On the goethite to hematite phase transformation |
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Authors: | Stefano Gialanella Fabrizio Girardi Gloria Ischia Ivan Lonardelli Maurizio Mattarelli Maurizio Montagna |
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Institution: | 1.Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali,Università degli Studi di Trento,Mesiano, Trento,Italy;2.Dipartimento di Fisica,Università degli Studi di Trento,Povo, Trento,Italy |
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Abstract: | This study deals with some microstructural and crystallographic aspects of the thermally induced transformation of goethite
(α-FeOOH) into hematite (α-Fe2O3), occurring at about 300 °C. Powder specimens of goethite have been annealed in air at different temperatures, ranging from
200 °C up to 1,000 °C. The resulting products have been analyzed for a complete characterization of the changes brought about
by the thermal treatments, using a multianalytical approach, based on: thermogravimetry, differential thermal analysis, transmission
electron microscopy, Raman spectroscopy, and X-ray diffraction. At lower temperatures, the transition to hematite produces
no important changes in size and shape of the original goethite grains. Recrystallization, and partial sintering, occurs only
at temperatures in excess of 800 °C. The relevant evolution of pores present in both phases has been also considered, as it
may provide important indications on the actual formation mechanism of hematite. |
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