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Electrical Behaviour of Natural Manganese Dioxide (NMD)

Published online by Cambridge University Press:  10 February 2011

H. F. Gorgulho
Affiliation:
Funrei- Fundação de Ensino Superior de São João del Rei -MG Brasil
R. Z. D. Fernandes
Affiliation:
Departamento de Química ICEx CP702 Universidade Federal de Minas Gerais 31270–901 Belo Horizonte MG Brasil (Rosanazd@oraculo.lcc.ufmg.br)
J. M. Pernaut
Affiliation:
Departamento de Química ICEx CP702 Universidade Federal de Minas Gerais 31270–901 Belo Horizonte MG Brasil (Rosanazd@oraculo.lcc.ufmg.br)
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Abstract

NMD samples from Brazil have been submitted to magnetic and particle size separations and characterized by X-ray diffraction and fluorescence and thermogravimetric analyses. Results showed that simple physical treatments can lead to more than 60% enriched MnO2 materials which could satistify some electrochemical applications. The electrical properties of the samples conditionated as pressed pellets have been investigated by four-points direct current probe and impedance spectroscopy, varying the conditions of preparation and measurement. It is proposed that the higher frequency impedance is equivalent to the intrinsic electronic resistance of the MnO2 phases while at lower frequencies occurs an interphase charge separation coupled with a possible ionic transport. The corresponding contact resistance depends on the article size distribution of the material, the compactation pressure of pellets and the iron content of the materials. The interphase dielectric relaxation does not behave ideally; the depression of the impedance semicircles as shown in the Nyquist plane is assumed to be related to the roughness of the bulk interfaces.

Type
Research Article
Copyright
Copyright © Materials Research Society 1996

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