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排序方式: 共有1635条查询结果,搜索用时 15 毫秒
91.
Hiroshi Inoue Koshi Sekizawa Koichi Eguchi Hiromichi Arai 《Journal of the American Ceramic Society》1997,80(3):584-588
A coating of barium hexaaluminate (Ba0.75 Al11.0 O17.25 ) on an α-SiC substrate and the thermal stability of the formed film were investigated for a high-temperature catalytic application. The film prepared by sol coating consisted of BaAl2 Si2 O8 and α-Al2 O3 phases and always contained many cracks or exfoliations after heating at 1200C. A hexaaluminate porous film was successfully formed by slurry coating without void formation at the interface between the film and the substrate and exfoliation due to the formation of the intermediate layer after heating at 1200°C. The microstructure of the film remained unchanged, even after heating at 1300°C. 相似文献
92.
93.
Poly[(R)-3-hydroxybutyric acid] [R-P(3HB)] was hydrolyzed in high-temperature and high-pressure water at the temperature range of 180-300 °C and for a period of 360 min. The formation, racemization, and decomposition of 3-hydroxybutyric acids (3HBs) and molecular weight change of R-P(3HB) were investigated. The highest yield of (R)-3-hydroxybutyric acid (R-3HB), ca. 80%, was obtained at 200 °C in the hydrolytic degradation periods of 240-360 min. Too-high hydrolytic degradation temperature such as 300 °C induced the decomposition and racemization of formed 3HBs, resulting in decreased yield of R-3HB. The hydrolytic degradation of R-P(3HB) proceeds homogeneously and randomly via a bulk erosion mechanism. The molecular weight of R-P(3HB) decreased exponentially without formation of low-molecular-weight specific peaks originating from crystalline residues. The hydrolytic degradation rates in the melt estimated from Mn changes were lower for R-P(3HB) than for poly(l-lactide) (PLLA) in the temperature range of 180-220 °C. The activation energy for the hydrolytic degradation (ΔEh) of R-P(3HB) in the melt (180-250 °C) was 30.0 kcal mol−1, which is higher than 12.2 kcal mol−1 for PLLA in the melt in the temperature range (180-250 °C). This study reveals that hydrolytic degradation of PHB in the melt is an effective and simple method to obtain (R)-3HB and to prepare R-P(3HB) having different molecular weights without containing the specific low-molecular-weight chains, because of the removal of the effect caused by crystalline residues. 相似文献
94.
The crystallization mechanism of high-cordierite (2MgO·2Al2O3·5SiO2) from a bulkglass containing B2O3 and P2O5 as nucleating agents was studied using X-ray diffraction, differential thermal analysis and a polarizing microscope. Thin glass specimens, with a mirror surface, were heated rapidly in an electric furnace in the temperature range 888 to 1363° C for a desired time and then rapidly quenched to room temperature. The normal rate of growth of precipitated cordierite crystals was measured and their morphological change was observed photographically. The growth rate increased with temperature, and the maximum rate occurred at about 1250° C. The crystal morphology was hexagonalprismatic, elongated along thec-axis. Faceted interface morphology was observed when the range of undercooling was from 7 to 174° C. Judging from the relationship between the reduced growth rate and the degree of undercooling, the crystallization mechanism in the range of lower undercooling was governed by a layer growth depending on the surface nucleation mechanism. In the range of higher undercooling, continuous growth was seen and at intermediate undercooling a transition range from a layer growth to a continuous growth was evident. 相似文献
95.
Hiroaki Yonemura Koichi Yuno Yuuichi Yamamoto Sunao Yamada Yoshihisa Fujiwara Yoshifumi Tanimoto 《Synthetic Metals》2009,159(9-10):955-960
Nanowires consisting of regioregular poly(3-hexylthiophene) (P3HT) as a conducting polymer were prepared using p-xylene. Magnetic processing of the nanowires was carried out using two superconducting magnets with horizontal (Bmax = 8 T) and vertical (Bmax = 10 T) directions. The formation of the nanowires was confirmed by atomic force microscopy (AFM) measurement. The results from the AFM images and the polarized absorption spectra on glass plates indicated that the nanowires partly oriented themselves with their long axes, which are parallel to the π–π stacking direction, being perpendicular to the magnetic field. The magnetic orientation is most likely ascribed to anisotropy in the magnetic susceptibilities of the ordered P3HT in the nanowires. 相似文献
96.
A facile approach to the fabrication of ultrathin polymer films on a flat or curved substrate is presented. Polymers with unsaturated pendant groups were spin-coated on a photoinitiator tethered surface, which was then photoirradiated and washed with a solvent. The obtained films were uniform, smooth (Ra < 0.2 nm) and exhibited robustness toward solvents. The thickness of the films was determined by the molecular weight of the coated polymer and was not dependent on the initial spin-coated thickness. A mechanism for the formation of the ultrathin film and application to optical lenses is presented. 相似文献
97.
