AES AND LEED STUDIES OF THE INITIAL-STAGES OF OXIDATION OF BETA-NIAL WITH AND WITHOUT PLATINUM DOPING

The initial states of the oxidation of beta-NiAl single crystals with the orientations (110), (100) and (111) were followed at 700-degrees-C using LEED and AES, in the same way similar specimens were investigat ed which were doped with Pt by diffusing a layer of 50 nm Pt into thei r surface. Upon oxidation selectively A;l2O3 is formed. On NiAl(110) a complex surface structure is observed which already was described by other authors, on NiAl(111) upon oxidation the hexagonal structure rem ains, on NiAl(100) submicroscopic facetting occurs. By the Pt doping, these phenomena are not principally changed, however there are some di fferences: (1) the oxidation and also the facetting are occurring more easily, i.e. at a lower oxidation dosing, (2) the sputtering of the o xide layer on the Pt-doped samples was retarded and the oxide layer wa s not very stable and not reactive. Pt seems to hinder the Al segregat ion on the unoxidized samples. These phenomena are described and discu ssed in relation to thermogravimetric studies of the oxidation behavio ur at higher oxygen pressure.