An electroplating technique using the post supercritical carbon dioxide mixed watts electrolyte

The nickel films with nano-sized grains, high hardness and smooth surface have been prepared using a new electroplating technique involving the post supercritical mixed electrolyte. After mixing watts bath with Sc-CO2, the pH value of exposed electrolyte got lower but then raised backward gradually. The released CO2 concentration from this Sc-CO2 mixture has also been evaluated within 3 h of agitation. As the plating result, average grain size of the 20 μm-thick coatings were 16, 34, and 210 nm for those plated from pure Sc-CO2, post Sc-CO2 and conventional method, respectively. Evaluated on the cross section, microhardness of a 100 μm-thick post Sc-CO2 nickel coating has reached 650 Hv within the regions below 50 μm from the substrate interface then decreased to 350 Hv on further away regions. The high hardness region of nickel coating was found closely related to the electrodeposited duration when electrolyte still possessed high CO2 concentration. Moreover, the incorporation of carbon in nickel electrodeposit was found not only at the pure Sc-CO2 coating but also at the post Sc-CO2 one. Therefore, this new plating technique not only confirms the roles of dissolved CO2 bubbles in electrolyte but also provides a potential to overcome most issues associated with the cost in building high-pressure environment for large size products and continuous plating using supercritical method.