Fe3O4 Phase Research Articles

Raman identification of the different glazing technologies of Blue-and-White Ming porcelains

Shards of Blue-and-White Ming porcelain from shipwrecks of Portuguese ships found on the coasts of South Africa plus a shard from Mombasa (Kenya) were analyzed by optical microscopy, SEM-EDS and Raman microspectroscopy (458 nm). Whereas the Raman signature of porcelain body paste compositions which are based on mullite, quartz and an amorphous phase with the minor presence of anatase and feldspar are very comparable whatever the variable alumina content, at least two types of glazes are observed: a high-temperature soda-potassium glaze, and glazes richer in calcium and similar to a celadon glaze (with the possibility of wollastonite formation). The blue decoration is obtained with a material rich in manganese typical of the Ming productions. Some shards exhibit a two-layer glaze and the blue decoration is either placed under-glaze, or in-glaze as found in the Vietnamese productions of the same period. Previous assignments of the Raman signature of feldspar to cobalt aluminate are now not favoured (blue colour is obtained with Co2+ ions dissolved in the glassy silicate) and several black spots exhibit the characteristic spectrum of an epsilon Fe2O3 phase being present.

γ-FeO(OH) with multiple surface terminations: Intrinsically active for the electrocatalytic oxygen evolution reaction.

Due to poor conductivity, the electrocatalytic performance of independently prepared iron oxy-hydroxide (FeO(OH)) is inferior whereas FeO(OH) derived in situ from the iron based electro(pre)catalyst shows superior performance in the oxygen evolution reaction (OER). Use of mixed phase FeO(OH) and/or incorporation of CoII/NiII metal into the FeO(OH) structure has also been demonstrated as a convenient approach to achieve high OER activity. Nevertheless, preparation of phase-pure, albeit active FeO(OH) material with fair electrochemical performance remains a perdurable challenge. Moreover, the role of the crystalline phase and its surface structure in controlling the OER activity is still unclear. Herein, a simple synthetic protocol has been developed to prepare a series of phase-pure α-FeO(OH) (goethite) and γ-FeO(OH) (lepidocrocite) materials. By changing the reaction conditions such as iron salt and reaction temperature, the crystallinity as well as the phase of the oxy-hydroxide material have been varied. The isolated α- and γ-FeO(OH) materials with different crystallinity were thereafter deposited on nickel foam (NF) for alkaline OER study. The recorded overpotential value at 10 mA cm-2 has been found to be dependent on the phase and crystallinity of the FeO(OH) materials. The partially crystalline γ-FeO(OH) isolated at room temperature (γ-FeO(OH)@RT) turns out to be the most active with a lowest overpotential of 260 mV at 10 mA cm-2 and a long term stability of 12 h. The γ-FeO(OH)@RT/NF anode can furnish high current densities like 50-100 mA cm-2 which makes this anode distinct from the previously reported FeO(OH) materials. Detailed electrochemical study suggested that the fair activity of the γ-FeO(OH)@RT arises due to a facile electrokinetics as evident from the small Tafel slope and charge transfer resistance (Rct value from the Nyquist plot). Owing to the superior activity of the γ-FeO(OH)@RT/NF, the anode can further be incorporated into an overall water splitting electrolyzer that can operate at a cell potential of 1.68 V. The microscopic characterization provides concrete evidence in support of the polycrystallinity of the γ-FeO(OH)@RT. The superior activity of the γ-FeO(OH)@RT perhaps can be correlated to its polycrystalline nature with more defect edges, the presence of a large exposed surface and random atomic arrangements. The highest degree of multiple surface active terminals (-O, -OH and -Fe) available in this polycrystalline γ-FeO(OH) perhaps makes the catalyst more active compared to the crystalline FeO(OH) analogue with a limited number of surface terminals. From a comparative study with a series of FeO(OH) materials, this work highlights a direct relationship between the surface functionality and the electrochemical activity of the FeO(OH) material.

