Mineralogical, chemical, and physical characterization of synthetic al-substituted maghemites (γ-fe2-xalxo3)
Batista, Marco Alexandre da Silva (Universidade Estadual de Maringá. Departamento de Agronomia)
da Costa, Antonio C. S. (Universidade Estadual de Maringá. Departamento de Agronomia)
Bigham, Jerry M. (The Ohio State University. School of Environment and Natural Resources)
de Santana, Henrique (Universidade Estadual de Londrina. UEL, Departamento de Quemica)
Zaia, Dimas A. M. (Universidade Estadual de Londrina. UEL, Departamento de Quemica)
de Souza Junior, Ivan G. (Universidade Estadual de Maringá. Departamento de Agronomia)

Data:	2010
Resum:	Maghemite (γ-FeO) 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 Al) 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 FeSO·7HO with increasing amounts of Al(SO)·7H2O to obtain hypothetical Al for Fe substitutions ranging from 0. 0 to 40. 0 mol %. The Al-substituted magnetites were washed and dried, and then heated to 250°C 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 Al substitution to an experimental maximum of 15. 9 mol % decreased both the a dimension of the cubic unit cell (a = 0. 8339- 396. 157×10 Al, r = 0. 99) and the mean crystallite dimension (MCD = 76. 4 - 3. 15Al, r = 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 Al 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.
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Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Fe Oxides ; Isomorphic Substitution ; Mass Specific Magnetic Susceptibility ; Specific Surface Area ; X-ray Diffraction
Publicat a:	Clays and Clay Minerals, Vol. 58, Núm. 4 (2010) , p. 451-461, ISSN 1552-8367

DOI: 10.1346/CCMN.2010.0580401

11 p, 1.2 MB  Accés restringit a la UAB

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