Jefferson Leixas Capitaneo

Preparation of electrodeposited cobalt nanowires

Nanostructured magnetic materials have great interest because of their applications in high-density magnetic information storage and for magnetic sensors. The electrodeposition of materials into porous alumina arrays is a suitable technique to produce nanomaterials, since highly ordered uniform nanomaterials can be obtained simply and cheaply. In this work, template-assisted Co nanowire arrays were prepared by electrodeposition into nanometer-sized pores of an alumite film using a two-electrode electrochemical cell. The Co nanowires were electrodeposited from a solution of 400 g/L of CoSO4.7H2O and 40 g/L of H3BO3. The morphology of the samples was investigated by means of TEM and AFM. The structural characteristic of the samples was examined using XRD, EDX and FTIR, which confirm the cobalt nanowire formation.

Microwave absorption properties of Co, Cu, Zn: substituted hexaferrite polychloroprene nanocomposites

The magnetic behavior and its relationship with microwave absorbing properties have been investigated for doped Z-type barium hexaferrites (Ba3Co1.3Zn0.3Cu0.4Fe 24O41)/ polychloroprene (CR) nanocomposites. Simultaneous substitutions by Co2+, Cu2+, and Zn2+ ions make possible the use of these materials as RAMs, due to the frequency dependence of µr* (permeability), responsible for the location of the hexaferrite natural resonance. The Cu2+ ions distort the crystalline field due to their electronic configuration, and this behavior results in an increase in the saturation magnetization (Ms), which improve the magnetic permeability. Similarly, the superparamagnetic contribution (associated to the nanometric size) led to the improvement of the microwave absorption.

Co2Z hexaferrite obtained by the citrate precursor method in an inert atmosphere

Nanoparticles of Co2Z hexaferrite were synthesized by the citrate sol-gel process under an inert atmosphere, then thermally analyzed by Thermogravimetric and Differential Thermal Analysis and characterized by X-ray Diffraction, Scanning Electron Microscopy, Atomic Force Microscopy, X-ray Fluorescence and Vibration Sample Magnetometry. Z-type barium hexaferrite is a promising material for application in high frequency electronic devices involving up to 100 MHz, such as multi-layer chip inductors (MLCI), which require magnetic materials with high initial permeability, high resistivity, low magnetic and dielectric loss, and good thermal stability.

Method to Separate Nanometric Particles of Clays

There are several types of polymeric nanocomposites, but the most commercially advanced are those that involve dispersion of small amounts of nanoparticles in a polymeric matrix. Polymer/clay nanocomposites have exhibited enhanced mechanical properties at low weight fractions of clay. Addition of these nanoparticles not only improves the mechanical properties, but also has been shown to improve thermal stability. The clay can be considered as being essentially a rock consisting of clay minerals, which also contain organic substance and other impurities. Clay minerals possess nanometric particle sizes, being classified as crystalline silicates with structure in layers or lamellar and crystalline silicates with fibrous structure. In the present work, three clays from Rio de Janeiro, Brazil, were studied in order to identify and characterize the clay minerals presents. X-ray diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric (TG) and differential thermal analysis (DTA), Fourier transform infrared (FTIR) and transmission electron microscopy (TEM) were used to characterize the clay fraction previously separated using NH4OH aqueous solution and submitted to physical-chemistry treatment in an ethylene glycol atmosphere.