Hydrate Formation in the Restoration of Machine Parts by Electrodeposited Iron Coatings

The purpose. To study the process of formation of sparingly soluble hydroxides and basic salts in the cathode layer during the restoration of machine parts by electrodeposited iron coatings.

Methods. To determine the pH of the hydrate formation of ferrous electrolytes, the method of potentiometric titration with a glass electrode was adopted. The change in the course of the titration curves was recorded using an automatic high-precision potentiometric titrator ATP-02 by direct reading of pH values with an accuracy of ±0.05 units.

The pH of the cathode layer was studied using a microglass electrode. For research, an electrolyte containing 200 kg/m³ of ferrous sulfate and 150–200 kg/m³ of ferric chloride was adopted.

Results. Studies have shown that when using current densities above 30 A/dm², a decrease in the quality of coatings was noted (the appearance of a large number of cracks, local flaking upon impact). To obtain precipitation with satisfactory qualities, it is necessary to apply current densities up to 30 A/dm². An increase in the electrolyte temperature from 293 to 333 K leads to a drop in the pH of the near-cathode layer from 5.9 to 5.2 units. A change in pH in the volume of the solution from 0.3 to 1.8 units leads to an increase in pH in the cathode layer.

Also noteworthy is the rather low quality of the coatings (peeling on bending) obtained at an electrolyte pH above 1.4 units. Therefore, the best condition for electrolysis is the use of an electrolyte acidity of up to 1.4 units.

Conclusion. The study of the pH of the cathode layer of the sulfate-chloride electrolyte depending on the various additions of iron chloride and the effect of electrolysis conditions (current density, temperature and pH of the electrolyte) on the pH shift of the cathode layer showed that an increase in the concentration of iron chloride in a solution of 200 kg/m3 of sulfate reduces the pH of the cathode layer, an increase in temperature also reduces the pH of the catholyte of the sulfate-chloride solution, and an increase in the current density and pH in the volume of the solution increase the pH of the cathode layer.

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