Self-diffusion of Co2+ ions in CoSO4 in agar gel medium: Concentration dependence of obstruction effect and activation energy

The obstruction effect and activation enerqy for the self-diffusion of Co²⁺ ions in CoSO₄ have been computed using the zone-diffusion technique in agar gel medium at five different concentrations of the electrolyte. Both parameters are found to decrease with an increase in electrolyte concentration. The decrease in obstruction effect expressed in terms of is attributed to the competitive hydration between ions and agar molecules in a diffusion system while the decrease in activation energy is explained by considering the changes in the physical properties of the solution with concentration at microscopic level.     

Diffusion studies of cobalt ions and their salts in agar gel medium: Obstruction effect and gel hydration

The obstruction effect in the electrolyte diffusion of cobalt halides and in tracer diffusion of Co²⁺ ions in the presence of different supporting electrolytes at various concentrations has been studied at 25 °C using the zone diffusion technique. It has been observed that obstruction effect expressed in terms of increases with concentration and is higher for electrolyte diffusion than in tracer diffusion. Further, for a given concentration it is found to decrease with increasing charge density of an anion. These observations are explained on the basis of competitive hydration between ions and agar molecules.     

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.     

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.     

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.     

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.     

Effect of supporting electrolyte on obstruction effect and activation energy for the tracer diffusion of cobalt ions in agar gel

The effect of some alkali metal chlorides on obstruction effect // and activation energy /E/ for the tracer-diffusion of cobalt ions is studied in agar gel medium using the zone-diffusion technique. It is observed that both the parameters, and E, decrease with increasing charge density of cation of the supporting electrolyte. This trend is explained on the basis of competitive hydration between ions and agar molecules and the relative distortion in the water structure brought about by these different ions and agar molecules, respectively.     

Diffusion of Cesium Ions in Agar Gel Containing Alkali Metal Bromides

The present paper gives an account of different aspects of the tracer diffusion of Cs⁺ ions in alkali metal bromides. We have measured the diffusion coefficients, D, of cesium ions in 1% agar gel medium at 25 ^∘C using a zone-diffusion technique over a concentration range of 5 × 10⁻⁵ to 0.1 mol,dm⁻³. The values of the diffusion coefficients were found to deviate from theory, which are explained on the basis of different types of interactions occurring in the ion-gel-water system. The study is also focused on the effect of alkali metal bromides on the obstruction effect and activation energy for the tracer-diffusion of cesium ions in agar gel medium. It is observed that both parameters, extent of obstruction, ∝, and activation energy, E, decrease with increasing charge density of the cation of the supporting electrolyte. The influence of these trends is explained on the basis of competitive hydration between the ions and agar molecules, and the relative distortion in the water structure that is brought about by these different ions and agar molecules.     

Determination of Activation Energy for the Diffusion of Fe<Superscript>3+</Superscript> Ions in Agar Gel Medium Containing Various Transition Metal Sulfates

The study of the diffusion of ferric ions in agar gel containing transition metal sulfates was carried out. The effect of gel concentration, electrolyte concentration and temperature on the diffusion of Fe³⁺ ions in various transition metal sulfates was studied with a view to verify Wang’s model of diffusion and the applicability of transition state theory to diffusion in a gel medium. The diffusion coefficients were measured using the zone diffusion technique. For a given concentration of electrolyte the activation energy (E) is found to decrease with an increase in the charge density of the cation of the supporting electrolyte and for a given system it is found to decrease with increasing electrolyte concentration in agreement with Wang’s model. This observation is explained on the basis of the distortion in the water structure caused by ions and agar molecules. At a given electrolyte concentration the magnitude of the Arrhenius parameters, E and D _o, is found to decrease with increasing gel concentration in agreement with the transition state theory of diffusion.     

Application of NAA in diffusion studies

The diffusion of Mn₂+ ions in CoSO₄ , NiSO₄ and ZnSO₄ containing 1% agar gel as well as that of MnSO₄ in 1% agar gel was studied at 25 °C. The diffusion coefficientsat selected concentrations were determined by the zone diffusion techniqueand by measuring the concentration of diffusing ions using neutron activationanalysis.     

