Laser-Sintered Barium Titanate

Laser sintering of alkoxy-derived ultrafine BaTiO₃ powders was investigated. The temperature increases of the sample with laser irradiation were measured with a thermocouple. It was found that laser irradiation could generate enough heat to sinter ceramics. A slurry was prepared by mixing an alkoxy-derived BaTiO₃ powder, binder additives, solvent, and plasticizer. The slurry was tape cast and dried to give a green sheet. The green sheet was laser sintered and was then characterized by SEM, XRD, and density measurements. The effect of burnout before laser irradiation and the characteristic microstructure of laser-sintered BaTiO₃ are described.     

H2O-tolerant monolithic catalysts for preferential oxidation of carbon monoxide in the presence of hydrogen

Pt–Fe/mordenite (4 wt% Pt–0.5 wt% Fe) powder catalysts were wash-coated onto ceramic straight-channel monoliths by using silica- and/or alumina-sol as a binder, and were evaluated for the preferential oxidation of carbon monoxide (PROX) in a hydrogen-rich gas. In a synthetic reformate gas (1% CO, 1% O₂, 5% H₂O, 20% CO₂, and balance H₂), the CO concentration was reduced to less than 20 ppm at temperatures ranging from 100 to 130 °C. After a certain period of the PROX reaction, condensation of H₂O in the pores of the mordenite-support occurred over the monolithic catalyst, which was wash-coated with alumina-sol, in the lower temperature range (100–120 °C), resulting in a rapid increase in CO concentration. The monolithic catalyst wash-coated with silica-sol, however, showed an excellent tolerance against H₂O condensation and offered a stable catalytic performance, maintaining a CO concentration of ca. 20 ppm for 200 h. The H₂O-tolerant characteristic was attributed to the relatively small adsorption amount of H₂O over the silica-modified monolithic catalyst.     

The selective sorption of D,L-amino acids by chemically modified chitosan gels and its application to liquid chromatography

The sorption of D ,L -amino acids, DNP-L -amino acids and dipeptides by N-octanoyl- and N-benzoyl-chitosan gels was investigated under various conditions. The results indicate that optical resolution of D ,L -amino acids by liquid column chromatography has been achieved, using the chemically modified chitosan gels as a stationary phase.     

High temperature water–gas shift reaction over hollow Ni–Fe–Al oxide nano-composite catalysts prepared by the solution-spray plasma technique

The effect of Fe content in Ni–Fe–Al oxide nano-composites prepared by the solution-spray plasma technique on their catalytic activity for the high temperature water–gas shift reaction was investigated. The composites showed a hollow sphere structure, with highly dispersed Fe–Ni particles supported on the outer surface of the spheres. When the water–gas shift reaction was performed over an Ni–Al oxide composite catalyst without Fe, undesired CO methanation took place predominantly compared to the water–gas shift reaction, and significant amounts of hydrogen were consumed. When appropriate amounts of Fe were added to the Ni–Al oxide composite catalyst during the plasma process, methanation was suppressed remarkably, without serious loss of activity for the water–gas shift reaction. The catalyst was characterized by STEM, XRD and H₂ chemisorption measurements.     

Improvement of thermal stability of NO oxidation Pt/Al2O3 catalyst by addition of Pd

The present work has been undertaken to tailor Pt/Al₂O₃ catalysts active for NO oxidation even after severe heat treatments in air. For this purpose, the addition of Pd has been attempted, which is less active for this reaction but can effectively suppress thermal sintering of the active metal Pt. Various Pd-modified Pt/Al₂O₃ catalysts were prepared, subjected to heat treatments in air at 800 and 830 °C, and then applied for NO oxidation at 300 °C. The total NO oxidation activity was shown to be significantly enhanced by the addition of Pd, depending on the amount of Pd added. The Pd-modified catalysts are active even after the severe heat treatment at 830 °C for a long time of 60 h. The optimized Pd-modified Pt/Al₂O₃ catalyst can show a maximum activity limited by chemical equilibrium under the conditions used. The bulk structures of supported noble metal particles were examined by XRD and their surface properties by CO chemisorption and EDX-TEM. From these characterization results as well as the reaction ones, the size of individual metal particles, the chemical composition of their surfaces, and the overall TOF value were determined for discussing possible reasons for the improvement of the thermal stability and the enhanced catalytic activity of Pt/Al₂O₃ catalysts by the Pd addition. The Pd-modified Pt/Al₂O₃ catalysts should be a promising one for NO oxidation of practical interest.     

