Microwave-assisted synthesis and magnetic property of magnetite and hematite nanoparticles

Nanoparticles of magnetite (Fe₃O₄) and hematite (α-Fe₂O₃) have been prepared by a simple microwave heating method using FeCl₃, polyethylene glycol and N₂H₄·H₂O. The amount of N₂H₄·H₂O has an effect on the final phase of Fe₃O₄. The morphology of α-Fe₂O₃ was affected by the heating method. Crystalline α-Fe₂O₃ agglomerates were formed immediately at room temperature and most of these nanoparticles within agglomerates show the same orientation along [110] direction. After microwave heating, ellipsoidal α-Fe₂O₃ nanoparticles were formed following an oriented attachment mechanism. Both Fe₃O₄ and α-Fe₂O₃ nanoparticles exhibit a small hysteresis loop at room temperature.     

Iron oxide pigmenting powders produced by thermal treatment of iron solid wastes from steel mill pickling lines

Phase changes of iron containing solid wastes from steel mill pickling lines after thermal treatments were investigated aiming the determination of the appropriate conditions for its transformation to be useful for industrial raw materials. Above 275°C, the thermally treated wastes contain a mixture of α-Fe₂O₃ (hematite) and γ-Fe₂O₃ (maghemite) in different proportions, depending on the maximum heating temperature of the thermal treatment. Increasing the maximum temperature the maghemite participation is decreased through its transformation to hematite. Above 850°C hematite is the main constituent, suggesting that thermal treatment of the wastes in this temperature will give a product that could be used as red iron pigment.     

The effect of the starting material on the thermal decomposition of iron oxyhydroxides

The effect of the iron precursor on the thermal decomposition of iron oxyhydroxides was studied by DSC, DTA and TG in this work. Samples were prepared from iron nitrate, iron sulfate and iron chloride and the thermal curves obtained were analyzed by specific area measurements, X-ray diffraction and Mössbauer spectroscopy. It was found that the iron oxyhydroxide precursors affect the temperatures of the hematite formation as well as the textural properties of the final hematite producing particles with different diameters as following: iron sulfate (3.3 nm)相似文献   

Influence of the starting materials on the catalytic properties of iron oxides

The effect of iron nitrate, sulfate and chloride on the catalytic properties of hematite toward ethylbenzene dehydrogenation has been studied. Iron nitrate has been the best precursor to prepare the catalysts.     

Kinetics of Oleate Adsorption at a Nigerian Hematite-Water Interface

The rate of adsorption of oleate soap onto a Nigerian hematite in an aqueous medium was determined from 29 to 60°C using the differential analysis method. The activation energy and frequency factor were determined at 57.1 kJ mol⁻¹ K⁻¹ and 4.0 × 10³ liter mol⁻¹ min⁻¹, respectively, indicating that the chemical processes are the slow, rate-determining step and that the reaction proceeds relatively fast. The adsorption isotherm was the Langmuir type: chemisorption was considered the dominant mode of adsorption. The desorption isotherm indicated a minor contribution of physical adsorption to the overall adsorption process.     

Potassium Ferrites Formation in Promoted Hematite Catalysts for Dehydrogenation. Thermal and structural analyses

K-promoted hematite catalysts for ethylbenzene dehydrogenation were studied by thermal analysis (TG/DTG) and high-temperature XRD. The formation of potassium ferrite (K₂Fe₂O₄), considered to be a catalytically active phase, was observed during calcination of the Ce-promoted catalysts. A linear correlation of the catalytic activity and the temperature of potassium ferrites formation was found. This revised version was published online in July 2006 with corrections to the Cover Date.     

Defective α‐Fe2O3(0001): An ab Initio Study

By using density functional theory calculations at the PBE+U level, we investigated the properties of hematite (0001) surfaces decorated with adatoms/vacancies/substituents. For the most stable surface termination over a large range of oxygen chemical potentials (${\mu _{\rm{O}} }$ ), the vacancy formation and adsorption energies were determined as a function of ${\mu _{\rm{O}} }$ . Under oxygen‐rich conditions, all defects are metastable with respect to the ideal surface. Under oxygen‐poor conditions, O vacancies and Fe adatoms become stable. Under ambient conditions, all defects are metastable; in the bulk, O vacancies form more easily than Fe vacancies, whereas at the surface the opposite is true. All defects, that is, O and Fe vacancies, Fe and Al adatoms, and Al substituents, induce important modifications to the geometry of the surface in their vicinity. Dissociative adsorption of molecular oxygen is likely to be exothermic on surfaces with Fe/Al adatoms or O vacancies.     

Electrochemical Formation of Fe(IV)=O Derived from H2O2 on a Hematite Electrode as an Active Catalytic Site for Selective Hydrocarbon Oxidation Reactions

The high-valence iron species (Fe(IV)=O) in the cytochrome P450 enzyme superfamily is generated via the activation of O₂, and serves as the active center of selective hydrocarbon oxidation reactions. Furthermore, P450 can employ an alternate route to produce Fe(IV)=O, even from H₂O₂ without O₂ activation. Meanwhile, Fe(IV)=O has recently been revealed to be the reactive intermediate during H₂O oxidation to O₂ on hematite electrodes. Herein, we demonstrated the generation of Fe(IV)=O on hematite electrodes during the electrochemical oxidative decomposition of H₂O₂ using in situ UV-visible absorption spectra. The generation of Fe(IV)=O on hematite electrodes from H₂O₂ exhibited 100 mV lower overpotential than that from H₂O. This is because H₂O₂ serves not only as the oxygen source of Fe(IV)=O, but also as the additional oxidant. Finally, we confirmed that the Fe(IV)=O generated on hematite electrodes can serve as the catalytic site for styrene epoxidation reactions.     

3D Monte Carlo simulations on the aggregate structures of a suspension composed of cubic hematite particles

In the previous study, from the viewpoint of surface modification technology, we considered a quasi-2D suspension in thermodynamic equilibrium in order to investigate the characteristics of magnetic cubic particles on a material surface. The present study has been expanded to include 3D Monte Carlo simulations of a suspension of magnetic cubic particles in order to discuss a regime change in the structures of cubic particle aggregates. We attempt to elucidate the dependence of a regime change in the aggregate structures on a variety of factors. The main results obtained here are summarised as follows. If the magnetic interaction strength is sufficiently large, closely packed clusters are formed by repeat and expansion of a cluster unit composed of eight particles, which may be the most preferred configuration as it gives rise to a minimum energy. A regime change in the internal structure of aggregates appears in a narrow range with increasing magnetic interaction strength. As the applied magnetic field strength is increased, closely packed clusters collapse and are transformed into wall-like clusters that are formed along the magnetic field direction. An increase in the volumetric fraction of particles induces a regime change from thick chain-like clusters to the formation of wall-like clusters.