Effect of surfactant on the electrodeposition of Ni–P coating in emulsified supercritical CO2 baths

The electrodeposition behavior and material properties of the Ni–P alloy coatings produced in emulsified supercritical CO2 (sc-CO2) bath with different surfactants (dodecyl octaethylene glycol ether (C12EO8) and a commercial fluorosurfactant) were investigated. The formation of holes or voids which is normally found in conventional aqueous coating could be avoided if the electrodeposition was conducted in the emulsified sc-CO2 bath with proper addition of surfactant, but with the sacrifice of current efficiency. At a lower concentration of surfactant addition, the experimental results showed that fluorosurfactant was more effective than C12EO8 in reducing the surface roughness and void formation in the coating. A significant increase in micro-hardness of the Ni–P coating was observed if it was electrodeposited in the emulsified sc-CO2 bath as compared with that formed at conventional aqueous bath. The wear rate of the Ni–P coating formed in the emulsified sc-CO2 bath was relatively lower with fluorosurfactant as the surfactant than that with C12EO8.

► Supercritical carbon dioxide caused a decrease in electroplating current efficiency.
► Low defect densities in the Ni–P coatings could be obtained.
► Ni–P coatings with enhanced hardness and wear resistance could be obtained.
► The surfactant concentration was critical in affecting the quality of Ni–P coatings.