Mössbauer Study of Iron Oxide Surface Layers Formed on Fine Iron Particles

Mössbauer studies of iron oxides formed on the surface of fine iron particles (acicular type about 15 nm in diameter and 100 nm long) and of an oxidation process in air have been done in the temperature range from 4.2 to 298 K. The Mössbauer spectra indicate that the main component of the oxide layers 2.1–5.6 nm thick, except for a few oxide layers from the iron surface, is composed of fine particles of γ-Fe2O3, and that fine iron oxide particles are produced freshly during the oxidation process at 110 °C in air with the growth of iron oxide particles. It is concluded that an oxide layer 2.1 nm thick is formed on the iron surface if a fresh iron surface is exposed to air at room temperature.