Impact of Silica-Modification and Oxidation on the Crystal Structure of Magnetite Nanoparticles

Abstract

At present, the widespread use of iron oxide nanoparticles, including for commercial purposes, requires strict preservation of their phase composition during their application. The choice of nanoparticle modifier and modification conditions is decisive due to their high sensitivity to oxygen in the case of using real conditions (O2, pH change, etc.). In this work, we studied the change in the phase composition of magnetite nanoparticles after modification with 3-aminopropyltriethoxysilane (APTES) and oxidation with nitric acid in order to estimate the protective potential of the silica shell. After modification by APTES and oxidation with nitric acid, the nonstoichiometric nature of the magnetite nanoparticles according to XRD data increased, which indicates an increase in transition forms compared to the initial sample (magnetite content decreased to 27% and 24%, respectively). In contrast, Mössbauer spectroscopy data detected a decrease in the nonstoichiometric index due to APTES modification conditions, but strong oxidation after exposure to nitric acid. It also showed that by analyzing the data of the diffraction analysis and Mössbauer spectroscopy for the same sample, one can obtain information not only about the ionic composition of “magnetite”, but also about the distribution of iron ions of different charges over the crystalline and amorphous parts of the preparation.

Low-Temperature Treatment of Boehmitic Bauxite Using the Bayer Reductive Method with the Formation of High-Iron Magnetite Concentrate

“…The rest of the spectrum could only be described using the many-state superparamagnetic relaxation model [ 37 ]. The models for the spectra obtained at different temperatures were consistent with each other through the ratio of the energy of the magnetic anisotropy of particles to the thermal energy: α = K × V/k B × T, where K—magnetic anisotropy constant; V—volume of the magnetic domain; k B —Boltzmann constant; T—temperature [ 38 ]. Obviously, this subspectrum refers to the forming particles of nanomagnetite, possibly partially oxidized [ 39 ].…”

“…There was a sextet with a characteristic splitting of 1–3 resonance lines, an increased intensity of 4–6 lines in the spectra at room temperature, and a noticeable asymmetric distortion of the sextet resonance lines in the spectra at the boiling point of nitrogen ( Figure 15 b,d). The general broadening of resonance lines to the inner region of the spectrum indicates the manifestation of superparamagnetism by the material [ 38 ]. Both spectra were satisfactorily described by the superposition of three sextets.…”

Low-Temperature Treatment of Boehmitic Bauxite Using the Bayer Reductive Method With the Formation of High-Iron Mag-Netite Concentrate

“…There was a sextet with a characteristic splitting of 1-3 resonance lines, an increased intensity of 4-6 lines in the spectra at room temperature, and a noticeable asymmetric distortion of the sextet resonance lines in the spectra at the boiling point of nitrogen (Figure 15b,d). The general broadening of resonance lines to the inner region of the spectrum indicates the manifestation of superparamagnetism by the material [38]. Both spectra were satisfactorily described by the superposition of three sextets.…”

The Waelz Slag from Electric Arc Furnace Dust Processing: Characterization and Magnetic Separation Studies

“…1 and 2, Table 2). The profiles of these sextets can be described using the many-state superparamagnetic relaxation model [40,41]. Obviously, these subspectra can be related to solid solutions of magnetite-maghemite Fe 3−δ O 4 [42], where δ varies from 0 to 1/3 for magnetite and maghemite, respectively [43].…”