Iron-containing Oxide Research Articles

METHOD FOR OBTAINING NANOPARTICLES OF IRON-CONTAINING OXIDES AND STUDYING THEIR PROPERTIES

The synthesis of iron-containing oxide nanoparticles is of interest in medicine, electronics and ecology due to their unique physical and chemical properties, such as magnetic, catalytic and adsorption properties, which allow their use in various technological processes. In this regard, this article presents the results of obtaining nanoparticles of iron-containing oxides and studying their physical and chemical properties. It is known that stabilization with natural polymers is of great importance in the production of metal nanoparticles. Therefore, in this work, the synthesis is carried out at high temperature by stabilization with potassium humate. To study the properties of the resulting iron-containing nanoparticles, methods of X-ray phase analysis, transmission electron microscopy and infrared spectroscopy were used. As a result of physicochemical studies, the heterogeneity and monodispersity of the synthesized metal nanoparticles was established. The average particle size of the synthesized samples was 8.3 nm, the crystal lattice parameter was 0.8426 nm. The result of the study using IR spectroscopy confirms the assumption of oxidation of the samples. In addition, it was found that the prepared samples have a high degree of crystallization. Transmission electron microscopy revealed no differences in the sizes of nanoparticles. Pure iron oxide is not formed during the synthesis of iron nanoparticles using the method used in the research work. The unique properties of iron-containing oxide nanoparticles obtained as a result of research are promising for the creation of innovative technologies and solutions aimed at improving the quality of life and sustainable development of society.

Study on the influence mechanism of austenitizing temperature on the surface of corrosion-resistant mold steel

Abstract The microstructure of 4Cr13 corrosion-resistant plastic mold steel was studied. The martensitic experimental steel obtained by different heat treatment processes was used as the object. The effect of austenitizing temperature on its corrosion behavior was studied by microstructure characterization and electrochemical test. The results show that the microstructure of the test steel is mainly composed of martensite laths. Under the same experimental conditions, the corrosion resistance of the test steel decreases with the increase of austenitizing temperature, and the corrosion products are mainly composed of iron-containing oxides. The austenitizing temperature of 1000°C improves the corrosion resistance of the material, because the precipitation of a large number of small-sized Cr-containing carbides hinders the further erosion of the material and improves the surface quality.

The Effect of Composition and Temperature on the Hydrogen Reduction Behavior of Sintered Pellets of Bauxite Residue-Lime Mixtures

This study explores the isothermal hydrogen reduction of sintered pellets made of a mixture of bauxite residue and calcite with varying compositions at different reduction temperatures. Sintered pellets with varying compositions show three primary iron-containing oxide phases including brownmillerite, srebrodolskite, and fayalite; however, brownmillerite is the major phase in all the sintered pellets. The sintered pellets were reduced in a thermogravimetry furnace to establish instantaneous weight reduction with respect to time. Phases and microstructural analysis were carried out using X-ray diffraction and scanning electron microscopy, respectively. Mercury intrusion porosimeter and pycnometer were utilized to assess the porosity and density of the reduced pellets. Thermochemistry calculations were performed using the thermodynamics software FactSage 8.2. The reduction rate is most pronounced at a temperature of 1000 °C for all pellet compositions. It is intriguing to note that the rate of reduction shows minimal variance across pellets with different compositions; however, the higher calcite pellets exhibit a higher initial rate of reduction. Various kinetic models were examined to determine the activation energies for three different composition pellets, and the three-dimensional diffusion model has been well suited for this process. Close activation energies in the range of 84.6 to 94.8 kJ were obtained. A slightly higher activation energy was obtained for lower CaCO3 added pellets, and it was attributed to their reduced porosity and increased sintering, impeding the reaction kinetics. There were no significant differences in the formation of mayenite with varying the calcite amount; however, higher calcite pellets indicated more mayenite formation.Graphical

Promotion of direct electron transfer between Shewanella putrefaciens CN32 and carbon fiber electrodes via in situ growth of α-Fe2O3 nanoarray

The iron transport system plays a crucial role in the extracellular electron transfer process of Shewanella sp. In this study, we fabricated a vertically oriented α-Fe2O3 nanoarray on carbon cloth to enhance interfacial electron transfer in Shewanella putrefaciens CN32 microbial fuel cells. The incorporation of the α-Fe2O3 nanoarray not only resulted in a slight increase in flavin content but also significantly enhanced biofilm loading, leading to an eight-fold higher maximum power density compared to plain carbon cloth. Through expression level analyses of electron transfer-related genes in the outer membrane and core genes in the iron transport system, we propose that the α-Fe2O3 nanoarray can serve as an electron mediator, facilitating direct electron transfer between the bacteria and electrodes. This finding provides important insights into the potential application of iron-containing oxide electrodes in the design of microbial fuel cells and other bioelectrochemical systems, highlighting the role of α-Fe2O3 in promoting direct electron transfer.

