In vitro degradation resistance of glucose and L-cysteine-bioinspired Schiff-base anodic Ca-P coating on AZ31 magnesium alloy

A Schiff base (a compound containing a C=N bond) induced anodic Ca-P coating was prepared on AZ31 Mg alloy in a mixed solution of CaCl2 and KH2PO4 at 60 degrees C in the presence of glucose and L-cysteine. The microstructure and chemical composition of the coatings were characterized using FE-SEM, FT-IR, XRD, and XPS. The in vitro degradation resistance of the coated samples was evaluated via potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and hydrogen evolution test. The experimental results show that the Ca-P-Schiff base coating is composed of CaHPO4 (DCPA) and hydroxyapatite (HA), whereas HA is not present in the Ca-P coating. The Ca-P-Schiff base coating thickness is about 2 times that of Ca-P coating (Ca-P coating: (9.13 +/- 4.20) mu m and Ca-P-Schiff base: (18.13 +/- 5.78) mu m). The corrosion current density of the Ca-P-Schiff base coating is two orders of magnitude lower than that of the Ca-P coating. The formation mechanism of the Ca-P-Schiff base is proposed.