The use of SIMS to investigate the incorporation of oxygen in CoO scales

SIMS was used to locate O¹⁸ in a thick oxide scale grown on a cobalt specimen oxidized first in O¹⁶ and subsequently in O¹⁸. Analyses were performed in depth profile from the oxide-gas interface and in step scan across a polished cross section. SIMS was found to be well suited to this type of oxygen tracer study. Eighty percent of the O¹⁸ was located in the inner quarter of the scale with a maximum value of 70% 10–15 from the metal-oxide interface. The distribution of the remaining O¹⁸ was essentially uniform in the outer 3/4 of the scale at an average value of 4.6%. There was, however, a layer 150 nm thick highly enriched in O¹⁸ at the oxide-gas interface. The O¹⁸ in the outer 3/4 of the porous scale is probably the result of normal exchange processes. The form of the distribution near the metal-oxide interface cannot be explained at this time.