Thermodynamics of the magnetite-ulvöspinel (Fe 3O 4-Fe 2TiO 4) solid solution

Kristina I. Lilova, Carolyn I. Pearce, Christopher Aaron Gorski, Kevin M. Rosso, Alexandra Navrotsky

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Abstract

The thermodynamics of mixing and its dependence on cation distribution in the Fe 3O 4-Fe 2TiO 4 (magnetite-ulvöspinel) spinel solid solution were studied using high-temperature oxide melt solution calorimetry and a range of structural and spectroscopic probes. The enthalpies of formation of ilmenite and ulvöspinel from the oxides and from the elements were obtained using oxidative drop solution calorimetry at 973 K in molten sodium molybdate. The enthalpy of mixing, determined from the fit to the measured enthalpies of drop solution calorimetry, is endothermic and represented by a quadratic formalism, δH mix = (22.60 ± 8.46)x(1 - x) kJ/mol, where x is the mole fraction of ulvöspinel. The entropies of mixing are more complex than those for a regular solution and have been calculated based on average measured and theoretical cation distributions. Calculated free energies of mixing show evidence for a solvus at low temperature in good agreement with that observed experimentally.

Original languageEnglish (US)
Pages (from-to)1330-1338
Number of pages9
JournalAmerican Mineralogist
Volume97
Issue number8-9
DOIs
StatePublished - Aug 1 2012

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All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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