Application of emulsion of dense carbon dioxide in electroplating solution with nonionic surfactants for nickel electroplating

An electroplating reaction using nickel was carried out in an emulsion of dense carbon dioxide (CO2) and an electroplating solution with nonionic surfactants. The current efficiency and electrical resistance values were measured as a function of CO2 volume fraction in the emulsion with three kinds of surfactants. These results show that dense CO2 beyond the critical point of CO2 is effective to form an emulsion for the electroplating reaction. The nonionic surfactant octa(ethylene oxide) dodecyl ether, two kinds of poly (ethylene oxide)-b-poly (propylene oxide) with molecular weights of 745 and 950, respectively, were employed for emulsification. Moreover, a hydrophilic CO2-philic balance of the surfactants strongly influences on the stability of the emulsion. On the basis of the electrical conductivity measurements, the emulsion was classified into a CO2 in water (C/W) type with the CO2 volume fraction ranging from 0 to 80%. Compared to electroplating from the only solution, higher quality nickel films have been prepared by this method. The nickel films that were produced have a higher uniformity, a smaller grain size (sub-100 nm), and a significantly higher Vickers hardness.