Navegando por Autor "Araujo, Jose Humberto"
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Artigo Anisotropy field and transverse susceptibility in nanocrystalline hexaferrites(Elsevier, 2006-10-01) Araujo, Jose Humberto; Soares, J. M.; Machado, F. L. A.; Cabral, F. A. O.; Rodrigues, H. A. B.; Ginani, Marconi FloripeNanocrystalline strontium and barium hexaferrites were produced by an ionic coordination reaction method. The average particle size obtained using the Rietveld X-ray refinement technique and by scanning electron microscopy was quite uniform and close to 50 nm. Transverse susceptibility measurements yielded both the coercive and the anisotropy magnetic fields. The results were analysed using a theoretical model proposed by Aharoni et al. [Bull. Res. Counc. Isr. A 6 (1957) 215]. This overall procedure seems to be quite useful in determining the distribution of the anisotropy magnetic fields in granular materials.Artigo Atomic hopping in AlCuFe quasicrystal(Elsevier, 1996-03) Araujo, Jose Humberto; Gomes, A. A.; Cunha, J. B. M. daHigh temperature 57Fe MOsshaner effect measurements in annealed icosahedral A1CuFe alloy are reported. The anomalous decrease in Debye-Waller factor is qualitatively interpretated. It is suggested using consistent parameters that the isomer shift decreases linearly with temperature in agreement with a second-order Doppler shift in the Debye approximation.Artigo Effect of High Energy Milling on the Magnetic Properties of the WC-10wt.%Co Cemented Carbides(Materials Science Forum, 2006-01) Araujo, Jose Humberto; Manuel, Joao Baptista; Costa, F. A.; Macedo, Harim Revoredo de; Gomes, Uilame Umbelino; Silva, Angelus Giuseppe Pereira daCemented tungsten carbides were produced by liquid-phase sintering. In these work high energy milling (HEM) was used to produce homogeneous and finely grained powder mixtures. The milling effect in the magnetic properties of sintered samples is studied. Differents mixtures in same composition (WC-10wt%Co) were prepared by conventional mixture technique and wet HEM up to 300 hs in planetary Mill. Magnetic hysteresis measurements on the sintered samples detected a significant increase in the coercitive field and a decrease in the saturation magnetization with milling time increasing. X-ray diffractogram show phase transformations with milling time. The Magnetic properties are correlated with phase relations and microstructural properties of the sintered samples.Artigo Mössbauer effect characterization of Brazilian iron ores for mining industrial purposes(Elsevier, 1993-04-04) Araujo, Jose Humberto; Costa Jr., M. I. da; Kunrath, J. I.; Cunha, J. B. M. da; Moro, J. T.Iron ore is one of the important export products of Brazil. As only ore bodies with over 50% iron contents are mined, continuous efforts in prospecting are made. The use of Mössbauer spectroscopy as an aid to these efforts is illustrated by an example given in this report.Artigo A Mössbauer study of plasma nitrided iron(AIP Publishing, 1998-10-13) Araujo, Jose Humberto; Cabral, F. A. O.; Araujo, R. C.; Gama, S.Iron powder has been nitrided in a glow discharge plasma of a mixture of nitrogen and hydrogen, in order to verify the existence of a metastable iron nitrogen solid solution, previously observed from the Sm2Fe17N3 phase decomposition process. Our results show that, for short nitridation times, we obtain a mixture of Fe4N, a small amount of α-Fe and an iron nitrogen solid solution the amount of which increases after heat-treatment at 610 °C. This iron nitrogen solid solution is characterized by Mössbauer spectroscopy which shows a typical α-Fe spectrum, but with lower hyperfine field and broader linewidth. TMA measurements show that the Curie temperature is similar to that of α-Fe.