ABSTRACT
Iron specimens have been oxidised sequentially at 550°C in natural oxygen and oxygen enriched with the oxygen-18 isotope at 0.1 atm. The oxides formed were magnetite (Fe3O4) and haematite (Fe2O3).
Examination of the cross-sectioned scales by scanning electron microscopy (SEM) showed that the magnetite consisted of a small inner columnar layer, a middle columnar layer and an outer porous columnar layer at the magnetite-haematite interface.
The location of the oxygen-18 in the cross-sectioned scales was investigated by means of imaging SIMS (Secondary Ion Mass Spectrometry). The results show that substantial cation transport occurred in the scale but that appreciable shortcircuit transport of oxygen also took place either via grain-boundaries or micropores.
