Effects of surfactants on electrodeposition of nickel-carbon nanotubes composite coatings

The influences of surfactants sodium dodecylsulfate (SDS) and hexadecyltrimethylammonium bromide (CTAB) on electrodeposition of Ni-carbon nanotubes (CNTs) composite coatings were studied, with a 0.6 g/L addition for SDS or CTAB in Watts bath. The results showed that SDS in the bath slightly decreased but CTAB increased the co-deposited CNTs content in the coatings. The coatings deposited with SDS or CTAB became coarser in low CNTs concentration baths. While as CNTs concentration in the bath increased, the coatings deposited with either SDS or CTAB became more homogeneous. XRD analysis showed that both SDS and CTAB decreased the grain sizes of deposited coatings. The surfactants also affected the preferred orientations of the deposited grains: (220) plane was the preferred orientation in coatings without surfactant, while the preferred orientations for coatings formed in solutions with SDS or CTAB were (200) plane and (111) plane respectively. The addition of SDS in depositing bath increased hardness of the composite coatings and improved adherence of the coating to the matrix. Corrosion resistance of the composite coatings was also slightly improved. However, CTAB was detrimental to both mechanical property and corrosion resistance of the composite coatings. The affecting mechanism of surfactants on the coating properties was discussed.