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Oxidation of Molybdenum by Low Energy Ion Bombardment

CoCrMo alloy is currently one of the most important alloys for biomedical applications. This material is characterized by superior wear resistance, hardness and high corrosion resistance and is now frequently used for the metal - on - metal hip resurfacing joints [1]. The release of metal ions due to corrosion is thought to have adverse affects on the surrounding body tissue and ultimately leads to failure of the implant. Thus it is important to fully understand the oxidation mechanisms of CoCrMo alloy that seems to be quite complex [2] and also requires a very good knowledge of the oxidation mechanisms of pure metals: cobalt, chromium and molybdenum. In this study, we compare oxidation of molybdenum by low - energy oxygen ion beams with the thermal oxidation process es in oxygen atmosphere within an analytical ultrahigh vacuum chamber, using x - ray photoemission spectroscopy (XPS). A similar study has been carried out on NiTi alloys [3]. Thermal oxidation of molybdenum requires temperatures above 350°C [4]. At lower temperature the Mo surface remains almost unaffected. In contrast, oxygen ion bombardment of molybdenum surface at room temperature leads to the formation of thin oxide films. The fitting procedure clearly shows contributions of various oxidation states of Mo, Mo(IV), Mo(V) and Mo(VI). At the initial stage of irradiation, rapid surface oxidation was observed, indicating the ion bombardment is more efficient in creating molybdenum oxide films then thermal oxidation.

molybdenum ; oxidation ; XPS

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