SUELANNY CARVALHO DA SILVA
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Resumo IPEN-doc 29387 Effect of heat treatment in magnetic properties and microstructure of NdFeB-based permanent magnets produced by strip casting alloys2022 - 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.Artigo IPEN-doc 27241 A thermal method for obtention of 2 to 3 reduced graphene oxide layers from graphene oxide2020 - SILVA FILHO, J.C.; VENANCIO, E.C.; SILVA, S.C.; TAKIISHI, H.; MARTINEZ, L.G.; ANTUNES, R.A.In this work, a thermal reduction method was developed to obtain reduced graphene oxide (rGO) with 2 or 3 layers from graphene oxide (GO). The GO X-ray diffraction (XRD) patterns presented diffraction peak at 2θ = 10°, which is related to (002) reflection. After heat treatment under nitrogen ( N2(g)) atmosphere, this peak was shifted to 2θ = 25°, presenting an interlayer distance of 3.8 Å, associated to GO reduction. BET analysis of modified GO samples identified an average pore diameter of 45.38 Å and surface area of 23.06 m2/g. In the case of rGO1, rGO2 and rGO3 samples, they presented surface areas from 32.47 to 612.74 m2/g and an average pore diameter of 108.21–149.54 m2/g. Thermogravimetric analysis (TGA) indicated a higher mass loss between 150 and 230 °C. Raman spectra showed ID/IG ratios of rGO samples were higher than GO (1.36-GO; 1.45-rGO1, 1.87-rGO3) due to reducing GO and increasing sp2 clusters. XPS analysis revealed that the main carbon species in the samples were sp2- type bonds (14.99 at% for the GO and 47.85 at% for rGO3). The FTIR spectra of rGO1, rGO2 and rGO3 samples presented peaks at 3454.22 cm−1 (hydroxyl) and 1077.43 cm−1 (C–O).Artigo IPEN-doc 12476 X-ray diffraction analysis and magnetic properties of Pr-Fe-B HDDR powder and magnets2007 - SILVA, S.C.; DUVAIZEM, J.H.; MARTINEZ, L.G.; FARIA, R.N.; TAKIISHI, H.Artigo IPEN-doc 13188 X-ray diffraction analysis and magnetic properties of Pr-Fe-B HDDR powders anmd magnets2008 - SILVA, S.C.; DUVAIZEM, J.H.; MARTINEZ, L.G.; ORLANDO, M.T.D.; FARIA, R.N.; TAKIISHI, H.