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Open AccessArticle

In Situ TEM Crystallization of Amorphous Iron Particles

NABLA Lab, Biological and Environmental Sciences and Engineering (BESE) Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
Authors to whom correspondence should be addressed.
The authors contributed equally.
Crystals 2020, 10(1), 41;
Received: 18 November 2019 / Revised: 1 January 2020 / Accepted: 8 January 2020 / Published: 17 January 2020
Even though sub-micron and nano-sized iron particles generally display single or polycrystalline structures, a growing interest has also been dedicated to the class of amorphous ones, whose absence of a crystal structure is capable of modifying their physical properties. Among the several routes so far described to prepare amorphous iron particles, we report here about the crystallization of those prepared by chemical reduction of Fe3+ ions using NaBH4, with sizes ranging between 80 and 200 nm and showing a high stability against oxidation. Their crystallization was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and in situ heating transmission electron microscopy (TEM). The latter technique was performed by the combined use of electron diffraction of a selected sample area, and bright and dark field TEM imaging, and allowed determining that the crystallization turns the starting amorphous particles into polycrystalline α-Fe ones. Also, under the high vacuum of the TEM column, the crystallization temperature of the particles shifted to 550 °C from the 465 °C, previously observed by DSC and XRD under 105 Pa of Ar. This indicates the pivotal role of the external pressure in influencing the starting point of phase transition. Conversely, upon both the DSC/XRD pressure and the TEM vacuum conditions, the mean size of the crystal domains increases as a consequence of further thermal increase, even if with some pressure-related differences. View Full-Text
Keywords: in situ heating TEM; particles; amorphous-crystal phase transition; amorphous iron in situ heating TEM; particles; amorphous-crystal phase transition; amorphous iron
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MDPI and ACS Style

Falqui, A.; Loche, D.; Casu, A. In Situ TEM Crystallization of Amorphous Iron Particles. Crystals 2020, 10, 41.

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