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The influence of aluminium on iron oxides: XIII. Properties of goethites synthesised in 0·3 M KOH at 25°C

Published online by Cambridge University Press:  09 July 2018

D. G. Schulze  and
U. Schwertmann
D. G. Schulze
Affiliation:
Agronomy Department, Purdue University, West Lafayette, Indiana 47907, USA
U. Schwertmann
Affiliation:
Institut für Bodenkunde, Technische Universität München, 8050 Freising-Weihenstephan, FRG
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Abstract

Aluminium-substituted goethites were synthesised in 0·3 M KOH at either 25° or 70°C. The 25°C goethites had unit-cell a and c dimensions about 0·1–0·2% larger than the 70°C goethites of comparable Al substitution. Unit-cell b dimensions were similar regardless of synthesis temperature. The 25°C goethites contained larger amounts of Al in their structures than the 70°C goethites synthesised at the same initial Al/(Al + Fe) mole ratio in solution. The 25°C goethites had lower dehydroxylation temperatures and smaller differences between the two OH-bending bands than comparable 70°C goethites. These differences between the two sets of goethites are believed to be caused by the presence of more structural defects in the 25°C goethites than in the 70°C goethites. Goethites with the lowest Al substitutions consisted of crystals with several coherently diffracting domains, while at high Al substitutions the crystals were mainly monodomainic. Surface areas of the 25°C goethites varied in a complex manner as a function of thickness along [100], character of the domains, and physical size.

Type
Research Article
Information
Clay Minerals , Volume 22 , Issue 1 , March 1987 , pp. 83 - 92
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1987

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