Synthesis and magnetic properties of platelet γ-Fe2O3 particles for medical applications using hysteresis-loss heating

Platelet γ-Fe₂O₃ particles of particle size less than 100 nm were prepared for medical applications that use the hysteresis-loss heating of ferromagnetic particles. The γ-Fe₂O₃ particles were obtained through the dehydration, reduction, and oxidation of platelet α-FeOOH particles, which were synthesized by the precipitation of ferric ions in an alkaline solution containing ethanolamine, and the crystals grown using a hydrothermal treatment. The γ-Fe₂O₃ particles contained dimples formed by the dehydration of α-FeOOH particles. The coercive force and the saturation magnetization of the γ-Fe₂O₃ particles were in the ranges 11.9 to 12.7 kA/m (150 to 160 Oe), and 70 to 72 Am²/kg (70 to 72 emu/g), respectively. The specific loss power of the γ-Fe₂O₃ particles, estimated from their temperature-raising property measured under a peak magnetic field of 50.9 kA/m (640 Oe) and at a frequency of 117 kHz, was 590 W/g. This value is higher than that of spherical cobalt-containing iron oxide particles having equivalent coercive force and saturation magnetization, reflecting the larger area of the minor hysteresis loop measured under a peak magnetic field of 50.9 kA/m (640 Oe).     

Surface Analysis of Inhibitor Film Formed by 4-Amino-N-(1,3-thiazol-2-yl) Benzene Sulfonamide on Carbon Steel Surface in Acidic Media

Inhibitive properties of the antibacterial sulfa drug sulfathiazole—IUPAC name being 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide—on the corrosion of carbon steel in 1.0 M HCl solution were investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Sulfathiazole is a good adsorption inhibitor, and the inhibition efficiency increases with increasing concentration. Adsorption is spontaneous and is best described by Temkin isotherm. XPS analysis showed, at this stage, that the main product of corrosion is a nonstoichiometric Fe³⁺ oxide/oxyhydroxide consisting of a mixture of Fe₂O₃, α, and γ-FeO(OH) and/or Fe(OH)₃, where α, γ-FeO(OH) is the main phase.     

Nanowires of iron oxides embedded in SiO2 templates

To attain the complete filling of the channels of MCM-41 with magnetite and maghemite, we have tried out an alternative method to the incipient wetness impregnation. The mesoporous material was instilled with a Fe-carrying organic salt after subjecting the matrix to a silylation treatment. Thus, a solid of 7.7 wt.% iron-loaded MCM-41 was obtained. Different subsequent thermal treatments were used to produce γ-Fe₂O₃ or Fe₃O₄. The Mössbauer and magnetic results show that after this method, the as-prepared composite displays a size-distribution of magnetic particles. It is mainly made up of fine particles that display a superparamagnetic relaxation at room temperature and get blocked at ≈42 K for the AC susceptibility time-scale measurements both for γ-Fe₂O₃ and Fe₃O₄ particles. For both samples, about 24% of larger iron-containing phases are magnetically blocked at room temperature. For the Fe₃O₄ particles, this fraction undergoes the Verwey transition at about 110 K; in addition, there is a minor Fe (III) fraction that remains paramagnetic down to 4.2 K.     

Preparation and photocatalytic property of α-Fe2O3 hollow core/shell hierarchical nanostructures

We report the preparation of a novel kind of α-Fe₂O₃ hollow core/shell hierarchical nanostructures self-assembled by nanosheets. A green precursor powder is first prepared using nontoxic and inexpensive FeCl₃ and urea in ethylene glycol by a surfactant-free solvothermal method at 160 °C for 15 h. The α-Fe₂O₃ hollow core/shell hierarchical nanostructures are obtained by the thermal treatment of the green precursor powder. The as-prepared α-Fe₂O₃ hollow core/shell hierarchical nanostructures are porous, and exhibit a good photocatalytic activity for the degradation of phenol. The samples are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).     

Vacancy ordering in γ-Fe2O3 small particles

The effect of particle size on the formation of vacancy-ordered superstructure in γ-Fe₂O₃ powders has been investigated by using X-ray, Mössbauer and chemical analyses. Powders of γ-Fe₂O₃ with different average particle size were prepared by chemical precipitation and subsequent heat-treatment. The X-ray diffraction intensity of the superlattice lines decreases with the particle size of γ-Fe₂O₃ and finally disappears at a particle-size between 300-175 Å, possibly around 200 Å. Therefore ordering of the cation vacancies in ultrafine γ-Fe₂O₃ particles is ruled out. Although the vacancies do not form an ordered structure, they do exclusively occupy B-sites.     

