Acicular Metallic Particles Obtained from Al-Doped Goethite Precursors

• Published in: Chemistry of materials 2003-02, Vol.15 (4), p.951-957
• Main Authors: Nuñez, Nuria O, Pozas, Raul, Morales, M. Puerto, Tartaj, Pedro, Bonville, Pierre, González-Elipe, Agustín R, Caballero, Alfonso, Ocaña, Manuel, Serna, Carlos J
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Fine-particle systems; Magnetic properties and materials; Physics; Small particles and nanoscale materials; Studies of specific magnetic materials
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm021329h

Acicular metallic particles of different sizes were obtained by thermal treatment under a hydrogen flow of undoped and Al-doped goethite precursors. The acicular goethite particles were synthesized by the controlled oxidation−precipitation of iron (II) sulfate and aluminum nitrate solutions by addition of a base. Microstructural studies showed that the Al-doped goethite precursors consist of acicular particles with the aluminum mainly concentrated at the particle outer layers even though it was initially added during the synthesis. The mechanism for this rather atypical enrichment of aluminum can be explained in terms of the different stability of an Al-carbonate green rust phase formed during the goethite synthesis. Moreover, it was observed that the aluminum enrichment on the goethite particle surface is later enhanced during the reduction to iron. A detailed characterization of the final metal particles was carried out to correlate their chemical and magnetic properties with the structural properties of the goethite precursors. In this way, we have confirmed that the presence of aluminum is essential to preserve the acicular morphology in the metallic particles and thus, to obtain materials with good magnetic properties.