electrical conductivity of a C60 single crystal is presented in this letter. The single‐crystal samples free from solvent contamination were grown up to a size of millimeters order by sublimation of C60 powder with oscillation of the crystal temperature. The electrical conductivity of the single crystal was measured at temperatures between 250 and 295 K. The sharp decrease of the electrical conductivity with temperature around 256 K was observed in association with the phase transition of C60.

Cathodic reaction mechanism for dense Sr-doped lanthanum manganite electrodes

Abstract Dense La0.81Sr0.09MnO3 (LSM) electrode was prepared by a laser ablation method and electrochemical measurements were carried out. The electrode impedance was proportional to the film thickness and almost independent of the oxygen partial pressure. Steady-state polarization characteristics were measured and oxygen ionic conductivity of LSM as calculated using Hebb-Wagner polarization method. The slopes of log i − log a0 curves were calculated to be −1 2 . These results suggest that the cathodic reaction mechanism of the dense LSM electrode is quite different from that of porous electrode.

Preparation of low-dielectric-constant F-doped SiO2 films by plasma-enhanced chemical vapor deposition

The delay due to the dielectric constant of an interlayer film results in the limited performance of very large-scale integrated circuits (VLSI). One solution to this problem is the use of a low-dielectric-constant interlayer film such as F-doped SiO2. We were able to obtain F-doped SiO2 films with dielectric constants as low as 2.3 and good step coverage by adding CF4 to SiH4/N2O plasma-enhanced chemical vapor deposition (PECVD). Our study focuses on the mechanism of the decrease in the dielectric constant and that of process improvement. It appears that a decrease in the dielectric constant is due to the decrease in the ionic polarization. The change in the Si–O stretching mode due to CF4 addition seems to be the most important factor in the decrease in the dielectric constant. The improvement of the step coverage and the decrease in the film growth rate are due to the decrease in the sticking probability of the film-forming species.