Laura G. Pampillo

Facile synthesis of cobalt ferrite nanotubes using bacterial nanocellulose as template

A facile method for the preparation of cobalt ferrite nanotubes by use of bacterial cellulose nanoribbons as a template is described. The proposed method relays on a simple coprecipitation operation, which is a technique extensively used for the synthesis of nanoparticles (either isolated or as aggregates) but not for the synthesis of nanotubes. The precursors employed in the synthesis are chlorides, and the procedure is carried out at low temperature (90 °C). By the method proposed a homogeneous distribution of cobalt ferrite nanotubes with an average diameter of 217 nm in the bacterial nanocellulose (BC) aerogel (3%) was obtained. The obtained nanotubes are formed by 26-102 nm cobalt ferrite clusters of cobalt ferrite nanoparticles with diameters in the 9-13 nm interval. The nanoparticles that form the nanotubes showed to have a certain crystalline disorder, which could be attributed in a greater extent to the small crystallite size, and, in a lesser extent, to microstrains existing in the crystalline lattice. The BC-templated-CoFe2O4 nanotubes exhibited magnetic behavior at room temperature. The magnetic properties showed to be influenced by a fraction of nanoparticles in superparamagnetic state.

Influence of Nb Doping on Magnetic Properties of Nanocrystalline Nd-Fe-B Alloys

The influence of Nb doping was studied on ribbons of nominal composition Nd_yFe_86-x-yB₁₄Nb_x (y = 7, 8; x = 0, 2, 4). The alloys were prepared by melt-spinning and then annealed at 973 K for 20 minutes. The magnetic characterization revealed that niobium addition improves substantially the magnetic properties of the studied alloys. The structural characterization showed that, in most alloys, the magnetically hard phase Nd₂Fe₁₄B precipitated as the main phase. This was not the case for the ternaries (x = 0) and for the Nd₇Fe₇₇B₁₄Nb₂ alloys. Furthermore, the addition of Nb inhibited the precipitation of α-Fe, independently of the Nd content. From the complete set of samples studied in this work, we found that the sample with nominal composition Nd₈Fe₇₄B₁₄Nb₄ exhibited the highest coercive field H_C = 575 kA/m while Nd₇Fe₇₅B₁₄Nb₄ showed the highest maximum energy product, (BH)_max = 73 kJ/m³.

Synthesis and Characterization of Iron Oxyhydroxide Nanowires

A very simple method of synthesis of goethite, α-FeOOH, nanowire is reported. To fabricate the nanowires, an anodized alumina nanoporous template (AAO) is used. AAO has pores with an average diameter of 60 nm. The synthesis is based on a self-combustion reaction of the chemical precursor (Fe(NO3)3 saturated solution) which occurs inside the nanopores. The geometry of AAO determines the morphology of the nanowires and the confinement conditions in which the heat treatment determines the composition of the nanostructure. The nanowires are characterized using scanning electron microscopy, high resolution transmission electron microscopy and magnetometry [magnetization versus applied field (M versus H)]. TEM analysis indicates that nanowires are composed of several α-FeOOH single crystals. The nanowires have a clear magnetic oriented structure.

Synthesis and magnetic properties of cobalt-iron/cobalt-ferrite soft/hard magnetic core/shell nanowires

A straightforward method for the synthesis of CoFe2.7/CoFe2O4 core/shell nanowires is described. The proposed method starts with a conventional pulsed electrodeposition procedure on alumina nanoporous template. The obtained CoFe2.7 nanowires are released from the template and allowed to oxidize at room conditions over several weeks. The effects of partial oxidation on the structural and magnetic properties were studied by x-ray spectrometry, magnetometry, and scanning and transmission electron microscopy. The results indicate that the final nanowires are composed of 5 nm iron-cobalt alloy nanoparticles. Releasing the nanowires at room conditions promoted surface oxidation of the nanoparticles and created a CoFe2O4 shell spinel-like structure. The shell avoids internal oxidation and promotes the formation of bi-magnetic soft/hard magnetic core/shell nanowires. The magnetic properties of both the initial single-phase CoFe2.7 nanowires and the final core/shell nanowires, reveal that the changes in the properties from the array are due to the oxidation more than effects associated with released processes (disorder and agglomeration).

Fabricación de alúmina anódica porosa de bajo costo: Un estudio comparativo de la morfología producida por uno y dos pasos de anodizado

A simple and low cost method for the fabrication of Nanoporous alumina templates with potential applications for nanowires fabrication is described. As raw material, commercial aluminum has been used. The nanoporous templates obtained have a mean pore diameter of (20 ± 4) nm. The fabrication process consists mainly of two-step anodization. Both steps are described in detail, the obtained material for each anodization step is characterized. The Nanoporous template obtained after two-step anodization present a narrow distribution of the porous size, a better circularity and homogeneous distribution. Cobalt ferrite (CoFe2O4) nanowires structures have been synthesized from the obtained alumina templates. A simple equipment method has been developed. A morphological characterization of the obtained templates and nanowires, by the use of electron microscopy techniques, is also presented.