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Title: Structure and stability of pyrophyllite edge surfaces: Effect of temperature and water chemical potential

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 190; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-04 21:58:34; Journal ID: ISSN 0016-7037
Country of Publication:
United States

Citation Formats

Kwon, Kideok D., and Newton, Aric G. Structure and stability of pyrophyllite edge surfaces: Effect of temperature and water chemical potential. United States: N. p., 2016. Web. doi:10.1016/j.gca.2016.06.021.
Kwon, Kideok D., & Newton, Aric G. Structure and stability of pyrophyllite edge surfaces: Effect of temperature and water chemical potential. United States. doi:10.1016/j.gca.2016.06.021.
Kwon, Kideok D., and Newton, Aric G. 2016. "Structure and stability of pyrophyllite edge surfaces: Effect of temperature and water chemical potential". United States. doi:10.1016/j.gca.2016.06.021.
title = {Structure and stability of pyrophyllite edge surfaces: Effect of temperature and water chemical potential},
author = {Kwon, Kideok D. and Newton, Aric G.},
abstractNote = {},
doi = {10.1016/j.gca.2016.06.021},
journal = {Geochimica et Cosmochimica Acta},
number = C,
volume = 190,
place = {United States},
year = 2016,
month =

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.gca.2016.06.021

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  • Fe(II)-Al(III)-LDH (layered double hydroxide) phases have been shown to form from reactions of aqueous Fe(II) with Fe-free Al-bearing minerals (phyllosilicate/clays and Al-oxides). To our knowledge, the effect of small amounts of structural Fe(III) impurities in “neutral” clays on such reactions, however, were not studied. In this study to understand the role of structural Fe(III) impurity in clays, laboratory batch studies with pyrophyllite (10 g/L), an Al-bearing phyllosilicate, containing small amounts of structural Fe(III) impurities and 0.8 mM and 3 mM Fe(II) (both natural and enriched in 57Fe) were carried out at pH 7.5 under anaerobic conditions (4% H2 – 96%more » N2 atmosphere). Samples were taken up to 4 weeks for analysis by Fe-X-ray absorption spectroscopy and 57Fe Mössbauer spectroscopy. In addition to the precipitation of Fe(II)-Al(III)-LDH phases as observed in earlier studies with pure minerals (no Fe(III) impurities in the minerals), the analyses indicated formation of small amounts of Fe(III) containing solid(s), most probably hybrid a Fe(II)-Al(III)/Fe(III)-LDH phase. The mechanism of Fe(II) oxidation was not apparent but most likely was due to interfacial electron transfer from the sorbed Fe(II) to the structural Fe(III) and/or surface-sorption-induced electron-transfer from the sorbed Fe(II) to the clay lattice. Increase in the Fe(II)/Al ratio of the LDH with reaction time further indicated the complex nature of the samples. This research provides evidence for the formation of both Fe(II)-Al(III)-LDH and Fe(II)-Fe(III)/Al(III)-LDH-like phases during reactions of Fe(II) in systems that mimic the natural environments. Better understanding Fe phase formation in complex laboratory studies will improve models of natural redox systems.« less
  • We investigate the correct implementation of the exchange-correlation potential for the excited core electron in near-edge x-ray-absorption fine structure (NEXAFS). We examine the effects on NEXAFS spectra of the ground-state Slater and excited-state Dirac-Hara exchange potentials and current implementations of the Hedin-Lundqvist exchange-correlation potential on the muffin-tin model. For a test case of gas-phase acetylene, we find good agreement with prior experimental spectra only with the Hedin-Lundqvist potential implemented on the local-density approximation with a Thomas-Fermi-like requirement of constancy of the chemical potential.
  • The CaO-Al{sub 2}O{sub 3}-SO{sub 3}-H{sub 2}O system at 25 {sup o}C under 1 bar of pressure has been investigated with phase diagrams software (Zen + k) based on chemical potentials (or activities). The reported invariant points are similar to those obtained previously using equilibrium calculations. However Zen + k enables us to calculate systems at different relative humidities, and in conditions where water is not in excess, calcium monosulfoaluminate could be a stable phase and thus, as observed experimentally, remain for long times in an ordinary Portland cement paste.
  • Ab initio surfaces in reduced normal-coordinate space for water, for the potential energy and components of the dipole moment and second moment of charge about the center of mass, have been refined for use in calculating energies of vibration and expectation values of these properties in low-lying states of vibration. The two procedural refinements consist of (i) direct fitting of the surfaces to values obtained at a grid of points, where the internal coordinates for each point have been transformed to reduced normal coordinates by an iterative procedure, and (ii) (small) rotation of the axes into coincidence with a vibrationallymore » invariant set at each asymmetric configuration on the grid. The first refinement brings the calculated values of the constants of anharmonicity x/sub ij/ into much closer agreement with experiment. Both refinements generate significant changes in the fitted property surfaces. For several isotopic species of water calculated expansion coefficients are listed for the potential energy in reduced normal coordinates and the dipole moment in internal and reduced normal coordinates; expectation values are also given.« less