Hydrothermal synthesis of Fe3O4 and α-Fe2O3 nanocrystals as anode electrode materials for rechargeable Li-ion batteries

This paper describes a facile, economical and environment-friendly hydrothermal method of fabricating Fe₃O₄ and α-Fe₂O₃ nanoparticles at 180 °C for 12 h, respectively. The as-obtained products were characterized in detail. X-ray powder diffraction and transmission electron microscopy were used to investigate the products’ properties of crystal form, size, and morphology. The results showed the Fe₃O₄ and α-Fe₂O₃ nanocrystals’ diameter were about 5 and 20 nm, respectively. Moreover, the electrochemical performances of the Fe₃O₄ and α-Fe₂O₃ nanoparticles as anode materials for Li-ion batteries were also evaluated. The first-discharge capacities of Fe₃O₄ and α-Fe₂O₃ nanocrystals were 1,380 and 1,280 mAh g^?1, and stabled about 96 and 75 mAh g^?1 after 20 cycles, respectively. These materials offer substantial promise for developing alternative, high capacity negative electrodes for safer lithium batteries as energy storage and conversion materials.     

A further investigation on the MnO2-Fe2O3 system roasted under CO-CO2 atmosphere

Investigations on the MnO₂-Fe₂O₃ system roasted in air has been reported in our previous work. This study further investigated the MnO₂-Fe₂O₃ system roasted under CO-CO₂ atmosphere. Extensive investigations were concentrated on the reduction of simplex iron oxides or manganese oxides, and little attention were paid on the reduction of MnO₂-Fe₂O₃ system regarding to interactive reactions between them. In this work, it was found that spinel-type Mn_xFe_3?xO₄ with high magnetism formed easily under CO-CO₂ atmosphere. The reduction and thermodynamic analyses of pure MnFe₂O₄ were also researched to better understand the reduction behaviors of MnO₂-Fe₂O₃ system. Phase study showed that a series of Mn-Fe composite oxides, including Mn_xFe_3?xO₄ and (MnO)_y(FeO)_1?y, generated during the reduction of MnO₂-Fe₂O₃ system. Mn_xFe_3?xO₄ was readily generated under CO content of 2.5–25?vol% at 1000?°C. With further increase of CO content, Mn_xFe_3?xO₄ was reduced to (MnO)_y(FeO)_1?y and then to MnO and metallic iron. Reduction of manganese oxides, iron oxides and manganese ferrites happened concurrently during the reduction of MnO₂-Fe₂O₃ system. And the reduction of MnO₂, Fe₂O₃, Fe₃O₄ and MnFe₂O₄ were compared by TG and thermodynamic analyses. In addition, the morphology evolution and magnetism change of the MnO₂-Fe₂O₃ system reduced under different CO contents were also studied.     

Influence of laser processing and magnetically active inorganic coatings on the dynamic magnetic properties of soft-magnetic materials

We have studied the influence of magnetically active inorganic coatings and local laser processing on grain-oriented steels (Fe-3% Si) and amorphous alloys (Fe₇₈Ni₁Si₉B₁₂ (2NSR), Fe₈₁Si₇B₁₂, and Fe₈₁Si₄B₁₃C₂). The potentialities of different types of laser processing have been assessed. Local laser processing and coating parameters have been shown to have a significant effect on the domain structure and electromagnetic properties of the materials. A reduction in coercive force and magnetic loss by 20–28% has been demonstrated.     

Study of the thermal decomposition of complex ferric formate, /Fe3(HCOO)6(OH)2/HCOO.4H2O

The thermal dissociation of /Fe₃(HCOO)₆(OH)₂/HCOO. 4H₂O has been investigated. Heat-treatment in vacuo and in inert medium led to the formation of magnetite whereas the final product of decomposition in air was ferromagnetic γ-Fe₂O₃. The latter contained an admixture of α-Fe₂O₃ the lowest amount of which (below 1%) was established when the process took place with restricted access of oxygen and a temperature of 275–300°C. The magnetic parameters of γ-Fe₂O₃ obtained under different conditions were studied. Electron microscopy and BET determinations of the specific surface area showed the mean diameter of the γ-Fe₂O₃ particles to be about 0,035 μm.     

