Novel solid-state synthesis of α-Fe and Fe₃O₄nanoparticles embedded in a MgO matrix

Abstract

Thermally induced reduction of amorphous Fe2O3 nanopowder (2–3 nm) with nanocrystalline Mg (∼20 nm) under a hydrogen atmosphere is presented as a novel route to obtain α-Fe and Fe3O4 magnetic nanoparticles dispersed in a MgO matrix. The phase composition, structural and magnetic properties, size and morphology of the nanoparticles were monitored by x-ray diffraction, 57Fe Mössbauer spectroscopy at temperatures of 24–300 K, transmission electron microscopy and magnetic measurements. Spherical magnetite nanoparticles prepared at a reaction temperature of 300 °C revealed a well-defined structure, with a ratio of tetrahedral to octahedral Fe sites of 1/2 being common for the bulk material. A narrow particle size distribution (20–30 nm) and high saturation magnetization (95 ± 5 A m2 kg−1) predispose the magnetite nanoparticles to various applications, including magnetic separation processes. The Verwey transition of Fe3O4 nanocrystals was found to be decreased to about 80 K. The deeper reduction of amorphous ferric oxide at 600 °C allows α-Fe (40–50 nm) nanoparticles to be synthesized with a coercive force of about 30 mT. They have a saturation magnetization 2.2 times higher than that of synthesized magnetite nanoparticles, which corresponds well with the ratio usually found for the pure bulk phases. The magnetic properties of α-Fe nanocrystals combined with the high chemical and thermal stability of the MgO matrix makes the prepared nanocomposite useful for various magnetic applications.

Carbon Electrodes Modified by Nanoscopic Iron(III) Oxides to Assemble Chemical Sensors for the Hydrogen Peroxide Amperometric Detection

“…b-Fe 2 O 3 nanopowder (40 -70 nm) was obtained by thermally induced solid-state reaction of NaCl and Fe 2 (SO 4 ) 3 combined with the post-processing chemical separation [23]. Nanocrystalline magnetite (30 -40 nm) was prepared by thermal reduction of amorphous Fe 2 O 3 under hydrogen atmosphere at 300 8C [24]. Amorphous iron(III)-oxide nanopowder (2 -4 nm) was synthesized according to the procedure described in [25].…”

Low temperature synthesis, magnetic and electrical properties of iron–magnesium superparamagnetic nanoalloy

“…1 H NMR (DMSO, ppm): 8.440 (s, 6H, bipyH 6,6ǐ ); 8.220 (s, 6H, bipyH 3,3ǐ ); 7.797 (s, 6H, bipyH 4,4ǐ ); 7.299 (s, 6H, bipyH 5,5ǐ ). TGA: 188-225 • C (22.30% weight loss), 305-445 • C (28.10% residual mass).…”

“…Addition of small quantities of transition metals or their oxides [1,2] has shown to have an important catalytic effect on hydrogen sorption kinetics of the material [3,4]. Much of the work has been done on the alloys of Mg with Ni [4,5] and Co [6] as they are known to form intermetallic compounds with magnesium unlike Fe.…”

Sol-gel synthesis and characterization of magnetic TiO2 microspheres

“…The ratio of spectrum areas for A and B sites should be around 1/2 for well-established spectrum of magnetite. 21) However, this ratio for the present iron oxide particles was 69/31, indicating that more Fe 3+ exists in the particles. Therefore, it can be concluded that £-Fe 2 O 3 and Fe 3 O 4 coexist in the as-synthesized iron oxide particles and their composition can be calculated from the ratio of spectrum areas of A and B sites to be £-Fe 2 O 3 /Fe 3 O 4 = 1.73/1 in molar ratio.…”