Organic–silicate hybrid catalysts based on various defined structures for Knoevenagel condensation

Two types of organic–inorganic hybrid base catalysts are prepared. Organic-functionalized molecular sieves (OFMSs), particularly “amine-immobilized porous silicates”, are designed based on common idea to immobilize catalytic active sites on silicate surface. Silicate–organic composite materials (SOCMs), such as “ordered porous silicate–quaternary ammonium composite materials”, are the precursors of ordered porous silicates obtained during the synthesis. Both the OFMS and the SOCM are used as the catalysts for Knoevenagel condensation. Among the OFMSs, there is clear tendency that the use of molecular sieve with larger pore volume and/or surface area gives the product in higher yield. Aminopropylsilyl (AP)-functionalized mesoporous silicates such as AP-MCM-41 gives the product in high yield under mild conditions. No loss of activity is observed after repeated use for three times. The SOCMs are also active for the same reaction. The precursors of the mesoporous silicates are more active than those of microporous silicates. This material can be repeatedly used without significant loss of activity. High activity is not due to the leached species. The active sites of the SOCM catalysts are considered to be SiO⁻ moieties located on the pore-mouth. Activity of the SOCM increases when the reaction is carried out without solvent, whereas decrease in activity of the OFMS is observed in the solvent-free system.     

Design of new catalysts for ecological high-quality transportation fuels by combinatorial computational chemistry and tight-binding quantum chemical molecular dynamics approaches

Recently, we introduced a concept of combinatorial chemistry to computational chemistry and proposed a new method called “combinatorial computational chemistry”, which enables us to perform a theoretical high-throughput screening of catalysts. In the present paper, we reviewed our recent application of our combinatorial computational chemistry approach to the design of new catalysts for high-quality transportation fuels. By using our combinatorial computational chemistry techniques, we succeeded to predict new catalysts for methanol synthesis and Fischer–Tropsch synthesis. Moreover, we have succeeded in the development of chemical reaction dynamics simulator based on our original tight-binding quantum chemical molecular dynamics method. This program realizes more than 5000 times acceleration compared to the regular first-principles molecular dynamics method. Electronic- and atomic-level information on the catalytic reaction dynamics at reaction temperatures significantly contributes the catalyst design and development. Hence, we also summarized our recent applications of the above quantum chemical molecular dynamics method to the clarification of the methanol synthesis dynamics in this review.     

Synthesis and thermal stability of novel anion exchange resins with spacer chains

Spacer-modified anion exchange resins were prepared by suspension copolymerization of ω-bromoalkylstyrenes or ω-bromoalkyloxymethylstyrenes with 2–8 mol % of divinylbenzene, followed by quaternization with trimethylamine. The thermal stability of the spacer-modified anion exchangers of the OH form was examined by standing the resins in deionized water at 100–140°C for 30–90 days. The anion exchangers with alkylene chains such as butylene or heptylene groups between the benzene ring and the quaternary nitrogen exhibited higher thermal stability compared with commercial, strongly basic anion exchangers with benzylic ammonium groups. The thermal stability of the exchangers with butyleneoxymethylene or hexyleneoxymethylene spacers was also higher than that of the commercial exchangers. The exchanger with the propyleneoxymethylene spacer, however, had less stability than did the commercial ones. The decreased stability of this spacer-modified exchanger is due to the accelerated degradation of the spacer chain via Hofmann elimination. The excellent stability of the anion exchangers with alkylene or alkyleneoxymethylene spacers, except propyleneoxymethylene, results from the structure of the exchangers, where there are no reactive benzylic carbons, which are attached directly to the quaternary nitrogen. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1161–1167, 1997     

Preparation of bismuth nanowire encased in quartz template for Hall measurements using focused ion beam processing

ABSTRACT: Forming electrodes on opposite sides of an individual bismuth nanowire was attempted to prepare for Hall measurements. Although a 1-mm-long bismuth nanowire which is completely covered with a quartz template has been successfully fabricated to prevent oxidation, it is very difficult to attach Hall electrodes on the opposite sides of the nanowire due to the quartz covering. One side of the cylindrical quartz template was removed by polishing without exposure of the nanowire to the atmosphere; the thickness between the polished template surface and the nanowire was estimated to be several micrometers. Focused ion beam processing was successfully employed to expose both surfaces of the nanowire under high vacuum by removing part of the quartz template. A carbon thin film was then deposited in situ on the wire surface to fabricate an electrical contact on the bismuth nanowire sample. Furthermore, the energy dispersive X-ray analysis was performed to the area processed by focused ion beam, and the bismuth component of the nanowire was successfully detected. It was confirmed that the focused ion beam processing was applicable to attach electrodes to bismuth nanowire for Hall measurement.     

