Fe2O3 System Research Articles

Electromagnetic wave absorption of polymeric nanocomposites based on ferrite with a spinel and hexagonal crystal structure

We have investigated composites designed for microwave absorption based on magnetic filler, composed of phases within the SrO–Fe2O3 system, embedded in a polyphenylene sulfide matrix with a concentration ratio of 80:20 by weight. The formation of the nanosized particles of SrFe12O19 and Fe3O4, as the principal magnetic phases was achieved via the co-precipitation of Sr2+/Fe3+ ions using different molar ratios. The various precursors obtained were calcined between 600°C and 900°C in air. The electromagnetic parameters of the composites were measured with a vector network analyzer at 400MHz to 32GHz. The results show that with a composite composed of a complex magnetic filler comprising the nanoparticles of two magnetically diverse phases, i.e., a spinel phase as the electromagnetic wave absorber in the lower GHz range and a hexagonal phase operating at a higher GHz range, above 32GHz, a microwave absorber with an broad absorption range can be prepared.

Effect of different additions on the crystallization behavior and magnetic properties of magnetic glass–ceramic in the system Fe2O3–ZnO–CaO–SiO2

This work pointed out the preparation of a magnetic glass–ceramic in the system Fe2O3·ZnO·CaO·SiO2. The base composition was designed to crystallize about 60% magnetite. The influence of adding TiO2, Na2O and P2O5 separately or as mixtures was studied. The DTA of the glasses revealed a decrease in the thermal effects by adding P2O5, TiO2 and Na2O in an increasing order. The X-ray diffraction patterns showed the presence of nanometric magnetite crystals in a glassy matrix after cooling from the melting temperature. The crystallization of magnetite increased by adding TiO2, and P2O5, respectively, and decreased by adding Na2O. Heat treatment was carried out for the glasses in the temperature range of 1000–1050°C, for different time periods, and led to the appearance of hematite and β-wollastonite, which was slightly increased by adding P2O5 or TiO2 and greatly enhanced by adding Na2O. Samples containing mixtures of TiO2, Na2O, and P2O5 showed a summation of the effects of those oxides. The microstructure of the samples was examined by using TEM, which revealed a crystallite size of magnetite to be in the range of 52–90nm. Magnetic hysteresis cycles were analyzed using a vibrating sample magnetometer with a maximum applied field of 10kOe at room temperature in quasi-static conditions. From the obtained hysteresis loops, the saturation magnetization (Ms), remanence magnetization (Mr) and coercivity (Hc) were determined. The results showed that the prepared magnetic glass–ceramics are expected to be useful for a localized treatment of cancer.

Electronic structure of bismuth ferrite and hematite single crystals: X-ray photoelectron study and calculation

The X-ray photoelectron spectra of the inner levels and valence bands of the surfaces of BiFeO3 and Fe2O3 single crystals have been measured using X-ray photoelectron spectroscopy on an ESCALAB 250 X-ray photoelectron microprobe with monochromatization of X-ray radiation of the AlK α line. The ab initio calculations have been performed by the full-potential pseudopotential method in terms of the density functional theory (Quantum-Espresso program package). The band structure and the total and partial densities of states have been calculated for the BiFeO3 and Fe2O3 systems. A comparison of the theoretical and experimental results has demonstrated good agreement between theory and experiment.

Simultaneous Pressure and Optical Measurements of Nanoaluminum Thermites: Investigating the Reaction Mechanism

