Bio-corrosion assessment and surface study of hydroxyapatite-coated AZ31 Mg alloy pre-treated with vinyl tri-ethoxy silane

Abstract

Nowadays, the use of magnesium (Mg) alloys as operational metals for internal fixation has increased significantly due to their good mechanical properties and biocompatibility. However, the inadequate anti-corrosion performance of these metal alloys limits their usage. In this research, two steps of surface modification were implemented to increase the corrosion mitigation of AZ31 Mg alloy. First, the surface of Mg alloy was treated with vinyl tri-ethoxy silane (VTES) via a sol-gel route. To this end, two hydrolyzation times (1, 24 h) and three different immersion times (30, 60, and 180 s) were accomplished. After which, hydroxyapatite (HA) coating was applied on the silane-treated Mg alloy. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) images depict compact and fine particles uniformly distributed on the sample immersed in 1 h hydrolyzed VTES for 60 s. X-ray photoelectron spectroscopy (XPS) analysis revealed that Si–O–Si structures were formed on the surface of Mg alloy. The corrosion behavior of untreated, Si-treated, and Si/HA-coated samples was studied using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (DC) in 3.5 wt% NaCl and simulated body fluid (SBF) environments. The highest polarization resistance in the saline electrolyte (RP = 12,155 Ω cm2) was recorded for Si/HA-coated sample, which was about 50 times higher than the untreated sample. Bio-corrosion study in SBF solution revealed that after 1 h immersion, the polarization resistance increased significantly to 56,500 Ω cm2 for Si/HA-coated sample, which is a significant improvement in corrosion performance.