Search results for "magnetite"
showing 10 items of 98 documents
The role of nano-sized iron particles in slurry phase Fischer–Tropsch synthesis
2003
Abstract The slurry phase Fischer–Tropsch (F–T) activity of three α-Fe2O3-based materials, two unsupported nano-sized, NANOCAT (3 nm) and BASF (20–80 nm), and a supported micron-sized (32.5 μm ) UCI, are compared with respect to total hydrocarbon production from synthesis gas (H2/CO∼2/1) at 513 K. Low temperature Mossbauer spectra of the quenched slurry samples after 120 h on-line show that all three catalysts are essentially a mixture of oxide and carbide phases with magnetite (Fe3O4) being the dominant phase. TEM images of the quenched samples reveal unexpected particle characteristics. While both unsupported nano-sized materials essentially avoid expected agglomeration, the micron-sized …
A Raman spectroscopy study of the oxidation processes in synthetic chromite FeCr2O4
2020
Abstract A crystal of synthetic chromite FeCr2O4 has been annealed in air at 700 °C for 50 days at room pressure in order to study physical-chemical changes. After the annealing treatment, Scanning Electron Microscopy (SEM) images of the polished surface of the sample showed areas of different composition. Detailed Raman mapping revealed that the annealed chromite undergoes an oxidation process, proceeding inwards from the outer surface and leading to the transformation of chromite to magnetite, and ultimately to hematite. The oxidation process also leads to the formation of trellis-like lines, arguably via stress-related mechanisms associated with the phase transformation and consequent vo…
One step continuous hydrothermal synthesis of very fine stabilized superparamagnetic nanoparticles of magnetite
2011
International audience; Stable suspensions of citrated SPIO nanoparticles were synthesised in one step using a hydrothermal continuous process. Citrates control the crystallite size and the oxidation degree of metallic ions despite the very short reaction time (4 s). Magnetite particles, Fe2.94O4, with an average size of 4 nm and good monodispersity were obtained.
Iron Mineralogy of Venus' Surface Investigated by M�ssbauer Spectroscopy
2000
Abstract We discuss the use of Mossbauer (MB) spectroscopy to study Fe-bearing minerals on Venus' surface. At present, there is no direct information about the mineralogy of Venus' surface, although in situ chemical analyses by X-ray fluorescence (XRF) spectroscopy have been done by the Venera 13, 14, and Vega 2 spacecraft at three landing sites. The XRF elemental analyses are sensitive to major rock-forming elements heavier than sodium and show the presence of several mass percent iron. Normative mineralogical calculations model the Fe mineralogy at the Venera 13, 14, and Vega 2 landing sites, but the actual Fe minerals present are unknown. We calculate synthetic MB spectra for the normati…
(Ag)Pd-Fe3O4 Nanocomposites as Novel Catalysts for Methane Partial Oxidation at Low Temperature
2020
Nanostructured composite materials based on noble mono-(Pd) or bi-metallic (Ag/Pd) particles supported on mixed iron oxides (II/III) with bulk magnetite structure (Fe3O4) have been developed in order to assess their potential for heterogeneous catalysis applications in methane partial oxidation. Advancing the direct transformation of methane into value-added chemicals is consensually accepted as the key to ensuring sustainable development in the forthcoming future. On the one hand, nanosized Fe3O4 particles with spherical morphology were synthesized by an aqueous-based reflux method employing different Fe (II)/Fe (III) molar ratios (2 or 4) and reflux temperatures (80, 95 or 110 °
Thermal decomposition of chromite spinel with chlorite admixture
2008
Abstract The behaviour of minerals in a South African chromite ore during the increasing of the temperature has been studied. Firstly, the changes produced during the ignition process have been examined by means of thermal and differential analysis (TGA–DTA) until 1200 °C. The characterization of the initial mineral and those obtained after heating at several temperatures in room atmosphere has been performed by X-ray diffraction (XRD). Moreover, voltammetric analyses have allowed to determine the variation of the iron oxidation degree in the studied materials. Light microscopy was applied to find more information about the different phases by their colour. During the heating, a wide range …
Iron-clay interactions: Detailed study of the mineralogical transformation of claystone with emphasis on the formation of iron-rich T-O phyllosilicat…
2014
International audience; Iron-minerals-water interactions are of primary importance in the contexts of underground structure engineering (e.g. reactive barriers or deep geological storage) and for the understanding of secondary alteration processes in primitive meteorites. To improve our understanding of these systems, we determine the mineralogical transformations induced by the association of iron and silicates during a cooling through an experimental simulation of iron-clay interactions with a step-by-step procedure in the range of 90 degrees C to 40 degrees C. The run products and solutions are well characterised, by means of different techniques (X-ray diffraction, scanning and transmis…
Preparation of monolithic polymer-magnetite nanoparticle composites into poly(ethylene-co-tetrafluoroethylene) tubes for uses in micro-bore HPLC sepa…
2021
[EN] This paper describes the fabrication of a novel microbore monolithic column modified with magnetite nanoparticles (MNPs) prepared in a poly(ethylene-co-tetrafluoroethylene) (EFTE) tubing, and its application as stationary phase for the chromatographic separation of phosphorylated compounds. In order to obtain the composite column, a two-step procedure was performed. The formation of a glycidyl methacrylate-based monolith inside the activated ETFE tube was firstly carried out. Then, two incorporation approaches of MNPs in monoliths were investigated. The generic polymer was modified with 3-aminopropyltrimethoxysilane (APTMS) to be subsequently attached to MNP surfaces. Alternatively, AP…
Molecular Camouflage: Making Use of Protecting Groups To Control the Self-Assembly of Inorganic Janus Particles onto Metal-Chalcogenide Nanotubes by …
2011
Hard and soft: Binding of inorganic Pt@Fe3O4 Janus particles to WS2 nanotubes through their Pt or Fe3O4 domains is governed by the difference in Pearson hardness: the soft Pt block has a higher sulfur affinity than the harder magnetite face; thus the binding proceeds preferentially through the Pt face. This binding preference can be reversed by masking the Pt face with an organic protecting group.
Synthesis and characterization of highly ordered cobalt-magnetite nanocable arrays.
2006
Magnetically tunable, high-density arrays of coaxial nanocables within anodic aluminum oxide (AAO) membranes have been synthesized. The nanocables consist of magnetite nanowires surrounded by cobalt nanotube sheaths and cobalt nanowires surrounded by magnetite nanotube sheaths. These materials are a combination of separate hard (Co) and soft (Fe3O4) magnetic materials in a single nanocable structure. The combination of two or more magnetic materials in such a radial structure is seen as a very powerful tool for the future fabrication of magnetoresistive, spin-valve and ultrafast spin-injection devices with nonplanar geometries. The nanocable arrays were prepared using a supercritical-fluid …