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Your search keyword '"Ivashita, Flávio F."' showing total 22 results
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22 results on '"Ivashita, Flávio F."'

15. Nanometric particle size and phase controlled synthesis and characterization of γ-Fe2O3 or (α + γ)-Fe2O3 by a modified sol-gel method.

Author

Silva, Marcela F., de Oliveira, Luiz A. S., Ciciliati, Mariani A., Silva, Lais T., Pereira, Bruna S., Hechenleitner, Ana Adelina W., Oliveira, Daniela M. F., Pirota, Kleber R., Ivashita, Flávio F., Paesano, Andrea, Martin Pastor, J., Iñaki Pérez-Landazábal, J., and Pineda, Edgardo A. G.

Subjects
PARTICLE size determination, PARTICLES, IRON oxides, IRON compounds, SOL-gel processes
Abstract

Fe2O3 nanoparticles with sizes ranging from 15 to 53 nm were synthesized by a modified sol-gel method. Maghemite particles as well as particles with admixture of maghemite and hematite were obtained and characterized by XRD, FTIR, UV-Vis photoacoustic and Mössbauer spectroscopy, TEM, and magnetic measurements. The size and hematite/maghemite ratio of the nanoparticles were controlled by changing the Fe:PVA (poly (vinyl alcohol)) monomeric unit ratio used in the medium reaction (1:6, 1:12, 1:18, and 1:24). The average size of the nanoparticles decreases, and the maghemite content increases with increasing PVA amount until 1:18 ratio. The maghemite and hematite nanoparticles showed cubic and hexagonal morphology, respectively. Direct band gap energy were 1.77 and 1.91 eV for A6 and A18 samples. Zero-field-cooling-field-cooling curves show that samples present superparamagnetic behavior. Maghemite-hematite phase transition and hematite Néel transition were observed near 700 K and 1015 K, respectively. Magnetization of the particles increases consistently with the increase in the amount of PVA used in the synthesis. Mössbauer spectra were adjusted with a hematite sextet and maghemite distribution for A6, A12, and A24 and with maghemite distribution for A18, in agreement with XRD results. [ABSTRACT FROM AUTHOR]

Published
2013
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18. Synthesis of goethite in solutions of artificial seawater and amino acids: a prebiotic chemistry study

Author

Carneiro, Cristine E. A., primary, Ivashita, Flávio F., additional, de Souza, Ivan Granemann, additional, de Souza, Cláudio M. D., additional, Paesano, Andrea, additional, da Costa, Antonio C. S., additional, di Mauro, Eduardo, additional, de Santana, Henrique, additional, Zaia, Cássia T. B. V., additional, and Zaia, Dimas A. M., additional

Published
2013
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19. Interaction of forsterite-91 with distilled water and artificial seawater: a prebiotic chemistry experiment

Author

de Souza, Cláudio M. D., primary, Carneiro, Cristine E. A., additional, Baú, João Paulo T., additional, da Costa, Antonio C. S., additional, Ivashita, Flávio F., additional, Paesano, Andrea, additional, di Mauro, Eduardo, additional, de Santana, Henrique, additional, Holm, Nils G., additional, Neubeck, Anna, additional, Zaia, Cássia T. B. V., additional, and Zaia, Dimas A. M., additional

Published
2013
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22. Synthesis, structural characterization and Mössbauer study of LnV0.5Fe0.5O3 perovskites (Ln=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er)

Author

Ivashita, Flávio F., Biondo, Valdecir, Bellini, Jusmar V., Paesano, Andrea, Blanco, M. Cecilia, Fuertes, Valeria C., Pannunzio-Miner, Elisa V., and Carbonio, Raúl E.

Subjects
*PEROVSKITE synthesis, *CRYSTAL structure, *MOSSBAUER effect, *SOLIDIFICATION, *ELECTRIC arc, *FUSION (Phase transformation), *SOLID solutions
Abstract

Abstract: Perovskites LnV0.5Fe0.5O3 (Ln=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er) were synthesized by rapid solidification from arc-melted samples and characterized by the study of their crystal structure and hyperfine properties. These metastable solid solutions crystallized in the Pbnm symmetry, with the iron and vanadium cations randomly distributed in the transition metal octahedral sites. Depending on the lanthanide present at the A site of the perovskite, iron is present with two valences (i.e., Fe3+ and Fe2+). The volume of the unit cell for these perovskites increases linearly with the lanthanide ionic radius, as the perovskite approaches its ideal structure. At room temperature, the quadrupolar splitting of the trivalent paramagnetic Mössbauer component works as an indirect measurement for the Goldshmidt tolerance factor. Close to or below 100K, these perovskites undergo a crystallographic phase transformation, probably due to orbital ordering of the V3+ cations, originating two different magnetic iron sites. [Copyright &y& Elsevier]

Published
2012
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