KINETICS OF ELECTRODEPOSITION OF TIN-ZINC ALLOY FROM ALKALINE ELECTROLYTE: INVESTIGATION OF DIFFUSION-KINETIC CONTROL AND OPTIMIZATION OF CONDITIONS

This article presents the results of a study on the kinetics of tin-zinc (Sn-Zn) alloy electrodeposition from an alkaline electrolyte using potentiodynamic and rotating disk electrode (RDE) methods. It has been established that the process of joint deposition of tin and zinc is controlled by a mixed diffusion-kinetic mechanism, which is confirmed by the linear dependence of the inverse current density on the inverse root of the angular velocity of the electrode rotation. The diffusion coefficients of tin (D Sn ≈ 1,77×10 - 8 cm 2 / s ) and zinc (D Zn ≈ 1,97×10 - 7 cm 2 / s ) ions were determined, which were significantly lower than the values for free ions in aqueous solutions, which is associated with the formation of complexes (stannates and zincates) in an alkaline environment and the influence of additives (sodium citrate and sodium lauryl sulfate). Polarization curves showed that zinc is deposited at less negative potentials (-1.10 V instead of -1.20 V), demonstrating depolarization, while tin reaches its limiting current at -1.40 V, indicating diffusion limitations. The composition of the alloy depends on the potential and the rotation speed of the electrode: when the speed is increased from 100 to 1600 rpm, the proportion of zinc in the coating increases from 55% to 65% at -1.45 V. The side reaction of hydrogen evolution becomes significant at potentials below -1.8 V, reducing the efficiency of deposition. Temperature studies revealed a decrease in activation energy from 18.73 kJ/mol at -1.1 V to 14.42 kJ/mol at -1.4 V, indicating an increase in diffusion control at more negative potentials. Potentiodynamic measurements at sweep rates of 1-100 mV/s confirmed the influence of non-stationary factors on the displacement of the curves. The results obtained are important for the development of environmentally friendly technologies for applying protective coatings with controlled composition and improved properties. Promising areas for further research include studying the influence of new additives and optimizing the electrolyte composition to increase the efficiency of the process.