Determination of corrosion product film on pure Mg in Cl− environment using XPS etching

Abstract X-ray photoelectron spectroscopy (XPS) combined with Ar ion etching was used to analyse the surface film of pure Mg at different depth after immersion in 3.5 % NaCl solution for 10 min. The XPS spectra of specimen surface showed that the corrosion products are mainly made up of Mg(OH)2 and Mg2Cl(OH)3·xH2O. The formation process of Mg2Cl(OH)3 is the reaction of Mg(OH)2 and Cl− and H+ in weak acidic solutions. The XPS results indicated that the intensities of Mg2Cl(OH)3·xH2O decreased with the increase of etching time from 0 s to 4680 s. It is confirmed that the edge of Mg(OH)2 protrudes outward and then splits into Mg2Cl(OH)3 when Cl− attacks the Mg(OH)2 films, so the Mg2Cl(OH)3 attached to Mg(OH)2. Meanwhile, coupling the scanning electron microscope (SEM) and transmission electron microscopy (TEM) with the XPS to analyze the corrosion mechanism. Furthermore, the results displayed that the XPS combined with Ar ion etching is a good characterization method to understand the reaction of corrosion products.