X-ray photoelectron spectroscopy studies of the early-stage oxidation behavior of (Pt, Ni)3Al(1 1 1) surfaces in air

We have studied the early-stage of oxide formation on (1 1 1)-oriented (Pt, Ni)3Al single crystals in air. From X-ray photoelectron spectroscopy (XPS), the predominant surface oxide changed from NiO to Al2O3, as oxidation temperature increased from 900 to 1300 K. Some NiAl2O4 (spinel) also formed at the higher temperatures. Under conditions where NiO and/or NiAl2O4 were present, it resided atop a layer of aluminum oxide, mixed in some cases with metallic Ni. By comparing samples that contained 0, 10 and 20 at% Pt in the bulk, we found that the effects of Pt were to (1) promote the preferential formation of aluminum oxide over nickel oxide(s) in the top layer at all temperatures studied, (2) suppress the amount of metallic Ni mixed with Al2O3 in the underlying oxide region, (3) reduce the total oxide layer thickness, and (4) sharpen the interface between the oxide and the metallic alloy.