Kinetics of Thermal Transformation of Synthetic Al-Maghemites into Al-Hematites
| Autor: | Ivan Granemann de Souza Junior, Antonio Carlos Saraiva da Costa, Tadeu Takeyoshi Inoue, Marcelo Augusto Batista, Taiana Gabriela Moretti Bonadio, Adriele Galeti Nonaka |
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| Jazyk: | angličtina |
| Předmět: |
Materials science
Analytical chemistry Soil Science Maghemite 02 engineering and technology Thermal treatment engineering.material Differential thermal analysis Specific surface area mean crystallite dimension lcsh:Agriculture (General) Rietveld refinement 04 agricultural and veterinary sciences Hematite 021001 nanoscience & nanotechnology lcsh:S1-972 visual_art X-ray crystallography 040103 agronomy & agriculture visual_art.visual_art_medium engineering 0401 agriculture forestry and fisheries Crystallite 0210 nano-technology Agronomy and Crop Science thermal treatment |
| Zdroj: | Revista Brasileira de Ciência do Solo, Vol 41, Iss 0 Revista Brasileira de Ciência do Solo, Volume: 41, Article number: e0160384, Published: 27 APR 2017 Revista Brasileira de Ciência do Solo v.41 2017 Revista Brasileira de Ciência do Solo Sociedade Brasileira de Ciência do Solo (SBCS) instacron:SBCS |
| ISSN: | 1806-9657 |
| Popis: | 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 analysis (DTA), specific surface area (SSA) measurement, and total chemical analysis. XRD patterns were analyzed by Rietveld refinement, and maghemite and hematite contents were calculated using Rietveld refinement and the method proposed by Sidhu. Isomorphic substitution of Fe by Al increased the critical temperature of transformation and the time necessary for maghemite to hematite transformation. Rietveld refinement data showed a better fit than the data adjusted by the Sidhu method. Increasing isomorphic substitution also decreased lattice parameters and mean crystallite dimension (MCD) values in maghemite; but only c-dimension and MCD decreased with increasing Al-substitution in hematite. For maghemite, the SSA increased with isomorphic substitution, rising up to 5.9 mol% Al; for hematite, SSA increased linearly. SSA decreased with heating time, regardless of isomorphic substitution. |
| Databáze: | OpenAIRE |
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