Magali Silveira Pinho

Performance of radar absorbing materials by waveguide measurements for X- and Ku-band frequencies

Abstract In this work, samples consisting of an elastomeric matrix containing different kinds of active materials in particulate form were prepared for reflectivity measurements. The materials individually used in weight contents of 80% in polychloroprene matrix were: carbonyl-iron (CI) and doped ferrite powders. The microwave reflectivity levels were determined from the magnetic and dielectric properties of the elastomeric composites obtained from scattering data, by fitting the samples in a waveguide, for measurements in the frequency range from 8 to 16 GHz. Better microwave absorption for X-band was obtained for CI while doped ferrite absorbed at higher frequencies (Ku-band).

Aging effect on the reflectivity measurements of polychloroprene matrices containing carbon black and carbonyl-iron powder

Abstract The effect of aging, arising from salt spray exposure, on the microwave reflectivity was studied for polychloroprene (CR) matrices, containing different kinds of active material in particulate form. The materials used as microwave absorbers in different contents were carbon black (CB) and carbonyl-iron powder (CIP). The microwave reflectivities were determined for the frequency range of 8–16 GHz. The formation of a superficial layer of iron oxide on CIP:CR composites was responsible for a reduction and change of microwave absorption towards a higher frequency. The reflectivity curves of CB:CR composites did not display any significant difference before and after the exposure.

Conductive polyaniline–polychloroprene blends

The electrical conductivity of polychloroprene (CR)/polyaniline (Pani) blends prepared by bulk and solution processes were investigated. Pani doped with HCl (Pani · HCl) and p-toluenesulfonic acid (Pani · TSA) were employed in vulcanized blends obtained by the bulk process. These blends showed an increase in the conductivity only for blend composition of CR/Pani = 50:50 wt %. At this composition, blends with Pani · HCl and Pani · pTSA presented conductivity values of 10−9 and 10−10 S · cm−1, respectively. CR/Pani · HCl blend films prepared by the solution process displayed surface conductivity values of 10−4 S · cm−1 with as low as 10–15 wt % of PAni · HCl. Surface analysis of these blends by X-ray photoelectron spectroscopy indicated no traces of the conductive additive. The surface composition was found to be exclusively constituted of CR.

Electroconducting composites based on polyaniline and monomer‐swollen polychloroprene

Electroconductive polychloroprene (CR)-polyaniline (Pani) composites were prepared by swelling the vulcanized rubber material in aniline followed by immersing the specimen in an aqueous solution of HC containing ammonium persulfate as the oxidant. The results obtained from surface and volume conductivity, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analysis suggest that the Pani component is preferentially located in the surface layer. These composites display better electrical and mechanical performance than those obtained by mixing both polymer components in the bulk state.

Sulfonated polyaniline: influence of sulfonation routes on its thermal and structural characteristics

In order to study the influence of different sulfonation routes on its thermal and structural properties sulfonated polyaniline (SPAni) was prepared. FT-IR revealed that the formation of PAni salt or ring sulfonation depends on the route. UV-visible spectra pointed out that the level of the PAni protonation was dependent on the sulfonation route. A new approach was given for TG/DTG and DSC results correlating different energy levels with the distinguished sulfonation routes. The TG/DTG degradation steps and the amount of the released material corroborated the structural differences of the polyanilines. For each DSC first regime of heating, a broad and intense peak (from -30 to 250 oC) with different level of energy was noticed. That peak could be ascribed to the multiple relaxations and breaking of the PAni intra and inter hydrogen bonds after sulfonation.

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.

Avaliação do desempenho de materiais absorvedores de radiação eletromagnética por guia de ondas

Neste trabalho, amostras elastomericas contendo diferentes tipos de cargas absorvedoras de microondas, sob a forma de pos, foram obtidas para medidas de refletividade. Os materiais utilizados com diferentes composicoes percentuais em peso foram: ferrocarbonila, negro de fumo, polianilina e ferrita dopadas. As medidas de refletividade foram determinadas com base nas propriedades magneticas e dieletricas dos compositos elastomericos a partir de dados de espalhamento, atraves da insercao e fixacao em um guia de ondas, para a faixa de frequencia de 8-16 GHz. Os melhores resultados foram apresentados pelo ferrocarbonila e negro de fumo para as frequencias mais baixas, enquanto a ferrita dopada absorveu em uma frequencia mais elevada.

Avaliação da resistência à corrosão de compósitos ferromagnéticos com policloropreno ao ensaio de névoa salina

The corrosive effect from the exposure to salt spray was studied on chloroprene rubber (CR) matrices containing a particulate ferromagnetic filler, viz. carbonyl-iron powder (CIP). The experiments in salt spray chamber are able to create an aggressive condition of sodium chloride atmosphere (NaCl), being important to minimize the time of exposure of composites in comparison to the real conditions. The presence of corrosive products was visually observed at the surface of CI:CR composites (80:20 wt %). The surface and interior of these composites were characterized by scanning electron microscopy (SEM), equipped with an energy-dispersive X-ray (EDX) analysis system. From these experiments, it was possible to suggest the formation of a surface layer of iron oxide (Fe 2 O 3 ). This compound was not detected inside the bulk.