Influence of aeration rate and method of process activation on the degree of purification of zinc-containing waste water by ferritization

The aeration rate for the degree of purification of highly concentrated galvanic wastewater from zinc and ferrum ions was investigated using various activation methods. It is shown that the intensity of aeration has a significant effect on the quality of wastewater treatment and the characteristics of water treatment sludge. The efficiency of the use of an energy-saving method for activating the ferritization process with the use of electromagnetic pulses for the extraction of zinc ions from wastewater has been confirmed. It was determined that with an increase in the aeration rate to 3.5 dm3/min per 1 dm3 of the reaction mixture and the use of thermal activation of the process, the residual concentration of zinc ions remains within the range of 0.12÷0.2 mg/dm3. In this case, the concentration of ferrum ions decreases to values of 0.08÷0.14 mg/dm3. It was found that at an aeration rate of 2.5 dm3/min and the use of pulsed electromagnetic (EMP) activation, the residual concentrations of heavy metal ions decrease to values of 0.08÷0.16 mg/dm3. Comparison of the results indicates the advisability of using low rates of aeration of the reaction mixture. This, together with the use of resource-saving EMR process activation, allows to achieve a significant reduction in energy costs. The quantitative phase composition of ferritization precipitates was determined, in which the crystalline phases of zinc ferrite Zn2Fe2O4 and magnetite Fe3O4, as well as ferrum oxyhydroxide FeO (OH) and sodium sulfate Na2SO4, prevail. It is found that with an increase in the volumetric aeration rate, the proportion of the ferrite phase increases. At an aeration rate of 2.0 dm3/min, more than 85 % of the zinc ferrite phase was found in the sediments. Taking into account the qualitative and quantitative composition of precipitates, it is recommended to use them in the production of building materials. The experimental results obtained make it possible to provide a comprehensive processing of liquid galvanic waste.

Effects of theTiB2-SiC Volume Ratio and Spark Plasma Sintering Temperature on the Properties and Microstructure of TiB2-BN-SiC Composite Ceramics

TiB2-BN composite ceramics combine excellent electrical conductivity, thermal shock resistance, high-temperature resistance, corrosion resistance, and easy processing of TiB2 and BN. However, in practical applications, their high-temperature oxidation resistance is poor and the resistivity distribution is uneven and changes substantially with temperature. A TiB2-BN-SiC composite ceramic with stable and controllable resistivity was prepared by introducing SiC into the TiB2-BN composite ceramics. In this work, spark plasma sintering (SPS) technology was used to prepare TiB2-BN-SiC composite ceramics with various TiB2-SiC ratios and sintering temperatures. The samples were tested by XRD, SEM, and thermal and mechanical analysis. The results show that as the volume ratio of TiB2-SiC was increased from 3:1 to 12:1, the resistivity of the sample decreased from 8053.3 to 4923.3 μΩ·cm, the thermal conductivity increased from 24.89 to 34.15 W/(m k), and the thermal expansion rate increased from 7.49 (10−6/K) to 10.81 (10−6/K). As the sintering temperature was increased from 1650 to 1950 °C, the density of the sample increased, the mechanical properties were slightly improved, and the resistivity, thermal expansion rate, and thermal conductivity changed substantially. The volume ratio and sintering temperature are the key factors that control the resistivity and thermal characteristics of TiB2-SiC-BN composite ceramics, and the in situ from liquid phases of FeB and FeO also promotes the sintering of the TiB2-BN-SiC ceramics.

