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Title: Effects of water, cations, and structure on energetics of layer and framework phases, Na{sub x}Mg{sub y}MnO{sub 2}{center_dot}nH{sub 2}O

Abstract

The energetics of 14 synthetic manganese dioxides, including framework phases with todorokite structure and layer phases with birnessite and buserite structures, were studied using high-temperature solution calorimetry in molten 3Na{sub 2}O{sub 4}{center_dot}MoO{sub 3} at 977 K. The composition of these phases with a general formula of Na{sub x}Mg{sub y}MnO{sub 2}{center_dot}nH{sub 2}O was systematically varied. Using the measured enthalpies of drop solution, the enthalpies of formation from oxides based on 1 mol of Na{sub x}Mg{sub y}MnO{sub 2}{center_dot}nH{sub 2}O at 298 K, {Delta}H{degree}{sub f (oxides)}, were obtained. The {Delta}H{degree}{sub f (oxides)} data show no obvious correlation with either content of charge-balancing cations or content of water for the layer and framework phases. Using a new parameter, the hydration number of the charge-balancing cations (N{sub (hyd)} = the number of water molecules per cation), all of the {Delta}H{degree}{sub f (oxides)} data can be linearly correlated. The linear correlations are {Delta}H{degree}{sub f (oxides)} = 16.5N{sub (hyd)} {minus} 73.3 for the layer phases, and {Delta}H{degree}{sub f (oxides)} = 11.7N{sub (hyd)} {minus} 64.4 for the framework phases. The average N{sub (hyd)} values for the birnessite, buserite, and todorokite phases are 2, 4, and 2, respectively.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Univ. of California, Davis, CA (US)
OSTI Identifier:
20075922
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical
Additional Journal Information:
Journal Volume: 104; Journal Issue: 20; Other Information: PBD: 25 May 2000; Journal ID: ISSN 1089-5647
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; MANGANESE OXIDES; CALORIMETRY; ENTHALPY; HYDRATES; SODIUM COMPOUNDS; MAGNESIUM COMPOUNDS; MOLECULAR STRUCTURE; PHASE STUDIES

Citation Formats

Tian, Z.R., Xia, G., Luo, J., Suib, S.L., and Navrotsky, A. Effects of water, cations, and structure on energetics of layer and framework phases, Na{sub x}Mg{sub y}MnO{sub 2}{center_dot}nH{sub 2}O. United States: N. p., 2000. Web. doi:10.1021/jp9939219.
Tian, Z.R., Xia, G., Luo, J., Suib, S.L., & Navrotsky, A. Effects of water, cations, and structure on energetics of layer and framework phases, Na{sub x}Mg{sub y}MnO{sub 2}{center_dot}nH{sub 2}O. United States. doi:10.1021/jp9939219.
Tian, Z.R., Xia, G., Luo, J., Suib, S.L., and Navrotsky, A. Thu . "Effects of water, cations, and structure on energetics of layer and framework phases, Na{sub x}Mg{sub y}MnO{sub 2}{center_dot}nH{sub 2}O". United States. doi:10.1021/jp9939219.
@article{osti_20075922,
title = {Effects of water, cations, and structure on energetics of layer and framework phases, Na{sub x}Mg{sub y}MnO{sub 2}{center_dot}nH{sub 2}O},
author = {Tian, Z.R. and Xia, G. and Luo, J. and Suib, S.L. and Navrotsky, A.},
abstractNote = {The energetics of 14 synthetic manganese dioxides, including framework phases with todorokite structure and layer phases with birnessite and buserite structures, were studied using high-temperature solution calorimetry in molten 3Na{sub 2}O{sub 4}{center_dot}MoO{sub 3} at 977 K. The composition of these phases with a general formula of Na{sub x}Mg{sub y}MnO{sub 2}{center_dot}nH{sub 2}O was systematically varied. Using the measured enthalpies of drop solution, the enthalpies of formation from oxides based on 1 mol of Na{sub x}Mg{sub y}MnO{sub 2}{center_dot}nH{sub 2}O at 298 K, {Delta}H{degree}{sub f (oxides)}, were obtained. The {Delta}H{degree}{sub f (oxides)} data show no obvious correlation with either content of charge-balancing cations or content of water for the layer and framework phases. Using a new parameter, the hydration number of the charge-balancing cations (N{sub (hyd)} = the number of water molecules per cation), all of the {Delta}H{degree}{sub f (oxides)} data can be linearly correlated. The linear correlations are {Delta}H{degree}{sub f (oxides)} = 16.5N{sub (hyd)} {minus} 73.3 for the layer phases, and {Delta}H{degree}{sub f (oxides)} = 11.7N{sub (hyd)} {minus} 64.4 for the framework phases. The average N{sub (hyd)} values for the birnessite, buserite, and todorokite phases are 2, 4, and 2, respectively.},
doi = {10.1021/jp9939219},
journal = {Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical},
issn = {1089-5647},
number = 20,
volume = 104,
place = {United States},
year = {2000},
month = {5}
}