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Bentonite/iron oxide system is prepared by isothermal calcination of powder composed of bentonite clay and precursor containing ferric acetate. This preparation technique enables one to get the composite material directly, that is, iron oxide particles embedded in a bentonite matrix. Calcination temperature Tcalc is varied from 320°C to 700°C. The resulting series of samples is characterized by local methods based on hyperfine interactions: 57Fe nuclear magnetic resonance (NMR) and the Mössbauer spectroscopy. The results show that the phase composition changes significantly in dependence on calcination temperature. The amount of maghemite phase rapidly increases up to Tcalc = 420°C and decreases abruptly for Tcalc higher than 460°C.
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Křišťan et al. (2013) studied this question.
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