FABRICATION AND WEAR BEHAVIOR OF PEC/N HARDENED LAYER ON PURE IRON

In this paper, the antifriction carbonitriding (PEC/N) layers were prepared on pure iron by cathodic plasma electrolytic treatment (PET) in glycerin and carbamide aqueous solution under 360[Formula: see text]V for 1, 3 and 10[Formula: see text]min. Influence of discharge time on morphology, structure, surface roughness and microhardness of PEC/N layer was analyzed. The tribological performance of the PEC/N layer, growth mechanism and diffusion process during PEC/N treatment was investigated. The thickness of the PEC/N layer grew to 48[Formula: see text][Formula: see text]m for 10[Formula: see text]min treatment and the growth of the saturation layer met the parabolic law. The highest microhardness of the surface was up to 811 HV, which was 5 times of that of iron substrate. The PEC/N layer consisted of [Formula: see text]-Fe, Fe[Formula: see text]N, Fe4N, Fe3C, Fe5C2 phases and a little FeO phase. The wear rate of the PEC/N layer reduced by five-sixes comparing with the iron substrate and the surface of the wear track was much smoother. The temperature close to the surface during PEC/N fitted by the tested temperature values inside the sample was 801∘C (1074[Formula: see text]K), and the combination diffusion rate of C and N into pure iron during PET at 360[Formula: see text]V reached [Formula: see text][Formula: see text]m2/s. The electron temperature fluctuates between 3000[Formula: see text]K and 8000[Formula: see text]K. The antifriction PEC/N layer displayed a very good wear resistance and the higher diffusion rate makes plasma electrolytic carbonitriding a very effective technique for surface modification of pure iron.

Effects of Boriding, Nitrocarburizing, Nitriding and Post-oxidation Treatments on The Tribological Properties of DIN 32CrMoV12-10 Steel

In this study, the effect of different surface treatments was investigated to improve the friction and wear properties of DIN 32CrMoV12-10 steel. For this purpose, chrome plating, boriding, nitrocarburizing+oxidation, nitriding+oxidation processes were applied to the samples prepared from DIN 32CrMoV12-10 steel. After the procedures, the structural, morphological and mechanical properties of the samples were determined by XRD, SEM, hardness measurement device and profilometer. In order to determine the tribological properties of the samples, pin-on-flat wear tests were carried out. It was observed that a chromium layer was formed on the surface of the material after chrome plating. In boronized samples, it was observed that a boron layer was formed on the surface of the material and a diffusion layer was formed below it. The formed layers contain Fe2B and FeB phases. In nitrocarburized+oxidized and nitrided+oxidized samples, it was observed that the oxide layer on the material surface, a white layer just below it and a diffusion zone extending to the inner parts of the material were formed. The oxide layer formed on the surface consists of Fe2O3 and Fe3O4 phases, while the white layer and diffusion layers consist of ε-Fe2-3N and γ'-Fe4N phases. Due to the increased plastic deformation resistance with oxide layers, hard nitride phases and diffusion layers, the highest wear resistance was obtained from nitrocarburized+oxidized and nitrided+oxidized samples.

Raman area- and thermal-mapping studies of faceted nano-crystalline α-Fe2O3 thin films deposited by spray pyrolysis

Different advanced techniques including Raman area mapping and Raman thermal imaging have been used to investigate various properties of large area iron oxide thin films deposited by spray pyrolysis on a large area of crystalline silicon substrates under controlled external parameters. Morphological studies reveal that the obtained films acquired the lateral faceted crystalline structure of iron oxide. Together, the Raman and SEM images confirm the presence and large area distribution of the nano crystals of Fe2O3 phase. Thermal Raman imaging reveals that the obtained iron oxide thin films are robust and thus can be used for appropriate technological applications like electromagnetic shielding.

Spin Polarization-Assisted Dopant Segregation at a Coherent Phase Boundary.

