Cationic mobility in Li3?2xNbxFe2?x(PO4)3 complex phosphates

Synthesis and ionic conductivity of Li_3−2x Nb _x Fe_2−x (PO₄)₃ complex phosphates were studied by X-ray powder diffraction and impedance spectroscopy. These phosphates are formed only at 900–1000°C. Variations in their thermal expansivity and unit cell parameters induced by aliovalent doping were characterized. The conductivity of these materials increases monotonically in the series Li_0.5Nb_1.25Fe_0.75(PO₄)₃-LiNbFe(PO₄)₃ and Li_1.2Nb_0.9Fe_1.1(PO₄)₃-Li₃Fe₂(PO₄)₃, which is explained by consecutive occupation of the Li(1) and Li(2) positions in their structures. Original Russian Text ? A.R. Shaikhlislamova, I.A. Stenina, A.B. Yaroslavtsev, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 12, pp. 1957–1962.     

Kinetics of H<Superscript>+</Superscript>/Na<Superscript>+</Superscript> solid-phase ion exchange on iron(III) hydrogen sulfate

The kinetics of solid-phase reaction between iron(III) hydrogen sulfate and sodium chloride was studied by thermal analysis followed by analysis of leaving gases. The exchange kinetics are described by the soft cylinder model. The hydrogen and sodium ion interdiffusion coefficients were determined for various temperatures, as well as the activation energy of interdiffusion. Sodium ion diffusion through the product layer is the rate-controlling stage of the reaction.     

Transport properties of hydrous-silica-modified MF-4SK membranes

Composites are manufactured on the basis of MF-4SK perfluorinated cation-exchange membranes modified with hydrous silica nanoparticles 2–5 nm in size. Modification improves the ionic conductivity and diffusion permeability of the membrane. The modification efficiency increases with decreasing modifier particle size. The enhancement of transport processes is maximal when hydrous silica nanoparticles are synthesized directly in the membrane matrix.     

Adsorption of surface-active compounds with the skeleton molecular structure from dimethylsulfoxide solutions on carbon nanotubes

The adsorption of adamantane, adamantanol, thiocamphor, and sodium cryptate on electrodes of single-walled carbon nanotubes (SWNT) from dimethylsulfoxide (DMSO) solutions is studied by measuring the differential capacitance (C) vs. potential (E) dependences and cyclic voltammograms. In the tested systems, the high surface activity of these surfactants is observed to result in a noticeable increase in the C of such electrodes in the range of 0.2 ≤ E ≤ −(0.9−1.1) V (SCE). As in the case of aqueous solutions, this experimental fact is explained by the appearance of the so-called Rehbinder effect (the adsorption-induced decrease in the strength), which, in this particular case, consists in a decrease in the surface energy of a solid with the formation of adsorption layers on the side surfaces of SWNTs combined into bundles to afford the partial splitting of these bundles and, as a consequence, the increase in the nanotube surface accessible to the electrolyte. At the same time, the obtained results suggest that for the adsorption of surfactants from nonaqueous solvents (in contrast to aqueous), the interaction between solvent and adsorbate molecules may become important.     

Water self-diffusion and ionic conductivity in perfluorinated sulfocationic membranes MF-4SK

Water self-diffusion and ion mobilities in various ionic forms (H⁺, Li⁺, Na⁺, Rb⁺, Cs⁺, and Ba²⁺) of perfluorinated sulfocationic membranes MF-4SK were studied by NMR and impedance spectroscopy. When degrees of hydration are low, the self-diffusion coefficients of water and ionic conductivities are considerably affected by the water content of the membrane. The self-diffusion coefficients decrease in the order H⁺ > Ba²⁺ > Cs⁺ > Rb⁺ > Na⁺ > Li⁺, whereas the ion mobility decreases in the order H⁺ > Li⁺ > Na⁺ > Cs⁺ > Ba²⁺.     

Coadsorption of Halide Anions and 1-Adamantanol Molecules on a Mercury Electrode

Coadsorption of 1-adamantanol (AdOH) and halide anions (F^–, Cl^–, Br^–) at the Hg/H₂O interface is studied systematically. Experimental results are compared with calculations of these systems within a modified Alekseev–Popov–Kolotyrkin model complemented by a set of two Frumkin isotherms. A satisfactory agreement between experimental data and theoretical conclusions concerning dependences of the phase transition potentials and the adsorption-desorption potentials on the concentrations of supporting electrolyte and organic substances is established. The experimental and calculated potential dependences of the differential capacitance in the phase transition region in the case of the AdOH adsorption from electrolytes containing halide anions are compared. It is shown that the shape of experimental capacitance curves corresponds to either a weak attraction of species of different nature during concurrent adsorption or the absence of lateral interaction between them. Accounting for the contribution made by the energy of the diffuse double layer to the overall energy gain during the adsorption removes seeming contradictions in the interpretation of dependences studied.