JORGE COSTA SILVA FILHO

JORGE COSTA SILVA FILHO

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Effect of heat treatment in magnetic properties and microstructure of NdFeB-based permanent magnets produced by strip casting alloys
2022 - FARIA, M.E.; JANASI, S.R.; SILVA, S.C.; SILVA FILHO, J.C.; MARTINEZ, L.G.
Nd14FebalB6 sintered magnets were produced from a strip casting (SC) alloy, obtained in a pilot scale. The SC alloy was submitted to heat treatments (HT) of 2.5 h and 5 h at 1373 K under vacuum atmosphere and then processed by the powder metallurgy route to obtain the magnets. The SC alloys with and without HT were fragilized in hydrogen (H2), milled and, the powders resultants were aligned in a 6 T pulsed field, compacted in isostatic press at 200 MPa and vacuum sintered at 1373 K during 1 h. The X-ray diffraction results showed the presence of magnetic 2:14:1 phase and Fe in the SC alloy without the HT. After the HT of 2,5 h and 5 h, only the phase 2:14:1 was observed, indicating that the HT was sufficient to homogenize the alloy. The microstructural analysis of the alloy after 5 h of HT by electronic scanning microscopy showed the presence of 2:14:1 phase, confirming the XRD results and the Nd-rich phase, as well as the increase in grain size with increasing of the heat treatment time. The increase in grain size of the alloys after the heat treatment resulted in sintered magnets with larger grains than the magnet obtained from the alloy without the heat treatment. The highest magnetic properties among all samples were obtained in magnet produced from the alloy submitted to heat treatment during 5 h, which exhibited the following values of iHc = 462 kAm-1 and Jr = 1.27 T.
The influence of the addition of rGO and CNT on the electrochemical properties of the batteries the LaNi-based battery alloys
2020 - SOARES, E.P.; FILHO, J.C.S.; CASINI, J.C.S.; FARIA, R.N.; TAKIISHI, H.
In this article the results of the negative electrode performance produced by La0.7Mg0.3Al0.3Mn0.4Co0.5Ni3.8 as-cast alloy adding 1 to 10% of carbon nanotube (CNT) or reduced graphene oxide (rGO) were investigated as Ni-MH batteries. The as cast alloy were investigated with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The CNT and rGO were characterized by high resolution SEM-FEG. The discharge capacity obtained during the electrochemical characterization showed that in the addition of 1% rGO the discharge capacity was 332 mAh and 1% CNT 364 mAh , being that the rGO batteries maintaining better cyclic stability during the electrochemical test.
Synthesis and characterization of reduced graphene oxide-modified anatase TiO2 photocatalysts grown by MOCVD
2019 - BENTO, RODRIGO T.; SILVA FILHO, JORGE C.; CORREA, OLANDIR V.; TAKIISHI, HIDETOSHI; PILLIS, MARINA F.
Inadequate disposal of industrial waste, such as textile dyes and emerging contaminants, have been caused several environmental hazards. Titanium dioxide (TiO2) photocatalysis is an efficient green method for water treatment by solar energy. However, due to its large band gap of 3.2 eV, TiO2 absorbs mostly the UV radiation, which represents only 5-8% of the sunlight spectrum. Recent studies indicate that the surface modification of TiO2 results in an increase in photocatalytic efficiency. In this way, the present paper aims to evaluate the effects of TiO2 surface modification by reduced graphene oxide (rGO). The 470 nm thick anatase-TiO2 films were grown by MOCVD process in a conventional horizontal homemade reactor, on borosilicate substrates at 400 °C. The TiO2 films obtained were dipped into an alkoxide solution including 0.5, 1.5 and 3.0 mg of rGO and 30 mL isopropanol, ultrasonic-treated at room temperature for 40 min, and then dried in an oven at 100 and 150 °C for 24 h. The photocatalytic activity of rGO-TiO2 composites were evaluated by the methylene blue degradation under UV and visible light. The chemical, structural and morphological properties were also characterized. It was observed the presence of rGO agglomerates completely adhered to TiO2 surface. The diffraction peaks identified correspond to anatase phase. Peaks of graphene were also found. The results suggest that the rGO-TiO2 composites have a great potential to be used in water treatment under sunlight.
Caracterização e Tratamento Térmico do Óxido de grafeno para obtenção do Óxido de Grafeno reduzido
2018 - FILHO, J.C.S.; SILVA, S.C.; SOARES, E.P.; VENANCIO, E.C.; ANTUNES, R.A.; TAKIISHI, H.
Um dos grandes desafios para produzir o óxido de grafeno reduzido (rGO) é desenvolver rotas de obtenção que sejam viáveis economicamente e que apresentem um alto rendimento e qualidade estrutural. Neste trabalho, foi obtido o rGO por redução térmica do óxido de grafeno (GO) que foi sintetizado pelo método de Hummers modificado. As técnicas utilizadas para caracterização do GO e rGO foram por difração de raios X (DRX) e análise termogravimétrica (TGA). O DRX do GO exibiu apenas o pico característico em 2 teta =10°, correspondente ao conjunto de planos (002) e o termograma obtido por TGA determinou a melhor temperatura para a redução do GO. A perda de massa tem início próximo a 100°C, pela evaporação de voláteis e moléculas de água adsorvida nas camadas de GO e entre 150 e 230°C devido à remoção de grupos funcionais contendo oxigênio tais como (-OH), Epóxi e COOH. Entretanto, a maior perda de massa foi observada a 200°C, onde são obtidos o CO, o CO2 e vapor de água como subprodutos do processo de redução. Assim, observou-se que a temperatura e tempo de tratamento alteram o padrão das curvas das análises termogravimétricas sendo necessário, portanto seu controle. A redução térmica do GO, neste trabalho, foi realizada em atmosfera de nitrogênio, nas temperaturas de 200, 180 e 150°C e tempos de 30, 20 e 15 min, respectivamente. A análise das amostras obtidas por DRX, mostrou um deslocamento do pico 2 teta para 26° e a distância entre os planos atômicos d = 3,8 ?, referindo-se que houve a redução do GO em rGO. O rendimento (massa inicial GO – massa final rGO) das amostras obtidas foi superior a 50% em todos os experimentos, independente da temperatura e tempo utilizados, mostrando a viabilidade na obtenção do rGO no processamento pela redução térmica do GO.
The influence of the addition of rGO and CNT on the electrochemical properties of the batteries the LaNi-Based Battery Alloys
2018 - SOARES, E.P.; CASINI, J.S.; FARIA, R.N.; SILVA FILHO, J.C.; TAKIISHI, H.
In this article the results of the investigation are reported where batteries were made from the negative electrodes of the alloy La0.7Mg0.3Al0.3Mn0.4Co0.5Ni3,8, without annealing, adding 0, 1, 2, 5, 10% , both for carbon nanotube (CNT) and for reduced graphene oxide (rGO) where the discharge capacity obtained during the electrochemical characterization showed that in the addition of 1% rGO the discharge capacity was 332 mAh and 1% CNT 364 mAh , being that the rGO batteries maintaining better cyclic stability during the electrochemical test. The addition materials CNT and rGO were characterized by high resolution MEV-FEV - Field emission gun.
A importância do processamento na redução térmica do Óxido de grafeno
2017 - SILVA FILHO, JORGE C.; TAKIISHI, HIDETOSHI