Coherent phase boundaries are widely expected as segregation-free boundaries due to their low interfacial energies and lack of trapping sites for impurities. Here, we report an equilibrium segregation of W atoms at fully coherent terraces of a Fe3O4 (111)/Fe2O3 (0001) phase boundary that was never expected previously. Through comparison of pristine and W-doped Fe3O4/Fe2O3 phase boundaries, it is revealed that the spin polarization of O atoms at the interface plays an important role in the periodic segregation of W atoms. Unusual spin-polarized O atoms with large magnetic moments are periodically arranged in the interfacial O plane of the pristine phase boundary. After doping of W at this boundary, W atoms will selectively substitute the Fe atoms of Fe2O3 that directly bond with three spin-polarized O atoms, thereby resulting in the complete neutralization of the magnetic moments of the spin-polarized O atoms. These findings reveal that coherent phase boundaries are able to trap impurities and local spin polarization is one of the driving forces for dopant segregation, suggesting that elemental doping is an efficient way for tailoring the physical properties of boundaries in magnetic materials and devices.

Performance of reactively co-sputtered titanium chromium nitride films in artificial saliva: Corrosion protection and reduction in the release of potentially toxic elements

Having been deposited on 304 stainless steel (SS304) substrates by RF reactive co-sputtering, 1 μm-thick Ti-Cr-N films were annealed at 400 °C and 700 °C. Accordingly, nitride phases of TiN and CrN, and as a result of the lost capability as an oxygen diffusion barrier, oxide phases of Fe2O3, Cr2O3, and TiO2 formed after the annealing process at 700 °C. For short-term immersion (1 h), the corrosion testing illustrated that the film annealed at 400 °C shows greater corrosion resistance than the other films and SS304. For long-term immersion (30 days), all the films demonstrated greater corrosion resistance than SS304, with the as-deposited film delivering the best performance. It was found that protective passivation layer formation, porosity closures, and surface characteristics such as pits, trenches, grooves, cracks, and protuberances govern the corrosion behavior differences. The surface micrographs imply that pitting corrosion and superficial filiform corrosion are among the underlying mechanisms affecting the surfaces. Finally, given the concerns about the capability of SS304 to release toxic elements such as chromium, it was determined that not only can Ti-Cr-N films increase the corrosion resistance of SS304 but also they can reduce the release of chromium by almost 67% in the long-term exposure.

Obtaining of hematite from industrial steel waste using dry-milling and high temperature

In this work, the mill scale (MS) of hot rolling, a waste of steel processing, composed by a complex mixture of iron oxides, is transformed in a nanocrystalline powder containing only the hematite (α-Fe 2 O 3 ) phase. For that, the MS was dry-milled using a high-energy ball mill for 30 min and heat-treated up to 1200 °C for 25 min. The samples of this study were characterized by X-ray diffraction, Thermogravimetric Analysis and Vibrating Sample Magnetometry. The milling process decreases the amount of FeO phase content (FeO:Fe 3 O 4 phase ratio from 3:1 to 1:1), reduces the average crystallite size and increases the micro-strain of the iron oxides. The high-temperature experiments showed the complete transformation of the Fe 3 O 4 and FeO nanophases to the nanocrystalline α-Fe 2 O 3 with average crystalline domains greater than 180 nm after few hours of heat treatment. The thermal expansion coefficient of the α-Fe 2 O 3 nanophase was obtained considering anisotropic effects, mainly for the a -axis. Thermogravimetric analysis shows the oxidation of Fe 3 O 4 to α-Fe 2 O 3 . The milled MS sample shows a mixed magnetism that transforms to a weak ferromagnetism (or antiferromagntism) after thermal treatment. The temperature of the Morin transition of the α-Fe 2 O 3 nanophase at 110 K and a second magnetic transition at 50 K, related to a spin-glass state, seems to be strongly affected by the nanometric size of crystalline domains (about 180 nm).

Multiferroic behavior of the functionalized surface of a flexible substrate by deposition of Bi2 O3 and Fe2 O3.

