Bentonite/Iron Oxide Composites: Preparation and Characterization by Hyperfine Methods

Abstract

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 temperatureTcalcis 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 toTcalc=420°C and decreases abruptly forTcalchigher than 460°C.

Structure of Iron Oxide Nanoparticles Studied by ^{57}Fe NMR

“…at resonating nuclei, since the crystal and magnetic structure of nanoparticles is less perfect than in single crystals [5]. However, strong signal in the 6671 MHz spectral region seems to contain maghemite A and B resonance lines [2][3][4]6], beside magnetite A line. Close relation to maghemite is indicated also by the same resonance frequency range and similar spectral features in the spectrum of the studied sample at 4.2 K and in the maghemite spectrum [4] in Fig.…”

“…Temperature dependence of 57 Fe NMR resonance frequencies. Nanoparticle sample (80110 nm) compared to single crystals of stoichiometric magnetite [1,6] and magnetite with vacancies Fe 3(1−δ) O4, δ = 0.009 [7].…”