Magnesium Alloys Implants Coated with 58S Sol-Gel Bioactive Glass to Retard First Stage Corrosion

Two compositions of 58S (60 mol% SiO₂, 36 mol% CaO, 4 mol% P₂O₅) glass coatings were made by sol-gel and applied by dip coating onto two commercial magnesium alloys (AZ31 and AZ91) as a strategy to retard the hydrogen evolution and accelerate the deposition of a hydroxyapatite layer to enhance bioactivity. Surface studies with x-ray photoelectron spectroscopy, Raman spectroscopy, and scanning electronic microscopy techniques are presented after coating deposition and after immersion in Hanks’ balanced salt solution (HBSS) at 37°C. Electrochemical tests were also conducted to evaluate the evolution of the coating with immersion. It is observed that even though the coating presents defects, it is able to retard substrate degradation, and this effect is more pronounced for AZ91 as substrate. Coating performance is mainly governed by the substrate because of defective nature of the film.