Formation of nanosize iron particles, their morphology and interactionwith alumina support film

摘要

Nanosize particles of iron have been dispersed over alumina by thermal deposition under vacuum at substrate temperature of 500 deg C and studied with regard to their size distribution, shape, crystal structure and changes occurring in hydrogen, oxygen and vacuum by transmission electron microscopy. It is shown that deposits of mass thickness of 0.8-1.5 nm yield good dispersion of a platelet-type iron particles of bcc phase (a=0.286 nm) having average projected diameter approx 7.5-17.5 nm. The particles interact with the alumina support and undergo both physical and chemical changes in hydrogen, oxygen and vacuum at elevated temperatures. The resulting morphologies are identified either with core-and-ring or torus shape crystallites. While the former is attributed to Fe and Fe_3O_4 (magnetite, fcc with a=0.836 nm), the later corresponds to Fe_3O_4 and FeAl_2O_4. Reappearance of core-and-ring morphology is observed after heating the torus shape particles in oxygen at 500 deg C for 2h. In vacuum, Fe particles form Fe_3O_4 with some FeAl_2O_4 but assume irregular shapes/faceting character.