Shear elasticity of a liquid in bulk and in boundary layers

Resonance measurements at 7.5 × 10⁵ Hz reveal a measurable bulk shear elasticity for various liquids (water, acetone, benzene, alcohols, acetic acid, CCl₄, oil). The shear modulus of a nonpolar liquid is independent of the layer thickness. A polar liquid shows a sharp increase in the shear elasticity at distances less than 10^-5 cm from the surface of the quartz.     

固体氧化物燃料电池电化学阻抗谱差异化研究方法和分解

电化学阻抗谱技术(EIS)在固体氧化物燃料电池(SOFC)中已获得广泛应用。在EIS分析过程中,研究者能够清楚地获得燃料电池内部因纯离子(电子)导电引起的欧姆电阻和因电化学过程、扩散作用引起的极化阻抗的大小,但是对于极化阻抗的构成缺乏进一步解析。本文选用传统的Ni-YSZ阳极支撑电池,通过改变测试温度、阳极运行气氛和阴极运行气氛,设计了一套完整的阻抗差异分析(ADIS)实验。并基于弛豫时间分布法(DRT)和阻抗差异分析法,系统地分析并解释了阻抗谱中各频率段对应阻抗的物理或(电)化学含义,将该类型电池阻抗谱以6个RQ并联电路予以拟合,为之后燃料电池性能稳定性的研究奠定基础。     

Fast, low-level detection of strontium-90 and strontium-89 in environmental samples by collinear resonance ionization spectroscopy

Environmental assessment in the wake of a nuclear accident requires the rapid determination of the radiotoxic isotopes ⁸⁹Sr and ⁹⁰Sr. Useful measurements must be able to detect 10⁸ atoms in the presence of about 10¹⁸ atoms of the stable, naturally occurring isotopes. This paper describes a new approach to this problem using resonance ionization spectroscopy in collinear geometry, combined with classical mass separation. After collection and chemical separation, the strontium from a sample is surface-ionized and the ions are accelerated to an energy of about 30 keV. Initially, a magnetic mass separator provides an isotopic selectivity of about 10⁶. The ions are then neutralized by charge exchange and the resulting fast strontium atoms are selectively excited into high-lying atomic Rydberg states by narrow-band cw laser light in collinear geometry. The Rydberg atoms are then field-ionized and detected. Thus far, a total isotopic selectivity of S > 10¹⁰ and an overall efficiency of ξ = 5 × 10⁻⁶ have been achieved. The desired detection limit of 10⁸ atoms ⁹⁰Sr has been demonstrated with synthetic samples.     

稀土聚丁二烯的结晶行为与分子量及温度的关系

本工作研究了稀土催化聚合的聚丁二烯(Ln-PB)的结晶速率与分子量的关系。结果表明Ln-PB的结晶速率在_η=5.6×10⁵左右有一极小值,而在_η=3.4×10⁶左右有—极大值。 从实验中还发现,Ln-PB的结晶在-20℃左右,由单二维核生长逐渐转变为多二维核生长。 本作工根据结晶成核理论,计算了不同分子量Ln-PB结晶折叠面的比表面能,σ_e表明当 η<10⁶时,σ₃随分子量的变化很小;当_η>10⁶时,σ_e随分子量的增加明显增大。     

Synthesis and Characteristics of Fe_3C Nanoparticles Embedded in Amorphous Carbon Matrix

We proposed a new way to synthesize a nanocomposite consisted of cementite Fe3C nanoparticles and amorphous carbon by radio frequency plasma-enhanced chemical vapor deposition. Transmission electron microscope images show the existence of nanometric dark grains(Fe3C) embedded in a light matrix(amorphous carbon) in the samples. X-ray photoelectron spectroscopy experiment exhibit that the chemical bonding state in the films corresponded to sp3/sp2 amorphous carbon, sp3 C―N(287.3 eV) and C1s in Fe3C(283.5 eV). With increasing deposition time, the ratio of amorphous carbon increased. The magnetic measurements show that the value of in-plane coercivity increased with increasing carbon matrix concentration(from about 6.56×103 A/m for film without carbon structures to approximately 2.77×104 and 5.81×104 A/m for nanocomposite films at room temperature and 10 K, respectively). The values of saturation magnetization for the synthesized nanocomposites were lower than that of the bulk Fe3C (140 Am2/kg).     

