No abstract

Codeposition of a metal with a monomer capable of electrochemical polymerization at the electrode gives coatings with physicomechanical characteristics that are superior to those for metals used alone [1,2]. NMethylpyrrolidone (MP), which tends to polymerize when an electric current is passed, is of undoubted interest for such purposes. Transformations of MP in solution and at the electrode surface in its codeposition with the metal have been studied in detail [3]. The goal of this study was to elucidate the effect of the MP concentration on the nature of species adsorbed and reduced at the cathode and the wear resistance of coatings formed by copper electrodeposition from aqueous sulfate electrolytes containing N-methylpyrrolidone. EXPERIMENTALTest electrolytes were 1.25 M CuSO 4 + 0.5 M H 2 SO 4 (steady-state electrolysis) or 0.01 M CuSO 4 + 0.5 M H 2 SO 4 (pulse measurements). The concentration of N-methylpyrrolidone in the electrolytes was varied from 0.0001 to 1.0 mol/l. The electrolytes were prepared from twice-distilled water and reagent-grade chemicals. All electrochemical measurements were carried out in an atmosphere of electrolytic hydrogen at 298 K in a three-electrode cell with separate cathodic and anodic compartments. Supporting electrolytes were preelectrolyzed to remove electrochemically active impurities. A silver-chloride reference electrode was used. The diffusion jump of the potential was eliminated by the Pleskov method. The transient time was estimated and calculated as described in [4]. The capacitance and resistance of a copper electrode (electrolytic copper wire press-fitted into Teflon, the wire face diameter 1 mm) was measured with the P-5021 ac bridge for an equivalent series circuit at a frequency of 1 kHz. The results were converted to a parallel circuit in a potential range from 0 to -0.8 V (SCE). Before use, the electrode was pickled in H 3 PO 4 (60 g/l) + HNO 3 (20 g/l) + CH 3 COOH (40 g/l) until it turned evenly rose, washed with water, and polished in CH 3 COOH + HNO 3 (1 : 1) to brightness. Then the electrode was negatively polarized in the supporting electrolyte (0.5 M H 2 SO 4 ) at a potential lower by 100 mV than . Electrolysis was carried out in a 100-cm 3 glass cell under potentiostatic conditions. The electrode was made of steel-45 and electrolytic copper. The electrodes were arranged coaxially. The surface areas of the cathode and the anode were 2 and 10 cm 2 , respectively. The specific wear was assessed by testing electrodes covered with 20-µ m coatings at a reciprocal wobbling bench. The test bench was developed from an NGF-10 milling machine at the Don State Technical University. Measurements were performed as described in [5]. Adhesion to the base metal was estimated by applying a net of scratches. RESULTS AND DISCUSSIONThe initial polarization of the copper cathode ∆ E ini = E i -E p (where E p and E i are the equilibrium potential and the potential of the energized electrode, respectively) was determined from potential vs. time oscillograms. The oscillograms show...

First records of lichens for the Saratov Region, of mosses for the Franz Josef Land Archipelago, the republics of Karelia and Khakassia, Stavropol, Khabarovsk and Kamchatka Territories, Khanty-Mansi Autonomous Area – Yugra, Magadan Region and first records of liverworts for the Tula Region are presented. Data on localities, habitats, distribution of recorded species are provided.

A peculiarity of sulfate copper-plating electrolytes is a possibility of forming of Cu 2+ -S ionic pairs or polynuclear complexes of copper with sulfate ions [2]. The anions were supposed [3] to act as a bridge ligand promoting the electron transfer to the discharging metal ion, thus, in particular, causing a lower electrode polarization in sulfate electrolytes as compared with perchlorate electrolytes. However, replacing the water molecules in the coordination sphere of Cu 2+ cations, organic ligand molecules may be capable of the formation of associates involving sulfate ions, thus causing an "anionic effect" [4]. Electroneutral species, thereby forming in the adsorption layer, can blockade the cathode and significantly inhibit the electrode reaction, which improves the coatings [5]. In this work, we will study copper plating from sulfate baths containing 15-crown-5 cyclic polyester under conditions, when the molecules of both additives and organic component of mixed aqueous-ethanolic solvent adsorb at the cathode. EXPERIMENTAL PROCEDUREAqueous and aqueous-ethanolic electrolytes (alcohol mole fraction x 2 = 0.04) containing 0.01 M CuSO 4 + 0.5 M H 2 SO 4 + y M MgSO 4 ( y = 0, 0.25, 0.5, and 1.0) were studied. 15-Crown-5 in a concentration of 0.01 mol/l was studied as the additive. Chemically pure recrystallized or distilled reagents and twice-distilled water were used. All electrochemical measurements were performed in an atmosphere of electrolytic hydrogen at 298 K in a three-electrode cell with separated cathodic and anodic compartments. Supporting electro-O 4 2-lytes were subjected to preelectrolysis with the aim of removing electrochemically active impurities. A silverchloride electrode was used as the reference one. The diffusion potential drop was eliminated by the Pleskov method. The chronovoltammetric procedures, as well as estimation and calculation of transient time, are already described in [6], the electrode impedance measurements, in [7], and those of tribotechnical characteristics, in [8]. The adhesion to the substrate was estimated by a bend and scratching tests. Figure 1 gives the initial cathodic polarization plots ∆ E in = E i -E 0 (where E i and E 0 are the Cu potentials under the current and open-circuit conditions, respectively, vs. the polarizing current density i ) determined from potential vs. time oscillograms for various bulk concentrations of sulfate ions . At all of i and studied, a single wave of copper(II) ion reduction was observed. The presence of linear (Tafel) segments in the ∆ E in vs. log i curves indicates that, at the initial instants, the electrode process rate is determined by the electrochemical discharge-desolvation stage. The exchange current i 0 of this stage determined from the above plots in aqueous electrolytes free of additive, monotonically increases with an increase in (Fig. 2a, curve 1 ). RESULTS AND DISCUSSIONTo reveal the reaction scheme of the processes, we applied diagnostic criteria commonly used in chronovoltammetry and chronopotentiometry [9]. An analysi...