Fe2O3 aggregation and formation of Ba-ferrite

The effect of Fe₂O₃ aggregation on the formation of Ba-ferrite (BaFe₁₂O₁₉) was studied. BaCO₃-Fe₂O₃ mixtures were prepared by using partial precipitation mixing and ball mill mixing methods in two separate batches. Thermogravimetry, x-ray diffraction analysis, scanning electron photomicrographs and magnetic hysteresis loop tracer analysis were used for characterization of the materials. It is shown that the aggregation state of Fe₂O₃ powders as well as the mixing methods have a significant effect on the formation of Ba-ferrite, sintering and magnetic properties.     

Synthesis of maghemite (γ-Fe2O3) nanoparticles by thermal-decomposition of magnetite (Fe3O4) nanoparticles

In this research work, we prepared γ-Fe₂O₃ nanoparticles by thermal-decomposition of Fe₃O₄. The Fe₃O₄ nanoparticles were synthesized via co-precipitation method at room temperature. This simple, soft and cheap method is suitable for preparation of iron oxide nanoparticles (γ-Fe₂O₃; Fe₃O₄). The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), vibrating sample magnetometer and differential scanning calorimeter (DSC). The XRD and FT-IR results indicated the formation of γ-Fe₂O₃ and Fe₃O₄ nanoparticles. The TEM images showed that the γ-Fe₂O₃ and Fe₃O₄ were spherical, and their size was 18 and 22 nm respectively. Magnetic properties have been measured by VSM at room temperature. Hysteresis loops showed that the γ-Fe₂O₃ and Fe₃O₄ nanoparticles were super-paramagnetic.     

Mössbauer,infrared and magnetic characterization of iron/cobalt species in cage structure alumino-silicates (zeolites)

Magnetic, Mössbauer, and I.R. studies on S.P. (superparamagnetic) or M.D. (multidomain) particles of Fe and Co species dispersed in cage structure aluminosilicates in relation to syngas (CO + H₂) Fischer-Tropsch conversion are reported. The difference in the catalytic activity of such species has been shown to depend upon their degree of dispersion. The carbonyl impregnation gave ultra-fine S.P. Fe₃O₄, whereas the nitrate impregnation gave M.D. Fe₃O₄ or α-Fe₂O₃. The active Fe₅C₂ component was converted to Fe₃C during the above reaction.     

MGH956合金TIG焊原位合金化对其组织性能的影响

采用TIG焊对氧化物弥散强化(ODS)高温合金MGH956进行原位合金化焊接.在相同的焊接条件下,填加两种不同的填充材料:与母材化学成分相似的基体填充材料,以及在基体填充材料基础上加入了合金元素Al和Fe2O3的Al-Fe2O3填充材料.通过对比分析两组试样在焊接过程中发生的原位合金化反应机理,及其对焊缝微观组织和力学性能的影响,研究原位合金化反应对ODS合金TIG焊接头组织与性能的影响.结果表明:在填充材料中加入Al和Fe2O3合金元素时,焊缝处的气孔数量明显减少,气孔尺寸也较为减小;焊缝中原位生成了新的增强相颗粒Al2O3、TiC以及YAlO3,同时,基体中的纳米级增强相Al-Y复合氧化物团聚倾向降低.力学性能试验结果表明,填加Al-Fe2O3填充材料时焊缝显微硬度值明显提高,接头抗拉强度达到了578 MPa,为母材强度的80.3%.     

Synthesis and magnetic property of silica/iron oxides nanorods

To better understand the shape dependent property of binary nanostructure, magnetic silica/iron oxides (α-Fe₂O₃ and Fe₃O₄) nanocomposites in rodlike shape have been synthesized using β-FeOOH nanorods as the starting material. The silica layer was coated on the surface of β-FeOOH nanorods, which were prepared by hydrolyzing of FeCl₃ under hydrothermal conditions. Silica/α-Fe₂O₃ nanorods were prepared by calcining silica/β-FeOOH nanorods, and magnetic silica/Fe₃O₄ nanorods were obtained after the reduction of silica/α-Fe₂O₃ nanorods in an inert atmosphere. The role of the silica layer during the phase transformation process was discussed. The magnetic properties of silica/iron oxides (α-Fe₂O₃ and Fe₃O₄) nanorods were investigated and the results revealed that silica/iron oxides nanorods showed higher magnetic saturation value compared with the reported data.     

