An XPS investigation of the oxidationrcorrosion of melt-spun Mg

The oxide films formed on the surfaces of melt-spun Mg exposed to air, immersed in distilled water or 3% NaCl solution saturated with Mg OH.2 have been investigated by X-ray photoelectron spectroscopy XPS.. High resolution XPS spectra revealed two distinct oxygen species on the surface films: one assigned to O2yin MgO, the other to OHyin Mg OH.2. Depth profiling revealed that the two species had different depth distributions in the films. The oxide film formed in air comprised a contamination outer layer and a relatively thick 5–6 nm.predominantly MgO inner layer. The film formed in distilled water or 3% NaCl solution saturated with Mg OH.2was mainly a mixture of Mg OH.2and MgO. Mg OH.2 was predominant at the top layer and decreased gradually with depth while MgO exhibited the opposite behavior. The corrosion product formed in 3% NaCl solution was more hydrated and much thicker that the films formed in the other two conditions. Cly ion was incorporated in the oxide film formed in 3% NaCl solution. There exists both partial and complete dissociation of adsorbed water when melt-spun pure Mg ribbons are immersed in distilled water or 3% NaCl solution saturated with Mg OH.2. q2000 Elsevier Science B.V. All rights reserved.