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Thermochemistry of iron manganese oxide spinels

Guillemet, 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, 1 (1). 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
HAL Id:hal-03601633
Audience (journal):International peer-reviewed journal
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Institution:Other partners > University of California - UC Davis (USA)
Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UT3 (FRANCE)
French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
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Deposited On:06 May 2008 07:37

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