Abstract
The surface enthalpies of manganese oxide phases, hausmannite (Mn 3O4), bixbyite (Mn2O3), and pyrolusite (MnO2), were determined using high-temperature oxide melt solution calorimetry in conjunction with water adsorption calorimetry. The energy for the hydrous surface of Mn3O4 is 0.96 ± 0.08 J/m2, of Mn2O3 is 1.29 ± 0.10 J/m2, and of MnO2 is 1.64 ± 0.10 J/m2. The energy for the anhydrous surface of Mn3O4 is 1.62 ± 0.08 J/m2, of Mn2O3 is 1.77 ± 0.10 J/m2, and of MnO2 is 2.05 ± 0.10 J/m 2. Supporting preliminary findings (Navrotsky et al. 2010), the spinel phase (hausmannite) has a lower surface energy than bixbyite, whereas the latter has a smaller surface energy than pyrolusite. Oxidation-reduction phase equilibria at the nanoscale are shifted to favor the phases of lower surface energy-Mn3O4 relative to Mn2O3 and Mn2O3 relative to MnO2. We also report rapidly reversible structural and phase changes associated with water adsorption/desorption for the nanophase manganese oxide assemblages.
Original language | English (US) |
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Pages (from-to) | 1291-1298 |
Number of pages | 8 |
Journal | American Mineralogist |
Volume | 97 |
Issue number | 8-9 |
DOIs | |
State | Published - 2012 |
Externally published | Yes |
Keywords
- Calorimetry
- Manganese oxides
- Nanomaterials
- Phase equilibria
- Surface energy
- Surface hydration
ASJC Scopus subject areas
- Geophysics
- Geochemistry and Petrology