Abstract
The thermodynamics of mixing and its dependence on cation distribution in the Fe3O4-Fe2TiO4 (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, δHmix = (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 language | English (US) |
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Pages (from-to) | 1330-1338 |
Number of pages | 9 |
Journal | American Mineralogist |
Volume | 97 |
Issue number | 8-9 |
DOIs | |
State | Published - 2012 |
Externally published | Yes |
Keywords
- Calorimetry
- Enthalpies of mixing
- Magnetite-ulvö spinel solid solution
- Titanomagnetite
ASJC Scopus subject areas
- Geophysics
- Geochemistry and Petrology