BARRER volume

Barrer (3) makes similar calculations for the entropies of occlusion of substances by zeolites and reaches the conclusion that the adsorbed material is devoid of translational freedom. However, he uses a volume, area or length of unity when considering the partition function for translation of the adsorbed molecules in the cases where they are assumed to be capable of translation in three, two or one dimensions. His entropies are given for the standard state of 6 = 0.5, and the volume, area or length associated with the space available to the adsorbed molecules should be of molecular dimensions, v = 125 X 10-24 cc., a = 25 X 10-16 cm.2 and l = 5 X 10-8 cm. When these values are introduced into his calculations the entropies in column four of Table II of his paper come much closer together, as is shown in Table I. The experimental values for different substances range from zero to —7 cals./deg. mole or entropy units, and so further examination is required in each case to decide... 

Although a number of books now contain chapters or sections dealing with zeolites, this subject has been the primary focus in very few volumes. The most noteworthy of these is the treatise by D. W. Breck, Zeolite Molecular Sieves, published by Wiley in 1974. The earliest modem ones are the Russian texts on Molecular Sieves and Their Use, published by V. A. Sokolov, N. S. Torocheshnikov, and N. V. Kel tsev in 1964, and S. P. Zhdanov s Chemistry of Zeolites in 1968. Other significant works include the 1976 ACS Monograph on Zeolite Chemistry and Catalysis edited by J. A. Rabo, and the volume on Zeolites and Clay Minerals as Sorbents and Molecular Sieves by R. M. Barrer, published in England in 1978. 

Figure 1.7 then shows respective data for an ultrahigh free-volume and performance polymer, Teflon AF2400 of DuPont (P02 = 1140 Barrer [39]). One can recognize that... 

The study of zeolites as adsorbent materials began in 1938 when Professor Barrer published a series of papers on the adsorptive properties of zeolites [28], In the last 50 years, zeolites, natural and synthetic, have turned out to be one of the most significant materials in modem technology [27-37], Zeolites have been shown to be good adsorbents for H20, NH3, H2S, NO, N02, S02, C02, linear and branched hydrocarbons, aromatic hydrocarbons, alcohols, ketones, and other molecules [2,31,34], Adsorption is not only an industrial application of zeolites but also a powerful means of characterizing these materials [1-11], since the adsorption of a specific molecule gives information about the microporous volume, the mesoporous area and volume, the size of the pores, the energetics of adsorption, and molecular transport. 

R. M. Barrer (Imperial College, London) In counterdiffusion systems such as you have examined, the volume flow of Component 1 into the crystals is not necessarily equal to the volume flow of the displaced Component 2 into the external solution, because the degree of filling of the crystals may change with composition of the sorbed fluid. Thus, for... 

At present, all these theories are approximate, since all attempts to derive them using molecular mechanics have been largely unsuccessful, because there is a large number of degrees of freedom in describing concentrated polymer solutions. Among these approximate theories, such as those developed by Barrer (IQ), DiBenedetto (ID, and van Krevelen (12), the free-volume theory of diffusion is the only theory sufficiently developed to describe transport processes in concentrated polymer solutions. 

Essential facts and figures on the synthesis of crystalline microporous materials can be found in the textbooks by Breck [15], Barrer [16] and Szostak [8], and also within previous volumes on zeolite science and technology published in collaboration with the International Zeolite Association (IZA) [ 17,18], These sources contain (besides much other useful background material) chapters on the synthesis of zeolites, metallophosphates and other porous framework structures. 

Solid proplnts and their thermochemistry were reviewed in a major article in Vol 8, P402-L to P473-L. Liq proplnts have been reviewed in an earlier volume (Vol 7, L34-L to L44-R) as well as by Barrere (Ref 10) and Sutton (Ref 14). The properties of solid proplnt components such as metals, hydrides, non-metallic and metallic... 

Many of the macroscopic techniques can be apphed to the measurement of self-diffusion by using isotopically labeled tracers. Such methods, first introduced by Barrer and Fender [97], have been widely applied in order to obtain data which should be directly comparable with microscopic self-diffusion measurements. Such comparisons are presented in several of the chapters within the present volume. 

This equation gives the change of concentration in a finite volume element with time. In the approach of Barrer and Jost, the diffusivity is assumed to be isotropic throughout the crystal, as Dt is independent of the direction in which the particles diffuse. Assuming spherical particles. Pick s second law can be readily solved in radial coordinates. As a result, all information about the exact shape and connectivity of the pore structure is lost, and only reflected by the value of the diffusion constant. 

This volume is a complete progress report on the various aspects of zeolite systhesis on a molecular level. It provides many examples that illustrate how zeolites can be crystallized and what the important parameters are that control crystallization. Forty-two chapters cover such topics as crystallization techniques gel chemistry crystal size and morphology the role of organic compounds and novel synthesis procedures. It offers a complete review of zeolite synthesis as well as the lastest finding in this important field. Contains benchmark contributions from many notable pioneers in the field including R. M. Barrer. H. Robson, and Robert Milton. 

It has been observed [24] that for PEG (200g/mol) modified Pebax membrane for CO2 separation the CO2 permeability increased by a factor of about 2 (from 73 to 151 Barrer) and the separation factor CO2/H2 also increased by PEG addition (50 wt.%). This enhancement was attributed to the appearance of additional ethylene oxide (EO) units and free volume increase. Higher content of EO units results in an increase in the solubility of CO2. Later, the total free volume increase and hence the increase of the permeability was demonstrated by measurements of density and by positron annihilation lifetime spectroscopy (PALS) analysis [75]. 

Mica flakes embedded in a polymer and properly oriented in a plane can provide a tortuous path to vapors and liquids, similarly to the natural composites shown in Figure 1.1. Barrier properties can be imparted in blow-molded containers, packaging films, and corrosion-resistant coatings not only by mica but also by other impermeable lamellar fillers, including glass flakes, talc, and nanoclays. In blown LDPE film, the addition of 10% mica was found to reduce the oxygen permeabihty from 4.16 to 3.03 Barrer [37]. Assuming an impermeable, fully oriented lamellar filler, Eq. (8.1), [38] maybe used to predict the composite permeability. Pc, perpendicularly to the filler plane as a function of the matrix permeability, P , filler volume fraction, V(, matrix volume fraction, V , and filler aspect ratio a... 

Other theories within the general framework of the free-volume concept have been advanced. They include the works of Kumins and Roteman (1961), Bueche (1953), Barrer (1957), DiBenedetto (1963), DiBenedetto and Paul (1964), Wilkens and Long (Wilkens, 1957 Wilkens and Long, 1957), and Vasenin (1960). Part of the reason that these theories are not so popular lies in the fact that their predictions of D c) were no better than those obtained by Fujita and Doolittle. In addition, most of these other theories concentrated on the temperature dependence of the intrinsic mobility, which is less important compared to its concentration dependence. In spite of the predictive limitations of the free-volume theory, it is applicable at the widest concentration range, and certainly it is the best theory to use for modeling diffusion limited behavior of polymerization systems. 

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