Navegando por Autor "Barrero, C. A."

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    Characterization of soil-oxide analogues by applied-field Mossbauer spectroscopy.
    (1998) Grave, Eddy De; Costa, Geraldo Magela da; Bowen, L. H.; Barrero, C. A.; Vandenberghe, Robert Emile
    In this contribution, the effect of high external magnetic fields upon the Mössbauer spectra of aluminous _- and -Fe2O3, of aluminous _- and -FeOOH and of aluminous Fe3O4 is reviewed. It is shown that the shapes of these spectra are characteristic of these materials and also to some extent of their crystallinities and Al-for-Fe substitutions. Based upon this evaluation, the potential for application of external-field Mössbauer spectroscopy to soil-related analytical purposes is demonstrated for two soil samples. Limitations of the technique are discussed. Finally, some suggestions for further research in this field are indicated.
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    Mossbauer characterization of iron oxides and (oxy)hydroxides : the present state of the art.
    (2000) Vandenberghe, Robert Emile; Barrero, C. A.; Costa, Geraldo Magela da; San, E. Van; Grave, Eddy De
    M¨ossbauer spectroscopy is a powerful direct technique for the identification and quantification of iron oxides and (oxy)hydroxides in soils and sediments. However, further characterization with respect to structural properties such as crystallinity, Al substitution, stoichiometry, water content, etc. is rather limited. With some examples of synthetic and natural goethite and hematite sample series it is illustrated that the hyperfine parameters depend on much more structural features than the Al content and crystallinity alone. Neither the Morin transition in hematite nor the Verwey transition in magnetite is directly applicable for analytical purposes in natural samples.