Yu. D. Gamburg

The effect of hydrogen on amorphization of iron-tungsten alloys produced by electrochemical synthesis

It is shown that the transition from common crystal form (iron-based solid solutions) to the nanocrystalline form occurs at a hydrogen content exceeding 2–3 cube centimeters (at standard conditions) per 1 g of alloy. Therewith, the current density and potential of deposition can vary and depend on the solution composition and other conditions. It is proposed that the transition occurs as an explosive process: in a thin juvenile alloy layer containing a certain limiting amount of hydrogen, high stresses arise; as a result, the concentration of defects increases accelerating hydrogen incorporation. The relevant calculations are performed and the dimensionless constant of hydrogen codeposition is determined (within the framework of the model developed). An alternative supposition is that iron hydroxide precipitating in the near-electrode layer, which also enters into the alloy composition, plays an important role in these processes.

Electrodeposition, Structure, and Properties of Iron–Tungsten Alloys

The electrodeposition, structure, and properties of Fe–W alloys are studied. Working current densitiesirange from 1 to 5 A dm–2at 50°C. The W content (45 wt %) barely depends oni. The current efficiency is about 40%. Alloys obtained at ibelow 2 A dm–2are crystalline oversaturated solid solutions of W in Fe and are magnetic. Higher current densities yield amorphous nonmagnetic alloys of the same composition. Either alloy has a very high resistivity (nearly 300 μohm cm) and, after a treatment at 500–600°C, transforms into a more equilibrium binary system comprising a saturated solid solution and an intermetallic compound.

Peculiarities of morphology of silver microcrystals electroplated under potentiostatic conditions from ammonium solutions

Peculiarities of the morphology of silver microcrystals formed at the electroplating onto inert substrates under potentiostatic conditions are considered. The corresponding experimental data are shown. The prospects of practical application of synthesized objects are discussed.

Effect of cations of alkali metals and ammonium on the process of deposition and structure of iron-tungsten alloys

It is established that potassium ions facilitate expansion of the current density range where crystalline alloy deposits form. This is presumed to be connected with an increase in the hydrogen overvoltage, in connection with which alloy deposits turn amorphous at higher current densities and potentials corresponding to these, at which hydrogen evolution accelerates. A high alloy deposition rate and a sufficiently negative potential of its deposition are conditions not sufficient for transition from large-crystal to nanocrystalline and amorphous deposits. Here, a more important role is played by hydrogen that inserts itself into the crystal lattice. As one could assume, hydrogen in this case facilitates preservation of the emerging nonequilibrium structures, hindering crystallization processes as a result the iron hydride formation.

Electrodeposition of rhenium and its alloys

The processes of electrodeposition of rhenium and its alloys with nickel from aqueous solutions are considered. The results of theoretical and experimental studies of the process of perrhenate ion reduction are analyzed: the data on the possible mechanisms of the cathodic process, participation of atomic hydrogen in it, potentials of transition of rhenium to different oxidation degrees. Codeposition of rhenium and nickel is discussed. The effect of complexation on the current efficiency of rhenium deposition is considered. Information of the sources of data discussed in this paper is provided.

Number of Nuclei Formed during Electrocrystallization and Overall Time Dependence of Their Growth Current

A model for continuous (progressing) nucleation is developed. The model takes into account (1) the mixed kinetics of growth of every nucleus, (2) different degree of the diffusion influence on the growth rate of nuclei formed at different time instants after switching the current on, and (3) the presence of hemispherical diffusion simultaneously with the developing front of plane diffusion. Equations that are obtained for the time dependence of the current include, in addition to values of concentrations, diffusion coefficients, and individual parameters of metals, the exchange current density and the overvoltage. The nucleation in depleted-by-diffusion zones around the growing nuclei is considered. It is shown that the average nucleation retardation degree in such zones is time-independent. Therefore, at an arbitrary time instant, the entire surface may be represented as comprising areas with an ordinary nucleation rate (whose share diminishes) and areas with a lower (but constant) nucleation rate (whose share rises). At not-too-low overvoltages, the decrease in the nucleation rate is mainly due to the decrease in the surface concentration of ions-reactants. The overall number of clusters, calculated with the proposed model, is usually a few orders of magnitude than found by known models.

Electrodeposition of alloys with composition modulated over their thickness : A review

Calculations of near-electrode concentrations of reactant ions and their variations with time during electrodeposition of binary alloys with a modulated-over-thickness composition are presented for various types of pulsed electrolysis. Thicknesses of pure components and alloys of variable compositions at various ratios between component concentrations and pulse magnitudes are established. The role played by exaltation effects, alloying, crystallization factors, and dissolution of the electronegative component from the alloy in a next pulse is shown.

Electrodeposition, properties, and composition of rhenium–nickel alloys

The process of deposition of the Re–Ni alloy, its current efficiency, and the alloy composition are studied as a function of the current density and the solution temperature. The hydrogen content in the deposits, their surface morphology, internal structure, and properties as the cathodic material for HER are examined. It is assumed that besides the high rhenium content, the high catalytic activity of nickel–rhenium alloys is associated with the high degree of their structural disordering.

Some novel efforts to describe the nucleation and growth at electrodeposition

Some alternative ways are developed of looking at the model concepts on electrochemical nucleation. The article consists in several parts concerning several stages of the overall process of nucleation and growth: the statistical approach to nucleation kinetics, the kinetics of the initial stage of the nuclei growth, the growth of an individual cluster under combined charge transfer and diffusion control, nucleation rate and the overall number of clusters, the growth of an increasing number of clusters at overlapping of diffusionally depleted zones, and galvanostatic nucleation.

Microkinetic model of nucleation and its application in electrochemistry

The phenomenon of electrochemical nucleation in micro-and nanoparticles was investigated. The theory of metastable nucleation was developed on the basis of the first principles of statistical physics.