TITLE: Influence of the Surface Film Stability on the Corrosion Resistance of Mg in Aqueous Solutions

iii This thesis presents an investigation into the structure and composition of the surface film formed on Mg in aqueous solutions and describes the influence of film stability on corrosion resistance. The composition and structure of the surface film formed on pure Mg in pure H2O exposed at Ecorr for 48 h was investigated using plan-view SEM-EDS imaging and STEM–EDS analysis of a FIB cross-section. The film formed was duplex in nature, consisting of a thinner, more-porous, nano-crystalline MgO-rich inner layer (50-100 nm), and a thicker, less-porous, Mg(OH)2-rich outer platelet layer (700 nm). The results were consistent with the theory that a chemical breakdown (hydration) of the bulk inner MgO layer (native oxide) is a necessary precursor step to the corrosion process resulting in a significant thickening of the partially protective outer Mg(OH)2 layer. The surface film formed on pure Mg exposed in 0.01 M NaCl for 24 h at Ecorr was found to be a diffuse bilayer structure similar to pure H2O, including a thin and porou