Corrosion behavior of magnesium with hydroxyapatite coatings formed by hydrothermal treatment

Corrosion resistance of magnesium alloys must be improved for their applications to orthopaedic bioabsorbable devices. Since hydroxyapatite (HAp) is chemically stable in the body and is the main component of bones, HAp coatings have been well studied to improve the corrosion resistance and osteoconductivity of magnesium alloys. In this study, highly crystallized HAp coatings were formed on pure magnesium with a single-step hydrothermal treatment using a C₁₀H₁₂CaN₂Na₂O₈ solution with various pH values. Morphology of the HAp coating varied depending on the pH value. Corrosion behavior of the HAp-coated magnesium was investigated by anodic polarization, impedance and immersion tests in a simulated body fluid. It was revealed that the corrosion resistance of pure magnesium was improved more than 10 times with the HAp coatings. Stable localized corrosion was prevented with the HAp coatings although the occurrence and moderation of unstable localized corrosion appeared to take place at the defects of the HAp coatings. The initial protectiveness of the HAp coating depended on the treatment condition. During 4-day immersion, the precipitated HAp sealed the defects of the HAp coatings, resulting in the negligible release of magnesium ions regardless of the treatment conditions.