Electrolyte diffusion of ZnCl2 and self-diffusion of Cd2+ ions in agar gel medium at different temperatures

The values of activation energy required for the diffusion of ZnCl₂ and for Cd²⁺ ions in Cd/Ac/₂ are reported in agar gel medium at 5×10^–5 and 0.001M concentration, respectively. These values are compared with the previously reported values in the same systems at different concentrations. The decrease in activation energy with concentration of electrolyte is in agreement with the Wang's model.     

Activation Energy of Tracer-Diffusion of Manganese Ions (Mn2+) in Alkali Metal Chloride Solutions

The activation energy of the tracer diffusion of Mn²⁺ ions in alkali chlorid solutions (0.1M) has been determined in agar gel medium (1–2.5%) over the temperature range of 25–45 °C. The decrease in the value of the Arrhenius parameters, E and D ₀, with gel percentage is explained on the basis of the transition state theory. Further, the activation energy as a function of electrolyte concentration is also investigated using 1% agar gel in the temperature range of 25–45 °C. In both the cases, the activation energies are determined by the least square fitting of the diffusion coefficient data obtained at various temperatures through the Arrhenius plots.     

Diffusion of Cesium Ions Labeled with 134 Cs in Agar Gel Containing Alkali Metal Iodides: Obstruction Effect and Activation Energy

The effect of some alkali metal iodides on the obstruction effect and activation energy for tracer-diffusion of cesium ions in an agar gel medium was studied using the zone-diffusion technique. It to be observed that both the extent of obstruction (α) and the activation energy (E) decrease with the increasing charge density of the cation of the supporting electrolyte. These trends are explained on the basis of competitive hydration between ions and agar molecules and the relative distortion in the water structure that is brought about by these different ions and agar molecules, respectively.     

Activation energy for electrolyte diffusion of some zinc salts

Activation energies for electrolyte diffusion of Zn(NO₃)₂, ZnBr₂ and ZnI₂ in 1% agar gel at different concentrations are determined by the least-squares fitting of the diffusion coefficient data obtained at various temperatures through the Arrhenius plots. Energy of activation is found to decrease with an increase in electrolyte concentration. This trend is explained by considering the changes in the physical properties of the solution with concentration at microscopic level, as envisaged in Wang's model.     

Oxygen Transport in the SOFC Cathode

The impedance of the La_0.75Sr_0.2MnO₃-cathode/electrolyte interface for cathodes with different porosity is measured. The impedance spectra are fitted using a developed model of the oxygen transport at this interface. After the measurements, the cathode is removed from the electrolyte. The contact area and the three-phase boundary length (TPBL) at the interface are estimated from SEM images of the electrolyte surface. The dependence of the interfacial electrical resistance on the microstructure is discussed. It is shown that the bulk diffusion of oxygen vacancies at the interface at 950°C is high enough to use the whole La_0.75Sr_0.2MnO₃/YSZ contact area F for the oxygen transport into the electrolyte for microstructures with 2F/TPBL 2 m. The impact of the surface diffusion of oxygen species on polarization resistance at operation temperatures <900°C is discussed. The polarization resistance and the morphology of composite cathodes made from La_0.75Sr_0.2MnO₃/YSZ and yttria- or scandia-stabilized zirconia powders (3YSZ, 8YSZ, 10ScSZ) are investigated by impedance spectroscopy at 800–950°C. The polarization (interfacial) resistance decreases gradually with addition of electrolyte powder in the uLSM cathode material independent of the electrolyte powder used. The interfacial resistance of the uLSM/3YSZ, uLSM/8YSZ, and uLSM/10ScSZ composite cathodes is almost the same. The interaction between uLSM and doped zirconia particles is discussed on the basis of the interfacial resistance, activation energies, and high-frequency impedance.     

