Transport Coefficients in Water Plasma: Part I: Equilibrium Plasma

Knowledge of the transport coefficients of steam water plasma is important for modeling plasma flow processes and heat transfer. In this study, calculations of these properties were performed in a temperature range from 400 to 30,000 K and at pressures of 0.5, 1.0, 5.0 and 10 bar. Herein the composition of water plasma was determined at equilibrium. First, the most recent data on potential interactions and elastic differential cross sections for interacting particles were carefully examined in order to choose those most appropriate for determining the collision integrals. Second, we restricted the number of species to ten (e, H, O, H⁺, O⁺, O⁺⁺, H₂, O₂, OH and H₂O) and tested our collision integrals by comparing the thermal conductivity and viscosity to experimental data for water (at low temperatures). Finally, the total thermal conductivity, viscosity and electrical conductivity were calculated for different pressures.     

Indirect Synthesis System for Ammonia from Nitrogen and Water Using Nonthermal Plasma Under Ambient Conditions

The indirect synthesis of NH₃ from N₂ and H₂O through plasma processing is proposed and demonstrated. NH₃ is a promising hydrogen storage material because of its high hydrogen storage density. Mg₃N₂ is a key material for indirect NH₃ synthesis, because the reaction of Mg₃N₂ with water easily generates NH₃ at room temperature. In this paper, therefore, we focus on generating Mg₃N₂ by nitridation of MgO with nonthermal atmospheric-pressure dielectric barrier discharge (DBD) plasma in a N₂ atmosphere. By intermittent DBD nitridation treatment while the reaction device was cooled in a water bath, a maximum Mg₃N₂ generation efficiency of 93 mg/kWh was estimated. Because NH₃ is generated through a simple chemical reaction, our scheme does not cause NH₃ decomposition by plasma, which is one of the greatest concerns associated with plasma synthesis. Contrary to the conventional NH₃ generation process, which emits CO₂ and requires high temperature and pressure, our scheme enables NH₃ synthesis from N₂ and H₂O without CO₂ emissions. This allows for an onsite small-scale NH₃ synthesis system to be realized under mild conditions, which is necessary for a future low-carbon society.     

Concentration Effects in Size Exclusion Chromatography Under Equilibrium Stationary Conditions

Abstract

In size exclusion chromatography the elution volume increases with increasing concentration of injected polymer solutions. Several particular processes contribute to this concentration effect. Under model equilibrium stationary conditions, where the phases remain immobile, it is possible to eliminate dynamic phenomena connected with the higher viscosity of polymer solution in the chromatographic zone. The only factors operative here are the effect of changes in the effective size of macromolecules in solution with a change in concentration and the effect of the varying accessible pore volume with varying concentration. The ratio of these two contributions has been investigated both theoretically and experimentally. Theoretical calculations indicated that with both phenomena operating simultaneously, the elution volumes may increase or decrease with increasing concentration according to the given experimental conditions, as a result of the coupled influence of molecular parameters of the samples under study, of the thermodynamic quality of the solvent and of the distribution coefficient on the given porous material. Experimental results showed, however, that at least under stationary conditions secondary exclusion is probably operative to a less important degree.     

Plasma Characteristics and Plasma-Feedstock Interaction Under PS-PVD Process Conditions

Plasma spray-physical vapor deposition (PS-PVD) is a novel coating process based on plasma spraying. In contrast to conventional methods, deposition takes place not only from liquid splats but also from nano-sized clusters and from the vapor phase. This offers new opportunities to obtain advanced microstructures and thus to comply with growing demands on modern functional coatings. In this study, different process conditions were investigated with regard to the application of the PS-PVD process for ceramic thermal barrier coatings. Plasma characteristics were calculated under chemical equilibrium conditions by minimizing the Gibbs energy. The plasma-feedstock interaction was modeled taking into account the particular conditions at very low pressure. Since the plasma is highly rarefied, the small feedstock particles are in the free molecular flow regime. Hence, continuum methods commonly used in fluid mechanics and heat transfer approaches with continuous boundary conditions are not appropriate; alternative methods based on the kinetic theory of gases are required. The experimental results confirm the predictions about the degree of vaporization made by such calculations. In particular, they show that the feedstock treatment mainly takes place within the very first trajectory segment between injector and jet expansion.     

