Hostname: page-component-848d4c4894-xfwgj Total loading time: 0 Render date: 2024-06-21T22:02:26.945Z Has data issue: false hasContentIssue false
  • English
  • Français

The Transformation of Lepidocrocite During Heating: A Magnetic and Spectroscopic Study

Published online by Cambridge University Press:  28 February 2024

A. U. Gehring  and
A. M. Hofmeister
A. U. Gehring*
Affiliation:
Department of Soil Science, University of California, Berkeley, California 94720
A. M. Hofmeister
Affiliation:
Department of Geology, University of California, Davis, California 95616
*
1Present address: Swiss Federal Institute for Forest, Snow and Landscape Research, 8903, Birmensdorf, Switzerland
Get access Rights & Permissions [Opens in a new window]

Abstract

Infrared (IR) spectroscopy, in combination with magnetic methods, was used to study the thermally induced transformation of synthetic lepidocrocite (γ-FeOOH) to maghemite (γ-Fe2O3). Magnetic analyses showed that the thermal conversion began at about 175°C with the formation of superparamagnetic maghemite clusters. The overall structural transformation to ferrimagnetic γ-Fe2O3 occurred at 200°C and was complete around 300°C. At higher temperatures, the maghemite converted into hematite (α-Fe2O3). Observation of the transformation from γ-FeOOH to γ-Fe2O3 using variable-temperature IR spectroscopy indicated that dehydroxilation on a molecular level was initiated between 145°C and 155°C. The lag time between the onset of the breaking of OH bonds and the release of H2O from lepidocrocite around 175°C can be explained by diffusive processes. Overall dehydroxilation and the subsequent breakdown of the lepidocrocite structure was complete below 219°C. The comparison of the magnetic and IR data provides evidence that the dehydroxilation may precede the structural conversion to maghemite.

Keywords

DehydroxilationIR spectraLepidocrociteMaghemitePhase transformation
Type
Research Article
Information
Clays and Clay Minerals , Volume 42 , Issue 4 , August 1994 , pp. 409 - 415
Copyright
Copyright © 1994, Clay Minerals Society

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Chopelas, A., and Hofmeister, A. M., (1991) Vibrational spectroscopy of aluminate spinels at 1 atm and of MgAl2O4 to over 200 kbar: Phys. Chem. Miner. 18, 279–293.CrossRefGoogle Scholar
Farmer, V. C., (1974) The Infrared Spectra of Minerals: Mineralogical Society, London.CrossRefGoogle Scholar
Gehring, A. U., and Karthein, R., (1989) ESR study of Fe(III) and Cr(III) hydroxides: Naturwissenschaften 76, 172–173.CrossRefGoogle Scholar
Gehring, A. U., Karthein, R., and Reller, A., (1990) Activated state in the lepidocrocite structure during thermal treatment: Naturwissenschaften 77, 177–179.CrossRefGoogle Scholar
Glemser, O., (1938) Über Darstellung und katalystische Wirksamkeit von reinem γ-FeOOH und daraus gewonnenen γ-Fe2O3: Ber. Dtsch. chem. Ges. 71, 158–163.CrossRefGoogle Scholar
Gómez-Villacieros, R., Hernán, L., Morales, J., and Tirado, J. L., (1984) Textural evolution of synthetic γ-FeOOH during thermal treatment by different scanning calorimetry: J. Coll. Interf. Sci. 101, 392–1400.CrossRefGoogle Scholar
Hedley, I. G., (1968) Chemical remanent magnetization of the FeOOH, Fe2O3 system: Phys. Earth Planet. Inter. 1, 103–121.CrossRefGoogle Scholar
Hofmeister, A. M., (1991) Comment on “Infrared spectroscopy of the polymorphic series (enstatite, ilmenite, and perovskite) of MgSiO3, MgGeO3, and MnGeO3,” by M. Madon and G. D. Price: J. Geophys. Res. 96, 21959–21964.CrossRefGoogle Scholar
Hofmeister, A. M., Rose, T. B., Hoering, T. C., and Kushiro, I., (1992) Infrared spectroscopy of natural, synthetic, and 18O substituted α-tridymite: Structural implications: J. Phys. Chem. 96, 10213–10218.CrossRefGoogle Scholar
Joint Committee on Powder Diffraction Standards (JCPDS) (1980) Mineral Powder Diffraction File, Data Book: JCPDS International Center for Diffraction Data, Swarthmore, Pennsylvania.Google Scholar
Lebel, P., (1985) Inbetriebnahme und Verwendung einer Curiewaage: Diploma thesis, ETH Zürich, 73 pp.Google Scholar
Lewis, D. G., and Farmer, V. C., (1986) Infrared absorption of surface hydroxyl groups and lattice vibration in lepidocrocite (γ-FeOOH) and boethmite (γ-AlOOH): Clay Miner. 21, 93–100.CrossRefGoogle Scholar
Martin, D. H., (1967) Magnetism in Solids: MIT Press, Cambridge, Mass.Google Scholar
McDevitt, N. T., and Baun, W. L., (1964) Infrared absorption study of metal oxides in the low frequency region (700–240 cm–1): Spectrochim. Acta 20, 799–808.CrossRefGoogle Scholar
McMillan, P. F., and Hofmeister, A. M., (1988) Infrared and Raman spectroscopy: in Spectroscopic Methods in Mineralogy and Geology, Hawthorne, F.C., ed., Reviews in Mineralogy 18, 99–160.CrossRefGoogle Scholar
Morris, R. V., Lauer, H. V., Lawson, C. A., Gibson, E. K., Nace, G. A., and Stewart, C., (1985) Spectral and other physicochemical properties of submicron powders of hematite (α-Fe2O3), maghemite (γ-Fe2O3), goethite (α-FeOOH), and lepidocrocite (γ-FeOOH): J. Geophys. Res. 90, 3126–3144.CrossRefGoogle ScholarPubMed
Nakamoto, K., Maargoshes, M., and Rundle, R. E., (1955) Stretching frequencies as a function of distances in hydrogen bonds: J. Am. Chem. Soc. 77, 6480–6488.CrossRefGoogle Scholar
Schwertmann, U., (1989) Occurrence and formation of iron oxides in various pedeoenvironments: in Iron in Soils and Clay Minerals, Stucki, J. W., Goodman, B. A., and Schwertmann, U., eds., Reidel, Dordrecht, 267–308.Google Scholar
Schwertmann, U., and Taylor, R. M., (1972) The transformation of lepidocrocite to goethite: Clays & Clay Minerals 20, 151–158.CrossRefGoogle Scholar
Serna, C. J., Rendon, J. L., and Iglesias, J. E., (1982) Infrared surface modes in corrundum-type microcrystalline oxides: Spectrochim. Acta 38, 797–802.CrossRefGoogle Scholar
Subrt, J., Hanousek, F., Zapletal, V., Lipka, J., and Hucl, M., (1981) Dehydration of synthetic lepidocrocite (γ-FeOOH): J. Thermal. Anal. 20, 61–69.Google Scholar