Electroreduction Kinetics of Palladium(II) Complexes with α-Alanine: A Polarographic Study

The kinetics of the electroreduction of palladium(II) complexes with -alanine are studied on a dropping mercury electrode in solutions containing various supporting electrolytes (NaF, Na₂SO₄, NaClO₄). The study is carried out at variable concentrations of palladium(II) alaninate complexes, the ligand, and the supporting electrolyte, in the pH interval extending from 3 to 11. The obtained values of the half-wave potential for the electroreduction of palladium(II) complexes with -alanine and the diffusion coefficient for palladium(II) alaninate complexes suggest that, in the acidic and alkaline solutions studied, the slow electrochemical stage involves chelate dialaninate palladium complexes Pd(ala)₂. Palladium(II) complexes underwent reduction on the positively-charged surface of DME without any preceding chemical stages. This process was hindered by anions of the supporting electrolyte adsorbed on DME, and in alkaline solutions, by the alaninate ions as well.     

Hartley–Crank Equations for Coupled Diffusion in Concentrated Mixed Electrolyte Solutions. The CaCl2 + HCl + H2O System

Nernst—Planck equations and ionic conductivities are used to calculate accurate limiting interdiffusion coefficients D _ik ^o for mixed electrolyte solutions. The electrostatic mechanism for coupled electrolyte diffusion is investigated by calculating the electrostatic contribution to each D _ik ^o coefficient to give the flux of each electrolyte driven by the electric field, which is generated by the migration of ions of different mobilities. Ternary diffusion coefficients are measured for dilute aqueous K₂SO₄ + KOH and Li₂SO₄ + LiOH solutions. Because of the different mobilities of K⁺ and Li⁺ ions relative to SO ₄ ^2– ions, diffusing K₂SO₄ drives cocurrent flows of KOH, but diffusing Li₂SO₄ drives counterflows of LiOH. To describe coupled diffusion in concentrated mixed electrolyte solutions, the Hartley–Crank theory is used to correct the limiting D _ik ^o coefficients for nonideal solution behavior, viscosity changes, ionic hydration, and the zero-volume flow constraint. Diffusion coefficients predicted for concentrated aqueous CaCl₂ + HCl solutions are compared with recently reported data. The large amount of HCl cotransported by the diffusing CaCl₂ is attributed to the salting out of HCl by CaCl₂ and to the migration of H⁺ ions in the diffusion-induced electric field, which slows down the Cl^– ions and speeds up the less-mobile Ca²⁺ ions to maintain electroneutrality along the CaCl₂ gradient.     

Effects of thermal treatments on a NiMoO4 precursor prepared by immobilizing Ni aq 2+ and MoO 4aq 2 - in an organic matrix

A novel preparation methodology of NiMoO₄ catalysts is described, consisting in immobilizing a precursor aqueous solution containing Ni and Mo ions by gelation with agar. Compared with other precursors prepared by coprecipitation, the gel, on heating, begins to crystallize at a very low temperature, with the collapse of the gel structure.The elimination of the water representing the greatest part of the gel weight is the predominant phenomenon taking place during the thermal activation treatment and the phase composition of the oxide formed changes as follows: fast heating favours the stabilization at room temperature of the metastable tetrahedral -NiMoO₄ phase, while slow heating allows an increased formation of the more stable octahedral -phase.     

Kinetics of the yttrium fluoride electroreduction in chloride melts

To establish the effect of the nature of supporting electrolytes KCl; K, Na/Cl; K, Na, Cs/Cl; and K, Na, Ba/Cl on the electrochemical deposition of yttrium from melts, the electroreduction of yttrium fluoride in the said melts is studied by a linear voltammetry method. The discharge of ions Y³⁺ in all the melts occurs via one stage. The diffusion coefficients, activation energy, product of transfer coefficients and the number of electrons n , diffusion layer thickness, diffusion constant, and rate constant of charge transfer are determined.Translated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 48–53.Original Russian Text Copyright © 2005 by N. Gasviani, Dzhaparidze, Kipiani, S. Gasviani, Abazadze.