KINETICS OF ELECTRODEPOSITION OF ZINC-NICKEL ALLOY FROM SULFATE-GLYCINATE ELECTROLYTE

Abstract

Kinetics of electrodeposition of a zinc-nickel alloy from the acid sulfate-glycinate electrolyte and the properties of the formed coating have been studied depending on the composition of the electrolyte and the deposition mode. Chronoamperometric studies of the electrodeposition of the zinc-nickel alloy made it possible to establish that at polarization potentials of -1.00 -1.05 V relative to the CSE, processes on the electrode proceed with diffusion control. Changing the potentials to the region of more negative values leads to kinetic difficulties. The formation of the zinc-nickel alloy from the sulphate-glycinate electrolyte is affected by the concentration of the nickel salt. The process polarization, crystallization overvoltage, the amount of nickel in the alloy depends on its content in the solution. The maximum crystallization overvoltage corresponds to the NiSO4 content in the electrolyte in the amount of 0.12-0.14 mol/l. Large partial densities of the electroreduction current of nickel during the formation of the Zn-Ni alloy correspond to the same range of concentrations. It was found that with the content of nickel sulphate more than 0.16 mol / l, the amount of nickel in the precipitate decreases. During electrodeposition of the alloy, the pH of the near-electrode layer increases as a result of hydrogen evolution. It is assumed that with the cathode current density of more than 10 mA/cm2, the formation of the zinc-nickel alloy occurs with the participation of neutral and electronegative complexes. Determination of the protective ability of samples in a 3 % NaCl solution using both chronovoltamperometry and impedance spectroscopy showed that samples with a nickel content of 14.4 % obtained in the solution with a nickel sulfate concentration of 0.12-0.14 mol/l are characterized by maximum corrosion resistance.