This work investigates the reaction mechanism of metastable intermolecular composites by collecting simultaneous pressure and optical signals during combustion in a constant-volume pressure cell. Nanoaluminum and three different oxidizers are studied: CuO, SnO2, and Fe2O3. In addition, these mixtures are blended with varying amounts of WO3 as a means to perturb the gas release in the system. The mixtures with CuO and SnO2 exhibit pressure signals that peak on timescales faster than the optical signal, whereas themixtures containingFe2O3 do not show this behavior. The burn time is found to be relatively constant for bothCuOandSnO2, evenwhen a large amount ofWO3 is added. For Fe2O3, the burn time decreases asWO3 is added, and the temperature increases. The results are consistent with the idea that oxidizers such as CuO and SnO2 decompose and release gaseous oxidizers fast, relative to the burning, and this is experimentally seen by an initial pressure rise followed by a prolonged optical emission. In this case, the burning is rate limited by the aluminum, and it is speculated to be similar to the burning of aluminum in a pressurized oxygenated environment. For the Fe2O3 system, the pressure and optical signals occur concurrently, indicating that the oxidizer decomposition is the rate-limiting step.

Interface processes between iron containing aluminosilicate systems and simulated body fluid enriched with protein

The behaviour of iron containing aluminosilicate samples in Kokubo's simulated body fluid (SBF) and in SBF enriched with bovine serum albumin (BSA) has been investigated. Crystalline samples of (80-x)SiO2 X 20Al2O3 X Fe2O3 system, with x = 5, 10 or 15 mol%, obtained by sol-gel method and heat treated at 1200 degrees C in air for 24 h. Data on electrical conductivity, calcium, phosphorous and potassium concentrations in simulated body fluids after samples soaking in static regime at 37 degrees C, for several periods up to 14 days, were used to estimate the dynamics of these cations on the interface of aluminosilicate samples with SBF, and with SBF containing BSA. The UV-visible and fluorescence spectra recorded from the simulated body fluids after immersion of the investigated aluminosilicate samples evidence changes function on immersion time and Fe2O3 content.

Kinetics of Zn Removal from ZnO–Fe2O3–CaCl2 System

The chlorination and evaporation behaviors of Zn in the ZnO–Fe2O3–CaCl2 system was studied by gravimetry from 1173 to 1323 K and the effects of carrier gas flow rate, temperature and the initial Zn content of specimen on the chlorination rate were investigated. Moreover, thermodynamic calculation was carried out. Fe and Zn were separated because Zn was selectively chlorinated by CaCl2 from ZnO–Fe2O3 system and volatilized as ZnCl2 while Fe remained as oxide in chlorinated residue. From the chemical analyses, it was clarified that the volatilization of ZnCl2 mainly cause the weight loss of specimen. Based on these results, the chlorination mechanism and kinetic model were discussed. The weight change of specimen was expressed as a function of reaction time reasonably well by assuming the first order reaction with respect to presumed ZnCl2. Apparent activation energy of chlorination reaction, calculated from obtained reaction rate constants for various initial Zn contents, was in the range between 107 and 172 kJ/mol. It is considered the rate determining step of chlorination is chemical reaction, such as the reaction between ZnO and CaCl2, or the interfacial evaporation of ZnCl2 from the specimen.

Subsolidus area of the system CdO - V2O5 - Fe2O3

AbstractPhase diagrams in the subsolidus area of the systems FeVO4 - CdO and FeVO4 - Cd2V2O7 have been deduced using the results of XRD and DTA analyses. On the basis of these diagrams and some additional verifying research, a projection of the subsolidus area of the CdO - V2O5 - Fe2O3 system onto the plane that comprises the components’ concentration triangle has been presented. The H-type phase is the only phase formed in this system. It co-exists at equilibrium with other phases in six subsidiary subsystems.

Effect of Oxygen Partial Pressure on the Formation of Metastable Phases from an Undercooled YbFeO3 Melt Using an Aerodynamic Levitator

The Yb2O3–Fe2O3 system was studied to investigate the effect of oxygen partial pressure on the formation of metastable phases over a wide range of oxygen partial pressures from 105 to 10−1 Pa. Two kinds of metastable phases, with space groups of P63cm and P63/mmc, were found through rapid solidification of an undercooled YbFeO3 melt in an atmosphere with reduced Po2. The crystal structure of the as‐solidified samples changed from orthorhombic Pbnm to hexagonal P63cm and P63/mmc with decreasing Po2. X‐ray diffractometric and scanning electron microscopic results confirmed the existence of various phases in the as‐solidified samples. The stabilities of each phase were studied by annealing the bulk sample in the thermogravimetric–differential thermal analysis (TG‐DTA) furnace up to 1673 K, and the equilibrium phase diagram was constructed for the Yb–Fe–O system at 1473 K. TG analysis showed an increase of the sample mass during annealing and revealed that the existence of Fe2+, which has an ionic radius larger than that of Fe3+, decreases the tolerance factor and therefore destabilizes the perovskite structure.

