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Thermochemistry of iron manganese oxide spinels

Guillemet-Fritsch, Sophie and Navrotsky, Alexandra and Tailhades, Philippe and Coradin, Hervé and Wang, Miaojun Thermochemistry of iron manganese oxide spinels. (2005) Journal of Solid State Chemistry, vol. 1 (n° 1). pp. 106-113. ISSN 0022-4596

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Official URL: http://dx.doi.org/10.1016/j.jssc.2004.10.031

Abstract

Oxide melt solution calorimetry has been performed on iron manganese oxide spinels prepared at high temperature. The enthalpy of formation of (MnxFe1−x)3O4 at 298 K from the oxides, tetragonal Mn3O4 (hausmannite) and cubic Fe3O4 (magnetite), is negative from x=0 to x=0.67 and becomes slightly positive for 0.67<x<1.0. Relative to cubic Mn3O4 (stable at high temperature) and cubic Fe3O4 (magnetite), the enthalpy of formation is negative for all compositions. The enthalpy of formation is most negative near x=0.2. There is no significant difference in the trend of enthalpy of formation versus composition for cubic (x<0.6) and tetragonal (x>0.6) spinels of intermediate compositions. The enthalpies of formation are discussed in terms of three factors: oxidation–reduction relative to the end-members, cation distribution, and tetragonality. A combination of measured enthalpies and Gibbs free energies of formation in the literature provides entropies of mixing. ΔSmix, consistent with a cation distribution in which all trivalent manganese is octahedral and all other ions are randomly distributed for x>0.5, but the entropy of mixing appears to be smaller than these predicted values for x<0.4.

Item Type:Article
Additional Information:http://www.sciencedirect.com/science/journal/00224596
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:Other partners > University of California - UC Davis (USA)
Université de Toulouse > Institut National Polytechnique de Toulouse - INPT
Université de Toulouse > Université Paul Sabatier-Toulouse III - UPS
French research institutions > Centre National de la Recherche Scientifique - CNRS
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Deposited By:Thomas Bonnecarere

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