CONDITIONS OF ZINC-NICKEL ALLOY FORMATION FROM AMMONIA-GLYCINATE LOW-CONCENTRATED ELECTROLYTE

Abstract

Introduction. Zinc-nickel alloys coatings are considered to replace cadmium coatings. The corrosion resistance of the zinc-nickel alloy depends on the phase composition of the coating. Thus, the alloy coatings with nickel content of 8–14 wt. % (mainly the γ-phase) are characterized by corrosion resistance 5 times greater than zinc coatings. In turn, the composition and structure of the coatings is determined by the conditions of their production, primarily by the type of electrolyte and electrolysis modes. The aim of the work is to determine the effect of the low concentration ammonium glycinate electrolyte composition on electrode processes during the formation of coatings with a zinc-nickel alloy. Materials and research methods. The kinetics of electrode processes on zinc and nickel samples with surface area from 1 to 5 cm2 in ammonia-glycine electrolyte was studied by analyzing polarization dependencies using a PI-50.1 potentiostat with three electrode cell. A saturated silver chloride electrode was used as a reference electrode, and the potentials are given according to this electrode. Voltammograms were obtained at a potential scan rate of 50 mV/s. The pH value of the electrolytes was monitored using CT-6020A pH meter. Results. The effect of pH value of a mixed ammonium-amino acid electrolyte on the kinetic regularities of electrode processes during the nickel and zinc codeposition was determined by the polarization method. The shape of the polarization dependences of alloy deposition allows suggesting the presence of two limiting stages – electrochemical and diffusion. When pH of the electrolyte increases the alloy deposition occurs with greater overvoltage on both nickel and zinc electrodes. The zinc codeposition with nickel begins at potentials more negative than –1.2 V. Thus, it is possible to obtain zinc-nickel alloys with the necessary protective characteristics by changing the conditions of electrolysis.