Clays and Clay Minerals, Vol. 58, No. 4, 451–461, 2010.
Loading...
Authors
Batista, Marcelo A.
Da Costa, Antonio C. S.
Bigham, Jerry M.
De Santan, Henrique
Zaia, Dimas A. M.
De Souza Junior, Ivan G.
Issue Date
2010
Type
Article
Language
Keywords
Periodicals , Geology , Fe Oxides , Isomorphic Substitution , Mass Specific Magnetic Susceptibility , Specific Surface Area , X-ray Diffraction
Alternative Title
Mineralogical, Chemical, And Physical Characterization Of Synthetic Al-substituted Maghemites (g-fe2-xalxo3)
Abstract
Maghemite (g-Fe2O3) is a ferrimagnetic Fe oxide commonly found in tropical and subtropical soils, especially in the topsoil where it is usually a product of burning. Isomorphic substitution (IS) of the Fe in maghemite by different metals (mainly Al3+) can modify its mineralogical and chemical attributes, and these modifications may be important to understanding the formation and properties of this mineral in soils and sediments. The objective of this work was to evaluate the crystallochemical alterations of synthetic, Al-substituted maghemites prepared by the precipitation of magnetites from alkaline aqueous media containing FeSO4·7H2O with increasing amounts of Al2(SO4)3·7H2O to obtain hypothetical Al3+ for Fe3+ substitutions ranging from 0.0 to 40.0 mol %. The Al-substituted magnetites were washed and dried, and then heated to 250ºC for 4 h to form yellowish red maghemites that were characterized by total chemical analysis, X-ray diffraction, specific surface area (SSA), mass-specific magnetic susceptibility, infrared spectroscopy, transmission electronic microscopy, and color. Increasing Al3+ substitution to an experimental maximum of 15.9 mol % decreased both the a0 dimension of the cubic unit cell (a0 = 0.8339 - 396.157610-6 Al, r2 = 0.99) and the mean crystallite dimension (MCD = 76.4 - 3.15Al, r2 = 0.79) of the maghemites. With the decrease in MCD came a more yellowish color, an increase in SSA, and a decrease in crystallinity as measured through extraction of the samples with acid ammonium oxalate. The mass-specific magnetic susceptibility of the maghemites increased with Al3+ substitution up to 5.3 mol % and then decreased with further replacement of Fe by Al. Solid-phase aluminum in excess of 16 mol % substitution appeared to occur as a separate, poorly crystalline phase that was X-ray amorphous.
Description
gsccm58401-bat.pdf -- 668KB
Citation
Clays and Clay Minerals, Vol. 58, No. 4, 451–461, 2010.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018