Electromagnetic Behavior of Cu and Ni Nanofilms in the X-band

Currently, the presence of spurious microwave radiation is increasing in the environment, which has caused concern due to possible health problems in living beings and electromagnetic interference in electronic systems. To control this problem, studies in the materials area are taking place, aiming to attenuate the spurious radiation and meet requirements of good performance in broadband, low cost and low weight. The present work aimed to study Cu and Ni nanometric films with thicknesses of 65 and 200 nm, deposited on polyethylene terephthalate substrate by magnetron sputtering. Scanning electron microscopy with a field emission gun (FEGSEM) showed that the films produced have different morphological textures, due to the parameters used in the sputtering process and also the free energy of metals. Impedance spectroscopy measurements showed that the films have low conductivity values, due to the metallic oxides formed on the film surfaces, confirmed by X-ray diffraction, and also to the presence of defects. Electromagnetic characterization (8.2 – 12.4 GHz) showed that the Cu and Ni thin films had low performance, except the Ni_200 nm film, which showed a total shielding efficiency of about 30% in broadband. This result is promising considering the nanometric thickness of the Ni film

Estudo do processamento de rejeitos radioativos sólidos compactáveis por plasma térmico/ Study of compactable solid radioactive waste processing by thermal plasma

O uso de radioisótopos para as mais diversas finalidades tem se intensificado e destacado pelos benefícios que proporcionam. A geração de energia elétrica, a indústria, a agricultura, a medicina diagnóstica e terapêutica, são alguns exemplos. Porém, essas aplicações têm como desvantagem gerar rejeitos radioativos e estes requerem tratamento apropriado para deposição final. Neste âmbito, entre as tecnologias promissoras para o tratamento de rejeitos radioativos sólidos compactáveis, a utilização de plasma térmico para gerar uma descarga de arco transferido por meio de eletrodos de grafite se mostra uma tecnologia capaz de reduzir substancialmente a massa e o volume de rejeitos radioativos após expô-los a temperaturas superiores a 3.000ºC. Os resultados obtidos se mostraram bastante satisfatórios, alcançando aproximadamente 100% de redução em 30 min de processo. Esforços futuros devem ser empregados para maior confiabilidade do sistema, eliminação de radionuclídeos voláteis no efluente gasoso e otimização completa da operação

Electromagnetic properties of Carbon-Graphene Xerogel, Graphite and Ni-Zn Ferrite composites in polystyrene matrix in the X-Band (8.2 – 12.4 GHz)

The electromagnetic properties of Carbon-Graphene Xerogel (CGX), Flaky graphite (GR) and Nickel-Zinc ferrite (FeNiZn) composites in polystyrene (PS) matrix were studied in the X-Band range (8.2 – 12.4 GHz). In this work the Expanded Polystyrene (EPS) waste material was processed into polystyrene through the recycling of EPS. The polystyrene obtained was utilized as dielectric matrix, mainly because PS is a wellknown organic polymer that presents low dielectric loss and light weight, which contribute to applications in composites for the aerospace field. In order to produce the final composite specimens, the CGX additive was previously synthesized through a sustainable method that employed the use of waste from the paper and pulp industry (black liquor). Afterwards, the morphological and structural analysis were made through Scanning Electron Microscope (SEM) and Raman Spectrometer, respectively. On the other hand, the magnetic ferrite material, FeNiZn, was obtained for the composite production through calcination, whereas the GR utilized was commercially obtained. It was observed that the increase of CGX and GR influenced on the increase of the Complex Permittivity, and that 10 wt% CGX + 50wt% FeNiZn composite sample demonstrated an absorption peak at 10.5 GHz. The results are relevant concerning the recycling of EPS waste through its use as dielectric matrix, thus developing greener and low-weight composite materials to be used in microwave applications.Keywords: Carbon-Graphene. Composite. Recycling. Polystyrene. Microwave.

Efeito do tratamento térmico na microestrutura, turbostraticidade e superfície de carbono vítreo reticulado analisado por XPS, espalhamento Raman e voltametria cíclica Thermal treatment effect on the microstructure, turbostraticity, and surface of reticulated vitreous carbon analyzed by xps, Raman scattering, and cyclic voltammetry

<abstract language="eng">The structural and surface properties of reticulated vitreous carbon (RVC) were discussed as a function of its heat treatment temperature (HTT), for samples produced in the range from 700 to 2000 ºC, using the furfuryl precursor resin. The samples were analyzed by x-ray photoelectron spectroscopy, first and second order Raman scattering as well as electrochemical response. Exploring the material turbostraticity concept, the interdependence between the RVC chemical surface variation and its defects were demonstrated. The influence of heteroatom presence was discussed in the material ordering for HTT lower than 1300 ºC while the graphitization process evolution was also pointed out for HTT higher than 1500 ºC

Influence of the polymeric coating thickness on the electrochemical performance of Carbon Fiber/PAni composites

Abstract Carbon fiber/polyaniline composites (CF/PAni) were synthesized at three different deposition time of 30, 60 and 90 min by oxidative polymerization. The composite materials were morphologically and physically characterized by scanning electron microscopy and by Raman spectroscopy, respectively. Their electrochemical responses were analyzed by cyclic voltammetry, by galvanostatic test, and by electrochemical impedance spectroscopy. The influence of the PAni layer thickness deposited on carbon fibers for the composite formation as well as for their electrochemical properties was discussed. The CF/PAni-30 showed a nanometric thickness with more homogeneous morphology compared to those formed in deposition times of 60 and 90 min. It also showed, from the electrochemical impedance spectroscopy measurements, the lowest charge transfer resistance value associated to the its highest value for the double-layer capacitance of 180 Fg-1 making it a very strong candidate as a supercapacitor electrode

Caracterização eletromagnética do compósito de carbeto de silício e negro de fumo em matriz polimérica

Este trabalho apresenta as propriedades eletromagnéticas de um Material Absorvedor de Radiação Eletromagnética (MARE) feito a partir de Carbeto de Silício (SiC) e Negro de Fumo (NF) como aditivos. O compósito SiC/NF foi produzido utilizando 70 %(m/m) de matriz de silicone, e variando as concentrações do aditivo em 3 %(m/m), 2 %(m/m) e 1 %(m/m) de NF com 27 %(m/m), 28 %(m/m) e 29 %(m/m) de SiC, respectivamente. A estrutura química e a morfologia das partículas de SiC e NF foram analisadas através de espectroscopia Raman e Microscopia Eletrônica de Varredura (MEV). As propriedades dielétricas dos MAREs foram obtidas por meio do analisador de rede vetorial na faixa de frequência de 12,4 a 18,0 GHz. Os resultados de refletividade mostraram que o compósito SiC/NF com 1 %(m/m) de NF apresentou a melhor absorção de radiação eletromagnética, chegando a -47,9 dB em 16,8 GHz com uma amostra de aproximadamente 5,5 mm de espessura.Palavras-chave: MARE, banda Ku, refletividade, permissividade, material dielétrico.