Effects of Water, Cations, and Structure on Energetics of Layer and Framework Phases, NaxMgyMnO2·nH2O

Zheng Rong Tian, Guanguang Xia, Jian Luo, Steven L. Suib, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

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 3Na2O4·MoO3 at 977 K. The composition of these phases with a general formula of NaxMgyMnO2· nH2O was systematically varied. Using the measured enthalpies of drop solution, the enthalpies of formation from oxides based on 1 mol of NaxMgyMnO2·nH2O at 298 K, ΔHfo(oxides), were obtained. The ΔHfo(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(hyd) = the number of water molecules per cation), all of the ΔHfo(oxides) data can be linearly correlated. The linear correlations are ΔHfo(oxides) = 16.5N(hyd) - 73.3 for the layer phases, and ΔHfo(oxides) = 11.7N(hyd) - 64.4 for the framework phases. The average N(hyd) values for the birnessite, buserite, and todorokite phases are 2, 4, and 2, respectively.

Original languageEnglish (US)
Pages (from-to)5035-5039
Number of pages5
JournalJournal of Physical Chemistry B
Volume104
Issue number20
DOIs
StatePublished - May 25 2000
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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