Natural zeolitic material of the clinoptilolite type and its AgI form

The aim of this study was the preparation of the natural zeolitic material of the clinoptilolite type doped with silver iodide. Natural zeolite from the East Slovakian deposit was used. This natural zeolitic material doped with AgI (content of AgI: 28.5%) has been investigated by X-ray powder diffractometry, EDS analysis, scanning electron microscopy, IR spectroscopy and thermal analysis.     

A study of the silver form of a natural zeolitic material of the clinoptilolite type

The silver forms of a natural zeolitic material (from the East Slovakian deposit) on the clinoptilolite type has been prepared. The silver forms of the natural zeolitic material were investigated by X-ray powder diffractometry, IR spectroscopy, ESCA measurements, scanning electron microscopy and conductivity measurements. Depending on the preparation conditions, the content of silver ions in the zeolitic products was found to be in the range from 16 to 24%. In the sample with a silver loading of 18.6%, the silver uptake is due to an ion exchange process, mostly involving Na(I), Ca(II) and Mg(II) ions.     

Kinetics of proton transfer in the zeolitic tuff

The kinetics of a proton transfer into dilute acid solutions containing natural zeolitic tuff was studied by following the pH evolution of the liquid phase. Four different solutions with tuff contents of 9, 3, 1 and 0.5 (% wt) and three different particle size fractions (≤ 2000 μm) were studied. The proton concentration of the solution was decreased by increasing the zeolite amount and decreasing the particle size fraction. The proton transfer reaction was analyzed with chemical reactions and diffusion model equations. Analysis shows that the adsorption and/or ion exchange are possible mechanisms and are expressed by a second order reaction model.     

Water vapour adsorption on DNA

DNA adsorbed very low amount of water at low relative humidities, amount of adsorption increased to 140% at 98% relative humidity at 25°C. Heat of adsorption was 109 kJ mol^-1 H₂O for the increase of moisture content from 0 to 1.96%. At higher moisture contents the heat released approached heat of condensation of water vapour on free liquid surface, 40 kJ mol^-1 H₂O.     

Natural zeolitic material of the clinoptilolite type doped with iodine and its ions

The aim of this study was the preparation of natural zeolitic materials doped with iodine and its ions. Natural zeolite from an East Slovakian deposit was used. The content of iodine in the zeolitic products depended on the experimental conditions used for the preparation. The products and their intermediates obtained at 100, 200, 400 and 900°C were identified.     

Kinetics of metal ion sorption on clinoptilolite

From an investigation into the sorption kinetics of Na⁺, K⁺, and Sr²⁺ ions from standard solutions on finely dispersed clinoptilolite incorporated in a highly permeable inert polyacrylamide gel we have determined the characteristic kinetic size of clinoptilolite and the diffusion coefficients for Na⁺, K⁺, and Sr²⁺ in the clinoptilolite microcrystallites and transport pores. Diagrams have been constructed to enable a valid selection of kinetic models for sorption of the ions from any solutions on clinoptilolite.Institute of Chemistry, Far Eastern Branch of the Russian Academy of Sciences, 690022 Vladivostok. V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 117975 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 273–277, February, 1992.     

Cyclodextrins incorporated in natural zeolitic materials of the clinoptilolite type

Natural zeolitic material of the clinoptilolite type from a Czechoslovak deposit was found to be able to incorporate -cyclodextrin. The new compounds, possibly of the host:guest type, were studied by thermal analysis, IR spectra and diffractographic measurements.     

Cyclodextrins incorporated in natural zeolitic materials of the clinoptilolite type

Natural zeolitic material of the clinoptilolite type from a Czechoslovak deposit was found to be able to incorporate-cyclodextrin. The new compounds, possibly of the host:guest type, were studied by thermal analysis, IR spectra and diffractographic measurements.     

Study of secondary porosity by SAXS and N2 adsorption in composite materials obtained from a Cuban natural clinoptilolite

In this work, a study of the secondary porosity of two zeolite-based composites is carried out by small angle X-ray scattering (SAXS) and N₂ adsorption at 77 K. The composites were obtained by the inclusion of ZnO nanoparticles in a Cuban natural clinoptilolite by mechanosynthesis and ‘in situ’ methods. It was observed a decrease in the specific surface area as a result of ZnO nanoparticles inclusion from 149 m² g⁻¹ in the started material to 60 m² g⁻¹ in the composite prepared by in situ method, whereas the mesopore diameter remained almost constant. The results confirmed the presence of mesopores with diameter between 3 and 36 nm, with good match by both methodologies. These materials were developed in view of their future application as catalysts and adsorbents, where the presence of secondary porosity is key to favor the diffusion processes.     

Diffusion of water vapour in polymethyl methacrylate

Certain aspects of the concentration dependence of the diffusion coefficient and on the mechanism of sorption of water vapour in PMMA are investigated. Early time integral sorption kinetics follow the Fickian pattern of initial linearity. Diffusion coefficients deduced from the slopes of these lines are independent of concentration and satisfactorily agree with those obtained from late-time analysis; however, desorption values are higher throughout the whole range of activities than the corresponding absorption ones. On the contrary, typical “non-Fickian” features are discerned in differential absorption kinetics on membranes of different thickness. These anomalies are attributed to rate-determining relaxation processes concurrent with diffusion, whereas other sorption models are incompatible with the general behaviour of this system. General trends of the equilibrium and kinetic data are compared with those of other polymer—water systems and the observed differences are interpreted in terms of the molecular relaxation model.     