Laser additive processing of functionally-graded Fe–Si–B–Cu–Nb soft magnetic materials

Laser additive manufacturing is a novel tool for processing compositionally-graded alloys that are challenging to process via a conventional route. This article discusses a novel combinatorial approach for assessing composition–microstructure–magnetic property relationships, using laser deposited compositionally-graded Fe–Si–B–Nb–Cu alloys (by changing the silicon to boron ratios). The microstructure of Fe–Si–B–Nb–Cu alloys with a lower Si to B ratio consists of dendritic α-Fe₃Si grains, with B and Nb partitioning to the inter-dendritic regions, resulting in the formation of Fe₃B grains. As the Si/B ratio increases, the (Fe, Nb) enriched eutectic phase was observed along with α-Fe₃Si grains; and no Fe₃B was observed. These microstructural changes with varying Si/B ratios significantly affect the magnetic properties of these laser-deposited soft magnetic alloys.     

Influence of synthesis variables on the properties of barium hexaferrite nanoparticles

Barium hexaferrite (BaFe₁₂O₁₉) nanoparticles were synthesized by sol–gel auto-combustion route. Prepared samples were sintered at 950 and 1100 °C with Fe³⁺/Ba²⁺ = 12 and 20 mol ratio. The formation mechanism of barium hexaferrite was investigated by using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses. In addition, the effect of temperature and Fe³⁺/Ba²⁺ mole ratio on BaFe₁₂O₁₉ formation and magnetic properties, and the effect of increasing the Fe³⁺/Ba²⁺ upon gel ignition and subsequent phase development were investigated. Finally the magnetic behavior was monitored with VSM. DSC studies showed that pure barium hexaferrite phase was formed from maghemite (γ-Fe₂O₃), without the formation of hematite (α-Fe₂O₃). Also, XRD results confirmed the formation of barium hexaferrite phase in non stoichiometric Fe/Ba ratio. VSM results showed that the saturation magnetization was decreased and coercivity increased with decreasing the grain size.     

Bi4Ti3O12–(Ni0.5Zn0.5)Fe2O4 dielectric–ferromagnetic ceramic composites synthesized with nanopowders

Bi₄Ti₃O₁₂ and (Ni_0.5Zn_0.5)Fe₂O₄ nanopowders were prepared by co-precipitation and hydrothermal methods, respectively. It was found that ethanolamine is effective as a precipitating agent in the synthesis of Bi₄Ti₃O₁₂ nanopowders via co-precipitation, and it also plays an important role in the synthesis of (Ni_0.5Zn_0.5)Fe₂O₄ nanopowders. Bi₄Ti₃O₁₂–(Ni_0.5Zn_0.5)Fe₂O₄ multiferroic ceramics were obtained by sintering the as-prepared nanopowders. Lower sintering temperatures (800–900 °C) were available when compared with the traditional solid state method and ceramic composites with higher density and limited interfacial reaction were obtained. The ceramics also showed lower dielectric loss and higher magnetic moments. Both the ferroelectric and magnetic phases preserve their individual properties in bulk composite form and thus, these types of composite ceramics appear to be good candidate multiferroic materials.     

One-step solution auto-combustion process for the rapid synthesis of crystalline phase iron oxide nanoparticles with improved magnetic and photocatalytic properties

