Morphology and composition of coatings based on hydroxyapatite-chitosan-RuCl 3 system on AZ91D prepared by pulsed electrochemical deposition

Hydrxoyapatite-chitosan-RuCl3 nanocomposite coatings were pulsed electrochemical deposited on magnesium alloys AZ91D and studied using scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersion spectrometer (EDS), electron probe micro-analysis (EMPA), auger electron spectroscopy (AES) and Fourier transform infrared spectroscopy (FTIR). The corrosion resistance of coating was examined by impedance measurements and potentiodynamic polarization. It was shown that the coatings can be varied by the variation of RuCl3 concentration in the solutions used for pulsed electrochemical deposition (PED). The absorption rate of Ru element on composite coatings was varied in the range of 35.02%∼51.62% by the variation of RuCl3 concentration from 2.1 mmol L−1 to 8.4 mmol L−1 in electrolyte. The hydroxyapatite grain of the obtained coating was refined to 180 nm, which could be explained by this mechanism: the electronegativity value of Ru was higher than Ca, which resulted in the new formation of PO43− tended to prefer attracting RuCl3 firstly on the cathode. Moreover, electrochemical impedance spectroscopy and potentiodynamic polarization studies showed that higher RuCl3 absorption rate on the coating provide corrosion protection of AZ91D in Hank's solution. With higher RuCl3 absorption rate, the induced hydroxyapatite-forming ability of the composite coating in Hank's solution has improved remarkably. The composite coatings are promising materials for the fabrication of implantable bio-materials with advanced functions properties.