Thin films of bismuth and iron oxides were obtained by atomic layer deposition (ALD) on the surface of a flexible substrate poly(4,4'-oxydiphenylene-pyromellitimide) (Kapton) at a temperature of 250°C. The layer thickness was 50 nm. The samples were examined by secondary-ion mass spectrometry, and uniform distribution of elements in the film layer was observed. Surface morphology, electrical polarization, and mechanical properties were investigated by atomic force microscope, piezoelectric force microscopy, and force modulation microscopy. The values of current in the near-surface layer varied in the range of ±80 pA when a potential of 5V was applied. Chemical analysis was performed by X-ray photoelectron spectroscopy, where the formation of Bi2 O3 and Fe2 O3 phases, as well as intermediate phases in the Bi-Fe-O system, was observed. Magnetic measurements were carried out by a vibrating sample magnetometer that showed a ferromagnetic response. The low-temperature method of functionalization of the Kapton surface with bismuth and iron oxides will make it possible to adapt the Bi-Fe-O system to flexible electronics.

Synthesis and characterization of magnetic Fe3O4@Creatinine@Zr nanoparticles as novel catalyst for the synthesis of 5-substituted 1H-tetrazoles in water and the selective oxidation of sulfides with classical and ultrasonic methods

Tetrazoles and sulfoxide compounds have a wide range of applications in industries and are of great expectation to be environmentally friendly and cost-effective. This paper reports the introduction of zirconium supported on Fe3O4 nanoparticles through creatinine post-functionalization modification of Fe3O4 (Fe3O4@Creatinine@Zr). The Fe3O4@Creatinine@Zr was characterized by a vibrating sample magnetometer, X-ray powder diffractometry, Fourier transforms infrared, scanning electron microscope, energy dispersive X-Ray analysis, thermogravimetric analysis, and inductively coupled plasma. Fourier transform-infrared spectroscopy results confirmed that creatinine was successfully immobilized on the surface of Fe3O4Cl with the presence of ν (C = N), and ν (C = O) bands of creatinine. X-ray diffraction data confirmed that the crystalline phase of Fe3O4 was not destroyed after modification. Vibrating sample magnetometer analysis showed that the saturation magnetization of the Fe3O4@Creatinine@Zr was 28.6 emu/g. The SEM-EDX results revealed that the zirconium complex was successfully incorporated into the structure of Fe3O4.This catalyst displayed high catalytic performance in the synthesis of 5-substituted 1H-tetrazoles and the selective oxidation of sulfides with classical and ultrasonic methods. The catalyst conferred strong Lewis's acidity sites for the activity and selectivity of the reactions. The obtained results showed that the fast oxidation of sulfides was happened by 0.2 mmol g −1 of zirconium that immobilized on the Fe3O4 nanoparticle at optimum condition (Sulfide (1 mmol), H2O2 (0.6 mL), ethanol (3 mL) and catalyst (Fe3O4@Creatinine@Zr, 60 mg) at room temperature.) The results showed that ultrasonic was an appropriate method for the oxidation of sulfides to the related sulfoxide at the optimum condition. The 5-substituted 1H-tetrazoles were afforded at optimum condition (Nitrile (1 mmol), NaN3 (1.2 mmol), H2O (3 mL), catalyst (100 mg) at 90 °C). The catalyst was separated by simple recovery and reused for seven periods without any remarkable decrease in the catalysis activity and selectivity. The output of this research can open a window for the synthesis the other organic materials under mild condition.

Effect of calcium solubility on structural, microstructure and magnetic properties of SrFe12O19