Hydrophilic interaction liquid chromatography with indirect ultraviolet detection for the separation and quantification of pyrrolidinium ionic liquid cations

A method of hydrophilic interaction liquid chromatography with indirect ultraviolet detection was developed to determine three pyrrolidinium ionic liquid cations, i.e. N-methyl-N-ethyl pyrrolidinium cation ([MEPy]⁺), N-methyl-N-propyl pyrrolidinium cation ([MPPy]⁺) and N-methyl-N-butyl pyrrolidinium cation ([MBPy]⁺). Chromatographic separation was achieved on a hydrophilic column using imidazolium ionic liquids and organic solvents as the mobile phase. The effects of the background ultraviolet absorption reagents, the imidazolium ionic liquids, detection wavelength, organic solvents, column temperature and the pH value of the mobile phase on the separation and determination of pyrrolidinium cations were investigated and the retention behaviors in hydrophilic interaction chromatography were discussed. The optimized chromatographic conditions were selected. Under the optimal conditions, the detection limits (S/N = 3) for [MEPy]⁺, [MPPy]⁺ and [MBPy]⁺ were 0.59, 0.53 and 0.46 mg/L, respectively. The method has been successfully applied to the determination of the three ionic liquids synthesized in our chemistry laboratory. This research results may improve the analytical method of ionic liquid cations.     

Estimation of the emission temperature of an electrodeless discharge lamp and determination of the oscillator strength for the I(P3/2) 183.038 nm resonance transition

The 183.038 nm resonance absorption transition of I(²P_3/2) has been studied using a flash photolysis set-up for gas-phase chemistry and a radio frequency powered electrodeless discharge lamp filled with iodine. The dependence of self-absorption and self-reversal on iodine partial pressure in the discharge volume was measured. The optimum iodine partial pressure, with self-absorption minimized and acceptable intensity, is determined to be approximately 2.5×10⁻³ mbar. A method is described to estimate the temperature of the emitting atoms using direct measurements of relative absorption at different absorber concentrations. This yields an emission temperature of 923±50 K. Using this temperature, the oscillator strength for the I(²P_3/2) transition at 183.038 nm is determined to be f=(3.87±0.57)×10⁻³, corresponding to an absorption cross-section at the center of the line of σ=(5.42±0.8)×10⁻¹⁴ cm² atom⁻¹_. This shows a difference from one of two earlier measurements, but is close to the other. The remaining difference from the latter measurement is probably due to tendencies of opposite biases inherent to the experiments.     

Cu ion core conservation from reactant to product in the Cu+F2 chemiluminescent reaction

Electronic chemiluminescence from the reaction of selected ground state (²S_1/2) or metastable (²D_5/2, ²D_3/2) copper atoms with fluorine has been studied using a hollow cathode-flowing afterglow reactor. The observed signal related to the Cu(²S) and Cu*(²D) atom densities, indicate that the chemiluminescence cross-section for Cu*(²D) atoms is about 10⁴ times larger than for Cu(²S) atoms. This strong propensity is explained in terms of a direct reaction, initiated by a harpooning process, during which the Cu⁺ ion core of the reactant (3d¹⁰ for Cu(²S) and 3d⁹4s for Cu*(²D)) is conserved in the products (ionic structure Cu⁺(3d¹⁰)F⁻ for the CuF ground state and Cu⁺(3d⁹4s)F⁻ for the CuF*(a, A, B, C, D) chemiluminescent states).     

