The Influence of Aluminum on Iron Oxides. XV. Al-for-Fe Substitution in Synthetic Lepidocrocite

Udo Schwertmann1 and Emilia Wolska2
1 Lehrstuhl Für Bodenkunde, Technische Universität München 8050 Freising-Weihenstephan, Federal Republic of Germany
2 Adam Mickiewicz Universität, Grunwaldska 6, 60780 Poznan, Poland

Abstract: Lepidocrocite samples, γ-FeOOH, containing 0–10 mole % Al-for-Fe substitution were synthesized at 15°C and pH 8 by oxidizing mixed FeCl2-AlCl3 solutions. The unit-cell parameters a, b, and c were measured from step-counted X-ray powder diffractograms using seven lines and Si as an internal standard. With increasing Al substitution from 0 to 10 mole % the unit-cell edge lengths a, b, and c decreased regularly by 0.3, 0.8, and 0.6%, respectively. Furthermore, the crystals became smaller, but gained in thermal stability. Decrease in crystal size parallel to the y axis led to a significant increase of the OH-stretch vibration and a decrease of the out-of-plane OH-bending vibration due to a weakening of the hydrogen bond between the zig-zag layers in the structure.

Key Words: Aluminum • Infrared spectroscopy • Iron • Lepidocrocite • X-ray powder diffraction

Clays and Clay Minerals; April 1990 v. 38; no. 2; p. 209-212; DOI: 10.1346/CCMN.1990.0380213
© 1990, The Clay Minerals Society
Clay Minerals Society (www.clays.org)