Kinetics and mechanism of ferrous spinel oxidation studied by electrical conductivity and thermogravimetry

Autor: Gillot, B., Jemmali, F., Rousset, A.
Zdroj: Journal of Materials Science; December 1986, Vol. 21 Issue: 12 p4436-4442, 7p
Abstrakt: A mechanism of valence transfer between Fe2+ and Fe3+ ions in the octahedral, as well as the tetrahedral position of the spinel lattice is suggested to account for the electrical behaviour with the number of Fe2+-Fe3+ pairs in either position for oxidation reactions in finely-grained ferrous spinels. From the s=f(t) curves which are identified with those obtained in thermogravimetry, it was established for inverse spinels such as Fe3O4 or for normal spinels such as FeCr2O4 that the kinetics is governed by a diffusion law under variable working conditions. For more complex spinels such as chromium-or titanium-substituted magnetites which exhibit both Fe2+ ions on octahedral and tetrahedral sites, the results are discussed only qualitatively although the profile of the s=f(t) curves can also be related to the electronic exchange between the Fe2+ and Fe3+ ions from the two cation sites.
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