Sorption and diffusion of water vapor in polyimide films

Sorption and diffusion of water vapor are investigated gravimetrically for polyimide films. The activity dependence of the solubility and diffusion coefficients, S and D, respectively, is classified under four types: (1) constant S and D type, (2) dual-mode sorption and transport type, (3) dual-mode type followed by a deviation due to a plasticization effect at high vapor activity, and (4) constant S and D type followed by a deviation due to water cluster formation at high activity. For the dual-mode type, the Henry's law component is much larger than the Langmuir component except at low activity, and therefore deviation in behavior from the first type is small. S is larger for polyimides with higher content of polar groups such as carbonyl, carboxyl, and sulfonyl. D is larger for polyimides with a higher fraction of free space, with some exceptions. The polyimide from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and dimethyl-3,7-diaminodibenzothiophene-5, 5-dioxide belongs to the third type and displays both large S and large D. The polyimide from 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride and 4,4′-oxydianiline belongs to the fourth type, and has the largest D but rather small S because of the hydrophobic C(CF₃)₂ groups. © 1992 John Wiley & Sons, Inc.     

The relevance of Jäntti's method for the fast measurement of sorption of water vapour

The time necessary for the measurement of gas adsorption on a solid can be substantially reduced by using Jäntti's directions for data interpretation. This procedure already delivers results after measuring only a few values of the adsorbed mass. In earlier papers we introduced a second order adaptation to Jäntti's method to broaden its applicability. In the present paper we apply this second order treatment to the adsorption of water vapour from moistened air. Specially we pay attention to the diffusion delay caused by the boundary layer around the sample.This revised version was published online in November 2005 with corrections to the Cover Date.     

Gravimetric measurement of water vapour sorption, moisture and dry mass

The gravimetric measurement of the moisture content of solids is discussed in comparison to other usual methods. Results of measurements of silica gel are reported. Furthermore, we inform on standardisation work. This revised version was published online in July 2006 with corrections to the Cover Date.     

Treatment of Anomalous Vapor Diffusion in Polymers

The mechanics of thermally-activated gaseous diffusion in polymers have long been studied for development of theoretical understanding of the interactive forces responsible for the non-linear nature of diffusion and the resultant enthalpic changes in the polymer. Methodologies and calculations have been developed in this work for treatment of experimental data for elimination of thickness-related anomalies in water vapor diffusion and for delineation of pressure effects. Linearized data for different polymer thicknesses and the attendant internal thermal effects have been generated by using calculated single molecule diffusion values. Equally linear data are obtained for different pressures by the use of a graphical method from which identical diffusion values are obtained, independent of material thickness and external pressure. True comparisons and classification of polymers as to their diffusivities are thus possible for development of barrier materials for food and drug packaging and for protective encapsulation of electronic devices. Results will be reported for three structurally different polymers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of Dual Diffusion and Non-linear Adsorption Isotherm with a Time Lag Method

This paper presents an application of the time lag method in the analysis of an adsorption system, where dual diffusion mechanism is assumed to exist and the equilibrium relationship between the fluid and adsorbed phases is non-linear. The derived time lag is expressed in terms of system parameters and operating conditions in the form of a quadrature. The feature of this solution is that the relative contribution of the pore and surface diffusions is a strong function of upstream pressure when the time lag experiment is operated over the non-linear range of the adsorption isotherm. It is this nice feature that we take advantage of to determine the pore and surface diffusivities without resorting to isolation of the pore diffusion by using non-adsorbing gas as a reference, as usually done in many other work. This advantage is not manifested in linear systems where the relative contribution of the pore and surface diffusions is a constant, rendering the delineation of these two processes impossible. Effects of various parameters on the utility of this time lag method are discussed in this paper, and application of the method is demonstrated with experimental data of sulfur dioxide adsorption onto Carbolac carbon (Proc. Roy. Soc., A271, 1–18, 1963).     

Diffusion of methyl ethyl ketone in polyisobutylene: Comparison of spectroscopic and gravimetric techniques

In this study, vapor sorption FTIR–ATR (Fourier Transform Infrared Attenuated Total Reflectance) spectroscopy was combined with a conventional gravimetric sorption balance to examine diffusion in polymers. Mutual diffusion coefficients of methyl ethyl ketone in polyisobutylene were measured using both methods at various penetrant activities and temperatures in the range 40–60°C. Actual penetrant concentrations were determined from the sorption balance. The diffusion coefficients from the two techniques agree very well with each other. In addition, the diffusivity data from both techniques could be correlated successfully as a function of temperature and concentration with the Vrentas and Duda free-volume model. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1261–1267, 1997     

Adsorption of water vapor on a non-porous carbon surface and evaluation of the mesopore surfaces of active carbons

Adsorption of water vapor on non-porous carbon adsorbents (blacks) with different specific surfaces and a sufficiently high concentration of primary centers was studied. The maximum value of the adsorption is proportional to the surface and corresponds to the formation of (1.7±0.3) dense monomolecular layers. A method was proposed for determining the surface of non-porous carbon adsorbents and for evaluating the mesopore surfaces of active carbons.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2048–2051, December, 1993.This work was supported by the Russian Foundation for Basic Research (Grant 93-035635).     

Sorption and diffusion of water vapour on edible films

Two types of films consisting of sodium salt of carboxymethyl cellulose (NaCMC) and hydroxypropyl cellulose (HPC) as film forming materials and glycerin as plasticizer were prepared, characterized and their water vapour sorption properties were determined. The water sorption isotherms of the films were measured using a magnetic suspension balance. Results show that diffusion of water vapour in NaCMC based film is faster than that in HPC based films, due to the heterogeneous structure and larger pore dimensions of the NaCMC films.