The great technological advancement in wireless communication systems and devices generated the problem of electromagnetic pollution. Developing lightweight, sustainable, and low-cost materials is necessary to minimize electromagnetic pollution. A sustainable porous carbon (PC) absorber material was obtained from the crude black liquor by a simple and low-cost synthesis, and combined with carbon nanotube (CNT), presenting excellent microwave attenuation results. The PC absorber at 20 wt.% filling ratio exhibited an intense reflection loss of ‑35.7 dB at 15.5 GHz, and bandwidth of 1.15 GHz for a thickness of 5.90 mm. By adding 0.2 wt.% of CNT, the reflection loss was -34.6 dB at 17.9 GHz, and a bandwidth of 1.54 GHz for 4.90 mm. The study reveals that the combination of PC and CNT improves the attenuation capacity, allows adjustment in the frequency range of the attenuation peak, and promotes thickness reduction. The results obtained allow us to advance studies in developing high-performance, sustainable, and low-cost microwave-absorbing materials.

This study aimed to synthesize a composite material composed of bio-based, porous carbon matrix and Cu nanoparticles through a simple, low-cost, and environmentally friendly method. Concentrated Kraft black liquor was used as a carbon precursor, and Cu nanoparticles were homogeneously deposited on the carbon matrix using electrochemical deposition. The textural properties determined using N2 isotherms indicated increased surface area of a carbon matrix with a micro-mesoporous structure. Voltammetric tests demonstrated that the composite exhibited catalytic properties for electrochemical CO2 reduction. Compared to the bio-based, porous carbon sample (C matrix), the bio-based carbon electrode electrochemically decorated with Cu nanoparticles (C–Cu composite) exhibited increased current values of approximately 2.4 times, a potential shift of approximately 90 mV, and an onset potential of −1.02 V, under CO2 saturation.

Abstract Carbonaceous porous materials are strong candidates for producing low-cost, lightweight, and sustainable electromagnetic (EM) absorbing materials. This work investigates the production of radar-absorbing materials (RAM) by a simple method. Sustainable carbon xerogel (CX) was synthesized from tannin, a biosourced molecule. CX and commercial carbon nanotube (CNT) were embedded in a silicone matrix at proportions of 10 and 15 wt.% of CX and 0.1 wt.% of CNT to produce flexible composites. The morphology and structure of the carbonaceous materials were evaluated by field-emission scanning electron microscopy (FEG-SEM), Raman spectroscopy, X-ray diffraction (XRD), textural properties by N2 adsorption-desorption isotherms, and mercury porosimetry. The electromagnetic characterization of the composites was analyzed by a vector network analyzer (VNA) in the Ku-band. The results demonstrated that an increased concentration of CX in the composite improved reflection loss reaching -43.19 dB at 13.79 GHz.

ABSTRACT Radar absorbing materials (RAMs) are composites made with a polymeric matrix and an electromagnetic absorbing filler, such as carbon black (CB), silicon carbide (SiC) or manganese zinc ferrite (MnZn). To enhance their performances to attenuate an incident wave through reflection loss (RL), RAMs can be produced in multilayer structures. Usually, the RL analysis is done theoretically and experimentally validated with free space analysis. Here, it was demonstrated that multilayer structure can be designed and easily validated using rectangular waveguide, using a simpler setup and small samples. Three composites were produced using 2 wt% of CB (CB2), 40 wt% of SiC (SiC40) and 60 wt% of MnZn (MnZn60). They were characterized over the Ku-band and used to validate the multilayer structures, that were prepared by simply stacking each material inside the waveguide sample holder. One of the best results was obtained with structure SiC40+CB2 with 5.85 mm thickness, that presented a calculated RL of -21 dB at 17.8 GHz and a measured RL of -36 dB at the same frequency. In conclusion, using rectangular waveguide has been proven to be an easy, cheap, precise and fast approach to validate multilayer structures designs.

