A.I. Masliy

pH dependence of the composition of electrodeposited Co films in aqueous sulfate solutions

The electrodeposition of cobalt onto gold is studied as a function of the pH of the electrolyte. Electrochemical quartz crystal microgravimetry is used to identify the material deposited. Using a Co sulfate solution without additives, it is found that for pH <-3.2, Co metal deposits. For pH > 3.2 and at sufficiently negative applied potential, first Co hydroxide deposits and then Co metal. The addition of boric acid, H3BO3 to cobalt sulfate solutions leads to different results: measurements done up to pH 5.5 indicate that only Co metal deposits, showing that boric acid prevents the formation of cobalt hydroxide.

Polynuclear crystal growth in electrocrystallization of silver: Determining the nucleus size via the nucleation theorem

We employ the nucleation theorem for a model-independent determination of the size of the two-dimensional (2D) Ag nucleus with the aid of experimental data for nucleation-mediated electrochemical crystal growth. The growth is investigated of a screw dislocation-free Ag(100) single crystal face in aqueous solution of AgNO3 at 318 K. The data are for the stationary values of the overpotential during galvanostatic pulses with sufficiently high amplitudes to ensure polynuclear growth mechanism. It is found that the Gibbs-Thomson equation of the classical theory of 2D nucleation describes very well the experimentally obtained overpotential dependence of the size of the 2D Ag nucleus.

Peculiarities of metal electrodeposition inside a flow-through porous electrode with low initial conductivity in oxidant containing solution

The earlier developed dynamic model of a flow-through electrode is used for studying how the variations in initial conductivity of a porous matrix κs,ini and a metal deposit affect the rate of metal deposition from an oxidant-containing solution for the direct-flow operation mode of the porous electrode. It is found that in contrast to an oxidant-free solution in which the decrease of κs,ini improves the uniformity of deposit distribution inside the porous cathode and increases the deposit final mass mf, the opposite situation is observed in the presence of an oxidant, namely, a decrease in κs,ini, under otherwise similar conditions reduces the deposit mass and leads to its specific spatial distribution. The final metal deposit is divided into two separate fragments (rear and front) with a region of low conductivity of the initial porous matrix in between. Dynamics of the current and metal redistribution within the porous electrode, the reasons for the formation and stabilization of the rear fragment of coating, the correlation between the metal deposition rate and changes in the anodic zone position and intensity are discussed. It is shown that with the appearance of a specific profile of deposit distribution, the dependence of mf on the metal conductivity develops a limit that differs considerably from the deposit final mass for an equipotential porous electrode.

Effect of solution volume on the rate of metal recovery and its distribution in porous cathode

By means of earlier developed dynamic model of porous electrode, numerical analysis is given of the effect of the division into smaller parts of optimal volume Vopt of metal-containing solution circulating through the porous electrode, which ensures both achieving of the metal preset recovery and the prescribed final porosity in the critical cross-section of the porous cathode, most strongly filled with the deposit. It is shown that the result depends significantly on the presence (or absence) of oxidant ions in the solution. In the absence of oxidant, the division of Vopt is desirable; it entails some improving of the distribution uniformity and increase in the deposit eventual mass. On the contrary, in the presence of oxidant such a division brings about marked negative consequences: (1) the metal deposit stronger localization at the porous electrode front edge and (2) decrease in the deposit’s final mass. It was shown that these phenomena result from the formation of anodic zone in the porous electrode rear side in the initial stage of the processing of the second and subsequent portions of solution. This is promoted by low polarization in this part of the porous electrode and the presence of a soluble metal deposited here during the final stage of electrolysis of the solution preceding portion.

Problems of creation of flexible electromagnetic screens with a given levels of reflection and absorption

Problems of creation of the easy, flexible, air-penetrable, cheap and technological screens, having a high degree of shielding and the given level of reflection are considered.

Dynamics of metal deposition on non-equipotential porous electrode: Regard for unequal rates of deposition on different regions of the surface

The influence of different ratios of the rates of metal deposition at the initial and metal-coated surface of the non-equipotential porous matrix on the dynamics of its filling with the metal is investigated using numerical calculations. It is shown that an increase in the deposition rate on the regions coated with metal layer causes an increase in the time of PE filling with the metal and leads to substantial changes in the dynamics of deposition process, in good qualitative agreement with the experimental data.

Oxidation of sulfite and thiosulfate anions on a porous carbon fiber anode

Anode stability of carbon felt VNG-30 and the kinetics of the anode oxidation of sodium sulfite and thiosulfate solutions (initial concentration: 10 g/l) on this material under different electrolysis conditions are investigated. It is established that BNG-30 is rather stable at the anode polarization up to ap1.8 V and can be used for the anode oxidation of sulfite and thiosulfate. Oxidation rate increases with an increase in the anode polarization and especially noticeably with a decrease in the concentration of ions under oxidation. It is shown that the addition of KBr (up to 10 g/l) causes a noticeable acceleration of sulfite oxidation and has only a weak effect on the process of thiosulfate oxidation.