Function and mechanism of supercritical carbon dioxide emulsified electrolyte in nickel electroplating reaction

Physical properties of supercritical carbon dioxide emulsion (Sc–CO2–E) were controlled to evaluate the effects on properties of nickel film electroplated. Additive-free Watts bath was used to study sole-effect of Sc–CO2–E on nickel electroplating reaction. Experimental pressure, volume fraction of CO2 and surfactant were adjusted to control physical properties of Sc–CO2–E. Influence of current density was also studied. Surface roughness (Ra) was found to decrease with increase in pressure, volume fraction of CO2, volume fraction of surfactant and current density. Reduction in Ra was believed to be caused by improved homogeneity of Sc–CO2–E, enhanced desorption of hydrogen bubbles from surface of cathode, and increased nickel nuclei density. Grain refinement was observed when increasing pressure, volume fraction of CO2 and surfactant, which was believed to be caused by periodic plating characteristic of electroplating with Sc–CO2–E. On the other hand, grain coarsening was observed with increase in current density.