engleski

A Study of the Reduction and Reoxidation of Substoichiometric Magnetite

In the present work, the substoichiometric magnetite particles (Fe2.90O4)of micrometer dimensions were subjected to reduction and reoxidation at a temperature of up to 600 oC. The reduction of substoichiometric magnetite by hydrogen was performed under static conditions, whereas the reoxidation experiments were performed in a stream of oxygen. samples were characterized by FE-SEM, XRD, FT-IR and Mossbauer spectroscopy.The experimental condition for stoichiometric magnetite (Fe3O4) was obtained. It was found that Mossbauer spectroscopy is a powerful technique for monitoring the stoichiometry of magnetite, but limiting in terms of distinguishing a magnetite-maghemite mixture. FT-IR spectroscopy showed that samples, which by means of Mossbauer spectroscopy were characterised as nonstoichiometric magnetite, contained bands characteristic of magnetite and maghemite. After investigating the micrometer sized particles, all three peaks present in the XRD patterns of maghemite, but not in the XRD patterns of magnetite, at 2theta (CuKa)= 15, 24 and 26 degrees turned out clearly visible. The magnetite-to-maghemite transition mechanism will be discussed.

magnetite; maghemite; reduction; reoxidation; FE-SEM; XRD; Mossbauer spectroscopy

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