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121.
Ultrafine MgAl2O4 powder has been synthesized by a polymerized complex method. Heating of a precursor solution containing citric acid (CA), ethylene glycol (EG) and Mg and Al salts with a molar ratio of Mg/Al/CA/EG=1/2/8/32 at 180°C produced a transparent polymeric gel, which have been characterized by FT-IR spectroscopy and TG/DTA. The organic fraction was removed by controlled thermal treatments (350–1200°C) whereby the bimetallic oxide was formed. XRD analysis showed the presence of MgAl2O4 at 600°C. TEM observation showed that the spherical nanosized powders with good uniformity was obtained. Furthermore, these powders showed excellent sinterability, relative density up to 99.8% was achieved when sintered at 1550°C for 3 h in air without any sintering additive. 相似文献
122.
Crown ether-type macrocycles consisting of an enantiopure biarenol derivative and an oligoethylene glycol were synthesized by the Lewis acid-mediated tandem Claisen rearrangement. This is the first example of the successful application of the tandem Claisen rearrangement to the synthesis of enantiopure macrocyclic biarenol derivatives. The enantiopure macrocyclic biarenols were found to form 1:1 complexes with amino acid salts and to discriminate their chirality. 相似文献
123.
Daisuke Sasaki Yoshihiro Suzuki Hagiwara Toshiki Shoichiro Yano Takashi Sawaguchi 《Journal of Analytical and Applied Pyrolysis》2007,80(2):312-318
The reactive end groups of nonvolatile oligomers obtained by controlled thermal degradation of poly(propylene-ran-ethylene) and poly(propylene-ran-1-butene) were determined by 1H and 13C NMR spectroscopy. The molar ratio of unsaturated to saturated end groups was found to be about 9:1. The average number of unsaturated end groups per molecule was between 1.6 and 1.8, indicating that 60–80 mol% of the oligomer molecules were telechelic, having two terminal unsaturated end groups. These oligomers had a lower polydispersity than the raw material, despite their lower molecular weight and melting temperature. Although the end groups resulting from each monomer unit could be detected by 13C NMR, the end group composition differed from that of the main chains of the raw materials. The end group composition was satisfactorily explained by the differences in bond dissociation energy and activation energy of elementary reactions that occurred during thermal degradation, based on the monomer composition of the raw materials. 相似文献
124.
Michinori Karikomi Mari Yamada Hirohiko Houjou Kazuhisa Hiratani Tadao Uyehara 《Tetrahedron letters》2005,46(35):5867-5869
Oxidative coupling reaction of both 3-hydroxychrysene and 2-hydroxybenzo[c]phenanthrene by using Cu(NO3)2-3H2O under atmospheric air is described. The former gave the aimed coupled biaryl derivative. However, the latter gave a further oxidized helical quinone derivative. The unique helical structure was characterized by X-ray and NMR analysis. 相似文献
125.
S. Iwamoto A.N. Nakagaito H. Yano M. Nogi 《Applied Physics A: Materials Science & Processing》2005,81(6):1109-1112
The fibrillation of pulp fiber was attempted by two methods, a high-pressure homogenizer treatment and a grinder treatment. The grinder treatment resulted in the successful fibrillation of wood pulp fibers into nanofibers. The nanofibers demonstrate promising characteristics as reinforcement material for optically transparent composites. Due to the size effect, the nanofiber-reinforced composite retains the transparency of the matrix resin even at high fiber content such as 70 wt %. Since the nanofiber is an aggregate of semi-crystalline extended cellulose chains, its addition also contributes to a significant improvement in the thermal expansion properties of plastics while maintaining its ease of bending. Cellulose nanofibers have tremendous potential as a future resource since they are produced in a sustainable manner by plants, one of the most abundant organic resources on earth. PACS 81.05.Lg; 81.05.Qk 相似文献
126.
Novel stereospecific isomerization of 2-(1-bromoalkyl)-1-sulfonylaziridines into 2-(bromomethyl)-3-alkyl-1-sulfonylaziridines using magnesium bromide is described. The suitable choice of solvent led to good yields and diastereoselectivites. 相似文献
127.
Toughness enhancement of cellulose nanocomposites by alkali treatment of the reinforcing cellulose nanofibers 总被引:1,自引:0,他引:1
Nanocomposites were produced with NaOH aqueous solution-treated microfibrillated cellulose (MFC) and phenolic resin, and the
mechanical properties were compared with their microcomposite counterparts based on pulp fiber. Tensile tests showed that
strong alkali-treated MFC nanocomposites with resin content around 20 wt.% achieved strain at fracture values two times higher
than those of untreated MFC nanocomposites and five times higher than those of untreated pulp microcomposites. The improvement
in work of fracture of alkali-treated MFC nanocomposites was attributed to the ductility of the nanofibers caused by transformations
in the amorphous regions along the cellulose microfibrils. 相似文献
128.
Terrestrial carbonate deposits with a banded layer structure can be good tools for the extraction of past environmental information on global and local scales using trace element concentrations and stable isotope ratios. The absolute age dating is most important for the reconstruction of an environmental chronicle. The measurements of fluorescent annual bandings in stalagmites using a microscopic spectrofluorometer with an XY-stage can be a convenient dating method and are especially effective for young samples whose absolute age is very difficult to be determined by other methods. The number of annual bandings was objectively counted using a personal computer. The optimal conditions for the measurements are discussed. The annual banding in stalagmites is caused by the seasonal differences in the fulvic acid concentrations in the dripping water which forms speleothems. 相似文献
129.
K. Yano 《Physics letters. A》1973,46(3):223-224
A consistent theory of thermo-luminescent process is developed, following Johnson's classical explanation. The situation before the thermal excitation is explained. Expressions for the transition rate and the frequency factor are led out. 相似文献
130.