Coupling Process between Droplet and Iron Investigated by Reactive Molecular Dynamics Simulations.

The droplet-to-iron electrochemical reaction is common in nature and industrial production, and it causes damage to the economy, safety, and the environment. The electrochemical reaction of droplet-to-iron is a coupling process of wetting and corrosion. Presently, investigations into electrochemical reactions mainly focus on the corrosions caused by a solution, and wetting is rarely considered. However, for the droplet-to-iron electrochemical reaction, the mechanism of charge transfer in the process is still unclear. In this paper, a reactive molecular dynamics simulation model for the droplet-to-iron electrochemical reaction is developed for the first time. The electrochemical reaction of droplet-to-iron is studied, and the interaction between droplet wetting and corrosion on iron is investigated. The effects of temperature, electric field strength, and salt concentration on the electrochemical reaction are explored. Results show that droplet wetting on the iron surface and the formation of a single-molecular-layer ordered structure are prerequisites for corrosion. The hydroxyl radicals that penetrate the ordered structure acquire electrons from iron atoms on the substrate surface under the action of Coulomb forces and form iron-containing oxides with these iron atoms. The corrosion products and craters lead to a reduced droplet height, which promotes droplet wetting on iron and further intensifies the droplet-to-iron electrochemical reaction.

Hexakis(urea-O)iron Complex Salts as a Versatile Material Family: Overview of Their Properties and Applications.

Due to their Fe- and N-containing reactive urea ligand content, the hexakis(urea-O)iron(II) and hexakis(urea-O)iron(III) complexes were found to be versatile materials in various application fields of industry and environmental protection. In our present work, we have comprehensively reviewed the synthesis, structural and spectroscopic details, and thermal properties of hexakis(urea-O)iron(II) and hexakis(urea-O)iron(III) salts with different anions (NO3-, Cl-, Br- I-, I3-, ClO4-, MnO4-, SO42-, Cr2O72-, and S2O82-). We compared and evaluated the structural, spectroscopic (IR, Raman, UV-vis, Mössbauer, EPR, and X-ray), and thermogravimetric data. Based on the thermal behavior of these complexes, we evaluated the solid-phase quasi-intramolecular redox reactions of anions and urea ligands in these complexes and summarized the available information on the properties of the resulting simple and mixed iron-containing oxides. Furthermore, we give a complete overview of the application of these complexes as catalysts, reagents, absorbers, or agricultural raw materials.

Structural and Magnetic Behavior of MFe<sub>2</sub>O<sub>4</sub> Nanopowders for Water Treatment

This study describes the sol-gel method's synthesis of ferrites [MFe2O4, M(II) = Co, Cu, Mg, Ni, and Zn]. The structure was studied by X-ray diffraction analysis. The surface morphology was studied using scanning electron microscopy (SEM), and the magnetic properties were studied using Mössbauer spectroscopy. The diffraction peaks at 30.1◦, 35.6◦, 43.2◦, 53.6◦, 57◦, and 62.6◦ can be attributed to Bragg reflections (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), and (4 4 0) planes confirm the formation of a cubic spinel structure of ferrite nanocrystals. The average size of magnesium ferrite crystallites calculated from the half-width of the most intense peak (3 1 1) was 25.96 ± 4.32 nm. Magnesium ferrite is a magnetically soft ferromagnetic powder with a predominance of the magnetite phase and relatively high magnetisation values. The magnitude of the hyperfine magnetic field for the studied nanoparticles is in the range of 440-490 kOe, which confirms the hypothesis that the analysed samples are particles of an iron-containing oxide with a disordered structure.

Comparison of reduction kinetics of Fe2O3, ZnOFe2O3 and ZnO with hydrogen (H2) and carbon monoxide (CO)

Electric arc furnace dust (EAFD) recycling is based on the reduction of oxides containing iron and zinc. With regard to the sustainability of industrial processes, hydrogen reduction processes could be the key technology to replace current recycling technologies based on carbothermal reduction. In this context, hydrogen is often claimed to provide better reduction kinetics, but it is mostly unclear how much faster it is. The present work gives a comprehensive comparison of the reduction kinetics of the major zinc- and iron-containing oxides in EAFD (Fe2O3, ZnOFe2O3, and ZnO) using hydrogen and carbon monoxide under various process parameters. The influence of specimen size, reduction gas flow rate, and temperature were evaluated. The kinetic advantage of hydrogen compared to carbon monoxide was confirmed, enabling the reduction of direct CO2-emission. Hydrogen results in a 2.5 times faster reduction of Fe2O3 and a doubling of the reduction rate for ZnOFe2O3. ZnO reduction was determined to be 1.5 faster. Furthermore, ZnO was found to be the rate-limiting substance in the recycling of EAFD, regardless of the reducing agent.

