CATHODIC PROCESSES IN SOLUTIONS OF Fe(II) METHANOSULPHONATE

A comparative assessment of iron coating electrolytes for the repair of worn machine parts in the practice of repair production has indicated that the performance of iron coatings from existing electrolytes does not fully meet the requirements for restored machine parts. In particular, the main disadvantages of chloride electrolytes are their high corrosive activity, and boron hydrogen fluoride electrolytes pose a significant environmental hazard. Sulphate electrolytes do not have these disadvantages, but they do not allow for high current densities due to the relatively low solubility of iron salts. Electrolytes based on organic sulfonic acids, primarily methanesulfonic acid (MSA), are promising. Methyl sulfonate solutions are extremely attractive in terms of their use in the electroplating of structural materials. In aqueous solutions, the methyl sulfonate anion is electrochemically inactive and chemically stable. Salts of methanesulfonic acid have high water solubility, and methyl sulfonate anion is an environmentally safe compound. This greatly simplifies wastewater treatment, reduces the requirements for corrosion resistance of electroplating equipment and simplifies the technology. However, at present, there are no technologies for electrochemical deposition of iron and iron-based alloys from methane-sulfonate electrolytes to restore machinery parts. Studies aimed at substantiating the technological performance of such coatings are relevant. To substantiate the required concentration of iron (II) methanesulfonate in electrolytes and determine the technological parameters of the electrochemical plating process based on aqueous solutions of methanesulfonic acid, the kinetics of combined cathodic processes in the range of concentrations of 0.5...2.0 mol·dm-3 iron (II) were studied. The working solutions of electrolytes were prepared by direct etching of iron powder of the PZhRV2-200 brand with a solution of MSC. The resulting solution had a concentration of iron (II) methasulfonate of 2.1 mol·dm-3 and a pH of 1.6. Subsequently, this electrolyte was diluted with distilled water to the required concentration. The voltammetric cathodic dependences in the studied solutions on the steel cathode showed a significant effect of the concentration of iron (II) methanesulfonate on the electrochemical parameters of iron reduction. Thus, an increase in the concentration of iron (II) methane sulfonate leads to a decrease in the cathodic potential. This indicates an increase in the concentration of Fe2+ in the cathode layer, which positively affects the course of the target process - iron reduction and inhibits the side process - hydrogen production. For each Fe2+ concentration, the current densities were determined, at which the cathode process is limited by the electrochemical stage - Fe2+ reduction. To assess the effect of the combined hydrogen production on the cathode process, the volt-ampere characteristics of the cathode process in a solution of 0.5 mol·dm-3 of iron (II) methanesulfonate on a copper electrode were studied. The Tafele plot of iron release at the copper cathode is characterised by a low overvoltage of about 80 mV and a wide range of current densities - from 0.004 to 0.1 A·cm-2. Similar indicators for the steel cathode in the studied electrolyte were: overvoltage - about 120 mV, current density range - from 0.001 to 0.01 A·cm-2. These results indicate a significant negative effect of the combined hydrogen release reaction on the precipitation of iron from the methane-sulfone electrolyte. The expediency of using 2 mol·dm-3 of iron (II) methanesulfonate for further research on the development of technological indicators of iron electroplating was established. It is this concentration of iron (II) methane sulfonate that allows for maximum inhibition of the combined cathodic process - hydrogen production.