Electrodeposition of Chromium and Nickel‐Chromium from Amide Solvents

Abstract

Chromium was deposited from hexaamminechromium(III) formate in 30 mole per cent acetamide/formamide at cathode current efficiencies up to 50%. The current density range for optimum plating efficiency varied from 25 to 150 mA/cm2 depending on the chromic ion concentration in the bath. Aquation of this chromic complex during electrolysis takes place at an appreciable rate when the water content exceeds 400 ppm and results in decreased plating efficiency. There was no correlation between the effectiveness of bridging groups for electron transfer between chromous and chromic ion and the electrodeposition of chromium in the amide solvent system. The observed effectiveness of ligands for promoting chromium deposition was: . Sulfamic acid, boric acid, and sodium thiocyanate were effective in increasing plating efficiency at low concentrations; it was also observed that thiocyanate lowered the chromium deposition potential. Chromium‐nickel alloys were produced over the entire concentration range of 0–100% chromium by the addition of hexaamminenickel(II) formate to the bath. Alloy composition was influenced more by electrolyte composition and bath temperature than by current density.