The Role of zirconium additive in modifying Hydroxyapatite-based coating to increase the anti-corrosion performance for Mg implant applications

In this study, to improve the anti-corrosion properties of hydroxyapatite coating, zirconium has been used as an additive in different concentrations (0.1, 1 and 10 g/lit) in hydroxyapatite solution with optimal concentration and pH. The surface and electrochemical properties of coatings are compared with uncoated magnesium and magnesium covered by hydroxyapatite samples. AZ31 magnesium was immersed in a solution of hydroxyapatite and zirconium with different concentrations of hexafluorozirconic acid after surface treatment. The corrosion behavior of samples was studied by electrochemical impedance spectroscopy (EIS) and polarization tests in 3.5 wt% sodium chloride solution. The results of electrochemical tests showed that the best corrosion behavior is related to the samples with 1 g/lit zirconium. The corrosion resistance of this sample is 8870 Ω.cm2, which is significantly improved compared to the hydroxyapatite coating. The lowest corrosion current density (0.79 μA/cm2) among all samples is also belong to this coating. Field emission scanning electron microscopy (FE-SEM) and X-ray energy scattering spectroscopy (EDS) were used to study the morphology and evaluate the chemical composition of coatings. The results of EDS and FE-SEM confirmed the formation of hydroxyapatite crystals and amorphous zirconium layer. Contact angle test was performed to complete the surface studies of the samples. By adding 1 g/lit of zirconium to the hydroxyapatite solution, the surface became slightly more hydrophobic, which confirms the better anti-corrosion resistance.