TY - JOUR
T1 - Thermodynamics of manganese oxides
T2 - Effects of particle size and hydration on oxidation-reduction equilibria among hausmannite, bixbyite, and pyrolusite
AU - Birkner, Nancy
AU - Navrotsky, Alexandra
N1 - Copyright:
Copyright 2012 Elsevier B.V., All rights reserved.
PY - 2012/8
Y1 - 2012/8
N2 - The surface enthalpies of manganese oxide phases, hausmannite (Mn 3O 4), bixbyite (Mn 2O 3), and pyrolusite (MnO 2), were determined using high-temperature oxide melt solution calorimetry in conjunction with water adsorption calorimetry. The energy for the hydrous surface of Mn 3O 4 is 0.96 ± 0.08 J/m 2, of Mn 2O 3 is 1.29 ± 0.10 J/m 2, and of MnO 2 is 1.64 ± 0.10 J/m 2. The energy for the anhydrous surface of Mn 3O 4 is 1.62 ± 0.08 J/m 2, of Mn 2O 3 is 1.77 ± 0.10 J/m 2, and of MnO 2 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-Mn 3O 4 relative to Mn 2O 3 and Mn 2O 3 relative to MnO2. We also report rapidly reversible structural and phase changes associated with water adsorption/desorption for the nanophase manganese oxide assemblages.
AB - The surface enthalpies of manganese oxide phases, hausmannite (Mn 3O 4), bixbyite (Mn 2O 3), and pyrolusite (MnO 2), were determined using high-temperature oxide melt solution calorimetry in conjunction with water adsorption calorimetry. The energy for the hydrous surface of Mn 3O 4 is 0.96 ± 0.08 J/m 2, of Mn 2O 3 is 1.29 ± 0.10 J/m 2, and of MnO 2 is 1.64 ± 0.10 J/m 2. The energy for the anhydrous surface of Mn 3O 4 is 1.62 ± 0.08 J/m 2, of Mn 2O 3 is 1.77 ± 0.10 J/m 2, and of MnO 2 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-Mn 3O 4 relative to Mn 2O 3 and Mn 2O 3 relative to MnO2. We also report rapidly reversible structural and phase changes associated with water adsorption/desorption for the nanophase manganese oxide assemblages.
KW - Calorimetry
KW - Manganese oxides
KW - Nanomaterials
KW - Phase equilibria
KW - Surface energy
KW - Surface hydration
UR - http://www.scopus.com/inward/record.url?scp=84866692859&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84866692859&partnerID=8YFLogxK
U2 - 10.2138/am.2012.3982
DO - 10.2138/am.2012.3982
M3 - Article
AN - SCOPUS:84866692859
VL - 97
SP - 1291
EP - 1298
JO - American Mineralogist
JF - American Mineralogist
SN - 0003-004X
IS - 8-9
ER -