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| Batista,Marcelo Augusto; Costa,Antonio Carlos Saraiva da; Bigham,Jerry Marshal; Paesano Junior,Andrea; Berndt,Graciele; Inoue,Tadeu Takeyoshi; Nonaka,Adriele Galeti. |
| Synthetic aluminum-substituted maghemites were characterized by total chemical analysis, powder X-ray diffraction (XRD), Mössbauer spectroscopy (ME), and vibrating sample magnetometry (VSM). The aim was to determine the structural, magnetic, and hyperfine properties of γ-Fe2-xAl xO3 as the Al concentration is varied. The XRD results of the synthetic products were indexed exclusively as maghemite. Increasing Al for Fe substitution decreased the mean crystalline dimension and shifted all diffraction peaks to higher º2θ angles. The a0 dimension of the cubic unit cell decreased with increasing Al according to the equation a o = 0.8385 - 3.63 x 10-5 Al (R²= 0.94). Most Mössbauer spectra were composed of one sextet, but at the highest substitution rate of 142.5... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Isomorphous substitution; Hyperfine parameters; Spinel; Ferromagnetic. |
| Ano: 2013 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-06832013000600013 |
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| Nonaka,Adriele Galeti; Batista,Marcelo Augusto; Costa,Antonio Carlos Saraiva da; Inoue,Tadeu Takeyoshi; Bonadio,Taiana Gabriela Moretti; Souza Junior,Ivan Granemann de. |
| ABSTRACT Maghemite (γ-Fe2O3) and hematite (α-Fe2O3) are important iron oxides in Brazilian soils derived from basalt. Maghemite can transform into hematite when exposed to high temperatures. However, isomorphic substitution (e.g., Al3+) may largely influence this process. We analyzed the kinetics of thermal transformation of Al-maghemites into Al-hematites and some of its mineralogical aspects. Synthetic substituted maghemites with different degrees of Al-substitution (0.0, 1.0, 2.0, 2.9, 3.8, 5.6, 6.7, 10.0, 12.0, and 17.1 mol% Al) were subjected to a temperature of 500±10 °C for 0, 5, 10, 16, 64, 128, 192, 360, 720, 2160, 3600, 5040, and 6480 min. After thermal treatment, samples were characterized by X ray diffraction (XRD), differential thermal... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Rietveld refinement; Thermal treatment; Mean crystallite dimension. |
| Ano: 2017 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-06832017000100410 |
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