Pure thick nickel coating obtained by electroless plating. Surface characterization and wetting properties

Pure nickel coatings were directly plated onto steel by using an electroless plating process. The effect of different synthesis strategies on the morphological surface was investigated and the study of growth mechanisms has provided useful information about the surface properties of coating. In this paper, several plating parameters (pH, temperature, solution composition and the ratio between the sample surface area and the volume of solution) were investigated by studying their influence on the plating rate. High thickness (30 μm) coatings were obtained after 2 h of plating at 85 °C. XRD, SEM and AFM analyses were performed to evaluate microstructure morphology and chemical composition of the deposited coatings. Surface analysis has shown the presence of a hierarchical structure with a macro-nano hierarchical structure and a nanostructured roughness; the influence of surface morphology on wetting properties was assessed. Electroless Ni plated samples exhibit wetting properties changing over time: as-coated samples show a super-hydrophilic behavior with a water contact angle <5° while the coatings become super-hydrophobic after two weeks of standard air exposure, with a water contact angle > 150°. This phenomenon was studied analytically by measuring the water contact angle at different exposure times and by investigating the causes of the surface properties modification. Results confirm that the variation in wettability can be attributed to the presence of airborne hydrocarbon adsorbates on the coating surface.