The influence of protective coatings on the magnetic properties of acicular iron nanoparticles

Abstract

Core–shell acicular nanoparticles of ∼90 nm length and ∼5 axial ratio consisting of an iron core coated with an oxidized layer of different composition have been obtained by thermal reduction with hydrogen of coated goethite precursors. Uniform goethite particles were prepared by oxidation in air of FeSO4 solutions previously precipitated with Na2CO3. Al or Y oxide layers were deposited on the goethite particle surface by heterocoagulation. The efficiencies of both compounds as protecting agents for preventing particle sintering and corrosion and their effects on the magnetic properties of the final α-Fe nanoparticles have been evaluated. Yttrium oxide coating was found to be more effective than alumina coating, giving rise to iron nanoparticles with larger coercivity and higher corrosion resistance. This behaviour is mainly discussed in terms of the observed differences in location of the two sintering prevention agents during the transformation from iron oxide to metal, which give rise to different particle microstructures.

Improving Co distribution in acicular Fe–Co nanoparticles and its effect on their magnetic properties

“…Finally, the XPS spectra also showed the bands at 156.7 and 73.6 eV (data not shown) associated with Y(III) and Al(III) cations, respectively [24], whose proportion in the particle outer layers (30 and 18 mol%, respectively, as determined by XPS) was higher than that in the overall solid determined by XRF (5 mol% in both cases). These results confirmed that Y(III) and Al(III) cations were located on the particle's surface during reduction, thus preventing interparticle sintering [13,17]. These phases were not detected by XRD due to their amorphous character and low proportion.…”

“…Essentially, it consists of the preparation of Co-doped goethite acicular nanoparticles (GCo 10 ) and their further coating with Co(OH) 2 to increase their Co content. At the same time, they were also coated with yttrium oxide (Y/(Fe + Co + Y) atomic ratio = 5%), which has been shown to be the optimum preventing sintering agent [15,17]. This goethite precursor was first dehydroxylated yielding haematite (HCo 10 ), which was finally reduced to obtain the Fe-Co alloys by using three different protocols, aiming to increase the amount and to obtain a more homogeneous distribution of alloyed Co in the final particles.…”

“…The coated powders were dehydroxylated in the presence of N 2 for 4 h at the optimum temperature (500 • C) previously determined [17] and the resulting haematite particles were thermally reduced to metal as follows (figure 1).…”

Composite magnetic nanoparticles: Synthesis and cancer-related applications

“…This is important because many types of highmagnetism nanoparticles easily oxidize in air, diminishing their magnetism. [28,29] A protective layer that resists oxidation can significantly improve the applicability of these materials. Lastly , composite nanoparticles usually possess more than one type of surface, enabling them to be tethered easily, with multiple functionalities and minimal cross-species interference.…”

Synthesis, magnetic and electrical properties of Fe-containing SiO2 nanocomposite

“…However, Fe particles in nano form have a high affinity for oxygen. Despite the reduction of their total magnetic moment, when dispersed in non-magnetic matrix or coating, several studies have been conducted to encapsulate these particles in silica [1,3], alumina [4], yittria [5,6], gold [7], carbon [8], boron nitride [9], and Fe 3 O 4 [10,11] in order to improve their stability, electrical and magnetic properties. Fe-silica nanocomposites are of particular interest because they have higher resistivity and this combined with the good magnetic properties of metallic Fe, makes them a good candidate for dielectric applications and could possibly be a good replacement material for ferrites.…”