Effect of Heating on Microcrystalline Synthetic Goethite

Christian J. W. Koch, Morten Bo Madsen, Steen Mørup, Gunnar Christiansen, Leif Gerward and Jørgen Villadsen
Chemistry Department, Royal Veterinary and Agricultural University DK-1871 Copenhagen V, Denmark
Laboratory of Applied Physics II, Technical University of Denmark DK-2800 Lyngby, Denmark
Laboratory of Applied Physics III, Technical University of Denmark DK-2800 Lyngby, Denmark
Haldor Topsøe Research Laboratories, DK-2800 Lyngby, Denmark

Abstract: The effect of heating synthetic microcrystalline goethite at 60°, 80°, and 105°C was studied by X-ray powder diffraction, electron microscopy, weight-loss measurements, and Mössbauer spectroscopy. Heating led to no detectable changes in the unit-cell parameters or crystallite size (210, 150, and 170 Å in the [020], [110], and [120] directions, respectively), however, some of the X-ray diffraction lines were broadened due to an increase in microstrain in these crystallographic directions. The superferromagnetic transition temperature increased from 43° to 46°, 53°, and 54°C after heating to 60°, 80°, and 105°C, respectively, showing that the desorption of water from the surfaces led to an enhanced magnetic coupling among the crystallites.

Key Words: Crystallite size • Goethite • Microstrain • Mössbauer spectroscopy • Thermal treatment • X-ray powder diffraction

Clays and Clay Minerals; February 1986 v. 34; no. 1; p. 17-24; DOI: 10.1346/CCMN.1986.0340103
© 1986, The Clay Minerals Society
Clay Minerals Society (www.clays.org)