Magnetite

About: Magnetite is a research topic. Over the lifetime, 10277 publications have been published within this topic receiving 278071 citations.

Highly active heterogeneous Fenton-like systems based on Fe0/Fe3O4 composites prepared by controlled reduction of iron oxides

Abstract: In this work, a new and highly active heterogeneous Fenton system based on iron metal and magnetite Fe 0 /Fe 3 O 4 composites has been prepared by controlled reduction of iron oxides. Temperature-programmed reduction experiments with H 2 showed that iron oxides, i.e. Fe 2 O 3 , FeOOH and Fe 3 O 4 , can be reduced to produce highly reactive Fe 0 /Fe 3 O 4 composites with different metal to oxide ratios as determined by Mossbauer spectroscopy and powder X-ray diffraction. Mossbauer measurements revealed that these composites are reactive towards gas phase molecules and can be oxidized rapidly by O 2 even at room temperature. The composites showed also very high activity for the Fenton chemistry, i.e. the oxidation of an organic model contaminant, the dye methylene blue, and the H 2 O 2 decomposition. The best results were obtained with the composites with 47% Fe 0 obtained by reduction of Fe 3 O 4 with H 2 at 400 °C for 2 h, which produced a very rapid discoloration with total organic carbon (TOC) removal of 75% after 2 h reaction. Conversion electron Mossbauer spectroscopy (CEMS) measurements before and after H 2 O 2 reaction showed that Fe 3 O 4 and especially Fe 0 are oxidized during the reaction. The reaction mechanism is discussed in terms of the formation of HO radicals by a Haber–Weiss initiated by an efficient electron transfer from the composite Fe 0 /Fe 3 O 4 to H 2 O 2 . The higher activity of the composites compared to the pure Fe 0 and iron oxides has been explained by two possible effects, i.e. (i) a thermodynamically favorable electron transfer from Fe 0 to Fe 3 O 4 producing Fe 2+ magnetite active for the reaction and (ii) by the formation of very reactive small particle size Fe 0 and Fe 3 O 4 .

The physical theory of rock magnetism

Abstract: Magnetite and hematite are representative of the ferrimagnetic and weakly ferromagnetic minerals which are responsible for the magnetic properties of rocks reviewed in this paper. Magnetite grains are multi-domains in the size range of interest (0.1 μ–1000 μ), whereas hematite grains in the same size range are almost certainly single domains. Properties discussed are coercivity, susceptibility, magnetic viscosity, thermo- and isothermal remanence, alternating field demagnetization, anhysteretic, chemical and detrital magnetization, anisotropy, piezomagnetic effects and self-reversals. Problems requiring more experimental data are emphasized, especially the basal plane anisotropy of hematite, the Barkhausen discreteness of domains in magnetite and the possibility that grains of cubic minerals may have some uniaxial character arising from grain shape or internal strains.

Magmatic Features of Iron Ores of the Kiruna Type in Chile and Sweden: Ore Textures and Magnetite Geochemistry

Abstract: Magnetite lavas and feeder dikes on the flanks of the volcano El Laco in the Chilean Andes are characterized by textures demonstrating rapid crystal growth from supersaturated melts. Columnar magnetite, a conspicuous form of magnetite at El Laco with occasional dendritic branching, has been found in two other apatite iron provinces: the Cretaceous iron belt in Chile, a 600-km-long zone along the Pacific with about 40 deposits, and the Early Proterozoic Kiruna ore field in Sweden. Presence of columnar magnetite in an iron ore is suggested to be diagnostic of a magmatic origin. Platy magnetite, another dendritic form widespread at Kiruna, also occurs at El Laco. Moreover, many ores of the three provinces contain pyroxene or pseudomorphs after it with dendritic morphology. The occurrence of similar rapid-growth textures in the investigated apatite iron ores demonstrates a similar origin with emplacement of ore magmas at or near the surface. In fact, existence of vesicular ore lava and pyroclastic ore at Kiirunavaara shows that this deposit is volcanic.A common origin of the ores is supported by similar compositions of their magnetites. Analysis of ca. 50 concentrates from 17 deposits shows that the magnetites are very poor in Cr (<10 ppm) and relatively rich in V (ca. 1,000-2,000 ppm); the Ti content is typically low (ca. 100-1,000 ppm, with occasional values up to 5,000 ppm). Common ranges (in ppm) for other elements are Al = 200 to 1,500, Mg = 500 to 2,000, Mn = 200 to 900, Ni = 100 to 250, Co = 20 to 140, Zn = 50 to 120, and Cu = 10 to 50. The magnetites from El Laco and Kiruna are remarkably similar with the exception of Mg values which are about five times higher at El Laco (4,000-8,000 ppm). Magnetite in sedimentary ores appears to be significantly lower in V.

Molecular composition of iron oxide nanoparticles, precursors for magnetic drug targeting, as characterized by confocal Raman microspectroscopy

Abstract: The chemical and structural properties of ferrite-based nanoparticles, precursors for magnetic drug targeting, have been studied by Raman confocal multispectral imaging. The nanoparticles were synthesised as aqueous magnetic fluids by co-precipitation of ferrous and ferric salts. Dehydrated particles corresponding to co-precipitation (CP) and oxidation (OX) steps of the magnetic fluid preparation have been compared in order to establish oxidation-related Raman features. These are discussed in correlation with the spectra of bulk iron oxides (magnetite, maghemite and hematite) recorded under the same experimental conditions. Considering a risk of laser-induced conversion of magnetite into hematite, this reaction was studied as a function of laser power and exposure to oxygen. Under hematite-free conditions, the Raman data indicated that nanoparticles consisted of magnetite and maghemite, and no oxyhydroxide species were detected. The relative maghemite/magnetite spectral contributions were quantified via fitting of their characteristic bands with Lorentzian profiles. Another quality parameter, contamination of the samples with carbon-related species, was assessed via a broad Raman band at 1580 cm−1. The optimised Raman parameters permitted assessment of the homogeneity and stability of the solid phase of prepared magnetic fluids using chemical imaging by Raman multispectral mapping. These data were statistically averaged over each image and over six independently prepared lots of each of the CP and OX nanoparticles. The reproducibility of oxidation rates of the particles was satisfactory: the maghemite spectral fraction varied from 27.8 ± 3.6% for the CP to 43.5 ± 5.6% for the OX samples. These values were used to speculate about the layered structure of isolated particles. Our data were in agreement with a model with maghemite core and magnetite nucleus. The overall oxidation state of the particles remained nearly unchanged for at least one month.

Free-Standing Layer-by-Layer Assembled Films of Magnetite Nanoparticles

Abstract: A new technique for preparation of free-standing ultrathin films is presented. These films were made by layer-by-layer (LBL) deposition process, which is utilized for coatings on solid substrates and colloids. A film composed of alternating layers of magnetite nanoparticles and poly(diallyldimethylammonium bromide) was assembled on cellulose acetate, which was subsequently dissolved in acetone. From the suspended state, the LBL film can be transferred onto any solid or porous support. The strength of the film was observed to significantly increase when every other layer of magnetite was replaced with a layer of alumosilicate sheets serving as a molecular framework for the assembly.