The process of electrodeposition of nickel coatings from electrolytes based on a deep eutectic solvent (DES) mixture of choline chloride and lactic acid with a molar ratio of 1:3 was studied. The physicochemical properties and characteristics of DES, namely, con­ductivity, FT-IR and NMR analysis were determined. FT-IR results confirmed that H-bonds occurring between two components in DES were the main force leading to the eutectic formation. Electrochemical techniques were used to characterize the deposition process and scanning electron microscopy was used to study the deposit morphology. Based on polarization measurements, it has been found that at NiCl2·6H2O content of 1.14 M and a temperature of 75 °C, the limiting current density of nickel electrodeposition was near 2 A dm-2. The polarization of the cathodic nickel deposition varied within -0.63 to 1.1 V at current density of 0.25 A dm-2 It has been shown that an increase of water content in the electrolyte does not significantly affect the current efficiency of the nickel electrodeposition process, which was in a range 85-93 %. However, the increase in water content contributes to the increase of heterogeneity and crystal grains size distribution of galvanic deposits. The established values of the Wagner number indicate the predominance of the primary current density distribution in the process of electrodeposition of nickel coatings. Galvanic coatings possess a highly developed nanostructured surface, exhibit increased capillary properties, and can be used as electrode materials for the process of electrolysis of water.

D.Yu. Ushchapovskyi, A.I. Kushmyruk, G.S. Vasiliev, O.V. Linyucheva, R.M. Redko, O.G. Linyuchev, G.Yu. Pidvashetsky, T.A. Kurochenko CORROSION RESISTANCE OF GALVANIC NICKEL DEPOSITS AND ELECTROCHEMICAL ACTIVITY OF THEIR CORROSION PRODUCTS Background. Bright galvanic nickel coatings, with high sulphur content, are less corrosion resistant than matte. Bright nickel coatings are particularly susceptible to corrosion damage in conditions that simulate tropical humid climates and are characterized by the presence of acetic acid vapours. Objective. The purpose of the paper is to investigate: corrosion resistance of galvanic nickel deposits in concentrated acetic acid and its vapours, electrochemical activity of sulphide-containing corrosion products of bright nickel coatings. Methods. Potentiodynamic and cyclic volt-amperometry have been used to study the electrochemical activity of galvanic nickel deposits and their corrosion products. The corrosion rate of galvanic nickel deposits has been determined by gravimetric method. Investigation of surface morphology and composition of galvanic deposits were performed using scanning electron microscopy and X-ray fluorescence analysis. Results.The increased electrochemical activity of sulphide corrosion products of bright nickel coatings is evidenced by an order of magnitude higher cathodic current densities of CVA curves obtained in acetate buffer solutions, in comparison with bright and matte nickel galvanic deposits. It has been shown that at the deposition of sulphide corrosion products of bright nickel coatings on matte nickel foil the corrosion rate of last one increase at the exposition in concentrated acetic acid and its vapours. Conclusions. Significant intensifying effect of sulphur on the corrosion of galvanic nickel deposits in concentrated acetic acid and its vapours has been established. In particular, this can be explained by the decomposition of nickel sulphide (which incorporates in the coating) in acetic acid. Sulphur in the oxidation state (-2) interacts with passive oxide coatings to form an adsorbed monolayer, which leads to the transition of nickel to the active state. Further research will focus on a deeper study of the electrochemical properties of corrosion products of bright nickel coatings. Key words: nickel coatings, corrosion products, nickel sulphides, corrosion activity, catalyst.

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Background.Recently, the problem of recycling and regeneration of concentrated waste technological solutions containing non-ferrous metal ions, in particular copper, has become acute. The particular complexity of processing such type of solutions is caused by the presence of nitrates and chlorides in their composition, causing their chemical aggressiveness. There is a great number of works devoted to electrodeposition of copper from nitrate-containing solu-tions. However, the background technology for the regeneration of nitrate-containing solutions by electrowinning method is poorly developed. Objective. The aim of the investigation is to develop background technology for the purification of contaminated aquatic environment and to study the process of regeneration of concentrated nitrate-containing solutions by the method of copper electrowinning with establishing the influence of the cathodic current density and solution composition on the efficiency of copper extraction and the quality of cathode deposits. Methods. The effect of the solution composition on the polarization and limiting current density of copper deposition was determined by voltammetry. The influence of current density and inter-electrode distance on the cathodic copper current efficiency and the quality of the cathode sediments were determined on the basis of gravimetric studies. The quantitative and qualitative composition of copper cathode deposits was investigated by X-ray fluorescence analysis. Results. The possibility of compact copper obtaining in the solution with copper content of 2 M at the current densities of 15 -25 A/dm 2 with the current efficiency of about 100 % was shown. It was established that for current densities less than 10 A/dm 2 the copper current efficiency exceeds 100 %, which is due to the precipitation of basic copper salts in the cathode layer. On the basis of current-voltage measurements it was established that the electrodeposition of copper from the investigated nitrate-chloride-sulfate solutions occurs with diffusion limitations. Conclusions. As a result of the conducted research the main technological parameters of the copper electrowinning process from concentrated nitrate-sulfate-chloride solutions are established. The obtained data are not indispensable for solving the important environmental problems of removing the concentrated metal-containing industrial waste. Further investigations will focus on optimization of the current mode of copper electrowinning process and development of semi-industrial plant for copper electrowinning from nitrate-contain solutions.

Local electrochemical deposition is a type of electroplating used to plate metal locally or form metal objects using electrochemical principles at a short distance from the working electrode. In this work, deposition of the copper spot was modelled using COMSOL software and experimentally tested in copper sulfate electrolyte using soluble copper anode. The working capillary diameter was 4 mm and the interelectrode distance was 5 mm. The deposited copper of 100 µm height was investigated using the 3D-profilometry technique. The geometry of deposited metal was found to be in good accordance with the COMSOL model. The inclusions of anodic sludge were responsible for the surface inhomogeneity of the deposited copper.