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941.
BaCe1—xRExO3—0.5x的溶胶—凝胶法合成及离子导电性 总被引:3,自引:0,他引:3
用溶胶-凝胶法合成了系列钙钛矿结构的BaCe1-xRExO3-0.5x(RE=La,Nd,Sm,Eu,Gd,Dy,Ho,Er和Y)复合氧化物,通过XRD和热分析对样品结构及生成过程进行了研究.测定了不同温度下样品的交流阻抗谱,讨论了稀土离子掺杂对BaCeO3电性质的影响.溶胶-凝胶法比固相反应法合成温度降低了600~800℃,稀土掺杂使BaCeO3离子导电率提高了10~40倍. 相似文献
942.
943.
Zhiming Liu Jiming Hao Lixin Fu Tianle Zhu Junhua Li Xiangyu Cui 《Reaction Kinetics and Catalysis Letters》2003,80(1):45-52
SnO2/Al2O3 catalyst prepared by sol-gel method showed higher activity than those prepared by impregnation method, and their activity
was significantly improved by pre-treatment in the reaction gas. The increased activity is closely related to the agglomeration
of SnO2 species and the re-exposure of Al2O3, which was previously covered by dispersed SnO2 species.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
944.
A new method based on hollow fiber-protected liquid-phase microextraction (LPME) was developed for the simultaneous determination
of atrazine, desethyl atrazine and desisopropyl atrazine in environmental water samples. In LPME, analytes were extracted
into 1-octanol immobilized in the micropores of a poly(vinylidene fluoride) porous hollow fiber membrane, and back extracted
into the acceptor (4 M HCl) filled in the lumen of the hollow fiber. After LPME, the analytes trapped in the acceptor were
analyzed with high-performance liquid chromatography after neutralization. The effect of extraction factors such as sample
pH, acceptor pH, salinity, extraction time, stirring rate, and humic acid were studied. Under the optimized conditions, the
limits of detection and relative standard deviations were respectively in the range of 0.5–1.0 μg L−1 and 3.9–4.7% (n = 5). The proposed method was applied to determine atrazine, desethyl atrazine and desisopropyl atrazine in wastewater and
groundwater samples. The three analytes were below the limits of detection, but good relative spiked recoveries over 90.1
± 5.9% at 5 μg L−1 spiked level were obtained. 相似文献
945.
Alexander Kane Ren-Fan Shao Joseph E Maclennan Lixing Wang David M Walba Noel A Clark 《Chemphyschem》2007,8(1):170-174
We demonstrate, both theoretically and experimentally, that it is possible to use an electric field to drive the formation of macroscopic chiral (conglomerate) domains from an initially homogeneous fluid racemate. Field-induced segregation is exhibited in a fluid smectic liquid-crystal phase of a racemic mesogen, wherein enantiomerically-enriched domains are readily identifiable by their chiral electro-optical response. The sharp field-generated boundaries that form between opposite-handed domains broaden by diffusion in the absence of field, but reform rapidly if the field is switched on again, providing unambiguous evidence for the field-driven physical separation of enantiomers. A mean-field model successfully describes the steady-state and the dynamic evolution of conglomerate formation. 相似文献
946.
用密度泛函理论研究了CF3SO3CF2CF3 F^-的碳氧键断裂反应的机理。首先,用DFT方法优化了反应物、中间体、过渡态、产物的平衡构型,分析了碳氧键断裂反应的势能面变化,发现在SN2反应机理中,除了S-O断裂SN2反应外,引起C-O键断裂的同面进攻也是一个可能的反应途径。理论计算表明,最终反应的产物是受热力学控制的,S-O键的断裂绝对地优于C-O的断裂。因此,C-O断裂的同面机理虽然是可能的,但却难以被实验观察到,本文还讨论了端基-CF3在同面SN2反应中的邻位效应,以及基组对这个效应的影响。 相似文献
947.
反相高效液相色谱法测定3种中成药中的葛根素 总被引:7,自引:0,他引:7
建立了测定小儿清感灵片、步长新脑心通胶囊和感冒清热颗粒 3种中成药中葛根素含量的反相高效液相色谱方法。采用APEXODS色谱柱 ,以醋酸铵缓冲液 (10 0mmol/L ,pH 5 0 ) 甲醇 (体积比为 75∶2 5 )的混合溶液为流动相 ,检测波长为 2 5 0nm ,流速为 0 8mL/min。葛根素在 2mg/L~ 2 0mg/L时其色谱峰面积与质量浓度的线性关系良好 (r =0 9999) ;上述 3种中成药中的葛根素含量分别为 3 48mg/g ,1 0 8mg/ g及 1 5 2mg/ g(蔗糖型 ) ;其加样回收率分别为 99 0 % ,93 4%和 97 5 %。该法简便、快速、专属性强 ,可以作为多种中药制剂中葛根素含量的测定方法。 相似文献
948.
M. J. Whitcombe A. Gilbert G. R. Mitchell 《Journal of polymer science. Part A, Polymer chemistry》1992,30(8):1681-1691
The syntheses of three methacrylate monomers with cinnamate ester side-chains and of a further monomer with a corresponding cinnamide side-chain are described. Two of the monomers, with isomeric structures, were thermotropic liquid crystals. Although the clearing points were very similar the crystal melting points differed by 8°C. One compound also exhibited a monotropic smectic phase, behavior not shown by its isomer. The other two monomers were not liquid crystalline. The monomers were polymerized by free radical polymerization, both as homopolymers and as copolymers with methyl methacrylate. In the case of one of the mesogenic ester monomers, copolymers with a cyanophenyl benzoate monomer were also prepared. Three of the four monomers formed thermotropic liquid crystalline homopolymers and the copolymers with the benzoate monomer were also liquid crystalline. The monomers were considered as photoactive components of polymeric liquid crystals. As a preliminary investigation of their photochemistry, copolymers with methyl methacrylate were prepared and irradiated in solution with a broad-band source. Under these conditions two of the materials show a facile photo-Fries rearrangement of the aryl cinnamate ester group. © 1992 John Wiley & Sons, Inc. 相似文献
949.
溶胶凝胶法制氧化铝负载铜基超细粒子催化剂的研究 总被引:9,自引:1,他引:9
采用溶胶凝胶法制氧化铝负载铜基超细粒子催化剂的制备了氧化铝负载的铜基超细粒子催化剂,用TG-DTA,XRD,BET以及TEM等技术手段,对催化剂的物相结构,表面孔结构,粒子形貌以及催化性能等进行了研究。结果表明,利用溶胶凝胶法,可以直接帛备出高比表面积,低堆积密度的纤维状纳米级负载型Cu/Al2O3超细粒子;活性组分以远低于纳米级的微晶粒子簇状态,均匀地分散在纳米级氧化铝载体表面上,而且在低于50 相似文献
950.
使用疏水作用色谱研究蛋白质的构象变化 总被引:2,自引:0,他引:2
研究了高效疏水作用液相色谱中(HIC)色谱条件改变对蛋白质构象的影响。发现固定相配体的疏水性、温度及流动相中盐的阴离子、阳离子和pH值都影响蛋白质的构象。 相似文献