Ferrites nanoparticles of Ni1-xZnxFe2O4 ferrites with x varying between 0 and 1, in steps of 0.2, were obtained by solution combustion synthesis (SCS) and dispersed in oil paint at the concentrations of 10, 20, 30 and 40% by ferrite weight of ferrite, with the aim of producing electromagnetic wave absorbing composites, in the X band (8-12 GHz). The ferrite powders obtained were characterized by X-ray diffraction (XRD), and to determine to mean crystallite size, crystallographic phases, as well as lattice parameters, was used the Rietveld method. The XRD results revealed the majority presence of the spinel cubic ferrite phase for all stoichiometries with crystallite size between 44 and 81 nm. The composites were characterized by the rectangular waveguide transmission line method to measure the absorption of the electromagnetic wave in the X band. The nanocomposites with 40% of NiFe2O4 and Ni0.8Zn0.2Fe2O4 presented the highest electromagnetic wave absorption performance.

The energy absorption in ballistic tests of alumina-ultra high molecular weight polyethylene (UHMWPE) composites with 60, 80 and 90 wt% alumina submitted to gamma radiation doses of 25, 50 and 75 kGy was investigated. The ballistic tests were carried out at subsonic speed using a compressed air system. The results showed that the composite with 80% alumina irradiated with 50 kGy yields the best ballistic results. Gel content, Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results showed that this composite is the one with the highest concentration of crosslinks and the lowest volume fraction of amorphous UHMWPE. Scanning electron microscopy (SEM) images of the same composite showed a high pullout, suggesting that gamma irradiation increases the adhesion between alumina and UHMWPE.

The response to ballistic impact of alumina-ultra high molecular weight polyethylene (UHMWPE) composites with different relative concentrations of alumina was investigated. The impact tests were carried out at subsonic speed using a compressed air system. The results showed that the depth of penetration (DOP) in a Medium Density Fiberboard (MDF) bulkhead protected by a disk of the composite decreased with increasing concentration of alumina in the composite. Scanning electron microscopy (SEM) images of composites with 80 %, 85 % and 95 % alumina showed transgranular, intergranular and ductile fracture mechanisms.

Abstract This is a study of the preparation and characterization of polymeric-magnetic nanoparticles. The nanoparticles used were magnetite (Fe3O4) and the chosen polymers were alginate and chitosan. Two types of samples were prepared: uncoated magnetic nanoparticles and magnetic nanoparticles encapsulated in polymeric matrix. The samples were analyzed by XRD, light scattering techniques, TEM, and magnetic SQUID. The XRD patterns identified magnetite (Fe3O4) as the only crystalline phase. TEM analyses showed particle sizes between 10 and 20nm for magnetite, and 15 and 30nm for the encapsulated magnetite. The values of magnetization ranged from 75 to 100emu/g for magnetite nanoparticles, and 8 to 12emu/g for coated with chitosan, at different temperatures of 20K and 300K. The saturation of both samples was in the range of 49 to 50KOe. Variations of results between the two kinds of samples were attributed to the encapsulation of magnetic nanoparticles by the polymers.

The plastic instability in the stress-strain curve and work hardening of a type AISI 316 austenitic stainless steel was investigated in the high temperature range of 150°C to 800°C for two strain rates. The results indicate the occurrence of plastic instability and serrations between 200°C and 650°C with peaks in both the tensile strength and work hardening rate. These plastic instability/serrations are associated with dynamic strain aging behavior. As a consequence, within the temperature interval of plastic instability, a negative value for the strain rate sensitivity was found. Based on the activation energy, it is proposed that a mechanism of substitutional solute atoms interaction with dislocations be responsible for the plastic instability.

Natural fibers are attracting the interest of engineering sectors owing to specific advantages such as lightweight and lower cost as well as an inherent condition of being renewable, biodegradable, recyclable and environmentally correct with respect to CO2 emission. In addition, several natural fibers present mechanical and thermal properties appropriate for engineering applications. The fiber extracted from the stem of the banana plant is nowadays recognized by its mechanical properties. However, some thermal properties of the banana fibers have not yet been fully investigated. The present work investigated, by photoacoustic spectroscopy and photothermal techniques, the thermal diffusivity, specific heat capacity and thermal conductivity of the banana fiber. The results revealed that the banana fibers showed a promising thermal insulation capacity, comparable to those of conventional synthetic insulators.

O presente trabalho teve por finalidade a síntese de nanopartículas de NiFe2O4 utilizando o método de sol-gel/combustão e combustão homogênea. As nanopartículas foram caracterizadas por difração de raios X, ressonância magnética eletrônica (RME) e espectroscopia de infravermelho de transformada de Fourier (IV-FT). As medidas de raios X foram usadas para caracterizar e estimar o tamanho médio dos cristalitos. Nos espectros de infravermelho, são observadas a formação da fase ferrítica e a influência do tamanho médio de cristalitos em todas as amostras que apresentaram alto grau de cristalinidade, já que a banda de infravermelho na faixa de 600-550 cm-1 é característica por sítios tetraédricos da ferrita. Os espectros de ressonância magnética eletrônica mostram que as partículas sintetizadas possuem dimensão nanométrica.

This work aimed at the synthesis of NiFe2O4 nanoparticles using the methods of sol-gel combustion and homogeneous combustion. The nanoparticles were characterized by X-ray diffraction (XRD), electron magnetic resonance (EMR) spectroscopy and Fourier transform infrared (FTIR). The X-ray measurements were used to characterize and estimate the average size of crystallites. In the infrared spectra the formation of ferrite phase and the influence of the average size of crystallites in all samples which exhibited a high degree of crystallinity are observed, since the infrared band in the range 550 - 600 cm-1 is characteristic of tetrahedral sites of the ferrite. The electron magnetic resonance spectra show that nanoscale particles were synthesized.