聚丙烯的动态和平衡态热刺激电流

通常的热刺激电流谱是等速升温测量结果，但解谱时要假设热平衡态的两个基本方程成立。若改进为采用阶跃升温方法，则可不必用这两个假设，实验将直接给出冷冻下来的极化电荷驰豫时间随温度的变化。以聚丙烯为例对两种方法的测量结果作了比较。     

Excitation Temperature and Constituent Concentration Profiles of the Plasma Jet Under Plasma Spray-PVD Conditions

Plasma spray-physical vapor deposition (PS-PVD) is a promising technology to produce columnar structured thermal barrier coatings with excellent cyclic lifetime. The characteristics of plasma jets generated by standard plasma gases in the PS-PVD process, argon and helium, have been studied by optical emission spectroscopy. Abel inversion was introduced to reconstruct the spatial characteristics. In the central area of the plasma jet, the ionization of argon was found to be one of the reasons for low emission of atomic argon. Another reason could be the demixing so that helium prevails around the central axis of the plasma jet. The excitation temperature of argon was calculated by the Boltzmann plot method. Its values decreased from the center to the edge of the plasma jet. Applying the same method, a spurious high excitation temperature of helium was obtained, which could be caused by the strong deviation from local thermal equilibrium of helium. The addition of hydrogen into plasma gases leads to a lower excitation temperature, however a higher substrate temperature due to the high thermal conductivity induced by the dissociation of hydrogen. A loading effect is exerted by the feedstock powder on the plasma jet, which was found to reduce the average excitation temperature considerably by more than 700 K in the Ar/He jet.     

Estimation of Diffusion Coefficients in Biomembranes

In this paper, the determination of diffusion coefficients in plant biomembranes for the nonstationary diffusion state is discussed. It is suggested that any point in the heterogeneous structures may be considered to be in Donnan equilibrium with a given external salt concentration. For this purpose, the non-stationary-state nonlinear differential equation for the salt concentration profile is solved numerically, which could be used to determine the diffusion coefficients of biomembranes from experimental concentration values in the receiver phase as a function of time. Quantitative relations were obtained which describe the time-dependent concentration changes of a membrane system with equilibrium distribution. Copyright 2000 Academic Press.     

Thermal Degradation of Polychloroprene Rubber Under Isothermal and Non-Isothermal Conditions

The results of a kinetic investigation of the non-isothermal degradation and the isothermal degradation of the residual deformation under constant deflection for polychloroprene rubber are presented. A relationship was derived between the degree of non-isothermal conversion and the value of the investigated mechanical property. This revised version was published online in July 2006 with corrections to the Cover Date.     

溶剂在高分子中的扩散系数-Vrentas-Duda模型及其发展

自由体积理论是描述高分子材料中低分子量溶剂扩散现象的有效工具,以此为基础的Vrentas-Duda模型中多数参数不需要扩散实验测量,可以通过分子性质独立确定,对渗透物的扩散行为具有可预测性。综述了Vrentas-Duda自由体积理论的发展和修正情况,分析其对建立预测型溶剂扩散系数模型的贡献,为从分子基团水平上探索溶剂扩散现象奠定基础。     

Soret Coefficients for Aqueous Polyethylene Glycol Solutions and Some Tests of the Segmental Model of Polymer Thermal Diffusion

A thermogravitational cell is used to measure Soret coefficients (s) for dilute binary aqueous solutions of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and polyethylene glycol (PEG) fractions with average molecular weights from 200 to 20,000 g-mol^–1. The cell design allows the top and bottom halves of the solution column to be withdrawn and injected into a high-precision HPLC differential refractometer detector for analysis. Previously reported mutual diffusion coefficients D and the measured Soret coefficients are used to calculate thermal diffusion coefficients D _T. s and D vary with the PEG molecular weight M as M ^+0.53 and M ^–0.52, respectively; hence, D _T = sD is essentially independent of M. The segmental model of polymer thermal diffusion predicts D _T = D_seg U _S/RT ², where D _seg is the segment diffusion coefficient, U _S the solvent activation energy for viscous flow, R the gas constant, and T the temperature. The predicted D _T values, although independent of M, are too large by a factor of five. Additional tests of the segmental model are provided using literature data for polystyrene + toluene, n-alkane + CCl₄, and n-alkane + CHCl₃ solutions. Agreement with experiment is not obtained. In particular, the measured D _T values for the alkane solutions are negative.     

Relevance and Assessment of Molecular Diffusion Coefficients in Liquid Chromatography

Molecular diffusion plays an important role in high-performance liquid chromatography, especially in fundamental column performance studies. An accurate knowledge of the molecular diffusion coefficients (D _m) of compounds selected for column evaluation is therefore crucial. In this review, a general overview is presented of the advantages and drawbacks of correlation-based and experimental methods that can be employed to determine molecular diffusion coefficients. The former include the Wilke–Chang, Scheibel, Reddy–Doraiswamy, Lusis–Ratcliff and Hayduk–Laudie equations, and other empirical correlations based on the Wilke–Chang equation. It is discussed how the association factor (ψ) that is required in several of these correlations can be obtained from the solubility parameter (δ). Frequently used experimental methods include the light scattering, nuclear magnetic resonance, peak parking and Taylor–Aris method, and methods employing microfluidic devices. The principles of these experimental methods are elucidated in detail. Moreover, the influence of several parameters, such as solute characteristics, solvent viscosity, temperature and pressure on the molecular diffusion coefficient is described.     

