Functionalized graphene – Modified sol-gel coatings: Controlling the degradation of bioresorbable AZ31 magnesium alloy for biomedical applications

Abstract

The fast degradation of Mg alloys requires strategies tailored for the controlled delay of corrosion. Pristine hybrid silica sol-gel coatings (SG) and sol-gel coatings doped with 0.05 wt% COOH-functionalized graphene nanoplatelets (SG + GNP) were successfully generated on AZ31 magnesium alloy substrates by dip-coating. The physicochemical properties and the anticorrosion behaviour of the coatings were evaluated by Field Emission Gun – Scanning Electron Microscope (FEG-SEM), Energy Dispersive Spectroscopy (EDS), ASTM D3359 standard adhesion tests, scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET), and electrochemical impedance spectroscopy (EIS). Both coatings improved the behaviour in terms of localized and general corrosion, with the SG + GNP coating offering better protection. The presence of the COOHfunctionalized graphene nanoplatelets enhanced the mechanical properties of the sol-gel coating, improving their adhesion resistance and making them less brittle, and therefore offering a better barrier effect and anticorrosion protection. Also, high Ca–P accumulations were found after corrosion tests on both sol-gel coatings, indicative of in-vitro biocompatibility. Thus, SG + GNP coatings can enhance corrosion resistance and biocompatibility of magnesium alloys for biomedical applications.