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Correlation of reactivity with structural factors in a series of Fe(II) substituted cobalt ferrites |
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| Authors: | Elsa E Sileo Carlos O Paiva-Santos Pedro J Morando Miguel A Blesa |
| Institution: | a INQUIMAE, Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón II, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina b Unidad de Actividad Química, Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica, Avenida General Paz 1499, 1650 San Martín, Provincia de Buenos Aires, Argentina c Instituto de Tecnología J. Sábato, Universidad Nacional de San Martín, Avenida Gral. Paz 1499, 1650 San Martín, Provincia de Buenos Aires, Argentina d Instituto de Química, Universidade Estadual Paulista,UNESP. Araraquara, 14801-970, São Paulo, Brazil e Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA f National Research Council of Argentine (CONICET), Avenida Rivadavia 1917, C1033AAJ Buenos Aires, Argentina g Escuela de Posgrado, Universidad Nacional de San Martín, Peatonal Belgrano 3563 1er Piso, 1650 San Martín, Provincia de Buenos Aires, Argentina |
| Abstract: | A series of powdered cobalt ferrites, CoxFe3−xO4 with 0.66?x<1.00 containing different amounts of FeII, were synthesized by a mild procedure, and their Fe and Co site occupancies and structural characteristics were explored using X-ray anomalous scattering and the Rietveld refinement method. The dissolution kinetics, measured in 0.1 M oxalic acid aqueous solution at 70 °C, indicate in all cases the operation of a contracting volume rate law. The specific rates increased with the FeII content following approximately a second-order polynomial expression. This result suggests that the transfer of FeIII controls the dissolution rate, and that the leaching of a first layer of ions CoII and FeII leaves exposed a surface enriched in slower dissolving octahedral FeIII ions. Within this model, inner vicinal lattice FeII accelerates the rate of FeIII transfer via internal electron hopping. A chain mechanism, involving successive electron transfers, fits the data very well. |
| Keywords: | Cobalt ferrites X-ray anomalous scattering Rietveld method Kinetic dissolution Electron hopping |
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