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Research Article

Mechanisms of Combustion Synthesis and Magnetic Response of High-Surface-Area Hexaboride Compounds

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Raghunath Kanakala†, Roberto Escudero‡, Gabriel Rojas-George§, Mohan Ramisetty†, and Olivia A. Graeve†*

^† Kazuo Inamori School of Engineering, Alfred University, 2 Pine Street, Alfred, New York 14802, United States

^‡ Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360 México, D.F. 04510

^§ Department of Chemical and Metallurgical Engineering, University of Nevada, Reno, 1664 N. Virginia Street, MS 388, Reno, Nevada 89557, United States

ACS Appl. Mater. Interfaces, 2011, 3 (4), pp 1093–1100

DOI: 10.1021/am1012276

Publication Date (Web): March 26, 2011

*E-mail: graeve@alfred.edu. Tel: (607) 871-2749. Fax: (607) 871-2354. URL: http://people.alfred.edu/

graeve/.

Abstract

We present an analysis of the combustion synthesis mechanisms for the preparation of hexaboride materials using three compounds as model systems: EuB₆, YbB₆, and YB₆. These three hexaborides were chosen because of the differences in ionic radii between Eu³⁺, Yb³⁺, and Y³⁺, which is a factor in their stability. The powders were prepared using metal nitrates, carbohydrazide, and two different boron precursor powders. The resulting materials were analyzed by X-ray diffraction, which showed that combustion synthesis is effective for the synthesis of EuB₆, since the Eu³⁺ ion has an ionic radius greater than 1 Å. The synthesis of YbB₆ and YB₆ is not as effective because of the small size of the Yb³⁺ and Y³⁺ ions, making the hexaborides of these metals less stable and resulting in the synthesis of borates due to the presence of oxygen during the combustion process. Scanning electron microscopy and dynamic light scattering of the EuB₆ powders shows that the particle size of the hexaboride product is dependent on the particle size of the boron precursor. The magnetic susceptibility of our EuB₆ powders manifests irreversible behavior at low applied fields, which disappears at higher fields. This behavior can be attributed to the increase in size and number of magnetic polarons with increasing magnetic field.

Keywords:

hexaboride; combustion synthesis; boron; particle size; magnetic susceptibility; nanopowders

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History

Published In Issue April 27, 2011
Article ASAPApril 05, 2011
Just Accepted ManuscriptMarch 26, 2011
Received: December 13, 2010
Accepted: March 26, 2011

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Research Article

Mechanisms of Combustion Synthesis and Magnetic Response of High-Surface-Area Hexaboride Compounds