An Analytical Study of Molecular Transport in a Zeolite Crystallite Bed

Analytical solutions of the diffusion equations to obtain the diffusant concentrations in the macro- and micropores which constitute the pore system of a zeolite bed are presented. The parameter which determines the influence of each pore type on the evolution of the adsorbate/adsorbant system towards the equilibrium state is described. Examples are given to illustrate a qualitative and quantitative study based on the curves obtained from these equations.     

Role of Ion exchange in permeation processes

The single ion transport of transition metal ions like Cu²⁺, Co²⁺, Ni²⁺ and Zn²⁺ were carried out through the H⁺ and alkali metal ion forms of Nafion membrane. These studies showed that the ion exchange selectivity coefficient of the permeating ion had an effect on its transport process. It was found that the diffusion coefficient values (D) were directly proportional to the selectivity coefficient (K). This shows that the initial stage of permeation is governed by ion exchange process (effect of K on D).     

Phase separation and disorder in half metallic ferromagnetic manganite thin films: A theoretical study looking forward low noise nano-devices

The resistivity of thin La_0.7Sr_0.3MnO₃ films was first investigated in a wide temperature (T) range (10–750 K). Films grown by different techniques and on several substrates enabled to analyze samples with different amounts of disorder. The aim of this work was to elucidate the nature of the metal–insulator (M–I) transition occurring at T = T_p in these films and its relation with the different kinds of inhomogeneities they could present like intrinsic electric disorder and co-existence of two different electrical and/or magnetic phases. The low-temperature resistivity state was described mostly by a law which scales as T with  ≈ 2.5. This supports the theoretical proposal of single magnon scattering in presence of minority spin states localized by the disorder. In the whole range of temperatures the experimental data are found to be consistent with a phase separation (PS) scenario. In order to go through the origin of the characteristic length scale of inhomogeneity found, preliminarily low frequency noise measurements as a function of T in a range of temperature around the M–I transition were made. The samples used were patterned using photolithography into bridges with various widths and lengths. No clear sign of separation phase dynamic has been observed in our noise measurements. Unexpectedly the normalized Hooge parameter _H/n was found not to be volume (Ω) independent. The LSMO electrical properties may strongly be driven by disorder and new design for magnetoresistance sensors may have to take into account their intrinsic PS.     

Origin of the Landau-Lifshitz hydrodynamic fluctuations in nonequilibrium systems and a new method for reducing the Boltzmann equation

The Landau-Lifshitz fluctuating fluxes in fluctuating hydrodynamics are derived from the deterministic Boltzmann equation with the aid of a reduction method developed by Fujisaka and Mori. Thus it is shown that the hydrodynamic fluctuations innonequilibrium systems are generated by the reduction of variables from the-space distribution function to its five momentum moments, i.e., the hydrodynamic variables. This differs from the Bixon-Zwanzig and Fox-Uhlenbeck theories, in which the Landau-Lifshitz fluctuating fluxes are derived from the molecular fluctuating force in thestochastic Boltzmann-Langevin equation, which is, however, negligible in nonequilibrium systems. Thus the present method improves the Chapman-Enskog reduction method so as to include the hydrodynamic fluctuations generated by the reduction of variables.Supported in part by the Scientific Research Fund of the Ministry of Education.     

Transport properties of the Lorentz gas: Fourier's law

We investigate the stationary nonequilibrium (heat transporting) states of the Lorentz gas. This is a gas of classical point particles moving in a region gL containing also fixed (hard sphere) scatterers of radiusR. The stationary state considered is obtained by imposing stochastic boundary conditions at the top and bottom of , i.e., a particle hitting one of these walls comes off with a velocity distribution corresponding to temperaturesT ₁ andT ₂ respectively,T ₁ <T ₂. Letting be the average density of the randomly distributed scatterers we show that in the Boltzmann-Grad limit,,R 0 with the mean free path fixed, the stationary distribution of the Lorentz gas converges in theL ¹-norm to the stationary distribution of the corresponding linear Boltzmann equation with the same boundary conditions. In particular, the steady state heat flow in the Lorentz gas converges to that of the linear Boltzmann equation, which is known to behave as (T ₂-T ₁)/L for largeL, whereL is the distance from the bottom to the top wall: i.e., Fourier's law of heat conduction is valid in the limit. The heat flow converges even in probability. Generalizations of our result for scatterers with a smooth potential as well as the related diffusion problem are discussed.Research supported in part by NSF Grant no. Phy 77-22302.On leave of absence from the Fachbereich Physik der Universität, München. Work supported by a DFG fellowship.     