The synthesis of Sr1-xCaxFe12O19 (x = 0.0–1.0 at increments of 0.1) samples is reported via a sol-gel auto-combustion process. XRD data for Sr1-xCaxFe12O19 samples calcined at different temperatures indicates a) single-phase formation up to x = 0.20 in samples calcined at 900 °C, b) an increase in calcium solubility to 50 atomic % (x = 0.50) at 1200 °C, c) a decrease in lattice parameters and cell volume with increasing ‘x’ and d) the presence of segregated α–Fe2O3 phase for x > 0.50 at 1200 °C and for x ≥ 0.20 at 900 °C. As the maximum Ca solubility in SrM (SrFe12O19) phase has been observed at 1200 °C, most of the other characterizations have been performed on these samples only. An increase in grain size with ‘x’ was revealed in FESEM micrographs. Magnetic measurements show that in the x = 0.50 sample the maximum saturation magnetization (Ms) value is ≈ 70.67 emu/g. Coercivity (Hc) decreases monotonically, with an increase in Ca content in SrM (SrFe12O19), from 3822 Oe (x = 0.00) to 2045 Oe (x = 0.50). Among the samples calcined at different temperatures, coercivity (Hc) decreases monotonically from 5650 Oe to 3128 Oe with an increased calcination temperature for samples of x = 0.20. The samples could be vital for magnetic recording and applications as permanent magnets due to their excellent magnetic properties.

Ionic Porous Aromatic Framework as a Self-Degraded Template for the Synthesis of a Magnetic γ-Fe2O3/WO3·0.5H2O Hybrid Nanostructure with Enhanced Photocatalytic Property.

An ionic porous aromatic framework is developed as a self-degraded template to synthesize the magnetic heterostructure of γ-Fe2O3/WO3·0.5H2O. The Fe3O4 polyhedron was obtained with the two-phase method first and then reacted with sodium tungstate to form the γ-Fe2O3/WO3·0.5H2O hybrid nanostructure. Under the induction effect of the ionic porous network, the Fe3O4 phase transformed to the γ-Fe2O3 state and complexed with WO3·0.5H2O to form the n-n heterostructure with the n-type WO3·0.5H2O on the surface of n-type γ-Fe2O3. Based on a UV-Visible analysis, the magnetic photocatalyst was shown to have a suitable band gap for the catalytic degradation of organic pollutants. Under irradiation, the resulting γ-Fe2O3/WO3·0.5H2O sample exhibited a removal efficiency of 95% for RhB in 100 min. The charge transfer mechanism was also studied. After the degradation process, the dispersed powder can be easily separated from the suspension by applying an external magnetic field. The catalytic activity displayed no significant decrease after five recycles. The results present new insights for preparing a hybrid nanostructure photocatalyst and its potential application in harmful pollutant degradation.

A Milestone in the Chemical Synthesis of Fe3O4 Nanoparticles: Unreported Bulklike Properties Lead to a Remarkable Magnetic Hyperthermia.

Among iron oxide phases, magnetite (Fe3O4) is often the preferred one for nanotechnological and biomedical applications because of its high saturation magnetization and low toxicity. Although there are several synthetic routes that attempt to reach magnetite nanoparticles (NPs), they are usually referred as “IONPs” (iron oxide NPs) due to the great difficulty in obtaining the monophasic and stoichiometric Fe3O4 phase. Added to this problem is the common increase of size/shape polydispersity when larger NPs (D > 20 nm) are synthesized. An unequivocal correlation between a nanomaterial and its properties can only be achieved by the production of highly homogeneous systems, which, in turn, is only possible by the continuous improvement of synthesis methods. There is no doubt that solving the compositional heterogeneity of IONPs while keeping them monodisperse remains a challenge for synthetic chemistry. Herein, we present a methodical optimization of the iron oleate decomposition method to obtain Fe3O4 single nanocrystals without any trace of secondary phases and with no need of postsynthetic treatment. The average dimension of the NPs, ranging from 20 to 40 nm, has been tailored by adjusting the total volume and the boiling point of the reaction mixture. Mössbauer spectroscopy and DC magnetometry have revealed that the NPs present a perfectly stoichiometric Fe3O4 phase. The high saturation magnetization (93 (2) A·m2/kg at RT) and the extremely sharp Verwey transition (at around 120 K) shown by these NPs have no precedent. Moreover, the synthesis method has been refined to obtain NPs with octahedral morphology and suitable magnetic anisotropy, which significantly improves the magnetic hyperthemia performance. The heating power of properly PEGylated nano-octahedrons has been investigated by AC magnetometry, confirming that the NPs present negligible dipolar interactions, which leads to an outstanding magnetothermal efficiency that does not change when the NPs are dispersed in environments with high viscosity and ionic strength. Additionally, the heat production of the NPs within physiological media has been directly measured by calorimetry under clinically safe conditions, reasserting the excellent adequacy of the system for hyperthermia therapies. To the best of our knowledge, this is the first time that such bulklike magnetite NPs (with minimal size/shape polydispersity, minor agglomeration, and exceptional heating power) are chemically synthesized.

