The electrochemistry of gold in acetonitrile solutions containing thiocyanate ions

Gold dissolves anodically in acetonitrile solutions containing dissolved NaSCN, at 25°C. The reaction yields Au(I) and Au(III) complex ion species which can be cathodically electroplated. The voltammetric experiments indicate that the anodic dissolution is preceded by a partial surface saturation with the intermediate initially discharged, followed by a diffusion controlled process which depends on the SCN^? ion concentration. The electrochemical behaviour of the anodic and cathodic processes is comparable to that of gold in aqueous solutions containing Au-complex ions.     

The chemical passivation of copper in ammonia solutions containing chlorine ions

It was shown that the CuCl layers deposited on copper chemically and electrochemically from copper-ammonia solutions were different. The layer formed chemically was loose, and that formed on the anode, dense. During multilayer copper passivation, the chemically deposited CuCl layer interfered with the formation of electrochemical CuCl and Cu₂O layers.     

The electrochemistry of gold in acid aqueous solutions containing chloride ions

Results obtained with differently prepared gold electrodes in acid solutions containing chloride ion at temperatures ranging from 22 to 65°C are reported. Potentiostatic techniques and rotating disc electrodes were employed. The anodic dissolution, the onset of passivity and the cathodic deposition of the metal are investigated under different experimental conditions. The anodic dissolution of Au is discussed in terms of possible reaction mechanisms involving the participation of different adsorbed species. The onset of passivation is related to the depletion of chloride ion at the reaction interface. The experimental voltammograms can be reporduced by means of an equation which considers the diffusion of chloride ion, the activation polarization related to the dissolution of Au and the establishment of passivity.     

Silver dissolution in acid thiocarbamide solutions containing sulfide ions

Regularities of silver dissolution in acid thiocarbamide electrolytes are studied. The kinetics of the process is shown to be severely affected by the admixture of hydrogen sulfide molecules that form upon inserting sodium sulfide or accumulate in electrolyte with the passage of time elapsed since its preparation. Catalytic effect increases with increasing length of time of the electrode’s contact with solution prior to the beginning of experiment or following an increase in the concentration of sulfide ions. Experiments with the surface renewed in the course of potential scans show that the catalytic effect is connected with the adsorption of sulfide ions on an interface. At large values of the surface coverage with sulfide ions, the dissolution rate increases so much that the dissolution process starts to be limited largely by the process of supply of thiocarbamide molecules toward the electrode surface.     

The effect of poly(methacrylic acid) on electrosurface properties of titanium dioxide in aqueous suspensions

The electrosurface properties and aggregation stability of aqueous titanium-dioxide suspensions are studied in wide ranges of medium pH values and poly(methacrylic acid) concentrations. Using the 2pK model, the ionization constants of surface hydroxyl groups of titanium dioxide are found and it is established that the adsorption of poly(methacrylic acid) macromolecules substantially decreases the fraction of neutral (uncharged) hydroxyl groups and affects the ratio between the positively and negatively charged surface hydroxyl groups.     

Sol-gel synthesis of titanium dioxide and titanium dioxide-hydroxypropyl cellulose hybrid material and electrorheological characteristics of their dispersions in poly(dimethylsiloxane)

Particles of titanium dioxide and titanium dioxide-hydroxypropyl cellulose organic-inorganic composite are synthesized by the sol-gel method. The effects of an electric field on the shear stress, viscosity, tensile and compression stresses of dispersions of titanium dioxide, the hybrid material, and titanium dioxide-hydroxypropyl cellulose mechanical mixture are investigated. It is established that the value of the electrorheological effect observed for hybrid material dispersions is higher than that for dispersions of titanium dioxide and mechanical mixtures of the materials.     

Synthesis of anodic silicon oxide films in water-organic solutions containing orthophosphoric acid

Variations in electrophysical properties of anodic silicon oxide at the surface of semiconductor silicon are studied as a function of the composition of electrolytic solutions containing orthophosphoric acid and the conditions of reaching the final formation potential. The optimum conditions for the formation of anodic SiO₂ coatings that include phosphorus-containing admixtures are determined, the coatings being intended for application as diffusates in nanoelectronics.     

Electroreduction of carbon monoxide on palladium electrodeposits in solutions containing copper ions

It is shown that the electroreduction of CO proceeds on electrolytic deposits of palladium (edPd) in 0.5 M H₂SO₄ + (1–5) mM CuSO₄ + CO(sat) solutions at the potentials more positive than the Cu²⁺/Cu equilibrium potential. Among the CO reduction products, methanol and formaldehyde are identified. The current efficiency with respect to CH₃OH exceeds 75% on edPd formed in 1% PdCl₂+0.5 M H₂SO₄ solutions. In addition, Cu⁺ ions, which probably form complexes with CO, are detected in the solution and are assumed to play the role of intermediate species in the mediator catalysis along with copper adatoms.     

Charge-tranfer reactions of oxygen ions and titanium ions at titanium oxide films

The partial current densities for the transfer of titanium(IV) and oxygen ions, and of electrons at the interface between the electrolyte and the titanium(IV) oxide layer on titanium were measured as functions of total current density and pH value. It is shown theoretically, how conclusions regarding the mechanisms of the transfer reactions of both ions can be drawn from various relations between the ionic partial current densities and their dependence on solution composition, even if the electric potential difference at the oxide interface cannot be measured. Mechanisms for the transfer reactions of titanium(IV) and oxygen ions are derived from the experiments.     

