Reduced Iron Particles Research Articles

Preparation and magnetic properties of hybrid FeSiBCr amorphous Soft magnetic composites with carbonyl iron and reduced iron particles

Preparation and magnetic properties of hybrid FeSiBCr amorphous Soft magnetic composites with carbonyl iron and reduced iron particles

Kinetics and Mechanism of Red Mud Carbothermic Reduction and Reduced Iron Grain Growth: An Influence of Sodium Sulfate

The main waste formed during the production of alumina by the Bayer method is red mud. This waste has a high content of iron, which can be effectively extracted by the carbothermic reduction and magnetic separation methods. The crucial factors affecting the commercial efficiency of this process are the iron reduction rate and the size of reduced iron particles. This study considers the influence of sodium sulfate addition to red mud on the kinetics of iron reduction and the iron grain growth process. The isothermal kinetics of the iron reduction process at 1000–1200 °C and 5–30 min of time was investigated for the red mud processing without additives and with 13.65% Na2SO4 addition. It was shown that the activation energy value for the reduction without additives was 65 kJ·mol−1, while it was 39 kJ·mol−1 for the reduction with Na2SO4 addition, respectively. Based on the microstructure study of the roasted samples, models were obtained for the calculation of the average diameter of iron grains without and with the additives. The iron grain growth process was thoroughly discussed, and its main mechanism was proposed.

Study of the kinetics of the process of producing pellets from red mud in a hydrogen flow

The reduction kinetics of serial phase transitions of iron oxides during reduction to a metallized state with different modes of technical hydrogen supply has been studied and substantiated. The results of the pellets formation when 3-5 % molasses is added to the red mud as a binding reagent are presented. The dependences of the reduction rate of iron oxides on the hydrogen flow rate are obtained. Based on the results of the experiments, a kinetic model was constructed, and with the help of X-ray phase and spectral analysis, it was proved that the agglomerates formed after heat treatment received high strength due to the adhesion of reduced iron particles with red mud particles. The use of a new type of charge materials in melting units will reduce the amount of emissions and dust fractions, as well as increase the metal yield.

Catalytic graphitization in anthracite by reduced iron particles and investigating the mechanism of catalytic transformation via molecular dynamics

Anthracite graphitization was catalyzed by reduced iron particles, where iron was introduced in the form of Fe2O3, reduced during the carbothermal reaction. This graphite as an alternative solution for the lithium-ion battery anode material, and the precursor of the anode material was obtained. The degree of graphitization of synthetic graphite regulated via changing the amount of Fe2O3 and catalytic temperature. Graphite with the graphitization degree of 96.51% was obtained under the conditions of the catalytic temperature of 2400 °C, Fe2O3 content of 20%. HRTEM of graphite after Fe-catalyzed graphitization revealed that the graphite layer spacing gradually approached the ideal graphite. Molecular dynamics (MD) provides significant insight into the mechanism of Fe-catalyzed graphitization at the molecular level. The mechanism of Fe-catalyzed graphitization was inevitably related to the formation and breakage of Fe–C bonds. With the formation and breakage of Fe–C and C–C bonds, a regular aromatic 6-membered ring was finally formed due to the strong bonding between Fe and C. Fe promoted the integration of irregular 5- and 7-membered rings into two regular aromatic 6-membered rings. These two processes were continued in the process of catalytic graphitization. This result provided MD support to explore the mechanism of Fe-catalyzed graphitization.

Influence of Temperature and Holding Time on Number and Size of Metal Particles during Solid-Phase Reduction of Iron by Carbon

There is a lack of complete understanding of the mechanism and kinetics of reduction of metals from oxides. This paper presents results and methods of a series of experiments on direct reduction of metals by solid carbon in the form of graphite from a complex oxide with a low iron content in a laboratory muffle furnace at temperatures of 1300, 1400, 1500, 1600 °C and holding time of 1, 3, 5, 7 hours. The statistical analysis of amount and average size of reduced iron particles inside the oxide was studied. Dependence of amount and average size of the reduced iron particles on temperature and time of reduction is presented. The phenomena of iron crystals’ growth, occurring as a result of changes in the crystal lattice of oxide, was studied under experimental conditions. The influence of temperature and holding time on iron particles’ nucleation and their growth in the crystal lattice of a complex oxide were compared. Investigation of mechanism of metals’ reduction from complex oxides and influence of experimental conditions on the nucleation and growth enables to identify new patterns in the process of reduction of metals from their oxides, in general.

