Formation Of MgFe2O4 Research Articles

Influence of Magnesium Ions in the Seawater Environment on the Improvement of the Corrosion Resistance of Low-Chromium-Alloy Steel.

This study examined the synergic effect of alloying the element Cr and the environmental element Mg2+ ions on the corrosion property of a low-alloy steel in seawater at 60 °C, by means of electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) tests and weight-loss tests. The Mg2+ ions in seawater played an important role in lowering the electron transfer of the rust layer in the Cr-containing steel. The corrosion resistance of the Cr-containing steel is superior to that of blank steel in Mg2+ ions containing seawater. XPS and XRD results indicated that the formation of MgFe2O4 and a mixed layer (Cr oxide + FeCr2O4 + MgCr2O4) improved the corrosion resistance of the low-alloy steel in the seawater.

Modification of industrial BOF slag: Formation of MgFe2O4 and recycling of iron

Efficient recycling of iron oxide from industrial BOF (basic oxygen furnace) slags has always been an issue in metallurgy. In this study, a new method was developed for the efficient recycling of iron oxide: It was transformed into magnesioferrite spinel (MgFe2O4) by mixing the industrial BOF slag with 6.00% SiO2 first, and then the modified slag got cooled down from 1400 °C to 1270 °C at a rate of 1 °C/min. Finally, the Fe resources were recycled by magnetic separation. Various experiments and analyses such as XRD, SEM–EDS analyses, Factsage thermodynamic simulation, magnetization characterization, dry magnetic separation, and chemical analysis were carried out. The results show that the obtained MgFe2O4 has a high melting point (1716.76 °C in theory) and ferromagnetism (specific magnetic susceptibility of (8.03–206.84) × 10−5 m3/kg). Therefore, it could be separated from the weakly magnetic industrial BOF slag (specific magnetic susceptibility of (0.024–0.136) × 10−5 m3/kg). Furthermore, this new method could be applied to different BOF slags. The yield of MgFe2O4 increased to above 80% when the content of Fe2O3 was in the range 25.81–46.90%. After the modification and magnetic separation, the total Fe content increased by 15.80%, from 21.20% in the industrial BOF slag to 37.00% in the magnetic slag. This is better than the direct magnetic separation of iron oxide without any treatment. The magnetic slag could be reused as either a sintering or slag splashing material. The nonmagnetic slag can be used to produce high value-added building materials. Hence, this new method can be used to recycle the iron oxide from industrial BOF slags, achieving the sustainable development of the iron and steel industry.

Preparation and characterization of MgFe2O4 nanocrystallites via PVA sol-gel route

MgFe2O4 nanocrystallites were prepared by a polyvinyl alcohol (PVA) sol-gel route. Differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy and Environmental scanning electron microscope (ESEM) were used to characterize the precursors and the derived oxide powders. The effect of Mg/Fe molar ratio on the formation of MgFe2O4 were investigated. XRD analysis showed that single-phase MgFe2O4 was obtained from Mg/Fe = 0.55 and 0.6 precursor at a temperature of 500 °C for 2 h, without the formation of any intermediate phase. The crystallite size of MgFe2O4 with Mg/Fe = 0.55 calcined at 500 °C is ∼12 nm. For the Mg/Fe = 0.5 precursor, phase pure MgFe2O4 could not be obtained even at 800 °C, with α-Fe2O3 as impurity phase. The saturation magnetizations of the nanocrystalline MgFe2O4 (Mg/Fe = 0.55) calcined at 500 and 700 °C are 10.8 and 25.6 emu g−1, respectively.