Pressure induced phase transition of nanocrystalline and bulk maghemite (γ-Fe2O3) to hematite (α-Fe2O3)

Phase transition and bulk moduli of bulk and nanocrystalline γ-Fe₂O₃ were studied using synchrotron X-ray diffraction under high pressure. Contrary to most other nanomaterials, nanocrystalline γ-Fe₂O₃ begins to transform into α-Fe₂O₃ at the same pressure as bulk γ-Fe₂O₃, which is caused by a special structure of γ-Fe₂O₃, in which there exist vacancies of crystal. It is believed that phase transition starts from a certain site of vacancy because of the stress concentration at vacancy sites. Compared to bulk material, nanocrystalline γ-Fe₂O₃ has a larger bulk modulus, which is ascribed to the large ratio of surface to volume.     

Analysis of atmospheric corrosion products of steel and coated steel by means of scattering Mössbauer spectrometry

Wearthering steels treated with and without zinc phosphate solution were exposed to atmosphere for 15 years and rust layers produced on the steels were analysed by scattering Mössbauer spectrometry (CEMS and XMS). γ-FeOOH, fine α-FeOOH, 5Fe₂O₃·9H₂O, γ-Fe₂O₃ and Fe₃O₄ were identified to be present in the rust formed on the steel without phosphate coating. Large particles of γ-Fe₂O₃ and Fe₃O₄ formed on the uncoated steel exposed to atmosphere in a position facing north on vertical plane. The layer structure of rust was affected by the position. The thin rust layer formed on the phosphate + carylite resin coated steel was considered to consist of γ-FeOOH, fine α-FeOOH, and fine γ-Fe₂O₃.     

One-step solution synthesis of Fe2O3 nanoparticles at low temperature

A new synthesis method of α-Fe₂O₃ nanoparticles was developed, in which the ferrous and ferric salts as well as polyaniline acted as the precursor and dispersant, respectively. From the investigation of X-ray diffraction and FT-IR spectra, the α-Fe₂O₃ nanoparticles can be directly prepared by the co-precipitation method without high-temperature calcining. Transmission electron microscope (TEM) and scanning electron microscope (SEM) observation revealed that the α-Fe₂O₃ nanoparticles had average diameters ranging from 30.0 to 75.0 nm. Compared with previous methods, this present method shows an easy processing and can be applied on the large-scale produce of α-Fe₂O₃ nanoparticles in one step.     

Thermal decomposition of almandine garnet: Mössbauer study

The thermal decomposition of almandine garnet from Zoltye Vody, Ukraine, has been studied using⁵⁷Fe Mössbauer spectroscopy. Room temperature Mössbauer spectrum of the initial powdered sample is characterised by one doublet corresponding to Fe²⁺ in dodecahedral position 24c. In the room temperature spectra of all heated almandine samples, a doublet corresponding to γ-Fe₂O₃ nanoparticles appeared. Depending on experimental conditions (heating temperature and time), the additional spectral lines of α-Fe₂O₃ and ε-Fe₂O₃ were observed in Mössbauer spectra. It is obvious that the thermal transformation of almandine garnet in air is related to the primary formation of γ-Fe₂O₃ superparamagnetic nanoparticles. γ-Fe₂O₃ nanoparticles are transformed into ε-Fe₂O₃ and consequently into α-Fe₂O₃ at higher temperatures. The mechanism and kinetics of the individual structural transformations depend on experimental conditions — mainly on the heating temperature and size of the particles.     

Relaxation structure analysis of Li inserted γ-Fe2O3

γ-Fe₂O₃ has a spinel structure with cation vacancy and is expected to perform as a favorable electrode material for secondary lithium-ion battery. When lithium is inserted electrochemically into γ-Fe₂O₃, prolonged potential change is observed after the insertion. In this study, we inserted various amount of Li into γ-Fe₂O₃ (x = 0.66, 1.1, 1.5 in terms of Li_XFe₂O₃), then made the circuit open, measured X-ray diffraction (XRD) patterns at various elapsed time, and analyzed the crystal structure change of γ-Fe₂O₃ with time by the Rietveld method. The X-ray Rietveld analysis revealed that the iron occupancy of 8a site decreased and that of 16c site increased with lithium insertion process and after lithium insertion, the iron occupancy of 8a site increased and that of 16c site decreased gradually with relaxation time. It is indicated that lithium prefer 8a site to occupy kinetically, on the other hand, prefer 16c site thermodynamically.     

Mössbauer study of iron oxide modified montmorillonite

Montmorillonite particles were modified by iron oxides using the precipitation process with the aim to monitor the differences in the structural and magnetic properties of intercalated and adsorbed Fe³⁺. The Mössbauer spectra recorded at 5 K in zero and 6 T external fields, IR spectra and TG curves measured in zero and 32 mT fields identified the ferrihydrite pillars in an interlayer space of the montmorillonite structure and γ-Fe₂O₃ nanoparticles adsorbed on the mineral surface. The temperature dependent Mössbauer spectra (25–300 K) reflect the superparamagnetic behaviour of maghemite nanoparticles and ferrihydrite pillars with the blocking temperatures of about 80 and 25 K, respectively.     

