Studies about the dispersion process and structure of impregnated CuO/ZrO2 systems

The dispersion process and structure of impregnated CuO/ZrO₂ systems were studied by x‐ray diffraction (XRD) and extended x‐ray absorption fine structure (EXAFS). The results showed that, after being calcined at 773 K, monolayer dispersed cupric nitrate decomposed into monolayer dispersed cupric oxide on zirconia's surface. The dispersion threshold of CuO was related to its precursor, cupric nitrate. The surface‐dispersed Cu nearest coordination structure changed into about five equally long Cu–O bonds. Copyright © 2003 John Wiley & Sons, Ltd.     

Anomalous values of 〈Ŝ2〉 before and after annihilation of the first spin contaminant in UHF wave function

We present a number of molecular systems for which the average values 〈?²〉 before and after annihilation of the first spin contaminant in the wave function of the unrestricted Hartree-Fock method are anomalously large (they substantially exceed the expected value S (S + 1)). An example of such systems is N@C₂₀, for the doublet state of which the 〈?²〉 values are equal to 4.2595 before and 13.1390 after annihilation, respectively (calculated by UHF/6-31G* method). We show that four, at the least, spin multiplets (S′ = S, S + 1, S + 2, S + 3) contribute comparatively to the wave function of such systems. The relations are derived allowing one to estimate the contributions of the highest multiplets basing on the average values of 〈?²〉 before and after annihilation of the first spin contaminant.     

基质固相分散－高效液相色谱法测定玉米中痕量呋喃丹

本文研究了应用基质固相分散（ＭＳＰＤ）－高效液相色谱法测定玉米中痕量呋喃丹残留物的新方法，并讨论了应用ＭＳＰＤ技术进行前处理与传统残留分析的区别。本实验首次将ＭＳＰＤ技术用于玉米中呋喃丹残留物的高效液相色谱分析，并对定量检测条件作了详细的研究。     

Nb2O5/TiO2催化剂表面铌氧物种的分散状态和催化性能

用X射线粉末衍射(XRO)、拉曼光谱(LRS)、Hammett指示剂和微反测试等方法考察了负载型Nb2O5/TiO2催化剂表面铌氧(NbOx)物种的分散状态、表面酸性和催化异丁烯(IB)与异丁醛(IBA)缩合生成2，5-二甲基．2，4．己二烯(DMHD)反应的催化性能．实验测得Nb2O5在TiO2表面的分散容量为0．94mmol／100m^2TiO2，与“嵌入模型”理论计算值相近．当负载量低于分散容量的1／3时，Nb2O5主要以孤立的NbOx物种通过Nb—O—Ti链与载体表面相连，这种孤立的NbOx物种酸性很弱，催化活性很低．随负载量的增加，孤立的NbOx物种通过Nb—O—Nb键连接聚合，表面酸性增强，IB与IBA缩合生成DMHD的转化数(TON)增加．当Nb2O5负载量超过分散容量时，表面NbOx物种主要是通过Nb—O—Nb化学键相连形成多层的Nb2O5虽然催化剂的强酸中心数量有所增加，但NbOx物种表面利用率下降，催化活性增加幅度趋缓．     

载钯硅磷酸铝分子筛催化剂的一步合成及其结构

将不同形式的钯源加入到硅磷酸铝子筛反应物凝胶中，用一步法直接合成了ＰｄＳＡＰＯ－５双功能催化剂，并对其进行了改性和表征。结果表明，ＳＡＰＯ－５可在较宽的ＰＨ值范围内合成，当钯以Ｈ２ＰｄＣｌ４加入时，并不影响ＳＡＰＯ－５分子筛的形成，溶液中的钯可完全均匀地分布在分子筛孔道中，而硅的分布状态略有改变     

Facile approach to obtain individual‐nanotube dispersion at high loading in carbon nanotubes/polyimide composites

A big challenge in making a composite lies in achieving individual‐nanotube dispersion of carbon nanotubes (CNTs) in a polymer matrix, without aggregation and entanglement and excellent interfacial adhesion between the CNTs and the polymers matrix. In this communication, using polyethylene glycol‐200, we successfully prepared CNT‐reinforced polyimide composites that exhibit individual‐nanotube dispertion in the matrix at high‐loading CNT's. The content of CNTs in a composite can reach 43 wt%. Copyright © 2007 John Wiley & Sons, Ltd.     

DYNAMIC RHEOLOGICAL BEHAVIOR OF POLYPROPYLENE FILLED WITH ULTRA-FINE POWDERED RUBBER PARTICLES

Dynamic rheological characteristics of polypropylene (PP) filled with ultra-fine full-vulcanized powdered rubber (UFPR) composed of styrene-butadiene copolymer were studied through dynamic rheological measurements on an Advanced Rheometric Expansion System (ARES). A specific viscoelastic phenomenon, i.e. “the second plateau“, appeared at low frequencies, and exhibits a certain dependence on the amount of rubber particles and the dispersion state in the matrix. This phenomenon is attributed to the formation of aggregation structure of rubber particles. The analyses of Cole-Cole diagrams of the dynamic viscoelastic functions suggest that the heterogeneity of the composites is enhanced on increasing both particle content and temperature.     

Low-temperature and long-time anomalies of a damped quantum particle

The time evolution of a damped quantum particle is discussed. Dissipation is modeled by the bilinear coupling to a set of harmonic oscillators. Using a functional integral technique that accounts for initial correlations between the particle and the reservoir, one can express the dynamics of the damped particle entirely in terms of equilibrium correlation functions. The long-time behavior of these correlations is determined for memory damping arising from the coupling to a reservoir with spectral densityI() at low frequencies, where > 0. The time evolution of nonequilibrium initial states of the damped particle is discussed. At finite temperatures an initially localized state is found to spread subdiffusively or superdiffusively, depending on . For > 2 the damping becomes ineffective for long times, and the width of a state grows kinematically. At zero temperature and for < 1, an initially localized state remains localized for all times. For 1 the state spreads, but with a slower rate than at finite temperatures. Study of arbitrary initial states indicates that the process is ergodic at finite temperatures only for 2 and at zero temperature for 1 2.     

Effect of TiO2 crystallite size on the dispersion of Co on nanocrystalline TiO2

Nanocrystalline TiO₂ powders with average crystallite sizes of 9–15 nm were synthesized by the solvothermal method and employed as supports for Co catalysts. The value of H₂ chemisorption/specific surface area of Co/TiO₂ increased significantly with increasing TiO₂ crystallite size. It was suggested that the higher amount of Ti³⁺ surface defects on the larger crystalline TiO₂ resulted in a stronger interaction between Co and TiO₂, hence, higher dispersion of Co was obtained.