Design and Preparation of Impregnated Catalysts

Solid catalysts in common use are typically in the form of small metal crystallites dispersed on the internal surface of the porous support. Advantages of these supported-metal catalysts lie in their high surface-to-volume ratio and the high thermal stability endowed by the dispersion. Such catalysts are commonly produced by liquid-phase impregnation in which a dry or wet pellet of the porous support is impregnated with a solution of a compound of the desired catalytic constituent. During impregnation and subsequent drying, small crystallites of the catalyst precursors are deposited on the internal surface of the support material. The impregnation and drying steps involve mass and /or heat transfer processes which often do not reach equilibrium, resulting in nonuniform concentration profiles of impregnant, or “impregnation profiles” along the radius of the support pellet.     

Thermodynamic and Spectroscopic Studies on Am(III) and Eu(III) in the Extraction System of N,N,N',N'-Tetraoctyl-3-Oxapentane-1,5-Diamide in n-Dodecane/Nitric Acid

Abstract

Thermodynamic parameters (ΔG, ΔH, and ΔS) for the extraction of trivalent f-elements, M(III) (M = Am, Eu), with N,N,N',N'-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) were determined in nitric acid/n-dodecane extraction system. The extraction of M(III) with TODGA was more exothermic than those with octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) and dihexyl-N,N-diethylcarbamoylmethyl phosphonate (DHDECMP). The difference in ΔH between the extractants was attributed to the difference in the binding mode between them, i.e. tridentate (TODGA) and bidentate (CMPO and DHDECMP). In addition, from the results of luminescence lifetime measurement, it was found that the inner-sphere of extracted Eu(III) was dehydrated completely, and occupied by TODGA and/or NO₃ ^?.     

Generation of high photocurrent in three-dimensional silicon quantum dot superlattice fabricated by combining bio-template and neutral beam etching for quantum dot solar cells

We fabricated a three-dimensional (3D) stacked Si nanodisk (Si-ND) array with a high aspect ratio and uniform size by using our advanced top-down technology consisting of bio-template and neutral beam etching processes. We found from conductive atomic microscope measurements that conductivity became higher as the arrangement was changed from a single Si-ND to two-dimensional (2D) and 3D arrays with the same matrix of SiC, i.e., the coupling of wave functions was changed. Moreover, our theoretical calculations suggested that the formation of minibands enhanced tunneling current, which well supported our experimental results. Further analysis indicated that four or more Si-NDs basically maximized the advantage of minibands in our structure. However, it appeared that differences in miniband widths between 2D and 3D Si-ND arrays did not affect the enhancement of the optical absorption coefficient. Hence, high photocurrent could be observed in our Si-ND array with high photoabsorption and carrier conductivity due to the formation of 3D minibands.     

Temperature–field phase diagrams in Pb(Zn1/3Nb2/3)O3–4.5%PbTiO3 II

Temperature and field dependences of the dielectric constants under the DC biasing fields along the [011]- and [111]-directions in the cubic coordinate in Pb(Zn_1/3Nb_2/3)O₃–4.5%PbTiO₃ were investigated. The temperature–field phase diagrams were constructed in the field range below 10 kV/cm. It was confirmed that in Pb(Zn_1/3Nb_2/3)O₃–4.5%PbTiO₃ the intermediate tetragonal phase as a ground state of the system exists even without the DC field, and the tetragonal phase disappears in the external field above 4 and 3 kV/cm along the [011]- and [111]-directions, respectively. The field-induced orthorhombic-phase in the field along the [011]-direction was also found.     

Synthesis and properties of multiferroic 0.7BiFeO3−0.3BaTiO3 thin films by Mn doping

Multiferroic BiFeO₃?BaTiO₃ thin films that simultaneously exhibit ferroelectricity and ferromagnetism at room temperature were prepared by chemical solution deposition. Perovskite single-phase 0.7BiFeO₃?0.3BaTiO₃ thin films were successfully fabricated in the temperature range 600–700 °C on Pt/TiO_x/SiO₂/Si substrates. As the crystallization temperature was increased, grain growth proceeded, resulting in higher crystallinity at 700 °C. Although the 0.7BiFeO₃?0.3BaTiO₃ thin films exhibited poor polarization (P)?electric field (E) hysteresis loops owing to their low insulating resistance. The leakage current at high applied fields was effectively reduced by Mn doping at the Fe site of the 0.7BiFeO₃?0.3BaTiO₃ thin films, leading to improved ferroelectric properties. The 5 mol% Mn-doped 0.7BiFeO₃?0.3BaTiO₃ thin films simultaneously exhibited ferroelectric polarization and ferromagnetic magnetization hysteresis loops at room temperature.     

