Effect of hydrodynamic electrolysis conditions on the kinetics of cathodicprocesses in chromium(III) sulfate electrolytes

The effect of stirring on the kinetics of electrode processes in a chromium -plating electrolyte based on chromium(III) sulfate is studied. The electro lyte, in which thick (up to 120 mu m) hard chromium coatings can be obtaine d, is stirred with a magnetic stirrer. Hydrodynamic conditions in the syste m are calibrated in a modeling solution containing the same components as t he electrolyte (with the exception of chromium sulfate which is replaced by an equivalent amount of aluminum sulfate), by the reaction of discharge of hydronium ions. It is shown that reactions of discharge of hydronium ions and incomplete reduction of trivalent chromium ions occur in a diffusion mo de. The Cr(III)-Cr(II) system is classified with quasi-reversible redox ele ctrodes and is described by the known equation for diffusion kinetics. The electrodeposition of metallic chromium occurs in the mixed kinetics mode.