Preparation and Magnetic Properties of Fe@SiO<sub>2 </sub>Soft Magnetic Composites

In this work, the insulating SiO2 was coated successfully on the surface of reduced iron particles by a sol-gel method to decrease the core loss at low frequency. The scanning electron microscope images and elements analysis confirm that the surface of iron powders particles were covered by a thin insulating layer in the form of uniform core-shell structure. The samples were annealed at 400 °C in N2 atmosphere to obtain better magnetic properties. The annealed SMCs with 10 mL/h dropping rate of TEOS have optimum magnetic properties with low core loss Ps of 280.89 W/kg and high saturation magnetic flux density Bs of 1.038 T at 1000 Hz.

Process characteristics of catalytic thermochemical conversion of oily sludge with addition of steel slag towards energy and iron recovery

The improper disposal of oily sludge and converter steel slag can be of great environmental concerns, herein, we proposed an innovative methodology by coupling the catalytic thermochemical conversion of oily sludge with the high-temperature reduction of steel slag, where the gas energy and iron resources can be recovered simultaneously. It was found out that the gas yield, iron reduction efficiency, as well as the carbon conversion, were positively correlated with the temperature, the amount of steel slag added and slag particle fineness. With the addition of steel slag, the carbon conversion increased from 76.6 % to 90.1 %, and the iron reduction efficiency increased from 38.5 % to 70.6 %. The phase and microstructure characterizations revealed that the iron-bearing phases (RO phase, Ca2Fe2O5) in steel slag were reduced into metallic iron by pyrolytic gaseous intermediate products (600−800 °C) and solid char (800−1000 °C). The in-situ reduced iron particles in turn acted as an efficient catalyst for cracking/reforming reactions, resulting in remarkable fuel gases, i.e. H2, CO evolution. Hence, the reduction of steel slag and the catalytic cracking/reforming of oily sludge were both enhanced. Furthermore, the technical-economic analysis in terms of material and energy balances was performed. It revealed that the proposed process was favorable for energy recovery and high added material production.

Re-Oxidation Kinetics of Flash Reduced Iron Particles in O2–N2 Gas Mixtures Relevant to a Novel Flash Ironmaking Process

Re-Oxidation Kinetics of Flash Reduced Iron Particles in O2–N2 Gas Mixtures Relevant to a Novel Flash Ironmaking Process

Exergetic Assessment of a Syngas-Redox-Based IGCC Plant for Generating Electricity

Carbon capture from advanced integrated gasification combined-cycle (IGCC) processes should outperform conventional coal combustion with subsequent CO2 separation in terms of efficiency and CO2 capture rates. This paper provides a thermodynamic assessment, using an exergy analysis of a syngas redox (SGR) process for generating electricity. The power island of the proposed process uses syngas produced by coal gasification and is then cleaned through a high-temperature gas desulfurization (HGD) process. Hematite (Fe2O3) is used as an oxygen carrier to oxidize the syngas. To achieve a closed-cycle operation, the reduced iron particles are first partially re-oxidized with steam and then fully re-oxidized with pressurized air. One advantage of this design is that the resulting hydrogen (using steam in the re-oxidation section) can be utilized within the same plant or be sold as a secondary product. In the proposed process, diluted hydrogen is combusted in a gas turbine. Heat integration is central to the design. Thus far, the SGR process and the HGD unit are not commercially availiable. To establish a benchmark, the rate of exergy destruction within the SGR process was compared to a coal-fed Shell gasification IGCC design with Selexol-based precombustion carbon capture. Some thermodynamic inefficiencies were found to shift from the gas turbine to the steam cycle and redox system, while the net efficiency remained almost the same. A process simulation was undertaken, using Aspen Plus and the engineering equation solver (EES).