ABSTRACT This contribution reports the use of an organic gel, xerogel, as catalyst support for Cu. The xerogel was synthesized from the system tannin-formaldehyde at pH 3, using F-127 Pluronic as surfactant. The surface area values were higher than 900 m2/g even after the Cu (10%, wt) impregnation. The morphological analysis by SEM-FEG revealed the presence of spheres arranged in a tridimensional structure. XRD diffractograms showed the presence of CuO and Cu2O crystalline phases combined with the amorphous structure of the porous carbon. From XRD analysis it is possible to infer the Cu species are heterogeneously dispersed on the support with the co-existence of small and larger clusters, which is in agreement with Raman spectroscopy. Raman study also indicated a highly defect/disorder structure of the xerogel derivatives, ensuing the short-range structural order of the carbonic structure and oxygen groups decorating the carbon surface. XPS results corroborate with XRD and Raman results, detecting the presence of CuO and Cu2O. In addition to the mentioned Cu species, XPS also detected Cu0 which may be originated from the chemical interaction between the electron oxygen groups with the Cu precursor. The high surface area and the thermal stability (~ 300 ºC) of Cu/XCTF envisages its feasibly for relevant catalytic applications.

ABSTRACT Radar Absorbing Materials (RAMs) are composite materials able to attenuate an incident electromagnetic wave. Usually, RAMs are made of a polymeric matrix and an electromagnetic absorbent filler, such as silicon carbide or carbon black. Several materials have been investigated as potential fillers, aiming to improve the Reflection Loss (RL) and absorption bandwidth broadening. In this paper, a composite made with silicone rubber and biochar was investigated as a sustainable porous carbon made with biomass waste. Five different composites were characterized, composed of 1 - 5 wt.% of biochar in the silicone rubber. Although the RL of pure biochar composites is not significant, it was demonstrated here how a biochar composite can improve the RL of a RAM material when it is applied as a double-layer structure. While the RL of a ferrite-based RAM with 2.0 mm thickness reaches -28 dB, a combination of this RAM with biochar composite reaches ~ -60 dB with the same thickness. The double-layer structure with 2.3 mm thickness can have an absorption bandwidth of 2.95 GHz over the X-band frequency range, and a structure with 2.6 mm thickness can reach a RL of ~ -76 dB. This demonstrates a sustainable, cheaper, and lighter material application (i.e., biochar), which is successfully used in the development of high-efficient electromagnetic shield or sensors.

RESUMO 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.

ABSTRACT 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.

ABSTRACT 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 well-known 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.

In this manuscript, the electromagnetic wave absorption properties of sustainable porous carbon composites were evaluated over the X-band frequency range (8.2 - 12.4 GHz). The porous carbon material was made from the byproduct of cellulose production and was used as additive on the development of radar absorbing material (RAM) composites. These porous carbon materials have different characteristics, such as porosity size (180 µm < Ø1 < 250 µm and 425 µm < Ø2 < 500 µm) and particle size (ϕ1 < 250 µm and 250 µm < ϕ2 < 425 µm). Composite materials were also studied as frequency selective surface (FSS) structures. It was shown how complex permittivity and reflection loss (RL) can be manipulated over the frequency range using FSS structure. While regular RAM presented RL of 19 dB at ~11.8 GHz, FSS structure presented a RL of 19 dB shifted to 12.4 GHz regarding the same carbon porous material (with particles between 250 and 425 µm and porosity between 180 and 250 µm). It was demonstrated here the potential use of sustainable porous carbon as RAM, and how FSS structure can be used to tune the frequency of the RL maximum peak.

ABSTRACT The increment of recycling of steel using electric arc furnace and the tendency to coat of steel products with zinc, in order to prevent corrosion, has increased the proportion of galvanized scrap used worldwide in the recent years. Approximately 10 to 20 Kg/t of cast steel is generated in casting arcs. These collected dusts electric arc furnace (EAF dust) contains iron, zinc, lead, and cadmium. Mainly in the form of oxides and their wastes are considered hazardous typically in countries such as Brazil, U.S., Japan and Germany. It is estimated that from the total of 7.5 million metric tons of EAF dust generated worldwide only 45% is recycled. With Waelz process, the EAF dust can be treated to recover zinc by means of reduction-volatilization-oxidation reactions occurring within the rotary kiln. In this work the thermodynamics of the Waelz process is studied to optimize the recovery of volatiles especially zinc. Kinetic parameters were evaluated trough series of ten experiments, comprise the major process factors such as type of reductants (charcoal and petroleum coke), time (20 – 120 minutes) and temperature (450 - 1150°C). The mechanical behavior of the pellets was evaluated by compressive cold strength and drop tests. Characterization was performed using scanning electron microscopy, microanalysis EDS, X-ray diffraction, X-ray fluorescence, granulometric analysis by laser diffraction, as well as measurements of moisture, bulk density and percentage of volatiles, fixed carbon and ash. The small pellets (10mm) with charcoal used as a reductant, presented a higher compression and higher recovery of volatiles than those with petroleum coke.