Role of Au incorporation in the electrochemical behavior of Ag/a:C nanocomposite coatings

Abstract

This work aims to study the electrochemical and the corrosion resistance of amorphous carbon coatings with metallic (Ag) and bimetallic (AgAu) nanoparticles deposited on stainless steel 316L by dc magnetron sputtering technique. These coatings were designed to coat ureteral stents and, accordingly, the Ag release measurement, morphological and electrochemical investigations were performed on the coatings immersed into artificial urine solution during 14 days to imitate the ureter electrolyte (urine) where the stents are inserted. These coatings are intended for insertion into the human body; then, in addition to the biocompatibility, they should not corrode since the resulting products can cause different adverse reactions.The Ag release study showed that the concentration of Ag+ release from the Ag-doped coating is much higher than the AgAu one over the measured time. Moreover, scanning electron microscopy analysis on the immersed and non-immersed coatings supported the Ag ion release assessment. From STEM analysis, the formation of AgAu nanoalloys in a wide size distribution was confirmed. Additionally, the electrochemical characteristics and corrosion resistance behavior of the coatings were investigated in artificial urine solution over immersion time by electrochemical impedance spectroscopy. The Nyquist plots were successfully fitted with a proper equivalent circuit based on a two-layer model representing a porous outer layer and a barrier inner layer for the coatings. The electrochemical measurements revealed that the coating doped with AgAu nanoparticles has improved corrosion resistance and less porosity compared to the Ag-doped one. The enhanced protective feature of the Ag-Au/a:C coatings can be attributed to the formation of AgAu nanoalloys that helps to block the solution penetration into the substrate.