Study On The Degradation Behavior Of Anodized-PLGA Biological Caotings On Magnesium

In this paper, anhydrous organic solution were used as electrolyte foranodizing process to produce caotings on the surface of pure magnesium and itsalloys. The morphology of these caotings was uniform with nanometercharacteristics. To further improve the corrosion resistance of biological material,polylactide-glycolide polymer coatings were prepared on anodizing coatings bydipping method. Using scanning electron microscopy, X-ray diffraction, Fouriertransform infrared spectroscopy, Potentiodynamic polarization, electrochemicalimpedance spectroscopy were used to study anodized coating and subsequentcoating microstructure and corrosion resistance.Ethanol electrolyte containing zinc nitrate or calcium nitrate was used toprepare uniform anodic oxidation coating on the rolled magnesium, castmagnesium and cast AZ91magnesium alloy. Calcium nitrate and zinc nitratecoating systems were mainly containing amorphous phase of （CH₃COO）₂Mg andMg（NO₃）₂, MgO can detected in calcium nitrate coating system. Ethanol isoxidized to acetic acid at a high voltage, Acetic acid and Mg²⁺ in the electrolytereact to form magnesium acetate, high voltage and a long oxidation time drivemore （CH₃COO）₂Mg production. Coatings prepared on cast and rolledmagnesium surface in pure zinc nitrate had flaky-network surface morphologywith nano-sized level. The coating morphology and corrosion resistance aresubject to the electrolyte composition, oxidation time and oxidation voltage. Theresults of anodic polarization tests showed that the anodic oxidation coatingimproved corrosion resistance of the substrate. After heat treatment, the phase ofanodic oxidation coating turn to MgO, while the corrosion resistance can beimproved.PLGA caotings were prepared on rolled magnesium and its anodic oxidationcoating by dipping method. The surface morphology of the coating were denseand uniform, the corrosion resistance increases with increasing concentration ofthe PLGA solution. Polymer coatings prepared by a high concentrationsignificantly improved the corrosion resistance of the substrate. SBF immersionexperiments show that polymer coating degraded gradually result in decreasing the proetction for the substrate from corrosion. Electrochemical impedancespectroscopy results show that impedance values of PLGA coatings decreasedgradually with increasing immersion time, compared to the thinner PLGAcoatings, the thicker PLGA coatings provide better corrosion protection forsubstrate.