In situ XRD study of the phase transition of nanocrystalline maghemite (γ-Fe2O3) to hematite (α-Fe2O3)
| Autor: | Guido Schimanke, Manfred Martin |
|---|---|
| Rok vydání: | 2000 |
| Předmět: |
X-ray absorption spectroscopy
Materials science Oxide Analytical chemistry Maghemite General Chemistry Activation energy engineering.material Hematite Condensed Matter Physics Nanocrystalline material Crystal chemistry.chemical_compound Crystallography chemistry visual_art engineering visual_art.visual_art_medium General Materials Science Powder diffraction |
| Zdroj: | Solid State Ionics. :1235-1240 |
| ISSN: | 0167-2738 |
| Popis: | Nanocrystalline iron oxide was produced by inert gas condensation (IGC). The phase and crystal size analysis were done by X-ray powder diffraction (XRD), X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). All three methods show that the only oxide that was formed was maghemite. The crystal sizes vary for different samples from 9 nm to 16 nm. The kinetics of the phase transition from maghemite to hematite was observed by in situ XRD measurements at temperatures around 300°C. It is possible to describe the transition by first order kinetics with an activation energy which increases with increasing crystal size. The sizes of the produced hematite crystals were above 35 nm, but growing of the maghemite crystals was not observed. These results can be explained qualitatively under the aspect of the Gibbs energies. |
| Databáze: | OpenAIRE |
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