Multilayer adsorption with variable thickness at solid-liquid interfaces

 The multilayer adsorption on the solid/liquid interface in binary mixtures was studied by adsorption space filling with constant and variable layer thickness. Adsorption from benzene/n-heptane mixtures was examined on hydrophilic and hydro-phobic surfaces. The free enthalpy of adsorption, Δ₂₁ G=f (x ₁), was calculated from the adsorption excess isotherm by integration of the Gibbs equation. Supposing that the free enthalpy is mainly due to adsorption in the first layer, the composition of this layer can be calculated from the Δ₂₁ G=f (x ₁) function. It was established that the adsorption layer thickness in benzene/heptane mixtures increases significantly with increasing benzene content. This statement was supported by X-ray diffraction on hydrophobic clay minerals. Received: 2 April 1997 Accepted: 10 June 1997     

旋转薄层色谱分离聚合物

报道了旋转薄层色谱分级聚合物，及配合直接扫描密度法测定分子量分布的结果．在旋转薄层硅胶板上用混合溶剂成功地分离并直接收集了聚苯乙烯２１个级分，分子量测定结果与ＧＰＣ法基本一致．初步认为旋转薄层色谱以薄层吸附色谱分离机理为基础，采用连续注入流动相和旋转薄层板离心力相结合的方式，改善并加快了分离效果     

生物检材中乌头类生物碱的检验

 用薄层 (TLC)、高效液相 光电二极管阵列检测器 (HPLC/DAD)、动物实验等方法对生物检材中乌头生物碱进行检验 ,并对这些方法进行比较。结果发现 ,TLC法为此类药物检验筛选的首选方法 ,最小检出量为 0 3μg。在进行HPLC检测时 ,以乌头生物碱的特征紫外吸收光谱和动物实验结果为重要的定性手段 ,其特征吸收波长为 (2 2 8± 2 )nm和 (2 75± 2 )nm。乌头生物碱在 2mg/L～ 5 0mg/L时其峰面积与质量浓度有很好的线性 ,相关系数为 0 9996。经实际案件证明 ,方法准确、灵敏 ,可用于生物检材中乌头类生物碱的检验。     

Electrokinetic effects of adsorbed neutral polymers

On the basis of a previously developed hydrodynamic model for adsorbed polymers the charge flow along a charged interface with adsorbed (uncharged) polymer is calculated. An effective electrokinetic layer thickness is defined and its dependence on the characteristics of the adsorbed polymer and the ionic strength is studied. It is found that tails are very important for the hydrodynamic effects considered because they effectively screen the solvent flow from inner parts of the absorbed layer. The electrokinetic layer thickness increases with decreasing ionic strength, and tends to a limit equal to the hydrodynamic thickness at very low ionic strength.     

Theoretical analysis of the performance of a model supercapacitor consisting of metal oxide nano-particles

The factors influencing the electrochemical behaviour of a supercapacitor have been partly examined in this work. The effects of so-called intrinsic parameters, i.e. exchange current density, unit cell length and double layer (DL) capacitance; as well as the so-called application parameters, i.e. cell current, on the cell potential discharge time have been considered. The contributions of each type of capacitors, DL capacitor and faradaic supercapacitor under various states of operation and material have been analyzed, and the competing (compensating) effects of the two types of capacitors as regards to the discharge and power characteristics manifested by current–potential and energy–power (Ragone plots) are elucidated.     

A Procedure for Transforming Impedance Spectra for the Determination of Mechanism of Electrochemical Reactions

Transformation of impedance spectra into relaxation time spectra (RTS) is used for determining contributions of individual processes of the oxygen electroreduction reaction (OER) to the polarization resistance of the electrochemical cell. The transformation technique involves the solution of the convolution equation found with the aid of a modified Van Cittert iteration algorithm checked on model impedance spectra. The technique, when used to analyze impedance spectra of electrochemical cells air|Pt|YSZ|YSZ + Pt|air, shows that the conversion of a globular structure of the YSZ + Pt cermet layer to a columnar one is accompanied by a change of peak amplitudes in RTS. The revealed RTS dynamics when heated to 750°C is compared with peculiarities of individual processes in OER.     

碳纳米管添加剂对质子交换膜燃料电池低铂载量膜电极性能的影响研究

以碳纳米管（CNT）作为低铂载量膜电极（CCM）催化层（0.1 mg_Pt·cm^-2）添加剂，研究了CNT的添加方式对催化层微观结构以及膜电极性能的影响.结果表明，与常规低铂载量催化层相比，在其表面喷涂一层CNT或将CNT均匀分散到Pt/C催化层中均有利于提升低铂载量膜电极的输出性能，在70℃和100%相对湿度条件下最高输出功率比常规低铂载量膜电极的0.522 W·cm^-2分别提升了22.4%和60.0%，并且均匀分散添加方式优于分层添加方式.其原因在于分层添加CNT后改善了低铂催化层和气体扩散层之间的接触界面，降低了催化层与扩散层间的接触电阻，而均匀分散添加方式除了可降低界面接触电阻外，还显著改善了低铂催化层中的气体传输，大幅提升了Pt催化剂的利用效率，使得膜电极电化学反应电阻明显降低.进一步对均匀分散添加方式中CNT的载量进行优化，表明CNT添加量为37.5 μg·cm^-2时电池输出性能最佳，70℃和100%相对湿度条件下的最大输出功率达到0.91 W·cm^-2.本研究工作表明，将CNT均匀分散添加到催化层中是一种有效提升低铂载量膜电极性能的方法.     

Cathode of a fuel cell with a solid polymer electrolyte: Calculating overall currents in the presence of a gas-diffusion layer

Mathematical apparatus, which makes it possible to perform calculations of the current-voltage characteristics of cathodes of fuel cells with a solid polymer electrolyte in conditions where there are present extraneous diffusion restrictions is proposed. In so doing, the partial pressure of oxygen and the absolute pressure of gas in the gas chamber may assume any values. First of all presented are the results of calculations of the current-voltage characteristics intrinsic to active layers of the air and oxygen cathodes, which are performed under the assumption that the extraneous diffusion restrictions are absent altogether. Thereafter, in the same conditions (at the same parameters that characterize the active layer of a cathode), obtained are results of a calculation of the current-voltage characteristics inherent in the air and oxygen cathodes in the presence of extraneous diffusion restrictions. Afterward there is performed an analysis of the way a gas-diffusion layer restricts the process of generation of current in a cathode and of what measures should be taken in order for the extraneous diffusion restrictions to become less significant.     

无烟煤结构的高分辨电镜研究

镜质组不仅是煤结构变化最具规律性，也是影响煤质的主要微成分。用点分辨率为２．１Ａ的高分辨电镜对几种不同煤化程度的无烟煤大分子结构进行了研究。结果表明：电镜图像直接表征了无烟煤分子的非均匀性孔隙结构。京西煤分子方向化程度强，主要以芳层平行堆或有序化前结构为主；晋城煤方向化程度弱，主要以粒状嵌晶结构为主。高分辨电镜技术是研究煤分子结构和煤化作用实质的有效方法。