Synthesis of High-Quality Single- and Double-Walled Carbon Nanotubes on Fe/MgO Catalysts

In this study, Fe/MgO catalysts with three different iron contents (5, 10, and 15 wt.%) were prepared by three catalyst preparation methods: impregnation, solution combustion synthesis, and co-calcination of metal nitrates. The resulting catalysts were subjected to methane at 900°C in order to grow carbon nanotubes (CNTs). The powders and products were then studied by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning and transmission electron microscopy (SEM and TEM), and Raman spectroscopy. Formation of MgFe2O4 upon heating the catalysts to 900°C was confirmed by XRD. After the growth step, corresponding peaks of MgFe2O4 disappeared and metallic iron peaks appeared, indicating that MgFe2O4 is the responsible phase for production of iron nanoparticles. HRTEM images showed that the product on the 5 wt.% catalysts was mostly SWNTs and DWNTs with no evidence of carbon nanofibres or multi-walled carbon nanotubes on the co-calcination catalyst. Furthermore, ID/IG ratios obtained from Raman...

Structural and Magnetic Properties of MgFe2O4 Thin Films

The spinel-type ferrites are important due to their technological and industrial applications. Among magnetic ferrites with formula XFe2O4 (where X= Co, Ni etc.), magnesium ferrite with unique magnetic properties has a significant advantage. This ferrite is a soft magnetic, n-type semiconductor and has many applications in catalysis, brown pigments, high-density recording, gas sensors, transformers, magnet core and ferrofluids. In this work MgFe2O4 thin films are prepared using Sol-Gel method. The Mg/Fe ratio is varied as 0.45, 0.55 and 0.6. The presence of (220), (400), (331) and (533) peaks confirm the formation of MgFe2O4 at low synthesis temperature of 300˚C. It can be seen that variation in Mg/Fe ratio strongly affects the magnetic properties of magnesium iron oxide thin films.

Formation, microstructure and magnetic properties of nanocrystalline MgFe2O4

Nanocrystalline powder of MgFe2O4 was successfully synthesized by a cost effective novel combustion route. Nitrates of the constituent elements and glycine were respectively used as an oxidizer and fuel to drive the reaction. The effect of glycine to nitrate molar ratio (GN−1) on the structure and formation of MgFe2O4 was studied in view of thermodynamic considerations like adiabatic flame temperature and gas evolved during the combustion. The as prepared powder was characterized by X-Ray Diffraction (XRD), Fourier Transform Infra Red (FTIR) spectroscopy and Scanning Electron Microscopy (SEM) for formation and microstructure analysis at various GN−1 ratios. XRD results revealed that the crystallinity of MgFe2O4 is insensitive to GN−1 variations and fuel lean combustion also lead to appropriate MgFe2O4 phase formation. Thermo Gravimetric-Differential Thermal Analysis (TG-DTA) for the precursor gel demonstrated the occurrence of rapid chemical reaction between glycine and nitrates at around 194°C corresponding to ignition of precursors at this temperature. Transmission electron microscopy image for as prepared stoichiometric sample shows formation of nanoparticles of sizes from 28nm to 50nm. SEM images of MgFe2O4 nanoparticles at GN−1 ratio show remarkable change in microstructure regarding porosity and grain size. Room temperature magnetic measurements for stoichiometric sample show the magnetization (Ms) and remanence (Mr) of about 31.56emug−1 and 9.60emug−1 at ±10kOe respectively.

The Effect of Mechanical Activation on the Synthesis of MgFe2O4 from Mixtures of MgCO3· Mg(OH)2 · xH2O and FeC2O4 ·2H2O

The synthesis of MgFe2O4 has been attempted starting from mixtures of 4MgCO3 ·Mg(OH)2 · xH2O and FeC2O4 · 2H2O by combining mechanical activtion of the mixtures (by high-energy milling) with annealing at temperatures between 673 and 1073 K. TG measurements of mixtures of the precursors have been performed to assess the reaction mechanism, and to determine the minimum temperature where the two binary oxides (MgO and Fe2O3) are formed. X-Ray powder patterns of the milled / annealed mixtures have shown that MgFe2O4 is formed in an amorphous state already upon thermal treatment at 673 K, while annealing of the mixtures (not mechanically activated) at temperatures as high as 1473 K of the mixtures does not lead to the complete formation of MgFe2O4. The molar specific heat and the Curie temperature of the milled / annealed mixtures have been determined by DSC: MgFe2O4 is obtained provided that the annealing of the milled mixture is performed at temperatures as low as 873 K. The effect of the annealing temperature on the surface area of MgFe2O4 has been determined by BET measurements.