Shimizu M Miyashita K Kitagaki H Ito K Shimoi H 《Journal of Bioscience and Bioengineering》2005,100(6):678-680
Sake yeasts are used for sake brewing and have a crucial role in the quality of sake, since they produce not only ethanol but also various compounds that provide sake flavors. Therefore, the appropriate selection and monitoring of a strain used in sake mash is important. However, the identification of specific sake yeast strains has been difficult, because sake yeasts have similar characteristics in taxonomic and physiological analyses. We found amplified fragment length polymorphisms (AFLPs) in the PCR products of the AWA1 gene of sake yeast strains. The AWA1 gene encodes a cell wall protein that is responsible for foam formation in sake mash. This polymorphism of the AWA1 gene can be used for the identification of sake yeast strains. 相似文献
98.
Suga K Mochizuki N Harayama K Yamashita H 《Shokuhin eiseigaku zasshi. Journal of the Food Hygienic Society of Japan》2004,45(6):307-312
A simple method for analysis of trichothecenes [Type A: diacetoxyscirpenol, neosolaniol, HT-2 toxin, and T-2 toxin, Type B: deoxynivalenol, nivalenol, fusarenon-X, 3-acetyldeoxynivalenol, 15-acetyldeoxynivarenol] in barley tea and beer using liquid chromatography tandem mass spectrometry (LC/MS/MS) was developed. Trichothecenes were extracted with ethyl acetate-methanol (19:1). The solvent was evaporated to dryness and the residue was dissolved in water-methanol (3:1) for injection into the LC/MS/MS. The LC separation was performed with an octadecylated silica column at a flow-rate of 0.2 mL/min, using a mobile phase consisting of water, methanol and acetonitrile. MS/MS was used in multiple reaction monitoring, employing electrospray ionization (ESI-MRM). The recoveries of trichothecenes from drinks at 1 microg/L (Type A) and 10 microg/L (Type B) were 52.5-115.2% (barley tea) and 68.1-127.5% (beer). Five barley tea and ten beer samples were analyzed by this method. Trichothecenes were not detected in them. This method may have applications in quality assurance. 相似文献
99.
LIU JiangHao FU ZhengYi WANG WeiMin ZHANG JinYong WANG Hao WANG YuCheng LEE SooWohn NIIHARA Koichi 《中国科学:技术科学(英文版)》2014,57(6):1085-1092
The fast densification method of combustion reaction plus quick pressing was adopted to prepare nanocrystalline ceramics.The densification process of magnesia compact with a particle size of 100 nm was investigated,under the applied pressure of up to 170 MPa,and the temperature range of 1740–2080 K with ultra-high heating rate(above 1700 K/min).High-purity magnesia ceramics with a relative density of 98.8%and an average grain size of 120 nm was obtained at 1740 K,and the grain growth during the densification process was effectively restrained.The characteristic morphology of evaporation-condensation was observed in the compact prepared at 2080 K,which revealed the actual process of mass transfer by gas diffusion.Moreover,the investigation on the microstructure evolution and mechanism of grain growth was carried out,on the basis of as-preserved nanocrystalline ceramics.The result indicated that the grain growth of the nanocrystalline MgO was controlled by the mechanism of evaporation-condensation rather than surface diffusion.Furthermore,the pressure had an influence of restraining the grain growth based on solid diffusion and strengthening the effect of gas diffusion with the increasing temperature.Under the particular conditions,there existed an appropriate temperature for the densification of nanocrystalline magnesia,while the excessive temperature would exaggerate grain growth and impede densification. 相似文献
100.
Sugino A Miyazaki T Kawachi G Kikuta K Ohtsuki C 《Journal of materials science. Materials in medicine》2008,19(3):1399-1405
Polymethylmethacrylate (PMMA)-based bone cement is used for the fixation of artificial joints in orthopaedics. However, the
fixation is liable to loosen in the body, because the cement does not bond to living bone. So-called bioactive ceramics bond
directly to living bone through the apatite layer formed on their surfaces in the body. We previously revealed that modification
using γ-methacryloxypropyltrimethoxysilane (MPS) and water-soluble calcium salts such as calcium acetate and calcium hydroxide
was effective for providing the PMMA-based bone cement with apatite-forming ability in a simulated body fluid (SBF, Kokubo
solution) that closely reproduces the body environment. However, the effect of the chemical reaction forming the apatite on
the mechanical properties of the cements has not been clarified. The present work aimed to investigate this issue from the
viewpoint of the interface structure between the apatite and the cement. The surface of the cement modified with calcium acetate
and MPS was fully covered with newly formed apatite after soaking in Kokubo solution within 7 days, while half of the surface
area of the cement modified with calcium hydroxide and MPS was covered with the apatite. The bending strength of the modified
cements decreased after soaking in Kokubo solution. Porous structure was observed in the region about 50–100 μm in depth from
the top surface because of release of the Ca2+ ions by both modified cements after soaking in Kokubo solution. The decrease in bending strength of the modified cements could
be attributed to the formation of the pores. In addition, the pores on the top surfaces of the cements were filled with the
newly formed apatite. The apatite formation would be effective not only for bioactivity but also for decreasing the reduction
of mechanical strength. 相似文献