We report the solution auto-combustion (AC) process for the rapid synthesis of Fe₃O₄ nanoparticles derived from the sol–gel (SG) process. The citric acid (CA) and tartaric acid (TA) is used as gelling agents in the SG process, where the citric acid turns into a fuel that combusts the gel and yields a highly magnetic crystalline phase Fe₃O₄ nanoparticles in one step with an average particle size of 50 nm. In contrast, the citric acid at different concentrations and tartaric acid at any concentrations do not lead to any combustion process and yield amorphous iron oxides. Upon annealing, these CA and TA derived iron oxide samples are turned to crystalline phase α-Fe₂O₃ particles. In contrast, the as-synthesized AC sample (i.e. Fe₃O₄) is oxidized to γ-Fe₂O₃ phase, which is confirmed from their respective XRD, Rietveld refinement and XPS studies. All the synthesized iron oxide phases showed broad visible light absorption. The room temperature M?H hysteresis curves obtained from VSM revealed that the Fe₃O₄ and α-Fe₂O₃/γ-Fe₂O₃ phases exhibit super-paramagnetic and ferromagnetic properties, respectively. The photocatalytic efficiencies of the samples are found to be in the order of Fe₃O₄ > γ-Fe₂O₃ > α-Fe₂O₃ with 98, 87, 79/73% degradation of rhodamine B dye at the end of 3 h and H₂ evolution rate over these systems is found to be 2.1, 1.3 and 0.92/0.89 mmol/h/g, respectively under simulated solar light irradiation. The photocatalytic recycle studies demonstrated that all the synthesized photocatalysts possess excellent chemical and photo-stabilities.     

Influence of different materials on the microstructure and optical band gap of α-Fe2O3 nanoparticles

Composites of hematite (α-Fe₂O₃) nanoparticles with different materials (NiO, TiO₂, MnO₂ and Bi₂O₃) were synthesized. Effects of different materials on the microstructure and optical band gap of α-Fe₂O₃ nanoparticles were studied. Crystallite size and strain analysis indicated that the pure α-Fe₂O₃ nanoparticles were influenced by the presence of different materials in the composite sample. Crystallite size and strain estimated for all the samples followed opposite trends. However, the value of direct band gap decreased from ～2.67 eV for the pure α-Fe₂O₃ nanoparticles to ～2.5 eV for α-Fe₂O₃ composites with different materials. The value of indirect band gap, on the other hand, increased for all composite samples except for α-Fe₂O₃/Bi₂O₃.     

Growth,magnetic properties and the effect of cobalt addition in metal-organic chemical vapour deposited (MOCVD) gamma iron oxide thin films for magnetic recording applications

The present study aims at investigating MOCVD technique for the deposition of magnetic oxide thin films using volatile metal-organic compounds as source material. A three-step scheme has been described to form γ-Fe₂O₃ phase starting from α-Fe₂O₃ films as-deposited in optically heated atmospheric cold wall CVD reactor. Growth of γ-Fe₂O₃ in a two-step process has been performed by depositing Fe₃O₄ phase directly by resistively heated low-pressure CVD (LPCVD) technique. Role of substrate temperature in controlling the oxidation leading to direct formation of metastable γ-Fe₂O₃ phase (single-step scheme) by atmospheric CVD technique has been described. A new mode of introduction of cobalt in the film, namely heterogeneous dispersion of cobalt in the γ-Fe₂O₃ matrix, has also been described. Crystallographic structure, microstructure and magnetic properties of the films have been studied in detail. Biaxial vector coil and high-temperature magnetic studies were carried out for determining the nature of anisotropy in the γ-Fe₂O₃ film. Growth of γ-Fe₂O₃ films in different schemes have been discussed from the studies of growth kinetics in a cold-and hot-wall-type reactor chambers.     

Structure switch between α-Fe2O3, γ-Fe2O3 and Fe3O4 during the large scale and low temperature sol–gel synthesis of nearly monodispersed iron oxide nanoparticles

With same procedure and same starting materials, nearly monodispersed α-Fe₂O₃, γ-Fe₂O₃ and Fe₃O₄ nanoparticles were synthesized on an large scale of about 60 g in a single reaction through a low temperature sol–gel route. The simple preparation process includes the reactions between FeCl₂ and propylene oxide in ethanol solution at boiling point to form a sol and the following drying of the sol. The different iron oxide phases can be obtained just by changing of the drying conditions for the sol solution. The strategy developed in this study offers important advantages over the conventional routes for the synthesis of α-Fe₂O₃, γ-Fe₂O₃ and Fe₃O₄ nanoparticles, showing potential for its application in industrial production of iron oxides.     

