Electrodeposition of chromium from trivalent chromium urea bath containing sulfate and chloride

The reduction of Cr(III) to Cr(II) on copper electrode in trivalent chromium urea bath containing chromium sulfate and chromium chloride as chromium source has been investigated by potentiodynamic sweep. The transfer coefficient a for reduction of Cr(III) to Cr(II) on copper electrode was calculated as 0.46. The reduction is a quasi-reversible process. J-t responses at different potential steps showed that the generation and adsorption characteristics of carboxylate bridged oligomer are relevant to cathode potential. The interface behavior between electrode and solution for Cr(III) complex is a critical factor influencing sustained electrodeposition of chromium. The hypotheses of the electro-inducing polymerization of Cr(III) was proposed. The potential scope in which sustained chromium deposits can be prepared is from - 1.3 V to - 1.7 V (vs SCE) in the urea bath. Bright chromium deposits with thickness of 30 mu m can be prepared in the bath.