Influence of iron on polymorphic composition and structural features of solid solutions of ZrO₂⋅Y₂O₃⋅Fe₂O₃ system

Influence of iron on polymorphic composition and structural features of solid solutions of ZrO₂⋅Y₂O₃⋅Fe₂O₃ system

Chemical reactions in reactive powder metal mixtures during shock compression

A heterogeneous chemical reaction model is proposed and used to describe shock-induced chemical reactions that occur in reactive granular mixtures during shock compression. The proposed heterogeneous model is intended for application in mesoscale simulations at locations where reactant particles are in contact. Previous studies have employed homogeneous reaction rate models with Arrhenius type kinetics, in which the material transport mechanism is not spatially dependent. In contrast, the spatially heterogeneous model explicitly describes material transport at the interface between the reactants. A transport mechanism permits reactants to flow through the product that is formed between the reactant grains during reaction. Diffusion mechanisms alone are too slow to describe shock-induced chemical reactions. Therefore, the stress contribution is included in the activation energy to affect both the diffusion rate and the surface reaction kinetics. The model is demonstrated for the 2Al+Fe2O3 system, in which the pressure and temperature initial conditions are obtained from a mesoscale simulation. Calculated temperatures are compared with previously reported experimentally measured shock temperatures, showing the capability of the proposed model to describe this shock-induced chemical reaction.

Distribution of P2O5 between Solid Dicalcium Silicate and Liquid Phases in CaO–SiO2–Fe2O3 System

In most cases, the slag used in hot metal dephosphorization is saturated with dicalcium silicate (C2S) and contains two phases—solid C2S and liquid. It is known that C2S and tricalcium phosphate (C3P) form a solid solution over a wide range of composition. The distribution ratio of P2O5 between the solid solution and the liquid slag phase has been reported to be very high. In order to determine the maximum possible concentration of P2O5 in the solid solution, the distribution ratio of P2O5 in slag containing a high concentration of P2O5 was measured in this study, and the influence of MgO and MnO on the distribution ratio was also investigated. CaO–SiO2–Fe2O3 slag containing up to 18% P2O5 was melted at 1873 K and then cooled to 1673 K at a rate of 10 K/min. During cooling, the solid solution of C2S and C3P precipitated from the liquid slag. A linear relationship, which was independent of the lime/silica ratio and P2O5 content, was found to exist between the distribution ratio of P2O5 and the T·Fe content. On the contrary, the concentration of P2O5 in the solid solution was strongly influenced by the lime/silica ratio and P2O5 content. If the P2O5 content was high enough and the T·Fe content was controlled to show the high distribution ratio, the concentration of C3P in the solid solution can be increased to 100%. No significant change was observed in the distribution ratio upon the addition of MgO and MnO.

A low-temperature phase diagram for ilmenite-rich compositions in the system Fe2O3-FeTiO3

