Electrodeposition of Copper-Containing Polymer Coatings from Sulfate Electrolytes Containing N-Methylpyrrolidone

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...