Thermochemistry of iron manganese oxide spinels

Sophie Guillemet (1) , Alexandra Navrotsky (2) , Philippe Tailhades (1) , Hervé Coradin (1) , Miaojun Wang (2)

1 CIRIMAT - Centre interuniversitaire de recherche et d'ingenierie des matériaux
2 UC Davis - University of California [Davis]

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 0.670.6) 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.

Mots clés: Calorimetry; Oxide melt; Heat of formation

Domaines: Matériaux

Sophie Guillemet, Alexandra Navrotsky, Philippe Tailhades, Hervé Coradin, Miaojun Wang. Thermochemistry of iron manganese oxide spinels. Journal of Solid State Chemistry, 2005, 178 (1), pp.106-113. ⟨10.1016/j.jssc.2004.10.031⟩. ⟨hal-03601633⟩