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Title: Thermodynamics of manganese oxides: Sodium, potassium, and calcium birnessite and cryptomelane

Abstract

Manganese oxides with layer and tunnel structures occur widely in nature and inspire technological applications. Having variable compositions, these structures often are found as small particles (nanophases). This paper explores, using experimental thermochemistry, the role of composition, oxidation state, structure, and surface energy in the their thermodynamic stability. The measured surface energies of cryptomelane, sodium birnessite, potassium birnessite and calcium birnessite are all significantly lower than those of binary manganese oxides (Mn 3O 4, Mn 2O 3, and MnO 2), consistent with added stabilization of the layer and tunnel structures at the nanoscale. Surface energies generally decrease with decreasing average manganese oxidation state. A stabilizing enthalpy contribution arises from increasing counter-cation content. The formation of cryptomelane from birnessite in contact with aqueous solution is favored by the removal of ions from the layered phase. At large surface area, surface-energy differences make cryptomelane formation thermodynamically less favorable than birnessite formation. In contrast, at small to moderate surface areas, bulk thermodynamics and the energetics of the aqueous phase drive cryptomelane formation from birnessite, perhaps aided by oxidation-state differences. Transformation among birnessite phases of increasing surface area favors compositions with lower surface energy. Finally, these quantitative thermodynamic findings explain and support qualitative observationsmore » of phase-transformation patterns gathered from natural and synthetic manganese oxides.« less

Authors:
 [1];  [2]
  1. Univ. of California, Davis, CA (United States). Peter A. Rock Thermochemistry Lab. Nanomaterials in the Environment, Agriculture, and Technology; Duke Univ., Durham, NC (United States). Pratt School of Engineering
  2. Univ. of California, Davis, CA (United States). Peter A. Rock Thermochemistry Lab. Nanomaterials in the Environment, Agriculture, and Technology
Publication Date:
Research Org.:
Univ. of California, Davis, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1341471
Alternate Identifier(s):
OSTI ID: 1465689
Grant/Contract Number:  
FG02-97ER14749
Resource Type:
Journal Article: Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 7; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; manganese oxides; birnessite; cryptomelane; calorimetry; thermodynamics

Citation Formats

Birkner, Nancy, and Navrotsky, Alexandra. Thermodynamics of manganese oxides: Sodium, potassium, and calcium birnessite and cryptomelane. United States: N. p., 2017. Web. doi:10.1073/pnas.1620427114.
Birkner, Nancy, & Navrotsky, Alexandra. Thermodynamics of manganese oxides: Sodium, potassium, and calcium birnessite and cryptomelane. United States. doi:10.1073/pnas.1620427114.
Birkner, Nancy, and Navrotsky, Alexandra. Fri . "Thermodynamics of manganese oxides: Sodium, potassium, and calcium birnessite and cryptomelane". United States. doi:10.1073/pnas.1620427114.
@article{osti_1341471,
title = {Thermodynamics of manganese oxides: Sodium, potassium, and calcium birnessite and cryptomelane},
author = {Birkner, Nancy and Navrotsky, Alexandra},
abstractNote = {Manganese oxides with layer and tunnel structures occur widely in nature and inspire technological applications. Having variable compositions, these structures often are found as small particles (nanophases). This paper explores, using experimental thermochemistry, the role of composition, oxidation state, structure, and surface energy in the their thermodynamic stability. The measured surface energies of cryptomelane, sodium birnessite, potassium birnessite and calcium birnessite are all significantly lower than those of binary manganese oxides (Mn3O4, Mn2O3, and MnO2), consistent with added stabilization of the layer and tunnel structures at the nanoscale. Surface energies generally decrease with decreasing average manganese oxidation state. A stabilizing enthalpy contribution arises from increasing counter-cation content. The formation of cryptomelane from birnessite in contact with aqueous solution is favored by the removal of ions from the layered phase. At large surface area, surface-energy differences make cryptomelane formation thermodynamically less favorable than birnessite formation. In contrast, at small to moderate surface areas, bulk thermodynamics and the energetics of the aqueous phase drive cryptomelane formation from birnessite, perhaps aided by oxidation-state differences. Transformation among birnessite phases of increasing surface area favors compositions with lower surface energy. Finally, these quantitative thermodynamic findings explain and support qualitative observations of phase-transformation patterns gathered from natural and synthetic manganese oxides.},
doi = {10.1073/pnas.1620427114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 7,
volume = 114,
place = {United States},
year = {Fri Jan 27 00:00:00 EST 2017},
month = {Fri Jan 27 00:00:00 EST 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1073/pnas.1620427114

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Works referenced in this record:

Adsorption of Gases in Multimolecular Layers
journal, February 1938

  • Brunauer, Stephen; Emmett, P. H.; Teller, Edward
  • Journal of the American Chemical Society, Vol. 60, Issue 2, p. 309-319
  • DOI: 10.1021/ja01269a023