Phase transitions in double molybdates K<Subscript>2</Subscript>M<Stack><Subscript>2</Subscript><Superscript>II</Superscript></Stack>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> with M = Mg or Co

Phase transitions and cation mobility in double molybdates K₂M ₂ ^II (MoO₄)₃ with M = Mg or Co and the products of their heterovalent doping with scandium(III) and vanadium(V) have been studied. The transition from low to high conductivity in K₂M ₂ ^II (MoO₄)₃ is the result of a two-stage phase transition, whose occurrence is significantly extended in time. Heterovalent substitutions noticeably decrease the heat of the phase transition. The transition to the low-temperature phase is not achieved even after long-term exposure.     

Adsorption phenomena in the systems containing macrocyclic cavitand cucurbit [7]uryl

Adsorption phenomena at the mercury electrode/cucurbit[7]uryl aqueous solutions are studied by the measuring of the electrode differential capacitance C as a function of potential E. The data obtained showed that the adsorption potential region is abnormally wide (>2 V). Two segments are observed in the C,E-dependences, which relate to adsorption layers with different structure. The complicated adsorption layers forming in the studied systems can be explained by the structure of the cucurbit[7]uryl cavitand whose complexes with inorganic cations are formed by the cation binding by oxygen-containing groups of external portals, rather than their inclusion into the cavitand’s inner cavity as in the case of cryptate formation. Adsorption parameters for adsorbate layers formed in the cucurbit[7]uryl + Na₂SO₄ solution are calculated. The data obtained evidence a rather strong potential dependence of the properties of the adsorption layers formed at the electrode/solution interface in the studied system.     

Phase transitions and ion transport in NASICON materials of composition Li1 + xZr2 ? xInx(PO4)3(x = 0–1)

NASICON materials of composition Li_{1 + x} Zr_{2 − x} In _x (PO₄)₃(x = 0–1) were synthesized. The phase constitution, particle size, and conductivity of these materials were studied as s function of synthesis temperature. High-temperature X-ray powder diffraction was used to study phase transitions in the materials synthesized. Low levels (x ≤ 0.1) partial substitution of indium for zirconium considerably increase the lithium ion conductivity and reduce the activation energy for conduction compared to the parent compound.     

Determining Sodium Kryptate Adsorption Parameters on a Mercury Electrode in 1 M Na2SO4

The adsorption of a complex of sodium cations with a macrocyclic ligand (Kryptofix^R 222, composition C₁₈H₃₆N₂O₆) as a function of its concentration in 1 M Na₂SO₄ is studied by measuring the differential capacitance on a stationary Hg drop. Adsorption parameters of sodium kryptate are found using a regression analysis method and various versions of a model of two parallel capacitors complemented with the Frumkin adsorption isotherm. The differential capacitance curves, calculated on the basis of these, are compared with experimental data. The difference in model versions that most adequately describe the adsorption data, established for systems in 0.1 and 1 M Na₂SO₄, is explained by the influence of the supporting electrolyte on the adsorption layer structure. Conclusions are made on the absence in the system under study of the salting-out from the bulk solution and on a change in the properties of an adsorption layer of sodium kryptate in the region of potentials of the anodic adsorption–desorption peak following expansion of the adsorption region.     

Heat-treatment induced evolution of the morphology and microstructure of zirconia prepared from chloride solutions during

The properties of hydrous zirconia prepared from ZrOCl₂ solutions were studied as functions of precipitation pH and subsequent heat treatment. Precipitation at pH ≤ 6 yields hydrous zirconia containing excess sorbate anions (Cl^?), and at pH ≥ 7, ammonium ions. This difference considerably affects the thermolysis and morphology of the resulting samples. The samples prepared at pH ≥ 7 have far better developed surfaces. The morphological and structural evolution of hydrous zirconia samples during heat treatment is described. The involved processes are interpreted. At initial stages, the major process is the formation of metastable tetragonal ZrO₂, which transforms to the monoclinic phase during subsequent heating.     

Effect of Precipitation pH and Heat Treatment on the Properties of Hydrous Zirconium Dioxide

The effect of the precipitation pH and subsequent heat treatment is studied on the properties of hydrous zirconium dioxide precipitated by ammonia from nitrate solutions. Precipitation at pH ≤ 6 generates hydrous zirconium dioxide, which contains excess sorbate nitrate ions; the product precipitated at pH ≥ 7 contains excess ammonium ions. This distinction considerably affects the course of thermolysis and the morphology of products. The exotherm associated with the formation of the crystal structure of zirconia becomes more pronounced with rising precipitation pH. In addition, the samples prepared at pH ≥ 7 have a more developed surface. The morphologic and microstructural evolution of hydrous zirconium dioxide samples during thermolysis is described.     

The polyaniline/MF-4SK composite systems with modified surface layer

Processes of aniline polymerization in perfluorinated polysulfonic acid MF-4SK solution are studied by UV-spectroscopy. Membranes with polyaniline-modified surface layer are synthesized. It is shown by voltammetry and potentiometry that the composite materials demonstrate asymmetric ion transfer with respect to protons and sodium cations.     

Adsorption characteristics of electrodes containing nanostructured carbon of different morphology

The effect of camphor adsorption on the differential capacitance of electrodes of nanostructured carbon of different morphology (single-walled carbon nanotubes, filiform carbon, and columnar structures) in aqueous electrolyte solutions and also on the electrochemical reactions in these systems is studied. It is shown that irrespective of the ac frequency, the differential capacitance of the nanopaper and columnar electrodes increases 3–5-fold throughout the studied potential range. This experimental fact is explained by the substantial increase in the electrode surface accessible for electrolyte, which is a manifestation of the Rehbinder effect in electrochemistry. The revealed different kinds of effects of camphor adsorption layers formed at the nanostructured carbon/electrolyte interface on the electron transfer processes are as follows: partial inhibition of both the electron injection and the K₃[Fe(CN)₆] reduction; complete suppression of the reduction of sodium nitrate and nitrite; the absence of effects on the OH radical reduction and solvated electron oxidation.