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41.
Takuya Orihashi Toshihiro Nakamura Sadao Adachi 《Journal of the American Ceramic Society》2016,99(9):3039-3046
The europium titania materials, pyrochlore Eu2Ti2O7 and orthorhombic Eu2TiO5, were synthesized from a mixture of Eu2O3 and TiO2 using the solid‐state reaction method. The structural and optical properties of these titania materials were investigated using X‐ray diffraction analysis, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and diffuse reflectance spectroscopy. Temperature dependence of the PL intensity was measured between T = 20 and 450 K and analyzed on the basis of various theoretical models. A remarkable increase in the PL intensity with increasing T was observed in these titania materials at higher temperatures, above ~140 K, and well explained by a trap/reservoir model. Interestingly, a dramatic decrease in the electric‐dipole emission component relative to the magnetic‐dipole one was observed in Eu2Ti2O7 above T ~ 140 K. The schematic energy‐level diagram for Eu3+ in the Eu2Ti2O7 host was proposed for the sake of a better understanding of the PL and PLE processes in this type of phosphorescent material. 相似文献
42.
Praphan?Pinsirodom Yomi?Watanabe Toshihiro?Nagao Akio?Sugihara Takashi?Kobayashi Yuji?ShimadaEmail author 《Journal of the American Oil Chemists' Society》2004,81(6):543-547
Production of MAG by a lipase-catalyzed reaction is known to be effective at low temperature. This phenomenon can be explained
by assuming that synthesized MAG are excluded from the reaction system because MAG, which have low m.p., are solidified at
low temperatures. Consequently, MAG are efficiently accumulated and do not serve as the precursor of DAG. If this hypothesis
is correct, the critical temperature for MAG production, defined as the highest temperature at which DAG synthesis is repressed,
should depend on the m.p. of the MAG. Esterification of FFA with glycerol using Candida rugosa, Rhizopus oryzae, and Penicillium camembertii lipases produced MAG efficiently at low temperatures. However, Candida lipase showed very low esterification activity at high temperatures (>20°C), and Rhizopus lipase produced not only MAG but also DAG even at low temperatures. Meanwhile, P. camembertii lipase catalyzed synthesis of MAG only from FFA and glycerol at low temperatures, although the enzyme catalyzed synthesis
of DAG from MAG in addition to synthesis of MAG at high temperatures. We thus studied the effect of temperature on esterification
of C10−C18 FFA with glycerol using Penicillium lipase as a catalyst and determined the critical temperatures for production of MAG. The critical temperature for production
of each MAG showed a linear correlation with m.p. of the MAG, which supported the hypothesis. In addition, because the m.p.
of MAG are estimated from that of the constituent FA, the optimal temperature for production of MAG can be predicted from
the m.p. of the FFA used as a substrate. 相似文献
43.
Ryutaro Usukawa Toshihiro Ishikawa 《International Journal of Applied Ceramic Technology》2019,16(6):2111-2120
Most of the present production processes of SiC sintered bodies require some powder mixing using a mechanical milling process (ball milling, and so on). In this case, relatively long hours are required, and there is the problem of contamination during the preparation process. To avoid these problems, we developed a new process for obtaining a self-sinterable, stoichiometric SiC powder, whose precursor material is water-soluble; the precursor material was synthesized from aqueous silica and citric acid containing a small amount of aluminum compound. In order to obtain the stoichiometric SiC composition, the above aqueous precursor material was adequately cured in air (200°C-400°C); subsequently carbonization reaction (~800°C) in nitrogen atmosphere, carbothermal reduction (~1600°C) in argon atmosphere, and pressureless sintering (~1900°C) were performed. Among these processes, the curing process (cross-linking process) is very important for obtaining the equivalent composition (silica and carbon) for the subsequent carbothermal reduction. In this study, the adequate curing temperature and suitable preparation condition for the carbothermal reduction were investigated for the production of stoichiometric self-sinterable SiC powder. The pressureless sintered body achieved using the obtained SiC powder demonstrated a desirable trans-crystalline fracture behavior. 相似文献
44.
45.
Nobuo Nakada Hidetoshi Ito Yoshikazu Matsuoka Toshihiro Tsuchiyama Setsuo Takaki 《Acta Materialia》2010,58(3):895-903
We investigate deformation-induced martensitic transformation behavior in cold-rolled and cold-drawn specimens of type 316 stainless steel. Deformation-induced martensite preferentially nucleates at the twin boundary between the austenite matrix and a deformation twin. In the cold-rolled specimen, martensite formed at the twin boundary has a Kurdjumov–Sachs (K–S) relationship with both the austenite matrix and the deformation twin (“double K–S relationship”). In the cold-drawn specimen, two kinds of deformation twins with different twin planes are typically formed, and therefore deformation-induced martensites are formed where the deformation twin boundaries intersect: martensite thus has an imperfect “triple K–S relationship” with the austenite matrix and the two deformation twins. The complicated crystallographic orientation relationship between austenite and martensite grains strongly restricts the formation of some variants of deformation-induced martensites. Because of the difference in number of nucleation sites in the cold-drawn and cold-rolled specimens, martensitic transformation is more enhanced in the former than in the latter. 相似文献
46.
Aritomo Yamaguchi Takafumi Shido Yasuhiro Inada Toshihiro Kogure Kiyotaka Asakura Masaharu Nomura Yasuhiro Iwasawa 《Catalysis Letters》2000,68(3-4):139-145
The time-resolved reduction process of copper cations in/on ZSM-5 during temperature-programmed reduction (300–700 K) was studied by energy-dispersive X-ray absorption fine structure (DXAFS) as well as transmission electron microscopy (TEM). Two Cu-ZSM-5 samples with different Cu loadings were prepared by an ion-exchange method. The Cu K-edge DXAFS spectra for isolated Cu2+ species in the channels of ZSM-5 and CuO particles on the outer surfaces of ZSM-5 were recorded at an interval of 1 s during the reduction. The curve fitting analysis of the EXAFS data and the XANES analysis revealed that the isolated Cu2+ species in the channels were reduced stepwise. They were reduced to isolated Cu+ species at 400–450 K and the Cu+ species to Cu0 metallic clusters at 550–650 K. Small clusters like Cu4 were initially formed, followed by particle growth. A small part of them went out to the outer surfaces of ZSM-5 during the reduction. In contrast, CuO particles on the outer surfaces were reduced directly to Cu0 metallic particles around 450 K. 相似文献
47.
Laser-Sintered Barium Titanate 总被引:1,自引:0,他引:1
Toshihiro Kasai Yoshiharu Ozaki Hideki Noda Kenji Kawasaki Kei Tanemoto 《Journal of the American Ceramic Society》1989,72(9):1716-1718
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. 相似文献
48.
Nobutaka Maeda Takaaki Matsushima Masashi Kotobuki Toshihiro Miyao Hiroyuki Uchida Hisao Yamashita Masahiro Watanabe 《Applied Catalysis A: General》2009,370(1-2):50-53
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. 相似文献
49.
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. 相似文献
50.
Keita Watanabe Toshihiro Miyao Kazutoshi Higashiyama Hisao Yamashita Masahiro Watanabe 《Catalysis communications》2009,10(14):1952-1955
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. 相似文献