Carbon dioxide pressure induced heterogeneous and homogeneous Heck and Sonogashira coupling reactions using fluorinated palladium complex catalysts

The Heck reaction of iodobenzene and methyl acrylate was investigated with CO₂-philic Pd complex catalysts having fluorous ponytails and the organic base triethylamine (Et₃N) in the presence of CO₂ under solventless conditions at 80 °C. The catalysts are not soluble in the organic phase in the absence of CO₂ and the reaction occurs in a solid-liquid biphasic system. When the organic liquid mixture is pressurized by CO₂, CO₂ is dissolved into the organic phase and this promotes the dissolution of the Pd complex catalysts. As a result, the Heck reaction occurs homogeneously in the organic phase, which enhances the rate of reaction. This positive effect of CO₂ pressurization competes with the negative effect that the reacting species are diluted by an increasing amount of CO₂ molecules dissolved. Thus, the maximum conversion appears at a CO₂ pressure of around 4 MPa under the present reaction conditions. The catalysts are separated in the solid granules by depressurization and are recyclable without loss of activity after washing with n-hexane and/or water. When the washing is made with hexane alone, the catalytic activity tends to increase on the repeated Heck reactions, probably due to the accumulation of such a base adduct as Et₃NHI on the catalysts. When the washing is further made with water, however, the base adduct is taken off from the catalysts and they show similar activity levels in the repeated runs. The potential of CO₂ pressure tunable heterogeneous/homogeneous reaction system has also been investigated for Sonogashira reactions of iodobenzene and phenylacetylene under similar conditions.     

Preparation and photocatalytic activity of Keggin-ion tungstate and TiO2 hybrid layer-by-layer film composites

Keggin ions (PW₁₂O₄₀³⁻ (PW₁₂), SiW₁₂O₄₀⁴⁻ (SiW₁₂), H₂W₁₂O₄₀⁶⁻ (H₂W₁₂)) and TiO₂ hybrid thin films were prepared using the layer-by-layer method. Their photocatalytic activities were investigated using gaseous 2-propanol decomposition. All films were transparent in the visible wavelength range. For 2-propanol decomposition, H₂W₁₂ was the most effective for the combination with TiO₂ despite having the smallest TiO₂ deposition amount. The photocatalytic activity of the PW₁₂–TiO₂ hybrid film was increased 2.3 times by visible light with UV illumination. This increase was less remarkable for hybrid films of other Keggin ions, suggesting that the visible light excitation of reduced PW₁₂ plays an important role in the enhancement of 2-propanol decomposition.     

Precision die-casting of optical MU/SC conversion sleeve

The performance of MU/SC conversion sleeve produced by bulk metallic glass (Zr₅₅Al₁₀Ni₅Cu₃₀) was examined. A precision die-casting method was applied to improve size accuracy. The size accuracy of the conversion sleeve produced by the precision die-casting method was ±1 μm, and optical insertion loss (Li) was less than 0.3 dB for a standard value. The wear resistance of metallic glass is improved by surface oxidation treatment in air at 673 K. The MU/SC conversion sleeve produced from bulk metallic glass has superior characteristics for optical parts.     

Synthesis and properties of poly(phenylacetylene)s having dialkylamino groups

Summary Poly(phenylacetylene)s bearing dialkylamino groups were prepared by the polymerization of p-(N,N-dialkylamino)phenylacetylenes with [Rh(nbd)Cl]₂, and their electrochemical behavior was examined. Rh-catalyzed polymerization of p-(N,N-diethylamino)phenylacetylene (DEAPA) and p-(N,N-di-n-butylamino)phenylacetylene (DBAPA) in toluene in the presence of triethylamine gave good yields of the polymers (86 and 90%, respectively). Poly(DEAPA) was soluble in chloroform and dichloromethane, and poly(DBAPA) dissolved in various solvents such as toluene, THF, dichloromethane and chloroform. Poly(DEAPA) and poly(DBAPA) showed onset temperatures at 248 and 190°C, respectively, and absorptions around 300–400 nm. Electrochemical doping of the polymer films resulted in the shift of the absorptions to a region around 680 nm, which accompanied a color change of the polymer films from green ocher to deep blue. Received: 26 October 1998/Revised version: 6 November 1998/Accepted: 12 November 1998     

Mechanical properties of Al–Si–Cu alloys produced by the continuous casting process with heating process

The mechanical properties of aluminium alloys produced by the continuous cast process and heating process (heat-cast-sample) were investigated, where the aluminium alloys are heated continuously to high temperatures for 1 h immediately following heated mould continuous casting (HMC) and sand gravity casting (SGC). The material strength and ductility of the aluminium alloys were irregularly altered depending on the heating temperature. The mechanical properties decreased when the heating temperature increased to 400 °C and were then recovered when the temperature increased to 520 °C. However, these properties decreased again when heated to more than 540 °C. The mechanical properties of the HMC-heat-cast-sample showed overall higher than those for the SGC-sample. In addition to high tensile strength, high ductility was obtained for the HMC-520 °C samples compared with those for the as-cast-sample. Such changes were found to be directly attributable to the different severity of precipitate; moreover the crystal orientation was unchanged even after the heating process.