XANES study of chemistry of localised corrosion in artificial pits of 316L stainless steel and titanium

摘要

X-ray absorption near edge structure (XANES) experiments on artificial pits of 316L stainless steel were carried out to study the oxidation state and speciation of alloying elements in the pit solution. It was confirmed that the oxidation states of Fe, Cr and Ni are 2+, 3+ and 2+, respectively. Ni(H(_2)O)(_6)(^{2+}) was found to be the main solution species through the pit with no evidence of any Ni-Cl complexes. However, for iron and chromium, hexa-aquo ions (Fe(H(_2)O)(_6)(^{2+}) and Cr(H(_2)O)(_6)(^{3+})) were found near the pit mouth with chloro complexes close to the dissolving metal surface. The chemistry of molybdenum species in artificial pits of 316L stainless was investigated and the molybdenum oxidation state was found to be 3+. There was no evidence of any Mo(VI) polymolybdates, which have previously been proposed to explain the beneficial effects of Mo on the corrosion resistance of 316L stainless steel. High resolutions measurements did not detect any different molybdenum species adjacent to the salt film. XANES measurements on titanium artificial pits showed a presence of TiCl(_4), titanium oxides (rutile and anatse) and metal fragments that were generated during the electrochemical dissolution process. X-ray fluorescence and XANES were also carried out to study the titanium distribution and species in human tissues extracted from the vicinity of failed knee, BAHA (bone-anchored hearing aid) and dental implants. Metal fragments and titanium oxides (rutile and anatase) were found in the tissues. In addition, XANES was carried out on neutrophil cells that had been cultured in the presence of anatase. In one case, a spectrum of rutile was found, suggesting the cells may be able to convert anatase to rutile.