Fine structure of tooth enamel in the yellowing human teeth: SEM and HRTEM studies

Objective : The aim of this study was to clarify an influence of the fine structure of human tooth enamel to the yellowing teeth. Materials and methods : Sound maxillary first premolars of 15–50‐year‐old females that were extracted for the orthodontic treatment were used as the test samples. The tooth enamel sections of these teeth that prepared by ion polishing were observed by scanning electron microscopy (SEM). Furthermore, the fine structure of substance filling the inter‐rod spaces was analyzed by high resolution transmission electron microscopy (HRTEM). Results : In white tooth, the inter‐rod spaces were observed at the width of about 0.1 μm, while in yellow tooth, the inter‐rod spaces were not clearly observed by SEM. HRTEM observations revealed for the first time that the inter‐rod spaces were filled with fine particles of poorly crystallized hydroxyapatite in the yellow tooth. In yellow tooth, it was considered that the color of the inner dentin was recognized due to the decrease of light scattering by filling the tooth enamel inter‐rod spaces. The generation of particles in the tooth enamel inter‐rod spaces was considered to be caused by the long‐time progression of calcification. Conclusions : These results suggested that the change in fine structure, filling in inter‐rod spaces of tooth enamel, was related to progression of calcification in the inter‐rod spaces with advancing age and one of the factors of yellowness of human tooth. Microsc. Res. Tech. 79:14–22, 2016. © 2015 Wiley Periodicals, Inc.     

Luminescence properties of La1−χTmχTa7O19

The luminescence properties of Tm³⁺ in La_1−χTm_χTa₇O₁₉ solid solutions were examined systematically. The substitution of Tm³⁺ for La³⁺ was carried out by a decomposition reaction of nitrates involving the corresponding constituents at 1200 °C in air. X-Ray diffraction patterns of the solid solutions indicated that the crystal structure consisted of a network of (La_1−χ³⁺Tm_χ^staggered|3+, Ta⁵⁺)—O²⁻ polyhedra interstratified with a double layer of Ta⁵⁺—O²⁻ polyhedra. According to the excitation and emission spectra, the most intense emission was found near 460 nm and quenched above χ=0.14 in La_1−χTm_χTa₇O₁₉. Also, lifetime results verified that the emission could be assigned not to the transition ¹G₄ å ³H₆, but to the transition ¹D₂ å³H₄. Upon cathode ray excitation some emissions of Tm³⁺ were superimposed by a broad emission due to the clusters of Ta⁵⁺—O²⁻ polyhedra. As a result, a low dimensional arrangement of Tm³⁺ was much more preferable for getting intense emission because it reduced the energy migration between Tm³⁺ ions.     

Effects of Some Light Alloying Elements on the Oxidation Behavior of Fe and Ni-Cr Based Alloys During Air Plasma Spraying

The oxidation behavior of iron binary powders with addition of Si (1, 4 wt.%) and B (1, 3 wt.%) and that of a Ni-Cr based alloy powder with Si (4.3 wt.%), B (3.0 wt.%), and C (0.8 wt.%) additions during atmosphere plasma spray (APS) have been investigated. Analysis of the chemical composition and phases of oxides in the captured in-flight particles and deposited coatings was carried out. The results show that the addition of Si and B to iron effectively reduced the oxygen contents in the coatings, especially during the in-flight period at higher particles temperature. Ni-Cr based alloy powder with Si, B, and C additions reduced the oxidation of the base alloys significantly. Preferential oxidation and subsequent vaporization of Si, B, and C from the surface of the sprayed particles are believed to play a major role in controlling oxidation in the APS process.     

The effect of thickness on the steady-state creep properties of freestanding aluminum nano-films

To clarify the effects of film thickness on the creep properties of nano-films we conducted tensile creep experiments on freestanding aluminum films with thickness values in the range ～100–800 nm at room temperature. The nano-films showed typical creep behavior comprising transient, steady-state, and accelerated creep stages. The steady-state creep exponents of the 100–800 nm thick specimens were 0.84–2.7 in the stress range 30–120 MPa, which are close to the value for diffusion creep (1). Creep deformation clearly shows a thickness effect: the steady-state creep rate increases as the thickness decreases from 800 to 400 nm, shows a peak in the range 400–200 nm, and then decreases in the 200–100 nm thickness range. The creep experiments under a small stress of 1 MPa show a negative strain rate, indicating the presence of a driving force to reduce the surface area due to surface tension. The explanation for the thickness effect is as follows. Since the ratio of surface and grain boundary area to volume increases with decreasing thickness, diffusion creep along these paths is enhanced, resulting in an increase in the creep rate. As the thickness decreases to 200–100 nm, however, the surface tension effect to reduce the surface area becomes dominant, decreasing the creep rate. In addition, the creep rate of the nano-films is about two or three orders of magnitude smaller than that of the bulk material dominated by the dislocation creep mechanism.