A first quantitative XPS study of the surface films formed, by exposure to water, on Mg and on the Mg-Al intermetallics: Al_3Mg_2 and Mg_(17)Al_(12)

摘要

An XPS investigation was carried out of the surface films, formed by exposure to ultrapure water, on mechanically ground Mg and the two Mg-Al intermetallic compounds: Al_3Mg_2 and Mg_(17)Al_(12). The mechanically ground Mg surface had a film of MgO at the Mg metal surface covered by a Mg(OH)_2 layer, formed by the reaction of the MgO with water vapour in the air. Upon immersion in ultrapure water, this film converted to a duplex film with an inner MgO layer next to the Mg metal and an external porous hydroxide layer. For both intermetallics, the XPS data is consistent with (ⅰ) preferential dissolution of Mg and (ⅱ) a 10 nm thick film on the surface after immersion in ultrapure water; the film composition on Al_3Mg_2 was AlMg_(1.4)O_(0.2)(OH)_(5.4) whilst on Mg_(17)Al_(12) the composition was AlMg_(2.5)(OH)_8.