| Magnesium and magnesium alloy,as a new kind of biodegradable implant materials,have good biocompatibility,biodegradability,and mechanical properties.Due to such advantages,it has been widely studied by researchers.However,the corrosion rate of magnesium and magnesium alloys were too fast,when touching solutions containing Cl~-.So the clinical application was limited.Therefore,to improve the corrosion resistance of magnesium and magnesium alloys,research and development of magnesium alloy materials with controllable degradation ability for its application and popularization in biology is of great significance.In order to improve the corrosion resistance of magnesium alloys,the methods include two parts:the preparation of phytic acid conversion coating using aqueous chemistry conversion method and phytic acid/?-APS silane hybrid coating using sol-gel combined with dipping methods.The technological parameters were optimized,which were the pH of phytic acid pretreatment solution,the mole ratio of phytic acid and?-APS silane,hydrolysis temperature,the pH of sol and hydrolysis time,concentration of sol,dipping cycle,curing temperature,curing time.The biological activity and corrosion mechanism of phytic acid/?-APS silane hybrid coated magnesium alloy were analyzed by immersion tests,electrochemical tests and fitting circuit.The experimental results show that compared with the specimen treated by phytic acid in acidic conditions and the bare samples,when the pH of phytic acid pretreatment solution was 8.0,the corrosion resistance of the samples was the highest.The pretreated samples was further treated in the following conditions:the mole ratio of phytic acid/?-APS silane was 1:1,the pH of sol was 8.0,the hydrolysis temperature was 35 ~oC,the hydrolysis time was 1.5 h,the concentration of the sol for C(0.943 g phytic acid in 20 ml mixed solution),dipping for one cycle.Then samples were cured at 100 ~oC for 1 h.The hybrid coating coated magnesium alloy specimens showed the best electrochemical performance:the impedance of coated sample was around 27times larger than the impedance of naked samples;the corrosion current density of coated samples was 1/14 of the naked samples;the existence of vibration absorption peaks of silica polymer network and phytic acid chelate indicated that the coating had two strutures,which could be connected,showing the organic and inorganic structure were composited.The surface morphology was compact and no crack.Besides immersion test and electrochemical tests demonstrated that the coating can alleviate the corrosion of magnesium alloys and improve the corrosion resistance.The weight loss of coated samples after immersed in SBF for 9 days was lower than that of bared samples.Besides,after 9 days immersion,the pH of SBF used to immerse the coated samples was still lower than that of bared samples.The corrosion current density of coated samples was 1/3 times lower than that of bared samples.The Calcium phosphate compound deposited on the coating surface,which indicated the biological activity of the magnesium alloy and corrosion resistance was improved. |
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