Current efficiency and polarization behavior of trivalent chromium electrodeposition process

摘要

The influence of bath composition, mass transfer and applied potential on the trivalent chromium electrodeposition from a bath containing ammonium formate and sodium acetate as the complexing agents was studied by the potentiostatic current efficiency and rotating disk electrode experiments. The results indicate that the chromium electrodeposition process involved two consecutive reduction steps. The first step was the reduction of a trivalent-Cr complex ion to a divalent-Cr complex ion: [Cr(H{sub}20){sub}5L]{sup}(2+) + e{sup}- → [Cr(H{sub}20){sub}5L]{sup}+ where L{sup}- represents the complexing [formate]{sup}- or [acetate]{sup}- ligand. This was followed by the reduction of the divalent-Cr complex ion to metallic Cr(s): [Cr(H{sub}20){sub}5L]{sup}+ + 2e{sup}- → Cr(s) + 5H{sub}20 + L{sup}-. The rate of Cr deposition process was controlled by the transport of the trivalent-Cr complex ion, [Cr(H{sub}20){sub}5L]{sup}(2+), to the cathode surface.