Effect of surfactant on the electrodeposition of Ni–P coating in emulsified supercritical CO 2 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.