『Abstract
　The surface enthalpies of manganese oxide phases, hausmannite (Mn3O4), bixybyite (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±0.20 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/m². 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.

Keywords: manganese oxides; nanomaterials; calorimetry; surface energy; surface hydration; phase equilibria』

Introduction
Experimental methods
Calorimetric data, enthalpies of bulk phases, and surface enthalpies
Phase diagram calculations
Additional observations on hydration and phase transformation
Geochemical implications
Acknowledgments
References cited