PHYSICAL AND CHEMICAL PROPERTIES OF SULPHATE-GLYCINE ZINC ELECTROPLATING SOLUTIONS

Abstract

The interaction of components in sulphate-glycine solutions for the electroplating of zinc was studied with the content of ZnSO₄ 0.05-0.25 mol/l, NH₂CH₂COOH 0.6-0.95 mol/l and at the temperature range of 22-55 °С. The dependence of electrical conductivity, optical density, kinematic viscosity and the enthalpy of a viscous flow on the solutions composition and the concentration of components was analysed. The physical and chemical properties of sulphate-glycine solutions used for electroplating of zinc are defined by the structural changes in these solutions. The changes occur due to the formation of zinc with glycine complexes. It was determined that with the zinc sulphate concentration range from 0.10 to 0.21 mol/l and the glycine content of 0.7 mol/l, a complex is formed with a coordination number of 1 – ZnGly⁺. The stability of the complex formed depends on the temperature. The effect of the temperature on the structural transformations in the electrolyte is also indicated by a decrease in the enthalpy of a viscous flow from ~7.3 kJ/mol (temperature range 22-35 °С) to ~ 6.4 kJ/mol (temperature range 40-55 °С). The formation of ZnGly⁺ type of complexes in the solutions used for electroplating zinc should facilitate the formation of uniform, fine-grained coatings. Considering the formation of glycinate zinc complexes in the concentration range of ZnSO₄ from 0.10 to 0.21 mol/l, as well as the value of the electrical conductivity and viscosity of the solutions studied, the following composition of the electrolyte is recommended: ZnSO₄ 0.21 mol/l, Na₂SO₄ 0.5 mol/l, NH₂CH₂COOH 0.7 mol/l.