Effects of calcium and zinc on the adsorption of cobalt on γ-Fe2O3

The effects of calcium and zinc on the room-temperature coercivity of γ-Fe₂O₃ particles having cobalt ions adsorbed in 3M NaOH solution at 373K have been studied. When the Ca²⁺ ions are adsorbed on the γ-Fe₂O₃ prior to Co²⁺ ions adsorption, the coercivity of Co-modified γ-Fe₂O₃ significantly increases compared with that of γ-Fe₂O₃ modified only with Co²⁺ ions. In the case of Zn²⁺ ions, the coercivity of Co-modified γ-Fe₂O₃ is the same as that of γ-Fe₂O₃ modified only with Co²⁺ ions. The emission Mössbauer spectrum of⁵⁷Co²⁺ adsorbed on the surfaces of γ-Fe₂O₃ after pretreating with Ca²⁺ ions consists of a typical sextet of Fe³⁺ ions with hyperfine magnetic field, whereas those of γ-Fe₂O₃ modified only with Co²⁺ ions and with both Zn²⁺ and Co²⁺ ions show nonmagnetic components in addition to magnetic one. The effects of Ca²⁺ and Zn²⁺ ions on the adsorption of cobalt on the surface of γ-Fe₂O₃ are discussed from the viewpoint of site preference energy of cations in ferrite and distribution ratio of each cation.     

包钴型γ-Fe2O3磁粉矫顽力的研究

包钴型γ-Fe₂O₃磁粉分为包钴γ-Fe₂O₃(简记为Co-γ-Fe₂O₃)和包钴包亚铁γ-Fe₂O₃(简记为CoFe-γ-Fe₂O₃)两种,它们的矫顽力可比γ-Fe₂O₃磁粉的提高100至400Oe左右,本工作对这两种磁粉矫顽力增大的原因作了探讨,认为它们矫顽力增大的机制不同:CO-γ-Fe₂O₃矫顽力增大是由于表面包覆一层Co(OH)₂使表面各向异性增大,而CoFe-γ-Fe₂O₃则是由于表面包覆的是钴铁氧体,γ-Fe₂O₃与钴铁氧体之间发生耦合作用,使矫顽力增大。     

Dye-sensitized solar cells with 3D flower-like α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-decorated reduced graphenes oxide as photoanodes

For the first time, we report a one-step fabrication of an environment-friendly approach to synthesize flower-like α-Fe₂O₃ hierarchical nanoparticles (NPs)/reduced graphene oxide (RGO) hybrids by combining the graphene oxide (GO) with the growth of α-Fe₂O₃ NPs. The GO sheet which possesses the functional group, such as hydroxyl (–OH) and carbonyl groups (–OOH), can be easily incorporated with the petal of the flower-like α-Fe₂O₃ in ethanol and water solution through a solvothermal process, during which GO is reduced to RGO without the addition of any strong reducing agent or requiring any post-high-temperature annealing process. The as-prepared samples are loose and porous with flower-like structure, and the RGO hybrids were wrapped up uniformly on the sheet of α-Fe₂O₃ NPs. To demonstrate the potential applications, we have fabricated dye-sensitized solar cells (DSSCs) from the as-synthesized hierarchical flower-like α-Fe₂O₃/RGO and investigated it for the photoanode of DSSCs. Results show that the hierarchical α-Fe₂O₃/RGO solar cell exhibits improved performances in comparison with the free α-Fe₂O₃ NPs. The enhancement of photovoltaic properties is attributed to the unique porous nature and good conductivity which allow more efficient diffusion of I^? ions and facilitate the transfer of electron in the network.     

XRD and Mössbauer spectroscopy investigation of Fe2O3–Al2O3 nano-composite

Fe₂O₃–Al₂O₃ nano-composites were synthesized by sol–gel means. The properties of samples sintered at various thermal treatment temperatures were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). The experimental results show that the γ- to α-Al₂O₃ transformation occurs at lower temperature after iron oxide doping. The samples obtained at 1173 K contained poorly crystallized γ-Al₂O₃ phase and an amorphous iron oxide. When the temperature of heating was increased to 1373 K, the sample was composed of α-Fe₂O₃/α-Al₂O₃ nano-composite and some solid solution. A superparamagnetic phenomenon was observed until the thermal treatment temperature reached 1373 K.     

