Effect of fluoride treatment on corrosion behavior of Mg-Ca binary alloy for implant application

The influence of hydrofluoric acid (HF) treatment on the corrosion behavior of the Mg-0.5Ca alloys was investigated by immersion specimen in sodium hydroxide and HF solutions with various concentrations and durations at room temperature. Microstructural evolutions of the specimens were characterized by atomic force microscopy, X-ray diffraction, field-emission scanning electron microscopy. The corrosion resistance was examined through potentiodynamic polarization and immersion test in Kokubo solution. The results revealed that the fluoride treated Mg-0.5Ca alloys produced by immersion in 40% HF provided more uniform, dense and thicker coating layer (12.6 mu m) compared with the 35% HF treated specimen. The electrochemical test showed that the corrosion resistance of fluoride treated specimen was 35 times higher compared with the untreated Mg-0.5Ca alloy specimen in Kokubo solution. In vitro degradation rate of the fluoride treated specimens was much lower than untreated Mg-0.5Ca alloy in Kokubo solution. After immersion test the surface of 40% HF treated sample showed a few corrosion dots, while untreated specimens were fully covered by corrosion products and delamination. Fluoride treated Mg-0.5Ca alloy with 40% HF is a promising candidate as biodegradable implants due to its low degradation kinetics and good biocompatibility.