Tracer diffusion of Co2+ ions in multielectrolyte systems: Activation energy and obstruction effect

The activation energy for the tracer diffusion of Co²⁺ ions in multielectrolyte systems containing alkali bromides has been determined in agar gel medium over the temperature range of 25–45°C. The decrease in the value of the Arrhenius parameters, E and D_o, with gel percentage is explained on the basis of the transition state theory. Further, studies of the influence of electrolyte concentration on activation energy and obstruction effect reveal that both parameters decrease with the former. The decrease in activation energy is explained by considering the changes in physical properties of the solution with concentration at microscopic level, while the decrease in the extent of obstruction effect is attributed to competitive hydration between ions and agar molecules in a diffusion system.     

Self-Diffusion of Co2+ Ions in CoBr2, CoI2 and Electrolyte-Diffusion of ZnSO4 in Agar Gel Medium

Self-diffusion of Co²⁺ ions in CoBr₂ and CoI₂ is reported in the concentration range of 10^–5 to 0.25M in 1% agar gel at 25 °C. The deviations observed between the experimental and theoretical values of diffusion coefficients are explained by considering different types of interactions occurring in the ion-gel water system. The applicability of the transition state theory to the diffusion of ZnSO₄ in agar gel medium is tested by varying the temperature as well as the gel concentration at high concentration of the electrolyte. The activation energy E and D ₀ value decrease with increasing gel concentration in agreement with the theory.     

Tracer-diffusion of Co2+ ions in some transition metal chloride solutions

Tracer-diffusion coefficients of Co²⁺ ions have been determined in 1% agar gel containing transition metal chlorides, viz. ZnCl₂, NiCl₂ and MnCl₂ over the concentration range of 10^–6–0.15 M at 25°C using the zone-diffusion technique. The results are compared with calculated values on the basis of Onsager's theory and the deviations are accounted for on the basis of various types of interactions in the ion-gel water system. Further, activation energy for the tracer-diffusion of Co²⁺ ions in the above mentioned electrolytes has been obtained as a function of electrolyte concentration, using measurements in the temperature range of 25–50°C. The trend in activation energy is explained on the basis of the WANG's model.     

Determination of activation energy and the obstruction effect for tracer-diffusion of Co2+ ions in agar gel medium containing transition metal nitrates

Variation of activation energy for tracer-diffusion of Co²⁺ ions in Ni(NO₃)₂, Co(NO₃)₂ and Mn(NO₃)₂ is investigated using 1% agar gel over the temperature range of 25 to 45 °C. The activation energies are obtained by the least square fitting of the diffusion coefficient data obtained at various temperatures through the Arrhenius plots. Further, the extent of obstruction effect by gel macromolecules for Co²⁺ ions in Ni(NO₃)₂, Co(NO₃)₂ and Mn(NO₃)₂ systems at various concentrations of the electrolyte have been determined. The decrease in activation energy is explained by considering the changes in the physical properties of the solution with concentration at microscopic level, while the decrease in obstruction effect expressed in terms of a is accounted for on the basis of competitive hydration between ions and agar molecule.     

Tracer diffusion of131I− ions in a few 1–2 electrolytes in agar gel

Tracer diffusion of¹³¹I^– ions is studied at different temperatures /20°C–50°C/ in 2.5% agar gel containing sodium and potassium sulphate solutions over a wide range of concentrations. The results are in qualitative agreement with the theoretical values in the concentration range 10^–6–10^–1M. Agar gel shows an obstruction effect to diffusional flow. The activation energy for tracer diffusion was found to be of the order of 16.3 kJ mol^–1.     

Diffusion of zinc sulphate in agar gel medium

The activation energy for the diffusion of ZnSO₄ as a function of electrolyte concentration is computed by least squares fitting of the diffusion coefficient data obtained at various temperatures in the Arrhenius equation. It is observed that the activation energy decreases with increasing concentration of the electrolyte. This observation is accounted for on the basis of Wang's model. Further, the obstruction effect caused by the agar macromolecules in the diffusion path of ZnSO₄ uis also determined at these concentrations by varying the gel concentration at 25°C., The obstruction effect expressed in terms of a found to decrease with ZnSO₄ concentration and explained on the basis of competitive hydration of diffusing ions and agar molecules.     

Electrolyte-diffusion of cobalt sulphate in agar gel medium at 25 °C

The diffusion of cobalt sulphate is studied in 1% agar gel over a concentration range of 10^–5 to 0.2M at 25 °C. The experimental values of the diffusion coefficient at various concentrations determined by the zone-diffusion technique are compared with the theoretical values of diffusion coefficinets computed on the basis of Onsager-Fuoss theory. The observed deviations are interpreted in terms of relative contributions of diffusion-enhancing and diffusion-retarding interactions occurring in the water-gel-electrolyte system.     

