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121.
铕掺杂BaPbO3的EXAFS研究 总被引:3,自引:0,他引:3
采用扩展X射线吸收精细结构方法,研究了铕掺杂BaPbO3多晶粉末中Eu,Pb两种原子的近邻结构。Eu的掺杂,导致八面体中金属Pg,Eu的配位数降低。 相似文献
122.
本文研究了LiLn(π-C_3H_5)_4·nD(Ln=La、Tb,n=3;Ln=Ce、Pr、Nd、Sm、Gd、Er,n=2;Ln=Y、Dy,n=2.5;D为二氧六环)催化异戊二烯和苯乙烯的均聚合反应.其中,钇配合物的催化活性为最高.聚异戊二烯顺式-1,4链节含量在43-81%.聚合体系内少量给电子体的加入使聚合物中3,4-链节含量高达84%.所得聚苯乙烯为无规结构. 相似文献
123.
采用溶胶-凝胶法制备了系列多晶CMR材料La0.7Ca0.3Mn1-xCuxO3(x=0%,1%,5%,10%,15%,20%)。在77-350 K温度范围内测量了样品的电阻率及磁电阻大小。实验结果发现:系列样品TC随掺杂量增加而递减;系列样品的电阻率峰及磁电阻峰在整个测温范围内随掺杂量的增加均依次被展宽直至消失,当掺杂量为x≥10%时,电阻率随温度的变化在整个测温范围内呈现绝缘相行为;同时还发现,掺杂量为x≥10%时,样品的磁电阻在整个测温区内基本表现为隧穿磁电阻。基于我们采用蒙特卡罗模拟方法提出的逾渗模型及隧穿磁电阻模型,对样品的磁电阻行为进行了很好的解释。对系列样品的ρ-T曲线进行lnρ-T^-(1/4)系拟合,发现掺杂量为x=10%样品在整个温区内的lnρ-T^-(1/4)系基本呈线性。 相似文献
124.
Mujie Yang Xiaojun Zhang Jianfu Li Zhiquan Shen 《Journal of polymer science. Part A, Polymer chemistry》1992,30(1):63-69
The study of rare earth coordination catalysts for polymerization of 1-octene has been successfully carried out for the first time. Some features and kinetic behavior of polymerization of 1-octene by Nd(naph)3–AIEt3 catalyst system in tetrachloro-methane are described. The overall polymerization activation energy Ea measured was 74.5 kJ/mol and the rate equation could be expressed as Rp = kp [Nd] [M] (kp = 3.21 × 10?3 L/mol s, at 50°C). The catalytic activity of various rare earth elements in Ln (naph)3 and ligands in NdL3 for the polymerization was compared. A 1-octene oligomer with double bonds was obtained. It is either a white or pale yellow waxy semi-solid. Its number-average molecular weight is about 103 and the molecular weight distribution is less than 2. 相似文献
125.
T.?L.?Shanker Rao K.?N.?Lad A.?PratapEmail author 《Journal of Thermal Analysis and Calorimetry》2004,78(3):769-774
The crystallization kinetics of amorphous Cu50Ti50 has been studied using differential scanning calorimetry (DSC) under non-isothermal conditions. The curves at different linear heating rates (2, 4, 8 and 16 K min–1) show sharp crystallization peaks. The crystallization peak shifts to higher temperatures with increasing heating rate. The Kissingers method of analysis of the shift in the transformation peak is applied to evaluate the activation energy (E
c). The KJMA formalism, which is basically developed for isothermal experiments, is also used to obtain E
c and the Avrami parameter (n).The DSC data have been analysed in terms of kinetic parameters, viz. activation energy (E
c), Avrami exponent (n) and frequency factor K
0 using three different theoretical models. It is observed that the activation energy values derived from KJMA approach and modified Kissinger equation agree fairly well with each other. The activation energy values obtained from normal Kissinger method, and Gao and Wang expression underestimate the activation energy.The financial support provided by All India Council for Technical Education (AICTE), New Delhi (Govt. of India) is gratefully acknowledged. 相似文献
126.