Design and evaluation of an IGCC power plant using iron-based syngas chemical-looping (SCL) combustion

Chemical-looping combustion (CLC) is a novel and promising combustion technology with inherent separation of the greenhouse gas CO2. This paper focuses on the design and thermodynamic evaluation of an integrated gasification combined-cycle (IGCC) process using syngas chemical looping (SCL) combustion for generating electricity. The syngas is provided by coal gasification; the gas from the gasifier is cleaned using high-temperature gas desulfurization (HGD). In this study, the oxygen carrier iron oxide (Fe2O3) is selected to oxidize the syngas in a multistage moving-bed reactor. The resulting reduced iron particles then consist of FeO and Fe3O4. To create a closed-cycle operation, these particles are partially re-oxidized with steam in a fluidized-bed regenerator to pure Fe3O4 and then fully re-oxidized in a fluidized-bed air combustor to Fe2O3. One advantage of this process is the co-production of hydrogen diluted with water vapor within the steam regenerator. Both the HGD and CLC systems are not under commercial operation so far. This mixture is fed to a gas turbine for the purpose of generating electricity. The gas turbine is expected to exhibit low NOx emissions due to the high ratio of water in the combustion chamber. Cooling the flue gas in the HRSG condenses the water vapor to yield high-purity CO2 for subsequent compression and disposal. To evaluate the net efficiency, two conventional syngas gasifiers are considered, namely the BGL slagging gasifier and the Shell entrained-flow gasifier. The option of using a CO2 turbine after the SCL-fuel reactor is also investigated. A sensitivity analysis is performed on the SCL-air reactor outlet temperature, this being a key design parameter. It was found that the best net efficiency of 43% (based on HHV) can be obtained using a BGL gasifier without a CO2 turbine at an air reactor temperature of 1000°C including CO2 compression for transport and storage. Simulation data are based on software Aspen Plus® and EES (Engineering Equation Solver).

Soft magnetic composite particles of reduced iron coated with poly(p-xylylene) via chemical vapor deposition polymerization

Soft magnetic composite particles of reduced iron coated with ultrathin films of poly(p-xylylene) (PPX) were prepared via chemical vapor deposition (CVD) polymerization. The structure, morphology, magnetic properties, and chemical stability of PPX encapsulated reduced iron particles were studied. It can be confirmed from FTIR spectrum that the polymer covered outside the reduced iron particles is PPX. The thickness of PPX film is averagely 100 nm according to the results of transmission electron microscopy (TEM). The mean diameter of the composite particles is about 6.0 μm. The resistance to thermooxidation of the composite particles is much higher than that of the reduced iron particles due to the protection of PPX ultrathin film outside the iron powder. After being encapsulated with PPX ultrathin film, the resistance to acidic corrosion of the reduced iron particles is obviously improved. Although the saturation magnetization (Bs) of the composite particles is reduced from 1.42 T to 1.33 T after the coating process, their coercive force (Hc) decreases from 10.6 kA/m to 6.02 kA/m, which is advantageous for the application of soft magnetic particles in MR fluid.

Studies on preparation and chemical stability of reduced iron particles encapsulated with polysiloxane nano-films

The soft magnetic composite of reduced iron particles encapsulated with polysiloxane shell was prepared by hydrolysis–condensation polymerization of tetraethylorthosilicate (TEOS) on the surface of iron particles. The structure, morphology, magnetic properties, and chemical stability of the polysiloxane coated iron particles were studied. The thickness of the shell was about 60 nm according to the results of transmission electron microscopy (TEM) and laser particle size analysis, while the mean diameter of the iron particle was 4.45 μm. The chemical stability of the soft magnetic composites was greatly improved, though its magnetic properties were declined a little. However, encapsulated iron particles are still useful in MR fluids as its magnetic properties are much better than other soft magnetic particles like Fe3O4, etc.

Supersaturation of Carbon in Austenite during Carburization by CO Gas

Fine particles of electrolytic iron in austenite state absorbed carbon from CO gas to be in supersaturation. The carbon content in austenite was estimated from the spacing of lattice planes of iron, which was measured by a high temperature X-ray diffractometer. The supersaturation was depended on the flow rate of CO gas and temperature. The solute supersaturation ratio of carbon was from 1.2 to 1.8 at the temperature between 1452 and 1599 K. Iron particles reduced from hematite by H2 gas behaved as same as electrolytic iron particles. However, the iron particles reduced from hematite by CO gas were not in supersaturation of carbon and melted at the solubility of carbon in austenite state. The supersaturation can be explained by the decline of heterogeneous nucleation sites per unit volume. The spacing of lattice planes of reduced iron by CO gas abnormally increased and then decreased during heating. The reduced iron particles melted at the solubility of carbon in austenite and did not become supersaturation.