Thermal decomposition of silver cyano complex and characterization its decomposition products by ETA,DSC, DTA and TG

It was found by DTA and TG that [Phenyl₂I][Ag(CN)₂] in the solid state is chemically stable on heating in argon up to 160°C. During heating to higher temperatures it decomposes, forming volatile products such as [Phenyl]I, [Phenyl]NC and (CN)₂ [1]. After heating the sample to 500°C metallic silver resulted. The volatile and intermediate solid products were analysed by IR-spectroscopy.It was found by means of DTA and ETA that an isophase reversible transition takes place when the sample is heated and cooled, not higher than 100°C. At heating higher than 100°C the sample melts (melting pointT _m=135°C). The enthalpy melting was determined by means of DSC (H=–28 kJ·mol^–1).By means of ETA the disorder degree of the final decomposition product was estimated. The value of the activation energy of radon diffusion in the temperature range 720°–500°C equals 32.6 kJ·mol^–1.Dedicated to Prof. I. N. Bekman Moscow State University at the occasion of his 50th birthday     

Measurement of mutual diffusion coefficients,densities, viscosities,and osmotic coefficients for the system KSCN-H2O at 25°C

Mutual diffusion coefficients measured on the volume-fixed frame of reference are reported for KSCN-H₂O at 25°C over the concentration range 0.0 to 10.26 mol-dm^–3. The diffusion coefficient at infinite dilution was obtained from limiting ionic equivalent conductances of K⁺ and SCN^–. Low concentration conductances of KSCN-H₂O at 25°C used to obtain the limiting ionic equivalent conductance of SCN^– are reported. Values of density and viscosity for this system are reported from 0.0 to 10.30 mol-dm^–3. Osmotic coefficienss of KSCN-H₂O at 25°C were measured by the isopiestic method. These are reported over the concentration range of 0.30 to 24.94 molal (saturation). Values of thermodynamic diffusion coefficients for the concentration range 0.0 to 10.26 mol-dm^–3 are tabulated. Results are compared to other potassium salts with monovalent anions at 25°C.     

A study of metal complexes of a naturally occurring macrocyclic ionophore-monensin

The acid-base and complexing properties of a naturally occurring antibiotic ionophore-monensin (MonH)-were studied in anhydrous methanol solutions primarily by potentiometric measurements. The pK _a of the acid was found to be 10.30±0.05 at 25°C. Complexes of silver, thallium, and alkali ions with the undissociated ligand were also studied, and their stability constants were determined. The acid dissociation constant of MonH as well as the stability constants of Mon^– Na⁺ and MonH·NaClO₄ complexes were determined in the 5–45°C temperature range, and the enthalpy and entropy of the acidity and stability constants were determined from van't Hoff's plots. The formation of MonH and Mon^–Na⁺ species are both enthalpy and entropy stabilized, but the formation of the MonH·NaClO₄ complex is enthalpy stabilized but entropy destabilized.     

Surface characterization and heats of adsorption of chromatographic alumina gel

The porous nature of chromatographic alumina gel has been investigated by adsorption/condensation processes and electron microscopy. Having 63% porosity, the gel is very porous. Total pore volume as determined by the fluid-displacement method is 0.497 cm³ g^–1. Its specific surface area, as determined by water vapor adsorption, is 225 m² g^–1. Micropore volume, as determined by utilizing Gurwitsch's rule, turns out to be 0.262 cm³ g^–1. The greater portion of the surface area and pore volume occurs in small and transitional pores, with average pore radii (hydraulic) less than 2.1 nm.Organic vapors, such as methyl ethyl ketone, acetone, methyl acetate, and methyl alcohol, were adsorbed on the gel between 0 and 36°C under vacuum, and the data were recorded on a Cahn-1000 electrobalance device. Isosteric heats of adsorption were calculated by applying the Clausius Clapeyron equation to the adsorption isosters at different surface coverages. Two types of adsorption processes, one with low activation energy and other with high activation energy can be distinguished. The increase in values ofq _st indicates that increasing temperature changes physical adsorption into chemisorption.     

Diffusion of Manganese Ions in Agar Gel Containing Alkali Metal Chlorides

The obstruction effect for tracer-diffusion of Mn²⁺ ions in the presence of different supporting electrolytes (LiCl, NaCl, KCl, CsCl) at various concentrations has been studied at 25 °C using the zone diffusion technique. It has been observed that the obstruction effect determined in terms of increases with concentration of the electrolyte. Further, for a given concentration it is found to decrease with increasing charge density of the cation. We also report here on the effect of temperature on obstruction and found that is constant over the temperature range studied (25–45 °C). These observations are explained on the basis of competitive hydration between ions and agar macromolecules.     

The effect of pressure and temperature of self-diffusion coefficients in several concentrated deuterium oxide diamagnetic electrolyte solutions

The pressure dependences of the self-diffusion coefficients of deuterium oxide in 4.5m solutions of LiCl–D₂O and CsCl–D₂O (also 7m) and 3.06m CaCl₂–D₂O have been measured by the NMR spin-echo method at 30°C, 60°C, and 90°C. Shear viscosities and densities of these solutions have also been determined over the same range of experimental conditions. The experimental data show that the diffusion constantD decreases with the increasing structure-making ability of the electrolyte cation Ca⁺²>Li⁺. In contrast, the diffusion coefficient for D₂O in the 4.5 and 7m CsCl solutions is equal to that for pure D₂O at 30°C but lower at 60°C and 90°C. It has been found that the Stokes-Einstein equation relates well the diffusion coefficients to shear viscosity in these concentrated electrolyte solutions.     

