Role of oligomeric olated species in the deposition rate of chromium from a commercial chromium (III) electrolyte

The present investigation is a detailed study of a number of electrolytes based on a commercially available chromium (III) process for thin deposits. A simplified model was developed in which the formation, by CR(II) catalysis, of oligomeric olated forms and their subsequent build up, reduces the concentration of the electroactive form of Cr(III) and hence causes a continuous fall in deposition rate. The process studied, has now been shown to be resistant to extensive polymeric olation, which certainly would result in black, non-metallic deposits. The production of oligomeric species need not reduce the quality of metal deposited, but might instead reduce the concentration of the elctroative form of chromium (III) available, which on depletion would not be restored by equilibration due to the very slow ligand exchange reactions of the Cr(III). The present project is the first to consider the role of oligomeric species in the electrodeposition of chromium. This model has been extensively tested, over long deposition times through the electrolyte lifetime.