Reactive Growth and Properties of Epitaxial Fe-Mg-O Spinel Films on (100) MgO

ABSTRACTEpitaxial Mg-Fe-O spinel thin films were prepared by solid state reactions between MgO(lOO) substrates and thin films or vapors of iron oxide. Iron or iron oxide was deposited by electron beam evaporation in an oxygen background pressure onto a heated MgO crystal. The formation of MgFe2O4 at high temperatures proceeds via cation counter-diffusion in the fixed oxygen sublattice. Depending on substrate temperature, oxygen partial pressure and target material, epitaxial spinel films of different composition and magnetic properties were obtained. Crystal structure, composition and sub-micron morphology were investigated by RBS, XRD, TEM/SAED and EDX. Magnetic hysteresis loops were recorded at room temperature using the magneto-optic Kerr effect. Thickness interference fringes observed by XRD confirm the growth of smooth films. The main feature found in TEM plane view samples is a network of cation antiphase boundaries. The film composition measured by RBS varied from Fe2+ɛO3 films deposited at 340 °C substrate temperature to a solid solution of Fe2+E03 and MgFe2O4 at 500 °C to MgFe2O4 above 800 °C. EDX line-scans show a single phase MgFe2O4 spinel for a substrate temperature of 850 °C, without variation of composition with position or depth. At substrate temperatures higher than 800 °C Fe2+ was additionally dissolved in the MgO substrate, forming a FexMg1-xO solid solution.

Effects of Additives on Solid State Reaction. III. Effects of Halide Additives on the Formation of MgFe2O4

Abstract The promoting effects of halide additives on the formation of MgFe2O4 have been studied on the basis of both kinetic and thermoanalytical data. A mixture of MgO and α-Fe2O3 powder containing 10 mol% additive (LiF, NaF, MgF2, BaF2, NaCl, or KCl) and that without additive were isothermally heated in a vacuum (Po2=100–101 mmHg) in the temperature range 666–1018 °C. High temperature X-ray analysis on MgO–Fe2O3 and MgO–Fe2O3–additive systems was carried out at a heating rate of 3 °C/min in vacuo, (Po2=1−1 mmHg). In the case of fluoride, it seems that the reactions between the fluoride and the reactants, α-Fe2O3 or MgO, promote MgFe2O4 formation in the initial stage and that compounds produced by the initial reaction accelerate diffusion in the later stage. The same promoting mechanism seems to be applicable to the case of chloride additives. The interaction between solids of NaCl and α-Fe2O3 occurring just before the melting of NaCl seems to initiate MgFe2O4 formation.

Epitaxial Growth of Metal Oxides

Results of three methods of growing epitaxial layers of metal oxides and ferrites are reported. One of these is a vapor-solid displacement method which involves a partial or a total displacement of the metal ions in a given oxide by other metal ions present in gaseous form as halides. An example of this technique is the formation of MgFe2O4 from Fe3O4 via the reversible reaction MgCl2(gas)+Fe3O4(solid) lim 1000°CMgFe2O4(solid)+FeCl2(gas).Further displacement of iron by magnesium results in the formation of MgO. Single-crystal epitaxial films of MgO have been grown in this manner on single-crystal manganese ferrite and manganese zinc ferrite. The other two methods are variations of chemical transport which were used to grow single-crystal films of manganese ferrite on MgO substrates. One of these involves a close-space transport in which sintered manganese ferrite is used as a starting material and HBr as a transporting gas. In another variation, the oxides MnO and Fe2O3 are separately brominated in a stream of HBr diluted with helium; the deposition of ferrite takes place when water vapor is injected into the resulting gas mixture. By this technique, a wide range of compositions of manganese ferrite can be deposited which have varying magnetic properties and resistivities ranging over five orders of magnitude.