Study On Preparation And Properties Of Anti-abrasion, Anti-corrosion And Biology Of Superhydrophobic Coatings On Mg Alloy

Magnesium alloys have wide application prospect in aviation,aerospace,transportation and chemical industry owing to the advantages of light quality,high specific strength,high thermal conductivity and good casting properties.At the same time,magnesium alloys have biodegradability,biological conductivity and good mechanical properties,so magnesium alloys have potential applications in bone nails,vascular stent and vascular clamp et al..However,the applications of magnesium alloys are severely restricted by their high chemical activity and extremely corrosivity.It is urgent to improve the anti-corrosion performance and establish an anti-corrosion system that is compatible with their environment.The superhydrophobic surface is a functional surface that utilizes a micro-nano structure and a low surface energy material to achieve water-repellency.It can be used as an effective anti-corrosion coating for metal surfaces and has received much attention in recent years.However,in the course of use,the superhydrophobic coating is easily degraded when subjected to mechanical external force,and the low surface energy substance is also easily worn and failed,resulting in loss of hydrophobic properties.Therefore,the preparation of superhydrophobic coating with strong wear resistance is a key step for reaching to the practical application.In this work,robust PDMS/SiO₂ superhydrophobic coatings are successfully prepared on magnesium alloy by adjusted the content and proportion of different-sized SiO₂ nanoparticles with hydrophobicity.The effects of different sizes and ratios of SiO₂nanoparticles on hydrophobicity and wear resistance,hydrophobic mechanism of coating,stability of coating and corrosion resistance are investigated.In addition,magnesium alloys are the huge application prospects in biomaterials.As a preliminary study of implantable materials,we have prepared superhydrophobic coatings of Mg/Zn compounds on the surface of magnesium alloys by a simpler chemical treatment method.Their morphology,hydrophobic properties,self-cleaning properties,corrosion resistance,hemolytic properties of coatings,platelet adhesion,cytotoxicity,and degradation properties in simulated body fluids are researched.The main conclusions are listed as follows:（1）PDMS/SiO₂ superhydrophobic coatings are fabricated on the surface of magnesium alloys by a simple painting method.The coatings are superhydrophobic when the concentration of SiO₂ particles is more than 40 wt%,and the mass ratio of smaller/larger particles is less than 0.5.The contact angles of the samples with 0.2 g SiO₂（40 nm）/0.7 g SiO₂（50–250 nm）and 0.3 g SiO₂（40 nm）/0.7 g SiO₂（50–250 nm）reach more than 150o,and the roll angles less than 10o,so they are superhydrophobic coatings.（2）Their hydrophobicity after 50 cycle abrasion can be still maintained at a high level（138°–150°and 133°–153°）,and no significant change in morphologies and composition before and after abrasion is observed.The finger-wipe,knife-scratch and DSC tests confirmed of the composite coatings possess good mechanical and thermal stability.（3）The corrosion potential of magnesium alloys coated with PDMS/SiO₂superhydrophobic coating was higher than that of magnesium alloys,and the corrosion current density was lower than that of magnesium alloys,indicating that PDMS/SiO₂superhydrophobic coating improved the corrosion resistance of magnesium alloys.（4）The superhydrophobic coatings are fabricated by a simple chemical method which was that magnesium alloys are treated by ZnCl₂ and stearic acid（SA）successively.Their water contact angles reached 162±1o.The rough structures are formed by nano-flake structure whose main composition include Mg（OH）₂,Mg₂Cl（OH）₃·4H₂O,Mg（ClO₄）₂·6H₂O and Zn.The corrosion current density of superhydrophobic coating decreases one order of magnitude than magnesium alloy,indicating that the coating improves the corrosion resistance of magnesium alloy.（5）The biocompatibility and in vitro degradability of the Mg/Zn compound superhydrophobic magnesium alloy are investigated by using blood and phosphate buffered saline（PBS）.The results of hemolysis rate,platelet adhesion and cell activity assay showed that the biocompatibility of the superhydrophobic surface of the magnesium alloy treated by ZnCl₂ and ZnCl₂/SA is improved.The electrochemical and degradation tests in PBS solution indicate the Mg/Zn compound superhydrophobic magnesium alloy has a certain protective effect on magnesium alloy before its hydrophobic property is lost.