Tin–Nickel–Titania Composite Coatings

The effect of titania nanoparticles synthesized by direct oxidation of titanium powder on the cathodic polarization of the electrodeposition of Sn, Ni, and a Sn–Ni alloy in a fluoride–chloride electrolyte has been assessed using voltammetry. The morphology and phase composition of the coatings obtained have been studied by scanning electron microscopy and X-ray diffraction. The pH of the electrolyte has been shown to have a crucial effect on its stability and the quality of the coatings. The optimal pH of the electrolyte for the deposition process is 3.0 ± 0.1 and the optimal current density is 1.0 ± 0.1 A/dm2. The coprecipitation of nickel and tin into an alloy has been shown to be accompanied by a depolarization effect, due to the formation of NiSn2 and Ni3Sn2 intermetallic compounds. The addition of titanium dioxide shifts the alloy reduction process to more negative potentials. The addition of 2 g/L of titanium dioxide to an electrolyte leads to the incorporation of 0.7 wt % TiO2 into the composition of the coating.