aB stract An approximate low-temperature, metastable phase diagram is drawn for the system (1 – X) Fe2O3-(X)FeTiO3. It is based on published and new magnetic data from nine synthetic samples with bulk compositions in the range 0.6 < X < 1.0. Fields are plotted for (1) the paramagnetic phase (PM); the Fe2O3-rich ferrimagnetic phase (FM); (2) the FeTiO3-rich antiferromagnetic phase (AF); and (3) a re-entrant spin-glass phase (RSG). In addition, two subfields are plotted: (1) FM′, a subfield of the FM-phase, which occurs below a characteristic temperature TK, at which the magnetic susceptibility drops sharply on cooling, and (2) PM′, a subfield of the PM-phase (traditionally called superparamagnetic) forms below a sharp rise in susceptibility at TS, and exhibits measurable dispersion in the magnetic susceptibility at T < TS. The diagram is drawn with a bicritical point, Tλλ′, at X ≈ 0.87, T ≈ 39 K, which is the intersection of second-order magnetic phase boundaries for the paramagnetic → ferrimagnetic [PM(PM′) → FM] transition, TC(X), and the PM(PM′) → AF transition, TN(X). In addition, the RSG phase is plotted as one of four stable phases at Tλλ′, a construction that is not required by the phase rule, but is strongly favored by the physics of competition between the incompatible magnetically ordered structures of the FM- and AF-phases. These phase relations are at such low temperature as to be of little consequence for terrestrial magnetism, however, they may well be essential for interpreting the magnetism of the Moon, Mars, and other cold planets. These phase relations are also essential for the characterization of fine natural and synthetic intergrowths, and for understanding magnetic materials for low-temperature technologi cal applications.

Formation of ε-Fe2O3 Nanocrystals through Segregation in Mesoporous Silica Particles

Abstract Nanosized ε-Fe2O3 crystals with a diameter below 20 nm were successfully prepared at 600 °C in a mesoporous silica matrix. The formation of the metastable iron oxide occurred through nanoscale segregation in an immiscible SiO2–Fe2O3 system having a mesoporous structure. The nanocrystals incorporated into ca. 50 nm-size particles of the mesoporous silica exhibited a coercive field up to 8 kOe.

Mesoporous SBA-15 Supported Iron Oxide: A Potent Catalyst for Hydrogen Sulfide Removal

A novel silicate mesoporous material, SBA-15 supported Fe2O3, was synthesized by post-synthesis method via ultrasonic-assisted route. The desulfurization test from a gas mixture containing 0.1 vol% H2S was carried out over SBA-15 supported Fe2O3 in a fixed-bed system at atmospheric pressure and room temperature. The effects of the chemical nature of Fe2O3 and the textural properties of the material on desulfurization capacity were studied. Materials before and after the desulfurization test were characterized using nitrogen adsorption, XRD, TEM, FTIR, XPS, ICP and other standard methods. The characterization results suggest that modification process does not change the two-dimensional hexagonal mesostructure of SBA-15. Iron species disperses inside channels and the outside surface in the crystalline phase of iron oxide. The material with iron content of 31.3 wt% presented highest H2S uptake capacity. Structural properties of the material also play important roles in desulfurization performance besides the catalytic effects of iron oxide. The basic feature of material and enough oxygen supply are benefit for the reaction. SBA-15 supported Fe2O3 can be an effective alternative to capture H2S from gas streams.

Phase relations in the CoO–V2O5–Fe2O3 system in subsolidus area

Thermal properties of Co2FeV3O11 have been reinvestigated. It has been proved that this compound does not exhibit polymorphism. It melts incongruently at the temperature of 770±5°C and the phase with lyonsite type structure is the solid product of this melting. Phase relations in the whole subsolidus area of the CoO–V2O5–Fe2O3 system have been determined. The solidus area projection onto the component concentration triangle plane of this system has been constructed using the DTA and XRD methods. 15 subsidiary subsystems can be distinguished in this system.

