AMMONIUM OXALATE ELECTROLYTES FOR ELECTRODEPOSITION OF ZINC-IRON ALLOYS

The article discusses the kinetic regularities of the electrodeposition of zinc, iron, and zinciron alloys from oxalate-ammonium electrolytes. It is established that during the electrodeposition of zinc from an oxalate-ammonium electrolyte, there are areas of the limiting current having a diffusive nature on the polarization curves. The diffusion character of the limitations of the zinc cathode deposition process is confirmed by the values of the effective activation energy determined by the temperature-kinetic method, which are 13-15 kJ/mol. With increasing temperature, the limiting current density of the diffusion process increases from 1 to 1.5 A/dm(2), and the polarization decreases. Electrodeposition of iron from oxalate-ammonium electrolytes occurs without diffusion restrictions. An increase in temperature from 25 to 70 degrees C leads to a shift in the iron deposition potential to the region of more positive values. The polarization curves that characterize the joint electrodeposition of zinc and iron occupy an intermediate position between the polarization curves for individual metals. A decrease in the concentration of zinc in the oxalate-ammonium electrolyte leads to a slight decrease in the cathodic polarization during the deposition of alloys. The results obtained by cyclic voltammetry indicate that the coatings deposited during the cathodic polarization are quite easily dissolved during the anode half-cycle. On the anode branches of the curves, two current maxima are observed, the height of which decreases with a decrease in the content of zinc ions in the solution. In the case of an electrolyte containing the maximum amount of iron, there is no anode peak in the potential range from -950 to -900 mV. This is due to the fact that as the concentration of iron ions in the solution increases, its content in the coating increases, which increases the tendency of the alloy to passivation. It was found that with an increase in the concentration of iron sulfate in the electrolyte from 10 to 20 g/l, its content in the coating increases from 1.2 to 9.7 at. %. The results obtained indicate the possibility of using oxalate-ammonium electrolytes for electrodeposition of zinc-iron alloys. Alloying zinc with iron facilitates the passivation of coatings.