Reactions, Coalescence of Reduced Iron Particles, and Liberation of Carbon Particles in Carbon Composite Iron Ore Pellets

Reactions in carbonaceous material composite iron ore pellets of 18 mm heated at elevated temperatures were studied. The overall reduction rate is controlled by a complex combination of direct reactions and indirect reactions and never by gasification reaction. The final reduction of iron oxide is controlled by carburized carbon. The carburization of the reduced iron is mainly progressed by the direct carburization reaction, C(s)=[C]. As the carbon content approaches to the solidus line of the phase diagram of Fe-C system, the reduced iron particles are gradually forced to coalesce to grow in much larger particles. The coalescing rate is increased with temperature. Its driving force is the large surface energy of reduced iron due to its large specific surface area. Due to the coalescence, the particles of carbon are apt to lose the contact state with the reduced iron particles and to lose the ability to carburize the reduced iron. Therefore, the carburization exceeding the solidus line can be severely depressed. Consequently, the carburization up to the solidus line can be achieved at relatively lower temperatures, i.e. 1 200-1 250°C. As a result, the carbon content of reduced iron decreases with increasing temperature. Since the coal char has a very poor ability to directly carburize reduced iron, the carbon contents of reduced iron were very low and increased with increasing temperature. Graphite and coke possess the strongest and the intermediate carburizing abilities, respectively. And the carbon contents of the shell part and core part of reduced iron decreases with increasing temperature.

Rate of Iron Carbide Formation from Reduced Iron in CO-H2-H2S Mixtures under Pressurized Conditions

Under pressurized conditions up to 0.6 MPa, the rate of the iron carbide formation from completely reduced iron in CO-H 2 -H 2 S mixtures was measured by gravimetric technique. The fractional conversion for carbide formation, f θ , was defined as the weight gain divided by the weight of carbon for the complete conversion to cementite. First, the compositions of the partially reacted samples were analyzed by Mossbauer absorption spectroscopy. Then, the fractional conversion calculated from the composition, f M θ, was compared with f θ . The value of f θ agreed reasonably with that of f M θ in the range f θ <0.8, from which the gravimetric method is proved to be valid to the measurements for the rate of iron carbide formation. The carbide formation curves, f θ versus t relation, were not influenced by the weight of the sample and the flow rate of the reaction gas in the conditions; 50 mg, more than 3.33×10 -6 m 3 /s. Cross sectional view indicated the homogeneous distribution of cementite regions in the reduced iron particles partially converted to cementite. On the other hand, the rate was very sensitive to the conditions of the carburization reaction on the pore surface. The rate increased with increasing the content of carbon monoxide up to 80 to 90%, where the rate was the maximum, and then gradually decreased with further increasing the content. The rate increased with the total pressure, but decreased with the activity of sulfur. The rate controlling step of the iron carbide formation was discussed on the basis of the experimental results. The rate controlling step was assumed to be the carburization reactions on the pore surface of reduced iron particles.

Mechanisms of Pig-iron Making from Magnetite Ore Pellets Containing Coal at Low Temperature.

A new pig-iron making process using magnetite ore pellets containing coal as reducing agent has been investigated. The pellets were heated rapidly in argon at furnace temperatures between 1 573 and 1 723 K and the temperature and partial pressure of oxygen in the pellets were recorded in situ. Molten iron containing 1.1–3.6 mass% carbon over the composition on the liquidus line of iron–carbon system was produced at the furnace temperatures higher than 1 598 K within 16 min. The whole process consists of four steps, i.e., heating, reduction of iron ore, carburization and melting of pig iron. The solution-loss of carbon and the reduction of iron ore are coupled and concentrically take place from the surface to centre due to the heat transfer control because of the endothermic reaction of solution-loss. The reduced iron particles were carburised by CO gas, rapidly absorbed carbon from coal and become molten pig iron particles. The particles cohered to make large drops and the pellet suddenly collapsed to melt. The conditions determining the lowest temperature for producing pig iron are discussed.

