Measurement of sorption and diffusion in nonporous membranes by transient permeation experiments

The knowledge of sorption and diffusion of liquids or vapors and their mixtures in nonporous membranes facilitates systematic membrane selection and process design. A novel experimental technique for the measurement of sorption and diffusion in nonporous membranes is described. An experimental apparatus has been designed for carrying out the transient permeation experiments. A general time-lag analysis procedure has also been developed in order to obtain the sorption and diffusion parameters from the transient permeation data. The effects of concentration dependent diffusivities, polymer swelling and a thermodynamic correction factor have been included in the analysis. Transient permeation experiments have been carried out to determine the sorption and diffusion of acetone in polydimethylsiloxane (PDMS). The results obtained are in good agreement with data from the literature, indicating that the proposed technique is suitable for the measurement of sorption and diffusion in nonporous membranes.     

Real-time monitoring of Yb vapor density using an extended cavity violet diode laser

Based on laser absorption spectroscopy (LAS), we developed a vapor density monitor for controlling the vaporization rate of Yb using a tunable diode laser. The laser source consisted of an extended cavity violet diode laser which has an emission wavelength of 398.8 nm coincident with the Yb absorption transition line, 6s(2) 1S(0)-6s6p 1P(1). The light emitted from the diode laser was transmitted across an atomic vapor column generated by heating the Yb metal, while the laser frequency was scanned across the atomic transition line. By comparing the amount of incident light to the amount of light transmitted after the light passed through the vapor column, the vapor density was determined using the Beer's law. From the experimental results, we demonstrated that the diode-laser-based LAS operated successfully for the real-time monitoring of the Yb vapor density.     

化学气相沉积聚合制备羧基取代聚对亚苯基二亚甲基及其性能研究

用化学气相沉积(CVD)聚合法制备了羧基取代聚对亚苯基二亚甲基(PPX-carb)膜,采用FTIR和元素分析的方法证实了其化学结构.对膜溶解性和抗化学氧化性能的研究表明PPX-carb膜仍具有优异的耐溶剂性和抗化学氧化性能.对PPX-carb膜热性能的研究表明羧基的引入使得膜的玻璃化转变温度降低,室温柔性增强,动态力学阻尼性能增大,与聚对亚苯基二亚甲基(PPX)相比引入了羧基的PPX-carb热稳定性有所下降,热降解起始温度比PPX低,但主链降解温度比PPX反而高出约80℃.此外,羧基的引入使得膜的亲水性能大幅度提高,水汽渗透性能也有所提高.     

氯仿,乙醇,苯有关二元体系加压相平衡研究

氯仿、乙醇、苯有关二元体系加压相平衡研究马忠明，陈庚华，王琦，严新焕，韩世钧，余淑娴（浙江大学化学系，杭州，３１００２７）（江西大学化学系）关键词加压汽液平衡，醇烃体系，氯仿，乙醇，苯醇是极性分子，烃是非极性或弱极性分子，醇与醇、烃与烃分子及醇与烃分...     

Laser Photochemistry at Surfaces—Laser-Induced Chemical Vapor Deposition and Related Phenomena

The structural characterization of materials and the tailoring of their properties is an important area of chemical research. A new trend in this area is the recourse to lasers both for analytical as well as preparative purposes, exploiting the fact that lasers, by virtue of their properties (sharp energy, spatial and temporal resolution etc.), offer the most precise and selective interaction of energy and matter that we know. Furthermore, photochemical syntheses and material transformations can proceed “cold” and without causing damage to surface structures. Laser chemistry finds application in thin film deposition, in the formation of surface layers, as well as in (structuring) ablation or etching, and in the initiation and enforcing of reactions at surfaces. In the present paper an introduction to these new possibilities on the general basis of molecule-surface interactions is followed by a brief characterization of lasers suitable for such purposes. Thereafter, four examples are discussed: gas phase deposition from volatile organometallic compounds with photoelectric activation at the surface or photochemical activation of the gaseous species (e.g. by employing molecular beams). In this way (noble) metal contacts can be deposited on various substrates. Instead of surface deposition, nucleation can occur in the gaseous medium, yielding highly disperse powders, e.g. of silicon carbide. Finally, an etching reaction is discussed where the laser does not act as an energy source but as an analytical instrument to provide diagnostic and mechanistic information.     