Comprehensive study of electrosurface properties of detonation nanodiamond particle agglomerates in aqueous KCl solutions

The electrosurface properties of nanoporous agglomerates of detonation nanodiamond (DND) particles purified from acidic impurities by dialysis are comprehensively investigated. Acid-base potentiometric titration, laser Doppler electrophoresis, and conductometry are employed to measure the adsorption isotherms $\Gamma _{H^ + } (pH)$ and $\Gamma _{OH^ - } (pH)$ of potential-determining ions, as well as the dependences of surface charge density ??₀, electrophoretic mobility u _e, and specific conductivity K _p of the agglomerates on the pH = 3.5?C10.5 of aqueous 0.0001?C0.1 M KCl solutions. The obtained adsorption isotherms indicate heterogeneity of the DND surface, i.e., the presence of different proton-donor and proton-acceptor surface functional groups. Computer simulation of the adsorption isotherms is carried out for a DND surface containing two types of functional groups, namely, acidic carboxyl (-COOH) and amphoteric hydroxyl (-COH) groups, the predominant content of which is confirmed by FTIR spectroscopy data. The optimal values are determined for the reaction constants of ionization of these groups. It is revealed that the effective conductivity of the porous agglomerates is one or two orders of magnitude higher than the conductivity of equilibrium solutions. Corresponding values of electrokinetic potential ?? are calculated as functions of pH and KCl concentration from the electrophoretic mobility of the agglomerates using different equations of electrophoresis theory. It is shown that use of the Miller formula, which takes into account the electromigration fluxes of ions and electroosmotic flows of solutions in pores of dispersed particles, yields more correct ?? potential values for DND agglomerates.     

In situ formation of heterobimetallic salen complexes containing titanium and/or vanadium ions

A combination of high-resolution electrospray mass spectrometry and (1)H NMR spectroscopy has been used to prove that when a mixture of [(salen)TiO]2 complexes containing two different salen ligands (salen and salen') is formed, an equilibrium is established between the homodimers and the heterodimer [(salen)TiO2Ti(salen')]. Depending upon the structure and stereochemistry of the two salen ligands, the equilibrium may favor either the homodimers or the heterodimer. Extension of this process to mixtures of titanium(salen) complexes [(salen)TiO]2 and vanadium (V)(salen') complexes [(salen')VO] (+)Cl (-) allowed the in situ formation of the heterobimetallic complex [(salen)TiO2V(salen')] (+)X (-) to be confirmed for all combinations of salen ligands studied except when the salen ligand attached to titanium contained highly electron-withdrawing nitro-groups. The rate of equilibration between heterobimetallic complexes is faster than that between two titanium complexes as determined by line broadening in the (1)H NMR spectra. These structural results explain the strong rate-inhibiting effect of vanadium (V)(salen) complexes in asymmetric cyanohydrin synthesis catalyzed by [(salen)TiO]2 complexes. It has also been demonstrated for the first time that the titanium and vanadium complexes can undergo exchange of salen ligands and that this is catalyzed by protic solvents. However, the ligand exchange is relatively slow (occurring on a time scale of days at room temperature) and so does not complicate studies aimed at using heterobimetallic titanium and vanadium salen complexes as asymmetric catalysts. Attempts to obtain a crystal structure of a heterobimetallic salen complex led instead to the isolation of a trinuclear titanium(salen) complex, the formation of which is also consistent with the catalytic results obtained previously.     

Colloidal dispersions of tannins in water-ethanol solutions

The molecular interactions of grape-seed tannins dissolved in water-ethanol solutions have been studied through small angle neutron scattering, light scattering, and physical separation techniques. Through selective precipitation in different solvent mixtures, three populations of tannin macromolecules have been identified: T1 (2% of the total tannin), which forms colloidal particles when the ethanol content of the solvent is brought below phiA = 0.6; T2a (33% of the tannin), which phase-separates below phiA = 0.08 in ionic conditions that are typical of wine; and T2b (65% of the tannin), which remains in solution regardless of ethanol content. Each population remains molecularly dissolved (i.e., it does not form any association structures such as stacks or micelles) until the threshold where dense colloidal particles are formed through nucleation and growth. The colloidal dispersions are metastable, due to the adsorption of organic acids on the particle surfaces; increasing ionic strength and reducing ethanol content cause the loss of this metastability and the aggregation of the particles.     

Colorimetric and gravimetric determination of silicon in titanium and titanium alloys

Improved colorimetric and gravimetric methods are proposed for the determination of silicon in titanium and titanium alloys. In the colorimetric method the sample is dissolved in hydrofluoric acid. boric acid added and the; titanium oxidized with hydrogen peroxide and permanganate. The bulk of the titanium is precipitated as a crystalline precipitate by heating in boiling water, and the molybdenum color developed. A portion of the solution is filtered and the transmittance measured. In the gravimetric method the sample is fumed with milfuric acid. the silica ignited and fused with aodium carbonate, The silica is then dehydrated with perchloric acid. Thecolorimetric method is recommended for 0.003 to 1.5% silicon, and the gravimetric method for 0.3 to 5% silicon.     

Concentration factor and rheology of aqueous titanium dioxide dispersions

The rheological properties of aqueous titanium dioxide dispersions have been studied by rotational viscometry. It has been established that the studied disperse systems are highly structured, and their degree of structuring dramatically increases with the volume fraction φ of the solid phase. At solid phase contents φ ≥ 0.164, the breakage of the disperse structure is accompanied by the appearance of local discontinuities and an abnormal dependence of viscosity on shear stress. The results obtained have been analyzed in terms of the Uriev theory of aggregated systems. The radii of aggregates and maximum solid phase content φ_m that corresponds to the formation of a continuous disperse structure under the conditions of dynamic impact have been calculated.     

Anomalous shifts of solvent proton lines of solutions containing aromatic negative ions

A down field contribution to the NMR shifts of solvent proton lines is found for ethereal solutions containing phenanthrene, triphenylene and coronene anions. These exceptional down-field shifts are shown to be correlated with ionic association between the positive and negative ions.