Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1491528 | Materials Research Bulletin | 2014 | 8 Pages |
Abstract
The syntheses of nanosize magnetite particles by wet-chemical oxidation of Fe2+ have been extensively investigated. In the present investigation the nanosize magnetite particles were synthesised without using the Fe(II) precursor. This was achieved by γ-irradiation of water-in-oil microemulsion containing only the Fe(III) precursor. The corresponding phase transformations were monitored. Microemulsions (pH â¼Â 12.5) were γ-irradiated at a relatively high dose rate of â¼22 kGy/h. Upon 1 h of γ-irradiation the XRD pattern of the precipitate showed goethite and unidentified low-intensity peaks. Upon 6 h of γ-irradiation, reductive conditions were achieved and substoichiometric magnetite (â¼Fe2.71O4) particles with insignificant amount of goethite particles found in the precipitate. Hydrated electrons (eaqâ), organic radicals and hydrogen gas as radiolytic products were responsible for the reductive dissolution of iron oxide in the microemulsion and the reduction Fe3+ â Fe2+. Upon 18 h of γ-irradiation the precipitate exhibited dual behaviour, it was a more oxidised product than the precipitate obtained after 6 h of γ-irradiation, but it contained magnetite particles in a more reduced form (â¼Fe2.93O4). It was presumed that the reduction and oxidation processes existed as concurrent competitive processes in the microemulsion. After 18 h of γ-irradiation the pH of the medium shifted from the alkaline to the acidic range. The high dose rate of â¼22 kGy/h was directly responsible for this shift to the acidic range. At a slightly acidic pH a further reduction of Fe3+ â Fe2+ resulted in the formation of more stoichiometric magnetite particles, whereas the oxidation conditions in the acidic medium permitted the oxidation Fe2+ â Fe3+. The Fe3+ was much less soluble in the acidic medium and it hydrolysed and recrystallised as goethite. The γ-irradiation of the microemulsion for 25 h at a lower dose rate of 16 kGy/h produced pure substoichiometric nanosize magnetite particles of about 25 nm in size and with the stoichiometry of Fe2.83O4.
Keywords
Related Topics
Physical Sciences and Engineering
Materials Science
Ceramics and Composites
Authors
M. GotiÄ, T. Jurkin, S. MusiÄ,