Molecular alignment of the 4-octyl-4'-cyanobiphenyl liquid crystal filled with SiO2

The molecular dynamics and molecular alignment of the dispersed 4-octyl-4'-cyanobiphenyl (8CB) liquid crystal with 5 wt % of SiO₂ nanosphere particles have been studied using dielectric spectroscopy. The measurements were performed in the frequency range between 10²-10⁷ Hz in the SmA, N and I phases. The results show only one Debye relaxation process at high frequency (10⁵-10⁷ Hz). In the bulk material, activation energies of 40, 58 and 63 kJ mol^-1 were determined for the SmA, N and the I phases, respectively. In the dispersed sample, the activation energies were found to be 52, 76 and 81 kJ mol^-1, respectively. These results are compared with the available data in the literature. The reversible electromechanical response of the dispersed sample under the influence of an applied a.c. electric field was investigated in the SmA, N, and I phases.     

TiO_2纳米管阵列光电极的电化学阻抗及动力学特性分析

采用声电化学阳极氧化法,在无机溶剂(H3PO4+NaF水溶液)和有机溶剂(NH4F+水+乙二醇)体系电解液中加20V直流电压制得TiO2纳米管(TNT)阵列,其中无机溶剂样品(记为TNT-A)的管长为650nm,有机溶剂样品(记为TNT-E)的管长为2μm.基于X射线衍射(XRD)图谱、场发射扫描电子显微镜图(FESEM)、紫外-可见漫反射光谱(UV-VisDRS)的表征和电流-时间(I-t)曲线、Mott-Schottky图和电化学阻抗谱(EIS)的分析可知,在空气中经500℃煅烧后,TNT-E的吸光性能明显好于TNT-A的吸光性能.在紫外光((365±15)nm)辐照下,测得TNT-E的平均光电流密度与TNT-A的仅差0.05mA·cm-2,这是由于管长的增长增大了电荷转移电阻,并使得传质路径增长,增大了反应所需克服的势垒,降低了电极的反应速率,两者的电荷载流子密度分别为5.31×1020与9.86×1020cm-3.     

Proton mobility in hydrated sulfonated polystyrene: NMR and impedance studies

Different ionomers were obtained by sulfonation of a commercial polystyrene (PS), using acetyl sulfate as reagent. The sulfonation was assessed by FTIR and XPS spectroscopies and the thermal and mechanical properties were deduced from DMA measurements. The acid form of the ionomers was characterized by means of ¹H and ¹³C MAS-NMR spectroscopies. Polymer hydration under controlled humidity atmosphere was analyzed by gravimetric, NMR and complex impedance techniques. In the hydrated state, two stages associated with formation of hydronium (H₃O⁺) species and proton hopping between adsorbed water molecules were deduced from NMR data. Both processes are responsible for important changes detected in mechanical properties and conductivity of sulfonated polymers during hydration processes.     

Determination of picogram amounts of technetium in environmental samples by neutron activation analysis

A procedure for the determination of trace amounts of ⁹⁹Tc in filter paper and vegetation samples by neutron activation analysis has been developed. The procedure consists of the following major steps: (a) pre-irradiation separation of technetium from the sample and purification of the technetium fraction; (b) thermal neutron irradiation of the ⁹⁹Tc fraction to produce ¹⁰⁰Tc ; (c) post-irradiation separation and purification of ¹⁰⁰Tc from other activated nuclides: (d) counting of the 16-sec ¹⁰⁰Tc in a low-background β-counter.

The estimated detection limits for ⁹⁹Tc by this procedure with irradiations at a thermal neutron flux of about 5.10¹³ n cm^-2 sec^-1 are: 5.lO^-12g ⁹⁹Tc in filter paper samples, and 9. 10^-12 g ⁹⁹Tc in vegetation samples.     

溶液浓度对拉曼光谱线宽和频移影响的实验研究

将液芯光纤技术用于傅里叶变换拉曼光谱测量中,提高拉曼光谱强度10²～10⁴倍.应用该技术,在实验上研究了溶液浓度变化对β-carotene,rhodamine在CS²中的CC键π-π^*跃迁拉曼线频移和线宽的影响.实验结果表明,随着浓度降低(1×10^-7～1×10^-12mol/L),拉曼光谱线峰值发生红移,线宽变窄.     

