The current research shows the effect of structural and morphological differences of multilayer carbon nanotubes (CNT) on radar absorbing materials (RAM) performance. Two CNT samples, from different manufacturers, had their morphological and structural aspects investigated by XRD, SEM and SEM-FEG analyses. CNT/epoxy resin based nanostructured composites were prepared and characterized by reflectivity measurements in the X-band. SEM results show the formation of agglomerates in the composites and the XRD patterns show structural differences between the two CNT samples. The best RAM performance (-25 dB) was determined for the nanocomposite based on the CNT with the smallest stacking layers (Lc = 26.9 Å) associated to the longest length of nanofilament (10-20 µm). This characteristic can have contributed to the formation of an interconnected network in the composite favoring electrical conductivity and dielectric properties, with the consequent increase of the wave attenuation.

Abstract In this work, conductive polymers were prepared based on polypyrrole (PPy) and its blends with epoxy resin. The chemical syntheses of PPy used two oxidants (Fe2(SO4)3 and FeCl3.6H2O) and two surfactants (DBSNa and DBSA). PPy samples and their blends were characterized by scanning electron microscopy, electrical conductivity by four points, and measurements of complex parameters of electric permittivity (ε) and magnetic permeability, in the frequency range of 8.2 to 12.4 GHz. The micrographs of the fractured surfaces show that the PPy synthetized in the presence of surfactants has particles with smaller diameters, and the oxidant sulfate favored the formation of elongated structures, called fillets. The analysis of the blends found a homogeneous distribution of PPy clusters in epoxy resin matrix, which did not favor the electrical conductivity of these materials. On the other hand, the measurements of the complex parameters of the permittivity show that the blends have increasing values when the PPy concentration is increased in the epoxy resin.

Resumo: Materiais Absorvedores de Radiação Eletromagnética (MARE) são compostos que absorvem a radiação eletromagnética incidente em determinadas faixas de frequências e a dissipam sob a forma de calor. Esses materiais são obtidos a partir do processamento adequado de matrizes poliméricas incorporadas com compostos que atuam como centros absorvedores da radiação incidente, na faixa de micro-ondas. Este trabalho mostra a avaliação eletromagnética de MARE processados pelo uso de uma hexaferrita de cálcio modificada pela incorporação dos íons CoTi e La. A substituição realizada pelos íons mencionados mostra, via análises de MAV, que a ferrita apresenta baixos valores de magnetização de saturação (123,65 Am2/kg) e de campo coercitivo (0,07 T), indicando o seu amolecimento. Amostras de MARE preparadas com diferentes concentrações desta hexaferrita (40 - 80% em massa) apresentam mudanças nos parâmetros complexos de permeabilidade e permissividade e no desempenho da atenuação da radiação incidente. Valores de atenuação da radiação incidente entre 40 e 98% são obtidos.

Abstract: Radar Absorbing Materials (RAM) are compounds that absorb incidental electromagnetic radiation in tuned frequencies and dissipate it as heat. Its preparation involves the adequate processing of polymeric matrices filled with compounds that act as radar absorbing centers in the microwave range. This work shows the electromagnetic evaluation of RAM based on CoTi and La doped Ca hexaferrite. Vibrating Sample Magnetization analyses show that ion substitution promoted low values for the parameters of saturation magnetization (123.65 Am2/kg) and coercive field (0.07 T) indicating ferrite softening. RAM samples obtained using different hexaferrite concentrations (40-80 per cent, w/w) show variations in complex permeability and permittivity parameters and also in the performance of incidental radiation attenuation. Microwave attenuation values between 40 and 98 per cent were obtained.

Este trabalho foi desenvolvido com o objetivo de isolar e identificar bactérias presentes nos solos utilizados como camada de cobertura do cultivo de Agaricus blazei Murril. Foi avaliada a eficiência da desinfestação com vapor d'água e formol nos solos de cobertura. O tratamento com formol apresentou maior redução no número de bactérias na terra de barranco (Latossolo Vermelho distroférrico) e solo de pastagens (Latossolo Amarelo distrófico), enquanto que no solo hidromórfico, oriundo de várzea (Gleissolo Melânico), nenhum dos tratamentos foi eficiente para reduzir a comunidade microbiana. Foram identificadas bactérias do gênero Pseudomonas, Salmonella, Enterobacter e Shigella, dentre outras, denotando que os tratamentos de desinfestação não eliminam bactérias potencialmente benéficas, mas também não eliminam bactérias potencialmente patogênicas. Além disso, os tratamentos de desinfestação também não afetaram a produtividade do cogumelo A. blazei nas condições testadas.

The objective of this work was to quantify and to isolate the bacteria present in casing layer used for the cultivation of the Agaricus blazei Murril. It was evaluated the efficiency of the steam and formaldehyde disinfestation in the casing layer. The formaldehyde disinfestation showed a reduction of the bacteria population on the ravine soils (distroferric Red Latosol) and grazing land soil (distrofic Yellow Latosol), while in the hydromorphic soil coming from lowland (Melanic G]/leysol) none of the treatments used were efficient to reduce the bacteria population. Bacteria of the genera Pseudomonas, Salmonella, Enterobacter, Shigella, among others, were identified in all treatments analysed. It was observed that the disinfestation treatments did not eliminate neither potentially beneficial bacteria nor pathogenic bacteria. There was no significant effect of the disinfestation treatments on productivity of A. blazei mushroom. Moreover, the disinfestation treatments did not affect the productivity of the A. blazei in the studied conditions.