Development of Nanocomposite Coating by Hybrid Gas Condensation Process and Magnetron Sputtering Equipment: Electrochemical Characteristics and Surface Analysis

In the present work, a combination of conventional dc magnetron sputtering technique and gas condensation process was utilized to deposit a Ag–Au/a:C nanocomposite coating for application in stents. Quantitative evaluation of Ag+ release to the solution revealed a sharp increase of Ag+ releasing in the first 2 days of immersion, which continues but with a slower rate up to 14 days reaching a value close to 50 ppb. Atomic force microscopy surface morphology depicted that the roughness of the coating, Srms, increases after immersion from 5.86 to 14.22. X-ray photoelectron spectroscopy analysis showed two wide bands at 368.30 and 374.30 eV corresponding to the Ag 3d spin-orbit doublets for non-immersed coating. It was found that the Ag content drops to 5% of the initial concentration as the coating is exposed to artificial urine, due to the high affinity of Ag surface nanoparticles to solution anions. This Ag dissolution to artificial urine is followed by reprecipitating Ag salt clusters with a size less than 3 nm on the surface and the formation of a highly oxidized surface. The formation of the oxidation layer as a result of exposure of the coating to the solution is further confirmed by electrochemical impedance spectroscopy and polarization measurements. It was depicted the resistance of the coating increase from 1.80 to 2.86 MΩ as the coating is immersed into the solution for 14 days. The corrosion potential and corrosion current values collected from the polarization plot of the immersed coating were found to be −0.73 and 0.14, respectively, depicting the protecting character of the coating against the deteriorating solution. It was suggested that the formation of the oxidation layer on the coating surface seals the pores of the coating avoiding solution penetration to the substrate and consequently protecting it against corrosion.