Alexander V Lebedev Marina V Ivanova Alexander A Timoshin Enno K Ruuge 《Chemphyschem》2007,8(12):1863-1869
The unexpected effects of Ca(2+) on the free-radical chain reactions of dopamine, norepinephrine, isoproterenol, and pyrocatechol oxidation are studied using oxygen consumption measurements, EPR-spectroscopy, UV/VIS spectrophotometry, and by potentiometric titration. It is found that the formation of Ca(2+)-catecholate complexes is accompanied by an increase in the dissociation constants (K(ai) ) of their phenolic hydroxyls. At pH>pK(ai) and in the presence of alkaline-earth metal cations, the rate of catecholate oxidation increases (Ca(2+), Mg(2+)> Sr(2+), Ba(2+)), whereas on addition of Zn ions the rate decreases. The effects of Group II metal cations on catecholate autoxidation are concomitant with a transient increase of the EPR signal for metal-semiquinonate complexes. Therefore, the effects of Ca(2+) and other alkaline-earth metal cations on catecholate autoxidation can be defined as 1) additional deprotonation of catechol OH-groups involved in the formation of M(2+)-catecholate complexes, the latter exceeding catechols in the susceptibility to dioxygen-induced oxidation and 2) formation of relatively stable free-radical intermediates responsible for chain propagation. 相似文献
127.
Jenn-Lin Lin 《中国化学会会志》1984,31(4):395-399
The reaction of 3-(4-phenyl-2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PPDT) and tetraphenylborate (TPB) with cobalt (II) has been studied to determine the optimum conditions for the extraction and quantitative spectrophotometry determination of this metal. The ternary complex is extracted into molten naphthalene at pH 3.6–7.4. The solid naphthalene containing the cobalt associated complex is separated by filtration and dissolved in acetonitrile. Beer's law is obeyed in the concentration range 8–140 μg cobalt in 10 ml of acetonitrile solution. The molar absorptivity and sensitivity are 4.2×103 l·mol?1·cm?1 and 0.01408 μg/cm2, respectively. The other factors such as pH, amounts of reagents and naphthalene, shaking and standing times, and the effect of diverse ions are studied. The method has been applied to the determination of cobalt in iron steel alloys. 相似文献
128.
Radial viewing 40.68 MHz inductively coupled plasma atomic emission spectrometer was used in the determination of Y, Sc and rare earth elements in Eu2O3 or Lu2O3 as pure rare earth matrices. The Mg II 280.270 nm/Mg I 285.213 nm line intensity ratio was measured to evaluate the robustness of the operating conditions. The operating conditions were affected by varying the incident power and sheathing gas flow rate. The carrier gas flow rate remained a constant value. The relationship between the Mg II 280.270 nm/Mg I 285.213 nm ratio and the excitation temperature was obtained. A dependence of the magnesium ratio in the pure solvent and the corresponding values in the presence of the above matrices was established. 相似文献
129.
研究了熔盐被覆铬碳化物的工艺过程,着重探讨了稀土对T12A钢熔盐渗铬的催渗及微合金化作用机理。结果表明,在加入稀土的熔盐中渗中提高渗速30%-56%,同时还能提高工件表面的抗氧化和耐腐蚀性能以及工件的使用寿命。 相似文献
130.
The crystal structures of the intermediate solid solution HT (high temperature) Ni1+δSn with δ=0.28, 0.52 and 0.61 (refined Ni contents) have been analyzed in detail by X-ray diffraction on single crystals. The previously reported basic atomic arrangement, i.e., a NiAs/Ni2In structure type (P63/mmc, Ni(1) on 2a, 0 0 0, Ni(2) with an occupancy δ on 2d, and Sn on 2c, ), is confirmed. However, strong anisotropic atomic displacements occur for Sn within the a-b plane of the hexagonal unit cell, which require a Gram-Charlier expansion of the probability density function of Sn in order to obtain a good fit to the diffraction data. Direction, magnitude and the concentration dependence of the displacements can be interpreted in terms of the geometrical requirements of the different local atomic configurations in the planes z=±1/4, so that the displacements can be identified as static ones. 相似文献