Mössbauer study on reduction behavior of iron oxide supported on porous glass: hydrogen reduction and He+ ion bombardment effect

Hydrogen reduction behavior and the effect of 40 keV He+ ion bombardment were studied for iron supported on porous glass by Mössbauer spectroscopy. Iron species in as-prepared samples, gave two quadrupole-split doublets due to octahedrally coordinated Fe3+ species in Mössbauer spectra, were assigned to small α-Fe2O3 particles. Both hydrogen reduction and ion bombardment led to the formation of an Fe2+ species, whose Mössbauer spectra have been fitted with two Fe2+ quadrupole-split doublets attributable to tetrahedrally and octahedrally coordinated Fe2+ species. No metallics iron was produced by either of the reduction processes. The yield of Fe2+ species by ion bombardment went up unexpectedly to ca. 80%, indicating that the reduction occurs beyond the range of the incident He+ ions. The re-oxidation behavior of Fe2+ species by air exposure was also examined.