Effect of the Measurement Temperature on the Dispersive Component of the Surface Free Energy of a Heat Treated SiO2 Xerogel

The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, _S ^D, vary from 49.07 mJ·m^–2 at 25°C to 17.20 mJ·m^–2 at 150°C. The _S ^D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of _S ^D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the _S ^D values as well as in the dispersive component of the surface enthalpy, h _S ^D. Such abrupt change can be attributed to an entropic contribution of the surface free energy.     

Tracer-diffusion of Zn2+ ions in cobalt sulphate

Tracer-diffusion of Zn²⁺ ions in the presence of CoSO₄ is studied at 25°C in 1% agar gel over a concentration range of 10^–5 to 0.25M using a zone-diffusion technique. The deviations observed between experimental and theoretical values of diffusion coefficients are explained by considering different types of interactions occurring in the ion-gel-water system. Further, study of the obstruction, effect in the diffusion of Zn²⁺ ions at different concentrations of CoSO₄ reveals that the -value decreases with increasing concentration of the electrolyte. This observation is accounted on the basis of competitive hydration between ions and agar molecules.     

Oxidation of organic compounds by ozone on a surface

Adamantanol was obtained by the ozonization of adamantane, at -78 ° C, adsorbed on silica gel. Ozone does not decompose on silica gel in the absence of a substrate.Ozonization of adamantane on silica gel is accompanied by chemiluntinescence in the IR region. The chemiluminescence quenching is of first-order with the effective rate constantk'. In the range from 0.4 to 5 mmol, k' depends linearly on the amount of adamantane adsorbed on the silica gel. The activation energy E_a = 9.97±1.89 kcal mol^–1 and the pre-exponential factorA = (2.76±0.52) - 10⁶ were calculated from the temperature dependence ofk'.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 375–378, February, 1996.     

Viscosities and intradiffusion coefficients in the ternary system NaCl−MgCl2−H2O at 25°C

The intradiffusion coefficients of Na⁺, Cl^– ions and water and the tracerdiffusion coefficients of Ca²⁺ ion have been measured in the ternary system NaCl–MgCl₂–H₂O at 25°C. The intradiffusion coefficients of Mg²⁺ in this system have been estimated from the corresponding Ca²⁺ diffusion measurements. Viscosities were measured at the same solution concentrations as were used for the diffusion experiments. Intradiffusion and tracerdiffusion coefficients in a range of temperatures from 5 to 45°C are reported for standard sea-water which is a member of the above ternary set.     

Thermal Analysis of Casein

Case in was analyzed during thermal treatment and pyrolysis. The thermal degradation process of casein was interpreted and thermostability indices, rate, order and activation energy of thermode-structive reaction of casein were determined on the basis of thermogravimetric analysis. The thermodestruction of casein has the characteristics of a first order reaction with activation energy E _a=3.87 kcal mol^–1 (16.2 kJ mol^–1).The pyrolysis of casein was investigated and we determined optimal heating temperature — 550°C and yields of biochar, pitch, pyrolysis water and gases.This revised version was published online in November 2005 with corrections to the Cover Date.     

Sorption and Diffusion of p-Xylene and o-Xylene in Aluminophosphate Molecular Sieve AlPO4-11

This paper presents experimental results for equilibrium and diffusion of C₈ aromatics in laboratory synthesised crystals of AlPO₄-11. The samples were prepared by the hydrothermal method, starting from pseudobohemite (CONDEA), 85% phosphoric acid, water and di-isopropilamine as organic template. Adsorption and diffusion data were obtained mainly by gravimetry at temperatures between 60–100°C. Saturation capacities were found in the range of 4 wt%. Equilibrium constants were estimated using virial plots yielding heats of adsorption between 10–12 Kcal/mol at low coverage. Intracrystalline diffusivities at higher temperatures (150–180°C) were also measured, using the Zero-Length-Column (ZLC) method. Diffusivities from both methods (gravimetric and ZLC) agreed reasonably well and followed a typical Arrhenius behaviour, with low activation energy (ca. 7 Kcal/mol).     

Structural Aspect of a Thermal Activation Effect in the MnO x /γ-Al2O3 System

Solid-phase reactions in the aluminum–manganese oxide system, including the structural mechanism of the thermal activation of catalysts, were studied at temperatures up to 1100°C. It was found that the solid-phase reaction at 900–1000°C occurred via two pathways because of the diffusion of manganese ions to aluminum oxide and aluminum ions to manganese oxide. Nanoheterogeneous state of the active component, which was observed in the range 25–600°C, is the product of incomplete decomposition of the high-temperature aluminum–manganese phase Mn_{2.1 – x} Al_{0.9 + x} O₄ (0 x 0.6) with a cubic spinel structure; this phase was equilibrium at the synthesis temperature but metastable below 650°C.