THERMOSTIMULATED EVOLUTION OF THE CRYSTAL AND MAGNETIC STRUCTURE OF YTTRIUM FERRITE GARNET NANOPARTICLES

Iron-containing oxides form one of the most important classes of functional materials, which find a wide variety of applications. A promising approach is their use in biomedical technologies as components of systems for visualization, drug delivery, magnetic hyperthermia, etc. Nanocrystalline particles of Y3Fe5O12 garnet, obtained by glycine-nitrate combustion with subsequent thermal treatment, have been experimentally investigated. The results of studying the evolution of the crystal and magnetic structure of Y3Fe5O12 nanoparticles in dependence of the synthesis temperature are presented. A complex analysis using X-ray diffractometry, scanning electron microscopy, and Mössbauer spectroscopy has been performed. A relationship of the size and structural quality of Y3Fe5O12 nanoparticles with the observed magnetic characteristics is evealed.

Microwave synthesis of nanosized iron-containing oxide particles and their physicochemical properties

Microwave synthesis of nanosized iron-containing oxide particles and their physicochemical properties

Magnetic properties of ilmenite used for oxygen carrier aided combustion

Oxygen carrier aided combustion is a combustion process that utilizes oxygen carrying particles in a fluidized bed to transport oxygen from oxygen-rich to oxygen-poor regions in the reactor. A commonly used oxygen-carrying material is ilmenite (FeTiO3) which is a naturally occurring mineral. At higher oxygen partial pressures ilmenite can react to pseudobrookite (Fe2TiO5) and thereby take up oxygen. Upon reduction of pseudobrookite in oxygen-lean locations the oxygen is released, which enhances the distribution of oxygen through the reactor.Ilmenite was used as bed material in an industrial 115 MWth circulating fluidized bed (CFB) boiler where recycled waste wood and wood chips were utilized as fuel. Bottom ash samples were extracted after one and two weeks and the samples were separated into two fractions by a magnetic separator. The magnetic fraction was expected to be enriched in iron-containing oxides and was therefore aimed to be recirculated into the boiler.The SEM-EDS analysis revealed that the non-magnetic fraction consists to the largest extent of feldspar (KAlSi3O8) particles. A significant amount of freshly introduced ilmenite particles was also classified as non-magnetic by the magnetic separator. Characteristic for these particles was a lack of ash layer, suggesting they had only recently been added to the system. In the magnetic fraction, several feldspar particles were found which were covered by a layer rich in Ca, Fe, Ti, and Si. Comparing the XRD analysis of the ash prior to magnetic separation with its magnetic fraction revealed a decrease of the peaks corresponding to feldspar. The removal of feldspar particles by magnetic separation was further corroborated by XRF analysis, where the concentration of K, Al and Si was significantly higher in the non-magnetic fraction, however, no changes were observed in the concentration of Fe. The present analyses shows that prolonged exposure time of ilmenite increases its magnetic susceptibility. Non-magnetic feldspar was shown to acquire significant magnetic susceptibility by formation of a surface layer containing Fe-rich attrition products from ilmenite.

Size-Dependent Structural, Magnetic and Magnetothermal Properties of Y3Fe5O12 Fine Particles Obtained by SCS.

Iron-containing oxides are the most important functional substance class and find a tremendous variety of applications. An attractive modern application is their use in biomedical technologies as components in systems for imaging, drug delivery, magnetically mediated hyperthermia, etc. In this paper, we report the results of the experimental investigation of submicron Y3Fe5O12 garnet particles obtained in different sizes by solution combustion synthesis (SCS) using glycine organic fuel to discuss the interdependence of peculiarities of the crystal and magnetic structure and size’s influence on its functional magnetothermal performance. A complex study including Mössbauer and Raman spectroscopy accompanied by X-ray diffractometry, SEM, and measurements of field and temperature magnetic properties were performed. The influence of the size effects and perfectness of structure on the particle set magnetization was revealed. The ranges of different mechanisms of magnetothermal effect in the AC magnetic field were determined.

Enhanced Removal of Malachite Green Using Calcium-Functionalized Magnetic Biochar.

