The Electrodepositions of Copper and Nickel from Their Trifluoroacetate–<i>N</i>,<i>N</i>-Dimethylformamide Baths

Abstract

Abstract This paper will deal with the electrodepositions of copper and nickel from Cu(CF3COO)2–HCON(CH3)2, Cu(CF3COO)2–HCON(CH3)2–citric acid, Ni(CF3COO)2–HCON(CH3)2, and Ni(CF3COO)2–HCON(CH3)2–additives baths. The properties of these baths and the mechanism of the electrodeposition of copper from the Cu(CF3COO)2–HCON(CH3)2–citric acid bath were studied. The solubility of Cu(CF3COO)2 in 100 g of HCON-(CH3)2 was 180 g at 20 °C. The specific conductances of the Cu(CF3COO)2–HCON(CH3)2 and Ni(CF3COO)2–HCON(CH3)2 baths were lower than those of the Cu(CF3COO)2–HCONH2 and Ni(CF3COO)2–HCONH2 baths. Cu2O was electrodeposited at the cathode, while copper was not easily obtained from the Cu(CF3COO)2–HCON(CH3)2 bath. By dissolving citric acid in the bath, copper electrodeposition was made easier. Bright and smooth copper deposits were obtained at current densities in the range of 2.0–11.0 A/dm2 from the Cu(CF3COO)2 500 g/l–HCON(CH3)2–citric acid 200 g/l bath at 60 °C, the current efficiencies for cathode and anode being about 75% and above 100% respectively. The cross-section of the copper deposits showed that the deposits have a granular structure. The rate of the electrodeposition of copper from the Cu(CF3COO)2–HCON(CH3)2–citric acid 200 g/l bath at current densities ranging from 1.0 to 3.5 A/dm2 was found to be controlled by the charge–transfer reaction. A black powder nickel deposit was obtained from the Ni(CF3COO)2–HCON(CH3)2 bath. By dissolving NH4Cl, H3BO3, sulfamic acid or CCl3COOH in the bath, adherent bright and smooth nickel deposits were obtained. While the cathode current efficiency was lower in the bath containing sulfamic acid, the anode current efficiency was lower in the bath containing H3BO3 or CCl3COOH. NH4Cl and AlCl3 have the disadvantage that they are dissolved in HCON(CH3)2 only with difficulty. Since the bond between the metallic ion and the solvent in the HCON(CH3)2 bath is stronger than that in the HCONH2 bath, and since dielectric constant of the solvent in the former is lower than that in the latter, metal electrodeposition from the former is more difficult.