Highly efficient and stable catalytic reactivities of iron(-oxide) incorporated carbide nanofiber composite for environmental and bio-medical application

In this study, we applied iron (-oxide) incorporated carbide nanofiber composites as heterogeneous catalysts with wide visible-light absorption ability, catalytic reactivity, and catalytic stability for the highly efficient decomposition performance. Notably, water vapor activated iron (-oxide) incorporated carbide nanofiber catalyst (Act-Fe-CNF) showed high crystalline Fe3O4 phase, saturation magnetization point (17.76 emu/g), and large surface area (508.2 m2/g). In water vapor activation, Fe3C particles inside carbide nanofiber oxidized and aggregated to larger Fe3O4 particles, thereby forming a meso/macroporous structure and improving surface area offering more available active sites for catalytic reactivity. Under both UV-/real solar-light irradiation, it was demonstrated that the Act-Fe-CNF catalysts exhibited unprecedentedly excellent removal capabilities (>98%, [k] = 4.06 h−1) for rhodamine B, leading to complete water purification. Interestingly, the AF-CNFs catalysts also showed strong antimicrobial activities against gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) under incandescent-light irradiation. These results indicated that the Act-Fe-CNF catalysts might have utility in important environmental and bio-medical applications.

Temperature and phase transitions of laser-ignited single iron particle

The combustion behavior of single laser-ignited iron particles is investigated. Transient particle radiant intensities at 850 nm and 950 nm are measured by post-processing recorded high-speed camera images using an in-house developed particle tracking program. Then, the time-resolved particle temperature is obtained based on two-color pyrometry. A plateau-like stage shortly after the ignition is repeatedly observed, and identified as iron particle melting by the measured temperature and the estimated melting time. Besides, an abrupt brightness jump near the end of combustion is observed for most burning particles, while a small portion of the particles (< 10%) show a second plateau-like stage instead. The particle temperature right after the brightness jump (1880±70 K) is almost identical to that during the second plateau-like stage. This temperature corresponds to two phase-change temperatures in the Fe-O phase diagram: i) L2 <=> Fe3O4 (s) at 1869 K (congruent melting) and ii) L2 <=> Fe3O4 (s) + O2 (g) at 1855 K (eutectic reaction), where L2 represents a liquid iron oxide. Based on this, the presence of the brightness jump (spear point) is explained by a sudden solidification of supercooled iron oxide droplets with an atomic O/Fe ratio larger than or close to 4/3. Particles’ near-peak temperatures are also measured based on time-integrated spectra. The results indicate that the near-peak temperature increases first fast and then slowly with an increase of oxygen concentration. At higher oxygen concentrations, smaller particles have a slightly lower temperature. The effect of particle size on the near-peak temperature is negligible at lower oxygen concentrations due to weaker radiation. The morphology of combusted particles is examined by micrography. Some burned particles appear as hollow thin-shell spheres at all adopted oxygen concentrations. Additionally, nano oxides are found at 13–51% oxygen concentrations. Less traces of nano oxides were observed at reduced oxygen concentrations. The nano-oxide formation mechanisms are analyzed based on thermochemical equilibrium calculations.