Morphofunctional study of the statocyst of the cuban crayfishprocambarus cubensis

After replacing sand, a natural component of the endogenous otolithic apparatus of the Cuban crayfishProcamabrus cubensis by particles of reducible iron and subsequent exposure of the animals to a constant magnetic field, the following changes were noted in their behavior: during the first 24 h the motor activity of the animals increased and was accompanied by frequent strong beats of antennulae on water; animals tried to go away from the magnet attached to the aquarium wall and to hide in a shelter; by the day 10–12, there appeared signs of adaptation to the action of magnet; the animals spent most time near the wall with the magnet and were clinging close to it. If the magnet was moved the animals not only slipped to their side but also rotated around their longitudinal axis. The eyestalks also started moving. After molt and repeated introduction of reduced iron particles into the statocysts, a negative reaction to magnet was practically absent, and the crayfish preferred staying near the magnet. Study of structural organization of the statocysts under a scanning electron microscope showed that the iron particles in the otolithic apparatus of the crayfish are covered with a thinner layer of glycocalyx as compared to control animals whose otolithic apparatus is composed of sand grains. Besides, the otolithic apparatus of the experimental animals is a loose formation, unlike the dense glycocalyx rich in conglomerate in control animals.

Chain-of-cubes iron nanoparticles prepared by borohydride reduction of acicular akaganeite particles

Ellipsoid shaped akaganeite (β-FeOOH) particles, 70 nm long and 10 nm in diameter, were prepared by forced hydrolysis of ferric chloride. The β-FeOOH particles were suspended in a lamellar liquid crystal phase at 0 °C and reduced with dilute sodium borohydride solution to iron particles. These conditions allowed us to slow the reduction reaction and isolate partially reduced iron particles. Transmission electron microscopy images showed that the particles were being reduced from the outside and there were nanometer-sized spherical iron clusters on the surface. Fully reduced iron particles were chains of cubes, with the cubes about 20 to 25 nm in size. The cubes were connected either corner to corner, edge to edge, or face to face. The face to face chains of cubes had the desired acicular shape, with aspect ratios exceeding five. This face to face chain of cubes microstructure was also observed in commercial iron particles.

The Effect of Potassium Addition on the Surface Chemical Structure and Activity of Supported Iron

The surface activity of a Fe–K/ZrO2sample prepared from iron citrate and potassium carbonate has been investigated by the FTIR spectroscopy of adsorbed CO and NO and compared with the behavior of a Fe/ZrO2sample. The addition of potassium produces a strong decrease of the BET area and of the amounts of the adsorbed molecules. At the same time the spectrum of the sample reduced with H2at 573–773 K shows, under anhydrous conditions, the presence of small patches of reduced Fe0, not easily formed on Fe/ZrO2under the same thermal and reducing conditions. The formation of new phases containing iron and potassium in close combination, such as mixed iron–potassium oxalates and potassium ferrites that fully cover the zirconia surface, was inferred from FTIR data. CO adsorption favors the partial surface reduction of these phases producing small Fe-carbonyl clusters in tight contact with potassium and Fe,K-carboxylate surface species. The adsorption of NO, producing nitrosyl species on the reduced iron particles and nitrite groups on the potassium phase is in good agreement with the results of adsorbed CO. These results are confirmed by quantitative determinations of adsorbed gases and by TPR experiments.

Importance of the anatase-rutile phase transition and titania grain enlargement in the strong metal-support interaction phenomenon in [formula omitted] catalysts

The strong metal-support interaction (SMSI) in the system consisting of iron supported on high-surface-area titania powder was investigated. By observation of the anatase-rutile phase transition, titania grain enlargement, and the SMSI effect at several reduction temperatures in the range 643–873 K, it was found that these three phenomena occur simultaneously at reduction temperatures above 723 K. This suggests that the three phenomena are interrelated, and that the phase transition and grain enlargement are important factors concerning SMSI in high-surface-area powder samples. A mechanism has been proposed whereby Ti 3+ defect centers in the titania lattice formed from support reduction are responsible for acceleration of phase transition and grain enlargement, and the TiO x , species that migrates onto supported metal particles is formed during the chaotic state of simultaneous phase transition and grain enlargement. At the temperature of the onset of the above three phenomena (~723 K), a stabilization against high-temperature sintering of iron particles became evident, suggesting that this effect becomes operative at the onset of SMSI. Iron particles supported on rutile were significantly smaller than anatase-supported particles which were reduced at the same temperature. The rutile was formed from anatase before impregnation with iron by reduction in hydrogen at 873 K followed by oxidation with oxygen at 473 K. The smaller iron particles and incomplete iron reduction were attributed to O − 2 ions adsorbed to the titania surface which acted to anchor Fe 3+ and/or Fe 2+ ions to the support, preventing their migration and combination to form large fully reduced iron particles.