Heat capacity studies of the iron oxyhydroxides akaganéite (β-FeOOH) and lepidocrocite (γ-FeOOH)

Claine L. Snow, Stacey J. Smith, Brian E. Lang, Quan Shi, Juliana Boerio-Goates, Brian F. Woodfield, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

The iron oxides and iron oxyhydroxides exist as several different polymorphs, and a thermodynamic understanding of these polymorphs can provide us with an understanding of their relative stability and chemical reactivity. This study provides heat capacity measurements for lepidocrocite (γ-FeOOH) over the temperature range (0.8 to 38) K and akaganéite (β-FeOOH) over the range (0.7 to 302) K. Fits of the heat capacity of the two samples below T = 15 K showed similar behavior to previously published fits of goethite (α-FeOOH), which required a linear term and an anisotropic gap parameter to model accurately the antiferromagnetic spin-wave contributions. The akaganéite measurements were compared to previously reported measurements all of which showed significant disagreement. It is believed that the measurements reported here are the most reliable. Also, the presence of adsorbed water contributes significantly to the heat capacity of akaganéite, and the standard molar entropy at T = 298.15 K of the hydrated form was calculated to be (81.8 ± 2) J · mol-1 · K-1.

Original languageEnglish (US)
Pages (from-to)190-199
Number of pages10
JournalJournal of Chemical Thermodynamics
Volume43
Issue number2
DOIs
StatePublished - Feb 2011
Externally publishedYes

Keywords

  • Antiferromagnetic
  • Entropy
  • Iron oxide
  • Thermodynamic

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Materials Science(all)
  • Physical and Theoretical Chemistry

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