Corrosion Enhancement of PM Processed Magnesium by Turning Native Oxide on Mg Powders into Carbonates

Abstract

In addition to its use as a lightweight material, pure magnesium is a promising candidate for prospective bioimplants considering its excellent biocompatible properties. Regardless of what Mg application is used, the ultimate goal is to improve magnesium's mechanical properties and degradation behaviour. Because of the high affinity for oxygen native oxide layer of gas-atomized powders is naturally formed in contact with the atmosphere. S/TEM investigation of the native oxide of the Mg powder particles revealed a nonhomogeneous nano-crystalline MgO layer. MgO is relatively soluble in water and does not provide sufficient corrosion protection. Among various surface treatment methods, conversion of the non-protective magnesium oxide to carbonate products is possible depending on the environmental conditions. This work used a simple experimental method using CO2 and water vapour to achieve surface carbonation of Mg powders. Two carbonated samples and pure magnesium were prepared by direct extrusion. The samples after carbonation retained good mechanical properties and the layer of carbonates had a significant impact on corrosion resistance. 1 day carbonation resulted in transformation of native oxide into amorphous layer and reduction of corrosion rate. Longer carbonation (10 days) revealed layer growth and transformation of native oxide to crystalline nesquehonite structure.