A High‐Temperature Multinuclear NMR Study of Na3AlF6–FeO andNa3AlF6–Fe2O3 Melts

AbstractIn the Hall–Héroult process for the industrial production of aluminum, iron oxide impurities are known to lower the current efficiency as well as the metal quality. Iron can be present in the di‐ or trivalent form. The nature of dissolved FeIII and FeII species and the reactions taking place in cryolitic melts have been investigated by high‐temperature NMR spectroscopy. The evolution of 27Al, 23Na, and 19F NMR chemical shifts are reported in the Na3AlF6–FeO and Na3AlF6–Fe2O3 systems for different iron oxide contents. They express the formation of oxofluoroaluminate species. For the Na3AlF6–FeO system, the 19F signal appears only after 14 minutes at 1020 °C. The line position is shifted with heating time. This evolution is associated with a narrowing of the 27Al signal due to a decrease in the content of paramagnetic compounds in the sample. This effect is probably caused by the evaporation of an FeII compound, as already mentioned in the literature. For the Na3AlF6–Fe2O3 system we have never observed the 19F NMR spectra over the full heating time (ca. 30 min). This could be due to the influence of paramagnetic FeIII nuclei, probably in FeF63– species present in the melt. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)

Mössbauer spectroscopy study of mechanically alloyed Fe2O3–(Al, Co and WC) systems

Mossbauer spectroscopy revealed that a central hyperfine interaction doublet and an additional sextet characterized the appearance of new phases in the mechanically alloyed Fe2O3–Al and Fe2O3–Co systems. In the Fe2O3–Al system, the intensity of the central super paramagnetic doublet which represents small particles of iron, increased with increasing milling time from 5 to 30 h of mechanical alloying. The magnetic sextet characterizing hematite vanished in the room temperature Mossbauer spectra of samples produced after 25 h of mechanically alloying the 50% Fe2O3 and 50% Al system. In general XRD peak broadening was observed as a result of extensive material structural distortion and formation of small particles. Fe, Al2O3 and mixed iron–aluminium oxide phases were identified in the XRD patterns with a small persistence of the iron oxide up to 20 h of mechanically alloying the 1:1 system Al–Fe2O3. In the 50% Co–50% Fe2O3 system, a 55% abundant new phase CoFe2O4 was observed, from the Mossbauer spectra of the system. The presence of this new phase was confirmed by the XRD analysis. The high energy ball milling of WC–Fe2O3 revealed a more effective grinding compared to hematite alone. The hematite particles were reduced to nanosized particles.

Ceramic Pigments for Producing Black Glazes

A new black-color ceramic pigment has been developed on the basis of the CoO - Fe2O3 system under a decreased temperature of synthesis (1000 – 1200°C). The optimum temperature range of the spinel-forming reaction in the specified oxide system is determined. When the obtained pigment is introduced into raw glaze for sanitary ceramics in milling, the resulting glaze coatings have intense and stable black color within a sufficiently wide interval of firing temperatures.

Phase Transformations in Stabilized ZrO2 - Fe2O3 Compositions

Data on interactions in the ZrO2 - Fe2O3 system stabilized by oxides in a high-temperature form at 1750°C are obtained. Of all zirconia-based compositions, only magnesium-zirconium cubic solid solution enters into an active reaction with Fe2O3 to yield MgFe2O4. The solid solutions formed by ZrO2 with oxides of yttrium, neodymium, and calcium resist degradation by attack from Fe2O3; part of iron oxide undergoes dissolution in cubic ZrO2.

Characterization and transport properties of semiconducting Fe2O3–Bi2O3–Na2B4O7 glasses

Semiconducting oxide glasses of the system Fe2O3–Bi2O3–Na2B4O7 were prepared by a press-quenching method. Their DC conductivity was measured in the temperature range of 300–473K. In this temperature range, the DC conductivity increased from 10−9 to 10−5Scm−1 with increasing Fe2O3 concentration. Bi2O3 acted as a reducing agent for redox reaction during glass synthesis and affected the conductivity. Mössbauer results revealed that the relative fraction of Fe2+ increases with an increasing Fe2O3 concentration. The conduction mechanism was found to obey the non-adiabatic small polaron hopping model, and was mainly due to hopping between Fe-ions in the glasses. The small polaron coupling γp was calculated and found to be in the range of 17.06–26.25. For varying glass compositions, hopping mobility and carrier density were calculated and their values were in the range of 3.66×10−8–8.17×10−5 cm2V−1s−1 and 1.29×1017–5.04×1018 cm−3 at 400K, respectively.