Experimental study on high-pressure adsorption of hydrogen on activated carbon

A systematic measurement of H2 adsorption on activated carbon over a wide scope of conditions was completed for the first time using a novel cryostat developed by the present authors. The equilibrium temperatures covered 77-298 K with the space of about 20 K, and the equilibrium pressures increased from 0 to about 7MPa. A set of adsorption/desorption isotherms was obtained by a standard volumetric method. This set of experimental data was fitted to all the well-known models of type-I isotherms, and Dubinin-Astakhov (D-A) equation was found to be the best-fit one On the basis of D-A model one can predict adsorption with relative error of ±4%. A 3-dimensional adsorption surface was also constructed, and the isosteric heat of adsorption was analytically determined. Except in the low pressure area, the calculated values agreed well with the experimental ones. Finally, the troubles encountered in applying D-A equation to supercritical adsorption is discussed.     

聚合物介质中盐离解行为的温度依赖性研究

<正> 近十年来尽管聚合物-盐复合物作为潜在的理想电解质材料已得到广泛研究,人们对于在象聚合物这样的高粘度介质中盐的离解行为仍缺乏了解。特别是关于盐离解度的温度依赖性,不同的作者对相似的体系曾得出截然相反的结论。最近,Angell和许康等相继通过不同研究途径证实了在上述介质中盐离解产生的自由离子数n随温度上升而下降,其趋势可由Arrhenius公式表示:     

纳滤膜对电解质溶液分离特性的理论研究(II): 混合电解质溶液

假定纳滤膜具有狭缝状孔, 使用纯水透过系数、膜孔径及膜表面电势来表征纳滤膜的分离特征, 用流体力学半径和无限稀释扩散系数表征了离子特性. 采用扩展Nernst-Planck方程、Donnan平衡模型和Poisson-Boltzmann理论描述了混合电解质溶液中离子在膜孔内的传递现象, 计算了三种商用纳滤膜(ESNA1-LF, ESNA1和LES90)对同阴离子、同阳离子和含四种离子的混合电解质体系中离子的截留率, 并与实验数据进行了比较. 计算结果表明, 电解质溶液中离子在纳滤膜孔内传递的主要机理是离子的扩散和电迁移, 纳滤膜对混合电解质溶液中离子的分离效果主要由空间位阻和静电效应决定. 该模型在低浓度时对含一价离子的混合电解质溶液通过纳滤膜的截留率计算结果比较准确, 但对高浓度或含高价离子的混合电解质溶液则偏差较大.     

Mutual solubilities of hydrocarbons and water with the CPA EoS

The knowledge of hydrocarbon/water phase equilibria is important in the design and operation of equipment for petroleum transport and refining and petrochemical plants. The presence of water in a hydrocarbon mixture can affect the product quality and damage the operation equipment due to corrosion and formation of gas hydrates. Tracing the concentration of hydrocarbons in aqueous media is also important for technical purposes like preventing oil spills and for ecological concerns such as predicting the fate of these organic pollutants in the environment.     

Tafel slopes from first principles

Tafel slopes for multistep electrochemical reactions are derived from first principles. The derivation takes place in two stages. First, Dirac’s perturbation theory is used to solve the Schrödinger equation. Second, current–voltage curves are obtained by integrating the single-state results over the full density of states in electrolyte solutions. Thermal equilibrium is assumed throughout. Somewhat surprisingly, it is found that the symmetry factor that appears in the Butler–Volmer equation is different from the symmetry factor that appears in electron transfer theory, and a conversion formula is given. Finally, the Tafel slopes are compiled in a convenient look-up table.     

水在纳米管道中流动行为的分子动力学模拟

采用分子动力学方法模拟了纳米管道内水分子的流动行为. 考察了压强差、 管道直径和管道长度对通量的影响, 验证了流体在直径为2～2.8 nm管道中的流动行为符合Hagen-Poiseuille(HP)方程. 研究发现, 末端效应具有长度依赖性, 对于较短的管道其末端效应更为显著. 为了深入了解真实非均匀管道的流动行为, 使用直径不同的2种管道以不同的连接顺序组合成4种非均匀管道模型, 最终得到了不同的流量. 提出了二元管道模型, 对非均匀管道内的流动行为进行了初步探讨.     

Isometric crystallization of stretched poly(e-caprolactone) sheets for medical applications

Low melting temperature thermoplastic sheets based on poly(e-caprolactone) (PCL) can be formed directly on the patient and are used as immobilization device (mask) in the radiation therapy. The immobilization mask is allowed to harden in isometric conditions on the body at room temperature. A new method for isometric crystallization kinetics of thermoplastic polymer sheets is developed using a tensile-strength instrument. The isometric crystallization method allows investigating the shrinkage force on time of crystallization of stretched samples of thermoplastic polymer sheets or immobilization medical devices. The dependence of the shrinkage force on time is described by Avrami equation and the kinetics parameters of isometric crystallization are calculated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of defect induced surface heterogeneity in Metal-Organic Framework materials with alkali dopants employing adsorption isotherm modelling

In this article, an assessment of surface structural heterogeneity in porous metal organic framework (MOF) structure has been demonstrated by employing the methane and carbon-dioxide adsorption isotherms data. The virgin MIL-101-(Cr) MOF was synthesized by the hydrothermal method and defects were induced in the MOF structure by doping with various alkali (K, Na, Li) cations. The synthesized MOFs were characterized by XRD, SEM, EDX and BET measurement techniques. In order to understand the defect induced surface heterogeneity by alkali cation dopants, the surface energy distributions for CH₄ and CO₂ adsorptions on MOFs were measured by Dubinin – Astakhov model equation. The surface heterogeneity is mainly controlled by the limiting uptakes of adsorbates, the polarizability of adsorbates and the adsorbate-adsorbent interaction energy.     

斜波压缩下HMX晶体的弹塑性行为

开展了（010）、（011）晶向HMX晶体的斜波压缩实验,获得了约15 GPa压力下的速度响应剖面。实验结果表明,HMX单晶存在明显弹塑性转变行为,且速度波形有下降趋势,这是材料的黏性效应导致,材料的弹性极限随着样品厚度增加而变化,不同晶向的材料动力学特性存在差异。结合Hobenemser-Prager黏弹塑性本构关系和三阶Birch-Murnaghan物态方程开展了HMX晶体斜波压缩物理过程的数值模拟,计算结果可以很好地描述HMX晶体的弹塑性转变这一物理过程。