NMR Study of Pore Surface and Size in a Mesoporous Material FSM-16

Surface structure, pore size distribution and pore wall thickness of a mesoporous material FSM-16 have been studied by X-ray powder diffraction (XRD), ^lH and ²⁹Si MAS NMR and ¹H liquid-state NMR, and by applying surface silylation as a probe. Concentrations of surface hydroxyl groups for FSM-16 are estimated from ²⁹Si and ¹H MAS NMR, which are about 3×l0²¹ g^-1, corresponding to approximately 3 nm^-2. O₂ molecules contribute to ²⁹Si spin-lattice relaxation of Q² and Q³ as well as Q⁴, suggesting thin wall thickness. ¹H MAS NMR spectra indicate the presence of isolated and hydrogen-bonded hydroxyl groups. Both hydroxyl groups are silylated, where the silylated fraction is about 50%. The spatial distribution of surface hydroxyl groups is estimated from the line width in ¹H static spectra. A rather homogeneous distribution is demonstrated in one of the samples. The sample with less homogeneous distribution has a larger affinity for moisture. Pore size and pore wall thickness were determined by ¹H NMR measurements on water saturated FSM-16 samples, which are in good agreement with literature values obtained by N₂ adsorption isotherms and transmission electron micrographs on a similar sample. In benzene saturated samples, a non-freezing surface layer of benzene is much thicker than that of water, which indicates a stronger interaction between benzene and the FSM-16 surface.     

纳米八面体形FeP@PC的制备及催化析氢性能

以UIO-66为载体, 经过FeCl₃化学气相沉积、 原位碳化和磷化及HF刻蚀等步骤制备了多孔FeP@PC催化剂. 利用X射线衍射仪、 场发射透射电子显微镜、 X射线光电子能谱仪和气体吸附仪等对催化剂的结构、 形貌和比表面积等进行了表征; 同时采用线性扫描伏安法和电化学阻抗谱等对其电化学性质进行了考察. 结果表明, FeP@PC保持了原UIO-66的八面体多孔结构, 比表面积为83 m ²/g; 仅需要过电位156 mV即可驱动电流密度10 mA/cm ², 塔菲尔斜率为84 mV/dec, 电荷转移电阻为44 Ω, 电化学活性表面积为13.9 mF/cm ²; 在持续电解12 h和循环1000次后, 催化剂的活性几乎没有衰减.     

Spectra and structure of phosphorus-boron compounds : IV. Vibrational spectra of solid trifluorophosphineborane

The Raman spectra of F₃PBH₃ and F₃PBD₃ have been recorded (2500-10 cm⁻¹) of the liquids (−80°C) and solids (−196°C) as well as the infrared spectra (4000-33 cm⁻¹) of the solids. In the spectrum of the solid state many of the ¹⁰B and ¹¹B fundamentals were clearly defined and it was also possible to assign the BH₃ torsional frequency from the infrared and Raman spectra of the solids. A complete vibrational assignment is proposed and a normal coordinate calculation carried out. The force constant of 2.46 mdyn Å⁻¹ for the P-B stretching mode is consistent with the short P-B bond; this constant is compared to the similar quantity for several other phosphorus-boron compounds. All of the E modes for the “free” molecule are shown to be split by the site symmetry which indicates that the molecules occupy C_s or C₁ sites. The large number of observed lattice modes is consistent with two or more molecules per primitive cell. The torsional frequency was observed at 224 cm⁻¹ and 167 cm⁻¹ in hydrogen and deuterium compounds in the solid, respectively. These frequencies gave a periodic barrier of 4.15 kcal mole⁻¹ for F₃PBH₃ and 4.31 kcal mole⁻¹ for F₃PBD₃. CNDO/2 calculations have been carried out for F₃PBH₃ and the isoelectronic F₃SiCH₃ molecule in both the staggered and eclipsed forms and the dipole and barrier origins are discussed.     

