Effect of nature of side anion on kinetics of anodic processes in ‘Chromispel’ electrolytes developed for chromium plating

Abstract

Electrochemical chromium plating was carried out in non-standard ‘Chromispel’ electrolytes containing halogenide instead of sulphate anions. The amount of halogenide anions were varied through changing the CrO3∶I− and CrO3∶Cl− ratios within the range from 15∶1 to 35∶1. Some of the electrolytes used were also contained. Cyclic voltammetry and a kinetic method were applied for electrode polarisation determination. A anode, plate cathodes and a saturated calomel electrode were used. It was found that the nature of the side anion affected the values. In the Cl− containing electrolytes they were found twice as high as those in the presence of I− ions. The polarisation curves recorded in the iodide (‘Chromispel-I’) electrolytes were characterised by a single step, while those obtained in the chloride (‘Chromispel-C’) electrolytes were found to have a second step, although not so well resolved. It was suggested that oxygen and chlorine evolution reactions determined the first and the second step, correspondingly. The value of first step activation energy found in the chloride electrolytes was essentially lower than that calculated for the Cl− containing electrolytes which showed evidence that the oxygen evolution was facilitated there. The experimental data obtained indicated that the electrode polarisation in all electrolytes studied was a concentration one but some chemical interactions or electrochemical hindrances could be expected to interfere in the complex anodic process examined.