Oxide properties of a gamma titanium aluminide: A surface science study

The surface properties of oxides grown on a gamma titanium aluminide (2 at. % Nb) have been examined using a x-ray photoelectron spectroscopy (XPS) and secondary-ion mass spectroscopy (SIMS). An oxide formed on the sample during air exposure at room temperature was thermally destabilized in ultra-high vacuum. The heating largely decomposed the advanced Ti oxidation states to give a predominate +2 valence configuration at 600{degrees}C, while the Al oxide was somewhat enhanced for the same treatment. Growth of a post chemisorption oxide for various temperatures and exposure times at pressures {le} 10{sup {minus}6} Torr oxygen revealed the progressive development of Ti and AL oxide. At a temperature of 600{degrees}C the Ti component was greatly enhanced relative to the Al content in the surface region. This separation of Ti from Al was clearly visible in SIMS measurements. The development and thermal stability of these oxides is in agreement with the heats of formation and available valence states for the two majority components in the material. 12 refs., 4 figs