Bioactive Ca-P coating with self-sealing structure on pure magnesium.

Bioactive coatings containing Ca and P with self-sealing structures were fabricated on the surface of pure magnesium using micro-arc oxidation technique (MAO) in a specific calcium hydroxide based electrolyte system. Coatings were prepared at three applied voltages, i.e. 360, 410 and 450 V, and the morphology, chemical composition, corrosion resistance and the degradation properties in Hank's solution of the MAO-coated samples with three different applied voltages were investigated. It was found that all the three coatings showed similar surface morphologies that the majority of micro-pores were filled with compound particles. Both the porous structures and the compound particles were found to contain consistent chemical compositions which were mainly composed of O, Mg, F, Ca and P. Electrochemical tests showed a significant increase in corrosion resistance for the three coatings, meanwhile the coating obtained at 450 V exhibited the superior corrosion resistance owing to the largest coating thickness. The long term immersion tests in Hank's solution also revealed an effective reduction in corrosion rate for the MAO coated samples, and the pH values of the coated samples always maintained a lower level. Besides, all the three coatings were subjected to a mild and uniform degradation, while the coating obtained at 360 V showed a relatively obvious degradation characteristic and appreciable Ca and P contents on the surfaces of the three coatings were observed after immersion in Hank's solution. The results of the present study confirmed that the MAO coatings containing bioactive Ca and P elements with self-sealing structures could significantly enhance the corrosion resistance of magnesium substrate in Hanks' solution with great potential for medical application.

Rapid decolorization of acid orange II aqueous solution by amorphous zero-valent iron.

Some problems including low treatment capacity, agglomeration and clogging phenomena, and short working life, limit the application of pre-treatment methods involving zero-valent iron (ZVI). In this article, ZVI was frozen in an amorphous state through a melt-spinning technique, and the decolorization effect of amorphous ZVI on Acid Orange II solution was investigated under varied conditions of experimental variables such as reaction temperature, ribbon dosage, and initial pH. Batch experiments suggested that the decolorization rate was enhanced with the increase of reaction temperature and ribbon dosage, but decreased with increasing initial solution pH. Kinetic analyses indicated that the decolorization process followed a first order exponential kinetic model, and the surface-normalized decolorization rate could reach 2.09 L/(m2 x min) at room temperature, which was about ten times larger than any previously reported under similar conditions. Recycling experiments also proved that the ribbons could be reused at least four times without obvious decay of decolorization rate and efficiency. This study suggests a tremendous application potential for amorphous ZVI in remediation of groundwater or wastewater contaminated with azo dyes.

The in vitro degradation process and biocompatibility of a ZK60 magnesium alloy with a forsterite-containing micro-arc oxidation coating.

Magnesium has attracted much attention as a class of biodegradable metallic biomaterials. In this study, a silicate electrolyte-based micro-arc oxidation (MAO) treatment was adopted to prepare forsterite-containing MAO coatings on a ZK60 magnesium alloy in order to decrease the degradation rate and increase the biological property of the alloy. Four anodization voltages were chosen to prepare the MAO coatings. The cell experiment showed a cytotoxicity of grade 0 for the MAO-coated alloy to L929 cells and the hemolytic ratio was dramatically decreased for the MAO-coated alloy compared with the bare one. The corrosion resistance and the degradation behavior of the MAO-coated ZK60 alloy were studied using drop tests, electrochemical measurements and immersion tests. The results indicate that the MAO coating could effectively decrease the initial degradation rate of the alloy. The corrosion resistance of MAO coating was increased with the elevation of the preparation voltage. A degradation model for ZK60 alloy with a forsterite-containing MAO coating was proposed. Based on the model, the MAO-coated alloy experiences destruction and restoration simultaneously, and the coating fails in a peeling-off mode.