EXAFS investigation of iron local environment in metal-doped titania photocatalysts prepared by hydrothermal and high-energy ball milling routes

Iron local environment was investigated by EXAFS in Fe- and (Fe, Eu)-doped TiO₂ photocatalysts, prepared by hydrothermal and high-energy ball milling (HEBM) routes. In the case of the hydrothermal samples, the substitution of Ti⁴⁺ by Fe³⁺ ions was evidenced. For the samples prepared by HEBM, the iron environment corresponds to mixed metallic and oxidized (FeO, α-Fe₂O₃) configurations, without a clear evidence of iron incorporation into the TiO₂ lattice. This could be related to the catalyst contamination by iron microparticles detached from the balls during milling process.     

Formation Mechanism of Microstructure of Fe2(MoO4)3/Si3N4 Composite Powder by Hydrogen Reduction

观测Fe₂(MoO₄)₃和Fe₂(MoO₄)₃/Si₃N₄粉末H₂还原后的微结构特征, 研究了其微观组织结构的演变。 结果表明: Fe₂(MoO₄)₃还原后转变为20 nm厚的Fe薄层包覆Mo颗粒的微结构; Fe₂(MoO₄)₃/Si₃N₄粉末被还原后转变为两种结构形式颗粒粉末, 一种为3--5 nm的薄层Fe包覆在Mo颗粒表面粉末, 一种为粘附有纳米Fe--Mo氮化物、Si、Mo等颗粒的Si₃N₄粉末。Fe₂(MoO₄)₃/Si₃N₄粉末还原后形成这种微结构的原因是, 在还原过程中同时发生了两种反应: 一种是Fe₂(MoO₄)₃自身发生分解还原反应, 另一种是Fe₂(MoO₄)₃与Si₃N₄颗粒表面发生反应。     

Synthesis of phase pure iron oxide polymorphs thin films and their enhanced magnetic properties

The α-Fe₂O₃ thin film was prepared on liquid–vapor interface at room temperature by a facile and cost effective method, which was converted to Fe₃O₄ and γ-Fe₂O₃ films by reduction and oxidation process. The morphological and structural characterizations reveal the average crystallites size in α-Fe₂O₃, Fe₃O₄ and γ-Fe₂O₃ films 12.8, 9.2 and 19 nm with rms roughness 4.35, 4.60 and 8.21 nm, respectively. From magnetic measurements, the α-Fe₂O₃ thin film shows a room temperature super-paramagnetic behavior with saturation magnetization 18 emu/cm³, while Fe₃O₄ and γ-Fe₂O₃ thin films exhibit ferrimagnetic behavior with saturation magnetization values 414.5 and 148 emu/cm³, respectively. A significantly higher value of saturation magnetization is observed in α-Fe₂O₃ film, which is trusted due to the uncompensated surface spins in the film. The converted Fe₃O₄ film also shows enhanced saturation magnetization due to the reduction in antiphase boundaries, whereas the magnetization in γ-Fe₂O₃ film decreases comparatively. The magnetic property of the γ-Fe₂O₃ is explained on the basis of the Fe³⁺ ions vacancy at the octahedral position in its structure.     

Biomimetic fabrication of α-Fe2O3 with hierarchical structures as H2S Sensor

A facile sol–gel method is developed for the fabrication of α-Fe₂O₃ with quasi-honeycomb like structures inherited from Papilio paris butterfly wings. The exquisite hierarchical architecture is faithfully maintained in α-Fe₂O₃ from the skeleton of butterfly wings at the levels from macro to nano-scales. When used as a chemical sensor, the obtained α-Fe₂O₃ replica (P-α-Fe₂O₃) showed a much higher performance than that of the compared α-Fe₂O₃ nanoparticles synthesized under the same condition without biotemplate (S-α-Fe₂O₃). The P-α-Fe₂O₃-based sensor has a sensitivity of 19.2–50 ppm H₂S, which is four times more than that of S-α-Fe₂O₃, accompanied by a rapid response/recovery time within 1/10 s even at a relatively low working temperature of 180 °C. Compare to the S-α-Fe₂O₃, surface area of which cannot be detectable, the high sensing feature of P-α-Fe₂O₃ would be attributed to the relatively high-specific surface area 24.12 m²/g thus fabricated together with the unique 3D-network structures, which provide channel for the diffusion of H₂S. This strategy is expected to be used in fabrication of other kinds of metal oxide with unique structures for the potential application in gas sensor.