Experimental densities,vapor pressures,and critical point,and a fundamental equation of state for dimethyl ether

Densities, vapor pressures, and the critical point were measured for dimethyl ether, thus, filling several gaps in the thermodynamic data for this compound. Densities were measured with a computer-controlled high temperature, high-pressure vibrating-tube densimeter system in the sub- and supercritical states. The densities were measured at temperatures from 273 to 523 K and pressures up to 40 MPa (417 data points), for which densities between 62 and 745 kg/m³ were covered. The uncertainty (where the uncertainties can be considered as estimates of a combined expanded uncertainty with a coverage factor of 2) in density measurement was estimated to be no greater than 0.1% in the liquid and compressed supercritical states. Near the critical temperature and pressure, the uncertainty increases to 1%. Using a variable volume apparatus with a sapphire tube, vapor pressures and critical data were determined. Vapor pressures were measured between 264 and 194 kPa up to near the critical point with an uncertainty of 0.1 kPa. The critical point was determined visually with an uncertainty of 1% for the critical volume, 0.1 K for the critical temperature, and 5 kPa for the critical pressure. The new vapor pressures and compressed liquid densities were correlated with the simple TRIDEN model. The new data along with the available literature data were used to develop a first fundamental Helmholtz energy equation of state for dimethyl ether, valid from 131.65 to 525 K and for pressures up to 40 MPa. The uncertainty in the equation of state for density ranges from 0.1% in the liquid to 1% near the critical point. The uncertainty in calculated heat capacities is 2%, and the uncertainty in vapor pressure is 0.25% at temperatures above 200 K. Although the equation presented here is an interim equation, it represents the best currently available.     

Zum Chemischen Transport im System Mg/Mo/O ‐ Experimente und Modellrechnungen

On the Chemical Vapour Transport in the Mg/Mo/O System ‐ Experiments and Model Calculations Single crystals of MgMoO₄ and Mg₂Mo₃O₈ have been obtained via chemical vapour transport in a temperature gradient 1273 to 1173 K using Cl₂ and Br₂ as transport agents. Pure powders of the ternary compounds have been used as starting materials as well as mixtures of three coexisting phases. The observed transport behaviour is compared with results of thermodynamical model calculations. The influence of source composition, transport agent and the moisture contents is described in detail.     

Determination of Vapor Pressures Using Extrapolation of Adjusted Retention Times

Vapor pressure is one of the fundamental properties which govern the distribution of organic compounds in the environment. This property is estimated for five series of homologous substituted alkanes of the type H—(CH₂)_n—Y, where Y denotes Cl, Br, CHO, COOCH₃, OCOCH₃ and n varies from 5 to 14 using extrapolation of adjusted retention times to 25 °C. The results are compared with those obtained by using indirect methods for 40 compounds and a significant improvement is obtained. Indeed, the absolute average error percentage for the same series does not exceed 2.6%     

Vapor pressure studies of hydrophobic association. Thermodynamics of fluorobenzene in dilute aqueous solution

An automated vapor pressure apparatus has been used to obtain measurements of the vapor pressure of aqueous solutions of fluorobenzene at temperatures of 15, 25, 35, and 45°C, and in the concentration range 0 to 0.011M. The results have been interpreted to infer the dimerization constant of fluorobenzene in very dilute aqueous solutions, equivalent to the second virial coefficient of interaction between fluorobenzene molecules. The hydrophobic association of fluorobenzene molecules is thermodynamically quite similar to that of benzene at comparable temperatures and concentrations. A dimerization constant of fluorobenzene of 0.56 M^–1 at 30°C and an endothermic enthalpy of association equal to 3.9 kcal-mol^–1 are calculated from the measurements.