Preparation And Performance Study Of The Calcium-phosphorus Film And So-gel Composite Coating On The Magnesium Alloy

Magnesium and its alloy as a great potential biomedical materials, it has similarmechanical properties, biocompatibility to human bone, and excellentbiodegradability. These characteristics effectively avoid the stress shelter effect,Biological rejection, secondary operation problems in the clinical medicine. However,poor corrosion resistance of magnesium alloy cannot provide effective protectionduring the bone healing period. Therefore, the key point is how to improve thebiocompatibility and control the degradation rate.This experiment adopts AZ60magnesium alloy as the research object, preparecomposite coating on it surface combining chemical conversion technology andsol-gel method. The first step, prepare calcium phosphate coating on the surface as themiddle layer, and then take fluoride treatment in order to further improve its corrosionresistance. Select fluoride treatment temperature, treatment time and solution pHvalue as experiment variables, and then get the best process parameters. The secondstep, getting composite coating by sol gel method on calcium fluoride phosphatemembrane surface, choose membrane layer, fluoride molarity, spin coater speed,sintering time four variables in the orthogonal experiment, and obtained the best craftlevel. Use XRD, SEM, EDS, TG, FT-IR, delimit case law binding force test,polarization curve and electrochemical impedance, MTT cell toxicity experiment totest and represent the structure and properties of the coating, and discusses the variousfactors in the process of film forming effects on its performance.Experimental results show that the calcium phosphate film and fluoride treatmenteffectively improves the corrosion resistance, when fluoride treatment parameters forprocessing temperature is60℃, liquid pH value is12, fluoride liquid molarity is0.15M, the electrochemical ability gets optimal performance, corrosion currentdensity decreased three orders of magnitude to3.889×10-7A/cm2, corrosion potentialincrease323mV. Membrane layer surface is flaky texture, thickness is about8 microns, treatment of fluoride, globular particles can play a role of hole sealingstructure of aperture place, layer and substrate combine closely, can achieve crosscase law binding force test the highest rating level "0".Through orthogonal test we get the best technological level:5sol coating layers,fluoride molarity is2, sintering time is12h, spin coater speed is4000r/min.Compared with magnesium alloy matrix, the corrosion current density of compositecoating reduces the four orders of magnitude to1.004×10-8A/cm2, corrosion potentialraised344mV. Composite coating surface smooth and dense, through positive andsection observation, membrane layer thickness is about10μm, scaly structuredisappears, coating binding force attain rating level "0".We can found that composite coating sample effectively reduce the rate ofhydrogen evolution and the changing of pH value, the protection of matrix has playeda good role in7days of immersion test. Continuous impedance analysis showed thatthe impedance increases at the beginning of soaking, and then decreases gradually, buthigher than magnesium alloy matrix impedance value. It shows that compositecoating samples has good corrosion resistance on the other hand. Cytotoxicityexperiments(MTT) showed that composite coating cytotoxicity rating of "1", meetingthe requirement of biological materials.