Thermochemistry of iron manganese oxide spinels

Journal Article · Sat Jan 15 04:00:00 EST 2005 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2004.10.031· OSTI ID:20721673

Guillemet-Fritsch, Sophie ^[1]; Navrotsky, Alexandra ^[2]; Tailhades, Philippe ^[1]; Coradin, Herve ^[1]; Miaojun, Wang ^[2]

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1. Centre InterUniversitaire de Recherche et d'Ingenierie des Materiaux (CIRIMAT/LCMIE), Universite Paul Sabatier, Ba-hat timent 2R1, 118, route de Narbonne, 31062 Toulouse, Cedex 04 (France)
2. Thermochemistry Facility and NEAT ORU, University of California at Davis, One Shields Avenue, Davis, CA 95616-877 (United States)

Oxide melt solution calorimetry has been performed on iron manganese oxide spinels prepared at high temperature. The enthalpy of formation of (Mn{sub x}Fe{sub 1-x}){sub 3}O{sub 4} at 298K from the oxides, tetragonal Mn{sub 3}O{sub 4} (hausmannite) and cubic Fe{sub 3}O{sub 4} (magnetite), is negative from x=0 to x=0.67 and becomes slightly positive for 0.67<x<1.0. Relative to cubic Mn{sub 3}O{sub 4} (stable at high temperature) and cubic Fe{sub 3}O{sub 4} (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. {delta}S{sub mix}, 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.

• OSTI ID: 20721673
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 1 Vol. 178; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CALORIMETRY
CUBIC LATTICES
ENTROPY
FORMATION FREE ENTHALPY
FORMATION HEAT
IRON OXIDES
MAGNETITE
MANGANESE OXIDES
SPINELS