Magnetic Phase Transitions in Nanoclusters and Nanostructures

New phenomena – the first order magnetic phase transitions were observed in nanoclusters and nanostructures. For isolated ferrihydrite nanoclusters (d ～ 1–2 nm) in porous materials, for α-,γ-Fe₂O₃ nanoclusters (d ～ 20–50 nm) and for composites of nanostructured metallic Eu with additives of α-, γ-Fe₂O₃ nanoclusters and adamantane the critical temperatures (T _C, T _N) and magnetic cluster critical sizes (R _cr) were determined by means of thermodynamic models and Mössbauer spectroscopy. The first order magnetic phase transitions (jump-like) proceed by such a way when magnetization and magnetic order disappear by jump without superparamagnetic relaxation. According to thermodynamic model predictions the cluster and interface defects were suggested to play the main role in magnetic behavior. Thus, for the defective α-, γ-Fe₂O₃ nanoclusters, at R ≤ R _cr, the presence of the first order (jump-like) magnetic phase transition was described in terms of magnetic critical size of cluster. The action of high pressure (up to 2 GPa) with shear (120–240°) was effective for defect generation and nanostructure formation. For nanosystems including iron oxide nanoclusters, adamantane and metallic europium and subjected to shear stress under high pressure loading the critical value of defect density was estimated by the study of the character of magnetic phase transition. First-to-second-order (nanostructured metallic Eu) and second-to-first-order (α-, γ-ferric oxide nanoclusters) changes of the character of magnetic phase transition were shown to accompany by the variation of critical temperatures compared to the corresponding bulk values.     

Mössbauer spectroscopic properties of tin-doped iron oxides

The ⁵⁷Fe Mössbauer spectra recorded in situ from tin-doped Fe₃O₄ at elevated temperature in vacuo shows the Curie temperature to decrease with increasing concentrations of the dopant. Thermal treatment under oxidising conditions results in the initial formation of tin-doped γ-Fe₂O₃ which subsequently undergoes a phase transformation to tin-doped α-Fe₂O₃. ⁵⁷Fe Mössbauer spectroscopy at elevated temperatures shows the Néel temperature for tin-doped γ-Fe₂O₃ to be lower than that of pure γ-Fe₂O₃. The ¹¹⁹Sn Mössbauer spectra recorded from all the tin-doped iron oxides show the presence of a hyperfine magnetic field at the Sn⁴⁺ site which is more complex in the spectra recorded from tin-doped γ-Fe₂O₃ and α-Fe₂O₃.     

Study of the Morin Transition in Pseudocubic α-Fe2O3 Particles

We have studied the Morin transition in nanostructured pseudocubic α-Fe₂O₃ particles of about 1.8 μm side. The preparation was carefully chosen to obtain a system with a very narrow crystallite size distribution and particles of homogeneous morphology. Two samples were studied: one without thermal treatment (α-Fe₂O₃(ap)) and another annealed at 673 K in air for 12 h (α-Fe₂O₃(an)). Both were characterized by XRD, SEM, TGA and Mössbauer spectroscopy. The results indicate that the Morin transition is suppressed for α-Fe₂O₃(ap), however, α-Fe₂O₃(an) has a T _M ≈ 230 K and the transition is completed over a very narrow temperature range. These results are discussed in connection with the crystallite size, the cell parameters, and the presence of OH^? groups (hydrohematite) or incorporated water (protohematite).     

Solvothermal synthesis and characterization of α-Fe2O3 nanodiscs and Mn3O4 nanoparticles with 1,10-phenanthroline

α-Fe₂O₃ nanodiscs and Mn₃O₄ nanoparticles have been prepared by the 1,10-phenanthroline as complexing agent in the presence of sodium hydroxide under hydrothermal conditions. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) spectra. The average diameter of α-Fe₂O₃ nanodiscs is of 2 μm. In the case of Mn₃O₄ sample, the Mn₃O₄ crystallites are nanoparticles with an average size of 34 nm. A formation mechanism for the α-Fe₂O₃ and Mn₃O₄ nanomaterials was proposed.     

Fabrication, characterization, and measurement of viscosity of α-Fe2O3-glycerol nanofluids

Magnetic nanofluids, ferrofluids, are a special category of smart nanomaterials, consisting of stable dispersion of magnetic nanoparticles in different fluids. In this study, magnetic nanoparticles of hematite, α-Fe₂O₃, were prepared by solvothermal method using Fe(NO₃)₃ as a starting material. The nanoparticles were characterized by X-ray diffraction (XRD) and transmission electronic microscope (TEM).To the best of our knowledge, this is the first research on the rheological properties of nanofluids of α-Fe₂O₃ nanoparticles and glycerol. The experimental results showed that the viscosity of α-Fe₂O₃-glycerol nanofluids increases with increasing the particle volume fraction and decreases with increasing temperature. Our results clearly showed that the α-Fe₂O₃-glycerol nanofluids are non-Newtonian shear-thinning and their shear viscosity depends strongly on temperature. The experimental data were compared with some theoretical models. The measured values of the effective viscosity of nanofluids are underestimated by the theoretical models.