| Magnesium and its alloys have been recognized as promising biodegradable orthopedic materials due to their excellent mechanical and biocompatible properties.Firstly, the abundance of magnesium element is huge in the earth, thus, the magnesium-related products will not be limited by resource shortage. Secondly, the density, the strength and the elasticity of magnesium or its alloy is also close to those of human’s bone. Besides, magnesium ion is non-toxic to the health as the second abundant ion in human body. However, despite these advantages, the poor corrosion resistance ability has restricted their further application as medical materials for human beings. At present, the main anti-corrosion technique for using magnesium alloys in medicine is coating a hydroxyapatite conversion film on their surface. This technique is useful to some extents, but the coating process of it is complicated and the performance of this film is also precarious. Therefore, we must exploit more environmental-friendly coating technologies for magnesium and its alloy to extend their applications in biological medicine.In this paper, we present the influences of phytic acid and sodium alginate conversion coatings on the corrosion resistance of Mg alloy in simulated body fluid（SBF）. Both phytic acid and sodium alginate are clean and environmental-friendly molecules which are beneficial to humans’ health. At first, we separately optimized technological condition for coating the conversion films of these two molecules with electrochemical methods, including polarization curve and electrochemistry impedance spectroscopy. And then, the conversion film with best performance was deposited on magnesium alloy at the optimum condition. Afterwards, we compared the weight-loss of magnesium alloy with optimum films and the untreated one to evaluate the corrosion inhibition performance of the conversion film. Moreover, the microstructure and chemical composition of the films were also determined with scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）, aiming to theoretically clarify the formation mechanism of the two films. The main results are listed as follows:1) The results of polarization curve and electrochemistry impedance spectroscopy show that the optimum technological conditions for coating phytic acid conversion film on AZ31 Mg alloy are to treat the alloy in 2 g/L phytic acid solution with p H of 5 at25℃ for 50 min. Through weight-loss experiment, we found that the corrosion rate of Mg alloy with optimum phytic acid conversion coating in SBF is 0.1917 g/（m2·h）,which was reduced 89.48% compared with the untreated one. EDS measurement indicated that the main elements of phytic acid conversion film are Mg, P, Na and C,revealing the formation mechanism of phytic acid conversion film , and the main ingredient is NaPhy Mg212-xx.（2） The results of polarization curve and electrochemical impedance spectroscopy show that the optimum parameters for coating sodium alginate conversion film on AZ31 Mg alloy are to treat the alloy in 2 g/L sodium alginate with p H of 2 at 50℃for40min. Through weight-loss experiment, we found that the corrosion rate of Mg alloy with optimum sodium alginate conversion film in SBF is 0.3625 g/（m2·h）, which was reduced 80.11% compared with the untreated one. EDS measurement indicated that the main elements of sodium alginate conversion film are Mg, O and C, revealing the formation mechanism of sodium alginate conversion film is HMg OCHMg OC and the main ingredient is （C6H7O6）2Mg. |
PDF Full Text Request