Preparation Of Phytic Acid/silanes Hybrid Coatings On AZ31 Magnesium Alloys And Their Properties

Magnesium alloys are kinds of promising implant materials due to their high specific strength,excellent biodegradability,suitable density and low Young's modulus similar to natural human bone.However,the poor corrosion resistance of magnesium alloys limits their wide applications in biomaterials.In this paper,in order to improve the corrosion resistance and bioactivity of biodegradable magnesium alloys,a series of phytic acid/(3-aminopropyl)trimethoxysilane(?-APS)and phytic acid/bis(triethoxysilyl)ethane(BTSE)hybrid coatings were prepared on AZ31 magnesium alloys.The dense and homogeneous phytic acid/silanes hybrid coatings were in situ deposited on the surface of alkali-treated magnesium alloys in the hybrid sols prepared by sol-gel method.During the preparation process,some parameters were optimized,such as pH value of the sol,the solvent composition,the ratios of reactants and the hydrolysis time of silanes.The influences on the morphology and corrosion resistance of different parameters were evaluated by scanning electron microscope(SEM),electrochemical impedance spectroscopy(EIS)and Tafel polarization curve,meanwhile,the results from immersion test were used to predicate the corrosion resistance and bioactivity of hybrid coatings.The test results showed that the dense and homogeneous hybrid coatings could be prepared on the surface of alkali-treated magnesium alloys by immersing the alloys in the sols for 0.5 h at constant temperature of 35 °C.Phytic acid would chelate with magnesium alloy to form magnesium phytic acid,meanwhile,silane molecules would undergo self-crosslinking via siloxane bonds(Si-O-Si)in the composition of phytic acid/silanes hybrid coating.The coating resistance of phytic acid/?-APS hybrid coating was up to 17.62 ± 0.61 kohm·cm2,because ?-APS has functional group of-NH2.Meanwhile,the corrosion current density of phytic acid/BTSE hybrid coating got 100 times lower than the uncoated AZ31 magnesium alloy,for the structure of BTSE,which indicated that phytic acid/silanes hybrid coatings could highly improve the corrosion resistance of magnesium alloys.Besides,during the long-term immersion test,it was found that the morphology of Ca-P deposition induced by the hybrid coating prepared in acidic sols was tradational spherical agglomerates,while,the morphology of Ca-P deposition induced by the hybrid coating prepared in alkaline sols was clusters of needle.