苯与DOP在LDPE与PEMA基体中无限稀释扩散系数的测定及研究

用逆流气相色谱法测定了苯、邻苯二甲酸二辛酯(DOP)在293～373K间在低密度聚乙烯(LDPE)、聚甲基丙烯酸乙酯(PEMA)基体中的无限稀释扩散系数,拟合了扩散系数与温度倒数的对数线性关系,并求得扩散活化能,发现它在玻璃化温度附近出现转折,且两者之间存在0．6倍关系。通过检验Vrentas-Duda自由体积扩散模型,发现在小分子无相变情况下该模型比较准确。     

Facile Montmorillonite K-10-Supported Synthesis of Xanthene Derivatives Under Microwave and Thermal Conditions

Microwave-assisted and thermal condensations of aromatic and aliphatic aldehydes with β-naphthol adsorbed onto montmorillonite K-10 were conducted in a one-pot procedure leading to the formation of a variety of xanthene derivatives. Under microwave irradiation, reactions completed within 4–6 min. The procedure is applicable to both aromatic and aliphatic aldehydes, and the catalyst was recycled and reused efficiently in later reactions.     

锂和钙在汞中的扩散系数测定

用汞阴极电解法制备锂汞齐和钙汞齐。用毛细管取－小滴汞齐挂洋电极上，以悬汞电极作荼电极，用计时安培法在－０．２Ｖ下测定了锂、钙在汞中的扩散系数。在２５℃下其值为ＤＬｉ＝（８．６５±０．１７）×１０＾－６ｃｍ＾２／ｓ；ＤＣａ＝（７．４３±０．１６）×１０＾－６ｃｍ＾２／ｓ。用Ｓｕｔｈｅｒｌａｎｄ－Ｅｉｎｓｔｅｉｎ扩散方程式计算了汞中扩散粒子半径，其值分别２４７ｐｍ和２８８ｐｍ。这些数值说明锂和钙都是以     

Diffusion Impedance in Natural Convection Conditions

An expression for the diffusion impedance in conditions of natural convection, when the diffusion layer thickness depends on the redox pair concentration, is obtained. The theory predicts a decrease in the steady-state diffusion resistance R _dby 1.25 times and a change in the coordinates of the extremum in an impedance spectrum and in the dimensionless R _dfrequency at this point (3.2 instead of 2.5) as compared to the classical theory, which is confirmed by experimental data for a reversible [Fe(CN)₆]^3–/4–system. The theoretical results are employed for correct determination of the concentration coefficient of the solution density.     

Diffusion Coefficients of Imidazolium Based Ionic Liquids in Aqueous Solutions

Diffusion coefficients of the ionic liquids [C₂MIM][EtSO₄], [C₄MIM][OcSO₄], [C₂MIM][NTf₂] and [C₄MIM][NTf₂] in water at high dilution have been measured using the Taylor dispersion technique. Data on the diffusion coefficients have been obtained for each solute at six temperatures between 288 and 313 K. The data have been fitted by the Arrhenius equation and activation energies of diffusion have been determined. Effective radii of the ionic liquid molecules have also been obtained using the Stokes–Einstein relationship.     

Analysis of the Thermokinetics Under Dynamic Conditions by Relative Rate of Thermal Decomposition

A novel parameter of the relative rate of thermal decomposition has been defined on the basis of an analysis of equation relating the logarithm of the conversion degree on the temperature. The dependence of this parameter on temperature in the dynamic conditions has been analyzed and discussed. The dependence of the relative rate of thermal decomposition is a linear relationship involving two coefficients. These coefficients can be related to the enthalpy and activation energy. The parameter developed has been used for the analysis of a series of consecutive reactions of thermal decomposition of calcium oxalate monohydrate. This revised version was published online in August 2006 with corrections to the Cover Date.     

A New Reagent for the Generation of Tetramethylcyclobutadiene Under Thermal or Photochemical Conditions

A new, stable, easy to prepare synthetic equivalent for tetramethylcyclobutadiene is described. This reagent can be used under thermal or photochemical conditions and offers advantages over existing alternatives.     

应用平衡稳定条件分析化学平衡的移动

化学平衡的移动规律是物理化学中重要的知识点之一。平衡稳定条件在经典热力学中占有重要的地位,但很少用于处理化学平衡问题。根据热力学原理,推导了简单的均匀隔离系统的平衡稳定条件,并将其用于分析温度和总压力对化学平衡移动的影响,结论为改变温度和总压力,使化学平衡朝着稳定平衡的方向移动。这种分析方法非常简单,也加深了我们对稳定平衡的理解。同时,也指出了该方法的局限性。