Beiträge zur Chemie der Pyrrolpigmente, 78. Mitt.: Die Eigenschaften desb-Nor-bilatrien-abc-b-Nor-biladien-ac-Systems

The redox coupleb-nor-biladiene-ac (2)/b-nor-bilatriene-abc (3) exhibits an oxidative half wave potential of 800 mV in acetonitrile solution. It is demonstrated that it can be used as an extremely efficient electron carrier through bulk membranes. Whereas2 is not suitable as a ligand in carrier mediated cation transport,3 is a medium suited carrier for Cu(II) or Zn(II) ions, however, it is the most efficient one found so far for transport of Hg(II) ions. A 1:1 zinc chelate of3 is isolated and characterized. it is deduced to represent a polymer consisting of about 73 monomer units.

     

Improvement of the performance of facilitated transport membrane process through nonuniformity

Facilitated transport process has attracted much attention because high selectivity and high permeability may be achieved. However, most research on facilitated transport process is concerned only with uniform membranes. In this paper, a model predicting the gas separation performance of a hollow-fiber module with facilitated transport membrane is developed. The influence of feed rate, operation pressure, and permeant-feed flow pattern on the module performance are analyzed and the effect of the nonuniform distribution of reaction equilibrium constant is examined. The calculated results show that the nonuniform active distribution may cause an improved module performance. Because of the passive transport characteristics of the facilitated transport process, the mass transfer driving force across the membrane has a great influence on the improvement of the module performance through a facilitated transport effect.     

掺杂铕和铽的卤硼酸盐荧光体的制备及光谱特征

采用高温固相法在空气中合成了一系列掺杂稀土离子的卤硼酸盐荧光体, 研究了其发光性质和基质组成对稀土离子共掺杂的荧光体发光性质的影响. 研究结果表明, 在Eu3+和Tb3+共掺杂的体系中存在电子转移, 因此出现了Eu3+, Eu2+和 Tb3+共存于同一基质共同发射的现象. Ce3+对Eu2+和Tb3+具有敏化作用, 可增强其发射强度. 基质的组成对稀土离子的发射峰位和发射强度有明显影响.     

Mass transfer determining parameter in facilitated transport through di-(2-ethylhexyl) dithiophosphoric acid activated composite membranes

Activated composite membranes (ACMs) containing di-(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA) as a carrier have been found to facilitate the transport and separation of several cations. This paper describes an approach to the chemical characterisation of the transport phenomena of Zn²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Sn²⁺ and In³⁺ by an ACM. The selectivity of D2EHDTPA based ACM towards different metal ions is presented and discussed focusing in Zn²⁺ and Cd²⁺ transport and recovery. Selectivity demonstrates that zinc ions are removable from mixtures due to the different extraction strength of D2EHDTPA. Such selectivity is based on the differences of the dynamic behaviour of the metal ions transport. In addition, a correlation of the chemical behaviour of those ACM systems with the corresponding solvent extraction systems has been found.     

Conduction and Transport Numbers in Metacomposites MeWO<Subscript>4</Subscript> ⋅ WO<Subscript>3</Subscript> (Me = Ca,Sr, Ba)

The conduction and transport numbers of charge carriers for composites in the systems MeWO₄-WO₃ (Me = Ca, Sr, Ba) are studied as a function of the temperature and the activity of oxygen in a gas phase. The transport numbers are determined by an emf method and are estimated from dependences of conductance on the activity of oxygen in a gas phase. The deficiencies of the given procedure as applied to investigation of properties of composite phases are analyzed. The materials under study are classified with a class of metacomposites. The concentration intervals of the ionic, mixed, and electronic conductions are determined. The conduction of composites of compositions (100 − x)MeWO₄ ⋅ xWO₃ is predominantly ionic at x ≤ 10 (Me = Ca), x ≤ 60 (Me = Sr), and x ≤ 45 (Me = Ba). The obtained data are explained in the framework of a model that represents a composite as a distributed matrix system where a film of surface phase MeW-s with a high mobility of oxygen ions plays the role of a connected matrix. It is presumed that the surface phase MeW-s possesses double-sided surface activity (α _MeW-s ≤ ) and a higher mobility with respect to MeWO₄ and WO₃. The discovered anomalies of dependences (T) and partial dependences , σ_el(T) are explained by a change in the stoichiometry, morphology, and the degree of connectedness of surface phase MeW-s caused by with a change in the temperature and composition of composites.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 680–693.Original Russian Text Copyright © 2005 by Neiman, Pestereva, Sharafutdinov, Kostikov.Published on the basis of a report delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004).