FATIMA GOULART
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Artigo IPEN-doc 27006 Study on the microstructure of UNS S32304 duplex steel submitted to heat-treatments2017 - GOULART, F.; ICHIKAWA, R.U.; TURRILLAS, X.; MARTINEZ, L.G.Duplex stainless steels are characterized by a good combination of mechanical properties and corrosion resistance. Due to the metastable equilibrium between the ferritic (α) and austenitic (γ) phases, significant changes in the microstructure of these steels may occur when subjected to temperatures higher than the ambient, degrading their properties. In this work, it was investigated the influence of heat treatments on the microstructure and mechanical properties of a duplex stainless steel UNS-S32304. The heat-treatments were performed at four temperatures (300°C, 600°C, 900°C and 1000°C) with two treatment times (1 h and 6 h) and two processes of cooling down (in air and water). The samples were studied by X-ray diffraction using Pawley method to determine the lattice parameters, mean crystallite sizes and microstrain for the two phases and compared to Vickers microhardness results.Artigo IPEN-doc 24312 Characterization of Mn0.67Zn0.33Fe2O4 nanoparticles synthesized under different pH2017 - ICHIKAWA, RODRIGO U.; YOSHITO, WALTER K.; SAEKI, MARGARIDA J.; MARANHAO, WILLIAN C.A.; GOULART, FATIMA; MARTINEZ, LUIS G.Nanostructured Mn-Zn ferrites were synthesized using co-precipitation in alkaline solution with different pH. The samples were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), thermal analysis (TG-DTA), dynamic light scattering (DLS) and scanning electron microscopy (SEM) techniques. Monophasic nanoparticles were formed when synthesized with pH 10.5. This sample was heat-treated and its XRD data was refined by the Rietveld method. Mean crystallite sizes and microstrains were determined from X-ray line profile analysis using Single-Line and Warren-Averbach methods, which revealed a mean crystallite size of approximately 10 nm and negligible microstrains. Zn content was estimated using refined cell parameters, giving a value of 33 at %, in accordance with XRF result. TG-DTA revealed that the incorporation of α-Fe2O3 occurs around 1130 °C and 1200 °C with recrystallization of the Mn-Zn ferrite spinel phase. DLS showed that mean particle size increase with temperature up to 1159 nm at 800 °C. SEM analysis showed the samples agglomerate and present similar morphology with negligible size changing when calcined between 280 °C and 800 °C. However, the sample calcined at 1200 °C presents larger agglomerates due to the sintering process.Artigo IPEN-doc 21598 Characterization of Mnsub(0.67)Znsub(0.33)Fesub(2)Osub(4) nanoparticles synthesized under different pH2015 - ICHIKAWA, RODRIGO U.; YOSHITO, WALTER K.; SAEKI, MARGARIDA J.; MARANHAO, WILLIAN C.A.; GOULART, FATIMA; MARTINEZ, LUIS G.