Titanium Diboride–Tungsten Diboride Solid Solutions Formed by Induction-Field-Activated Combustion Synthesis

Solid solutions of titanium diboride–tungsten diboride (TiB₂–WB₂) were synthesized by induction-field-activated combustion synthesis (IFACS) using elemental reactants. In sharp contrast to conventional methods, solid solutions could be formed by the IFACS method within a very short time, ∼2 min. Solutions with compositions ranging from 40–60 mol% WB₂ were synthesized with a stoichiometric ratio (Ti + W)/B =½; however, samples with excess boron were also made to counter the loss of boron by evaporation. The dependence of the lattice constants of the resulting solid solutions on composition was determined. The "a" parameter decreased only slightly with an increase in the WB₂ content, whereas the "c" parameter exhibited a significant decrease over the range 40–60 mol% WB₂. Solid-solution powders formed by the IFACS method were subsequently sintered in a spark plasma sintering (SPS) apparatus. After 10 min at 1800°C, the samples densified to relative density 86%. XRD analysis showed the presence of only the solid-solution phase.     

Dissolving states of cellulose and chitosan in trifluoroacetic acid

Chemical structures of cellulose and chitosan dissolved in trifluoroacetic acid (TFA) and those of cellulose and chitosan films cast from their TFA solutions were studied by ¹³C-NMR and infrared (IR) spectroscopy. Cellulose is trifluoroacetylated selectively at the C6–hydroxyl groups in the TFA solution, and chitosan is dissolved in TFA by forming amine salts with TFA at the C2–amine groups. IR analyses of cellulose films cast from its TFA–acetic acid solutions showed that partly trifluoroacetylated cellulose in the solution state turns to partly acetylated cellulose in the solid state during evaporation of the solvents in air by the ester interchange. Chitosan films cast from its TFA–acetic acid solutions still have the amine salts with TFA. These acetyl groups in cellulose films and TFA in chitosan films are removable by soaking the films in 1N NaOH at room temperature for 1 day.     

Enantioselective Hosts for Neutral Derivatives of Amino Acids

A series of macropolycyclic receptors for hydrogen bond donor/acceptor guests were prepared and studied. Molecular modeling and X-ray crystallography provided structural information, while NMR titration studies allowed determination of free energies of association. Some of die receptors prepared showed enantioselectivity as high as 3 kcal/mol in binding derivatives of simple amino acids in organic solvents. These studies show that conformational homogeneity is one of the most important characteristics of a selective host and that molecular modeling can play an important role in the design of such substances.     

The Influence of ZrO2 Additions on Al2O3 Evaporation and AlN Crystal Growth by Thermal Nitridation of Al2O3–ZrO2 Pellets

The effects of ZrO₂ additions to Al₂O₃ were investigated to improve the evaporation rate of Al₂O₃ for bulk AlN crystal growth. The evaporation rate of Al₂O₃ increased concomitantly with increasing ZrO₂ concentration under a nitrogen gas stream at 2223 K. The ZrO₂ was predominantly nitrided. The nitridation of ZrO₂ kept the local oxygen partial pressure high at the pellet surface, which suppressed the nitridation of Al₂O₃. The nitridation of ZrO₂ caused the outward diffusion of ZrO₂ (Zr⁴⁺ and O^2?) in the pellet, which was accelerated further by the presence of Al₂O₃–ZrO₂ liquid phase in grain boundaries, leading to the prompt formation of ZrN porous layer on the pellet surface. The suppressed nitridation of Al₂O₃ and the formation of porous ZrN layer were the reasons for the enhanced evaporation of Al₂O₃, leading to enhanced bulk AlN growth.     

An analysis of interactive influences in Mazda’s Yokokai Keiretsu

In a keiretsu, i.e., a set of companies with interlocking business relationships, it is important for corporate management to identify those companies over which they reciprocally exercise greater influence and power. In this article we employ a DEcision MAking Trial and Evaluation Laboratory (DEMATEL) to illustrate the reciprocal influence of each company in Mazda’s Yokokai keiretsu, as measured by the number of transactions and cross-shareholdings. Furthermore, we calculate the centrality index of each company, and then analyze the relationship between centrality index and influence in order to identify the determinants of the influence. Based on the findings, we identify some characteristics of effective relationships which have important managerial implications.