Magnetic enhancement during the crystallization of ferrihydrite at 25 and 50°C
Cabello, E. (Universidad de Córdoba. Departamento de Ciencias y Recursos Agricolas y Forestales)
Morales, M. P. (Instituto de Ciencia de Materiales de Madrid)
Serna, C. J. (Instituto de Ciencia de Materiales de Madrid)
Barrón, V. (Universidad de Córdoba. Departamento de Ciencias y Recursos Agricolas y Forestales)
Torrent, J. (Universidad de Córdoba. Departamento de Ciencias y Recursos Agricolas y Forestales)

Date:	2009
Abstract:	Soil formation usually results in an increase in magnetic susceptibility. The magnetic properties of the products of transformation of ferrihydrite, a typical precursor of other soil Fe oxides, were examined in the present work. Synthetic 2-line ferrihydrite was aged at two temperatures (25 and 50°C) and two different relative humidities (80 and 100%) in the presence of silicate, phosphate, citrate, and tartrate as adsorbed ligands (molar anion/Fe ratio = 1-3%). The ligands delayed or prevented the transformation of ferrihydrite to hematite. The magnetic susceptibility of the ferrihydrite transformation products increased with aging, the rate of increase depending on the type of ligand added and its concentration. The largest increase in magnetic susceptibility, sixfold, was obtained with ferrihydrite in a citrate/Fe ratio of 1%, after 1500 days. The resulting magnetic products exihibited superparamagnetic behavior at room temperature and high coercivity at 5 K. The formation of an intermediate ferrimagnetic phase in the ferrihydrite-to-hematite transformation might explain the magnetic enhancement observed in many aerobic soils lacking other sources of magnetic minerals.
Grants:	Ministerio de Educación y Ciencia AGL2003-01510 Ministerio de Educación y Ciencia AGL2006-10927-CO3-02 Ministerio de Educación y Ciencia MAT2005-03179
Rights:	Tots els drets reservats.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Crystallization ; Ferrihydrite ; Ferrimagnetism ; Hematite ; Maghemite
Published in:	Clays and Clay Minerals, Vol. 57, Núm. 1 (2009) , p. 46-53, ISSN 1552-8367

DOI: 10.1346/CCMN.2009.0570105

8 p, 897.5 KB  UAB restricted access

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