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排序方式: 共有271条查询结果,搜索用时 15 毫秒
41.
Thermal oxidative degradation behavior of polypropylene (PP) with different tacticities was studied based on the activation energy (ΔE) data obtained by thermogravimetric analysis (TGA). The ΔE value showed a negative proportion to the content of meso pentad fraction (mmmm) in all of isotactic PP (iPP) samples, and that of syndiotactic PP sample considerably deviated from this negative proportion relationship. Since the value of mmmm was directly related to polymer chain conformation, the ΔE value was thought to have close connection with the concentration of 31 helix conformation in the iPPs. The ΔE changes would be caused by the competition between uni- and bimolecular hydroperoxide decomposition, which was controlled by concentration and character of conformations of PPs. 相似文献
42.
Hitoshi Matsuoka Boping Liu Hisayuki Nakatani Isa Nishiyama Minoru Terano 《Polymer International》2002,51(9):781-784
To investigate the role of the internal donor in a Ziegler–Natta catalyst, the nature and existing states of the internal donor were intentionally varied by alkylaluminium treatment before polymerization, and the catalytic properties during propene polymerization were accurately evaluated using the stopped‐flow method. A significant decrease in the amount of the remaining internal donor was observed during the initial stage of the extraction. The polymerization results show a gradual decrease in the polymer isotacticity with an increase in the extraction time. These different patterns, as a function of the extraction time, indicate that the amount of the remaining internal donor is not directly related to the isotacticity of the produced polymer. © 2002 Society of Chemical Industry 相似文献
43.
Strength improvement and purification of Yb2Si2O7‐SiC nanocomposites by surface oxidation treatment
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Son T. Nguyen Tadachika Nakayama Hisayuki Suematsu Tsuneo Suzuki Lingfeng He Hong‐Baek Cho Koichi Niihara 《Journal of the American Ceramic Society》2017,100(7):3122-3131
A two‐step processing was developed to prepare Yb2Si2O7‐SiC nanocomposites. Yb2Si2O7‐Yb2SiO5‐SiC composites were first fabricated by a solid‐state reaction/hot‐pressing method. The composites were then annealed at 1250°C in air for 2 hours to activate the oxidation of SiC, which effectively transformed the Yb2SiO5 into Yb2Si2O7. The surface cracks purposely induced can be fully healed during the oxidation treatment. The treated composites have improved flexural strength compared to their pristine composites. The mechanism for crack healing and silicate transformation have been proposed and discussed in detail. 相似文献
44.
Suguru?MotokuchoEmail author Takeshi?Matsumoto Yu?Nakayama Ryohei?Horiuchi Hiroshi?Morikawa Hisayuki?Nakatani 《Polymer Bulletin》2017,74(3):615-623
A chemical decomposition of polyurea (PUA) by hydrolysis under high pressure of carbon dioxide (CO2) was proposed. The hydrolysis of PUA was carried out at 190 °C for 2 h under 7.0 MPa of CO2 in the presence of water. The hydrolysis reaction gave white residual solid and water soluble compound. The white residual solid was characterized to be degraded PUA by FT-IR spectrum and elemental analysis. 1H-NMR spectra of the water soluble compound revealed that the hydrolysis of PUA produced diamine only from repeating unit of PUA, which was a component of PUA. This hydrolysis gave the corresponding diamine for quantitative yields. 相似文献
45.
Naohide Kinae Takashi Hashizume Toshio Makita Isao Tomita Ikuo Kimura Hisayuki Kanamori 《Water research》1981,15(1):17-24
Sediment samples collected at three different coastal points (Shinguu, Ooigawa and Tagonoura) were extracted with diethylether and then methanol. Each extract was separated into five fractions by high-speed liquid chromatography and they were submitted to mutagenic assay using B. subtilis and S. typhimurium and to GC-MS analysis.The ether fraction of sediment sample from Shinguu showed DNA damaging potency on B. subtilis and exhibited mutagenic effect on S. typhimurium TA 98, TA 100 and TA 1537. 2,4,6-Trichlorophenol, 3,4,5,6-tetrachloroguaiacol, dehydroabietic acid, pyrene and fluoranthene were mutagenic substances among 28 substances identified and tested. 相似文献
46.
Nishimura K Harada T Arita Y Watanabe H Iwabuki H Terada A Naganuma T Uzuka Y 《Journal of Bioscience and Bioengineering》2006,101(4):303-308
We have identified the enzyme responsible for erythritol utilization and its reaction product in the yeast Lipomyces starkeyi CBS 1807. The enzyme, a polyol dehydrogenase requiring NAD+ as a coenzyme, was induced by erythritol in this yeast. We confirmed that the enzyme product was L-erythrulose by MS, NMR, and polarimeter analyses, meaning that we clarified the first step of erythritol utilization in yeasts for the first time. In the case of the oxidative reaction, D-threitol, (2R,3R)-2,3-butanediol, and erythritol were much better substrates than 21 other polyols tested. These three substrates are tetroses and have an R configuration at C-3, and whose third carbon results in easiest oxidation in this enzyme. The research of the substrate specificity in the reductive reaction demonstrated that L-erythrulose and dihydroxyacetone were better substrates, that D-acetoin was inactive and L-erythrose (aldose) was slightly active. 相似文献
47.
Masayuki Taniguchi Yuki Kamikawa Teruyuki Okazaki Kenji Yamamoto Hisayuki Orita 《Combustion and Flame》2010,157(8):1456-1466
We have investigated an index for modeling a NOx reaction mechanism of pulverized coal combustion. The reaction mechanism of coal nitrogen was examined by drop-tube furnace experiments under various burning conditions. We proposed the gas phase stoichiometric ratio (SRgas) as a key index to evaluate NOx concentration in fuel-rich flames. The SRgas was defined as:
48.
49.
Further Improvement in Mechanical Properties of Highly Anisotropic Silicon Nitride Ceramics 总被引:1,自引:0,他引:1
Hisayuki Imamura Kiyoshi Hirao Manuel E. Brito Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》2000,83(3):495-500
Si3 N4 ceramics were fabricated by tape casting of a raw-powder slurry seeded with three types of rodlike β-Si3 N4 particles. The effects of seed size on the microstructure and mechanical properties of the sintered specimens were investigated. All the seeded and tape-cast silicon nitrides presented an anisotropic microstructure, where the elongated grains grown from seeds were preferentially oriented parallel to the casting direction. The orientation degree of these grains, f 0 , was affected by seed size, and small-seed addition led to the highest f 0 value. This material exhibited high bending strength (∼1.4 GPa) and high fracture toughness (∼12 MPa. m1/2 ) in the direction normal to the grain alignment, which were attributed to the highly anisotropic and fine microstructure. 相似文献
50.
Yong‐Woo Shin Hisayuki Nakatani Toshiya Uozumi Boping Liu Tsuneji Sano Koh‐hei Nitta Minoru Terano 《Polymer International》2003,52(1):29-34
During propylene polymerization with the Cr(acetylacetonate)3/MgCl2–Et2AlCl–ethylbenzoate catalyst system which shows high isospecificity for propylene polymerization, it was found that the chain transfer and termination reactions can be neglected. Based on this result, some stepwise polymerizations of propylene and ethylene were carried out with the same catalyst system varying polymerization conditions. The resulting copolymers were separated by temperature rising elution fractionation (TREF) and afforded two fractions which were eluted at different temperatures. From the 13C NMR, DSC and GPC analyses of each fraction, it was considered that the corresponding block copolymer existed in the fraction eluted at higher temperature. © 2003 Society of Chemical Industry 相似文献