Structure evolution of a magnetite iron ore/carbon composite pellet during solid-state reduction under microwave heating

In the present study, the structure evolution under direct reduction of a Minh-Son magnetite iron ore/carbon composite pellets in a microwave-heating kiln under different microwave wattage of 60 and 90 % (with the firing time from 15 to 120 min.) was investigated. The microstructure of the pellets was characterized by scanning electron microscopy coupled with energy dispersive spectroscopy and X-ray diffraction (XRD). The phase formation was indexed using MDI Jade from the peaks matching the reference sample. At the microwave’s wattage of 60 %: the wustite (FeO) has appeared after firing time of 60 min., the metallic iron and fayalite have appeared in the reduced samples after firing time of 90 min. to 120 min. with retained phases of Fe203, Fe304, FeO and Si02– While at the microwave’s wattage of 90 %, the metallic iron has appeared in the reduced samples after firing time of 30 min. to 120 min and fayalite has appeared in the reduced samples after firing time of 60 min. to 120 min. The final reduced pellet, under microwave’s wattage of 90 % and firing time of 120 min., shows the only phases of metallic iron and fayalite according to the XRD resolution. The present work could provide a scientific understanding to illustrate iron ore/carbon composite pellet behavior during solid-state carbothermic reduction under a microwave-heating.

A new application of the commercial high temperature water gas shift catalyst for reduction of CO2 emissions in the iron and steel industry: Lab-scale catalyst evaluation

In this study, we present a detailed investigation of a commercial iron-based high temperature water gas shift (HTWGS) catalyst (Johnson Matthey KATALCOTM 71-6) in a new application: the production of hydrogen from blast furnace gas (BFG), which originates from iron and steel manufacturing. During the lab-scale catalytic testing under BFG conditions the catalyst demonstrated: 1) high water gas shift activity and stability; 2) minimal methanation at reduced steam to CO ratios; 3) high resistance towards H2S impurities present in the feed. The results of post-characterization of the discharged samples confirm the robustness of KATALCO 71-6 towards BFG process conditions: no over-reduction of the catalytically active Fe3O4 phase and no formation of a less active FeS phase. An in situ X-ray absorption spectroscopy study revealed no over-reduction of the iron phase under BFG conditions and the stabilization of the iron phase by diffusion of chromium into the iron oxide matrix. The findings of this study demonstrate the suitability of the iron-based HTWGS catalyst KATALCO 71-6 for the production of hydrogen from BFG streams. Knowledge gained in this study is an essential step in the development and scale up of carbon capture and storage as well as carbon capture and utilization technologies, such as the sorption enhanced water gas shift (SEWGS) technology, aimed at reducing the CO2 footprint during steel manufacturing.

Yolk–shell Fe–Fe3O4@C nanoparticles with excellent reflection loss and wide bandwidth as electromagnetic wave absorbers in the high-frequency band

The performance of Fe3O4-based electromagnetic wave-absorbing materials is typically hindered by their low conductivity. Therefore, the introduction of carbon components with a rationally constructed microstructure has evolved as an effective approach for enhancing the electromagnetic properties of metal-oxide-based microwave absorbers. In this study, yolk–shell Fe–Fe3O4@C nanoparticles were synthesized via a hydrothermal–polymerization–vacuum carbonization method under a N2 flow. In addition to a polymer with suitable layer thickness, which is required to obtain a mixed Fe and Fe3O4 phase, an appropriate carbon layer is needed. Furthermore, Fe@C with cavities can be fabricated when the thickness of the polymer layer is higher than the optimum value. The optimized reflection loss, effective bandwidth, and thickness of Fe–Fe3O4@C were −51 dB, 5.1 GHz (12.9–18 GHz), and 1.2 mm, respectively, which were larger than those of most Fe3O4-based absorbing materials reported to date. The excellent microwave absorption performance of Fe–Fe3O4@C was attributed to its excellent electromagnetic properties, including complex permeability and permittivity, and yolk–shell structure, which favored multiple reflections and scatterings and multiple polarizations at the core–cavity and cavity–shell interfaces.