十氢萘/空气混合物高温着火延迟的激波管测量

在激波管上进行了气相十氢萘/空气混合物的着火延迟测量, 着火温度为950-1395 K, 着火压力为1.82×10⁵-16.56×10⁵ Pa, 化学计量比分别为0.5、1.0 和2.0. 在侧窗处利用反射激波压力和CH^*发射光来测出着火延迟时间. 系统研究了着火温度、着火压力和化学计量比对十氢萘着火延迟时间的影响. 实验结果显示着火温度和着火压力的升高均会缩短着火延迟时间. 首次在相对高和低压的条件下观察到了化学计量比对十氢萘着火延迟的影响是完全相反的. 当压力为15.15×10⁵ Pa时, 富油混合物呈现出最短的着火延迟时间, 而贫油混合物的着火延迟时间却是最长的. 相反, 当压力为2.02×10⁵ Pa时, 富油混合物的着火延迟时间最长. 着火延迟数据与已有的动力学机理的预测值进行对比, 结果显示机理在所有的实验条件下均很好地预测了实验着火延时趋势. 为了探明化学计量比对着火延迟时间影响的本质, 对高、低压条件下的着火延时进行了敏感度分析.结果显示, 压力为2.02×10⁵ Pa时, 控制着火延迟的关键反应为H+O₂=OH+O, 而涉及十氢萘及其相应自由基的反应在15.15×10⁵ Pa时对着火延迟起主要作用.     

Measurement of the Low-Frequency Shear Modulus of Polymeric Liquids

Abstract

The present work describes the resonance method for measurement of a low-frequency (about 10⁵ Hz) complex shear modulus of liquids by the use of a piezoquartz crystal. The problem of interaction of an oscillating system of the type piezoquartz-liquid interlayer-cover plate is analyzed. From the analysis of the problem there follow three methods for measuring the elasticity modulus of liquids. The investigation results of a homologous series of polymethyl siloxane liquids are presented. It has been shown that as the molecular weight of the series being investigated increases, the elasticity modulus value also increases, while the mechanical losses angle tangent passes through its maximum.     

空间高速粒子捕获用密度梯度气凝胶的热学与力学特性

采用正硅酸四乙酯(TEOS)的乙醇-水溶液为前驱体,氢氟酸为催化剂,结合溶胶-凝胶过程与CO2超临界流体干燥工艺,一步反应获得了密度为40-175mg·cm-3的单元气凝胶.以上述工艺为基础,通过逐层凝胶法、溶胶共凝法和梯度溶胶共凝胶法分别制备了三种密度梯度气凝胶样品,并研究了其功能梯度特性.结果表明:不同密度的气凝胶均具有粒径约为40-90nm球形颗粒构成的三维骨架结构,密度越低,骨架越疏松,峰值孔径越大,孔径分布也更为分散;三种方法制备的样品均具有明显的密度梯度,梯度特性由不连续到连续.动态热机械性能测试表明,随着密度的降低,气凝胶在低温(-100℃)和常温(25℃)下杨氏模量均有减小的趋势,其范围分别约为4.6×105-1.9×105Pa和5.0×105-2.1×105Pa.热学测试表明,随着密度的降低,气凝胶的热扩散系数增高,单位体积热容降低,而热导率则不成单调变化.     

Kinetic processes of Hg6s6p(P1) in xenon

The principal route for decay of Hg 6s6p(³P₁) in xenon is shown to be bimolecular deactivation to the mercury ground state, with rate coefficient 9.1 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹; relaxation to the ³P₀ state plays a negligible role. The equilibrium constant of the reaction Hg(³P₁) + Xe HgXe(A ³O⁺), has been recorded as 1.73 × 10⁻²⁰ cm³ molecule⁻¹ at 293 K.