To efficiently remove malachite green (MG), a novel calcium-functionalized magnetic biochar (Ca/MBC) was fabricated via a two-step pyrolysis method. Iron-containing oxides endowed the target complexes with magnetic properties, especially the chemotactic binding ability with MG, and the addition of calcium significantly changed the morphology of the material and improved its adsorption performance, especially the chemotactic binding ability with MG, which could be confirmed through FTIR, XPS, and adsorption experiments. Electrostatic adsorption, ligand exchange, and hydrogen bonding acted as essential drivers for an enhanced adsorption process, and the maximum theoretical adsorption capacity was up to 12,187.57 mg/g. Ca/MBC maintained a higher adsorption capacity at pH = 4–12, and after five adsorption–desorption cycles, the adsorption capacity and adsorption rate of MG remained at 1424.2 mg/g and 71.21%, highlighting the advantages of Ca/MBC on adsorbing MG. This study suggests that biochar can be modified by a green synthesis approach to produce calcium-functionalized magnetic biochar with excellent MG removal capacity. The synthetic material can not only remove pollutants from water but also provide an efficient way for soil remediation.

Application of Mössbauer spectroscopy to study the thermal behavior of iron-containing oxide coatings formed on titanium by plasma-electrolytic oxidation

Application of Mössbauer spectroscopy to study the thermal behavior of iron-containing oxide coatings formed on titanium by plasma-electrolytic oxidation

Effect of Fe2O3 on Electro-Deoxidation in Fe2O3-Al2O3-NaCl-KCl System

The reduction of Fe2O3-Al2O3 is one of the important reactions in the resource utilization of iron-containing oxide waste. Fe2O3-Al2O3 was electro-deoxidized in the NaCl-KCl system by molten salt electrolysis to prepare FeO/Al2O3. The effect of the Fe2O3 content on the electro-deoxidation reaction process was studied. The results show that under the conditions of 850 °C, 2.3 V, and electro-deoxidation for 4 h, FeO/Al2O3 could be obtained by controlling the content of Fe2O3. The deoxidation process was divided into three stages: electric double layer charging, Fe2O3 electro-deoxidation to Fe3O4, and Fe3O4 electro-deoxidation to FeO. With the increase in the Fe2O3 content, the deoxidation reaction rate increased, and the low-valence iron oxide particles obtained by electro-deoxidation became larger. The mechanism of the influence of Fe2O3 on the electro-deoxygenation process was determined by analyzing the experimental results. The increase in the Fe2O3 content increased the concentration of activated molecules in the system, while it reduced the resistance of electro-deoxidation. The migration of active particles in the cathode was smoother, which increased the percentage of deoxygenation of activated molecules, thereby shortening the process of the deoxidation reaction.

Use of dry grinding process to increase the leaching of gold from a roasted concentrate containing hematite in the thiosulfate system

Iron-containing oxides are the main minerals associated with roasted gold concentrates. The influence of different iron-containing oxides on the gold thiosulfate leaching process is very complex. In this study, we found the use of dry grinding methods can considerably eliminate the adverse effects on gold thiosulfate leaching under wet grinding conditions for a roasted gold concentrate containing hematite. The leaching results of gold ore showed that the gold leaching percentage was significantly improved from only 35% in 8 h under wet grinding conditions to 85% under dry grinding conditions. Using dry grinding to replace wet grinding, the loss of copper ions in the solution is much lower, and the diffusion coefficient of copper ions in the slurry is higher. Scanning electron microscopy (SEM) characterization shows that the passivation of the gold surface is much reduced. X-ray photoelectron spectroscopy (XPS) detection shows that the material adsorbed on the gold surface is mainly FeOOH. In addition, X-Ray diffraction (XRD) analysis results indicate that under wet grinding conditions, part of the hematite is transformed into goethite. Combined with the leaching results of gold powder, it is confirmed that the formed goethite during wet grinding is the cause of the deterioration of the gold leaching. Dry grinding can effectively avoid the formation of goethite and thus is a useful method to increase the gold leaching rate.

Improving Fly Ash Brightness with Carbon and Iron Oxide Removal

In this paper, the brightness of fly ash is improved by carbon removal by heating and iron-containing oxides removal by acid treatment using a two-step method to realize the application of fly ash as filler or coating in the future, which not only increases the range of resource utilization of fly ash, but also reduces dust pollution. The modification results show that the brightness of fly ash reaches the maximum value of 38.27% ISO (Brightness unit) after decarburization by heating at 600 °C. On this basis, the Box–Benhnken design scheme is adopted to optimize the brightening process for removing iron-containing oxides in fly ash. Finally, when the concentration of hydrochloric acid is 15%, the acid leaching time is 0.75 h, the reaction temperature is 74 °C, and the brightness of fly ash can eventually increase to 43.92% ISO.

Beneficial Effect of a Pre-ceramic Polymer Coating on the Protection at 900 °C of a Commercial AISI 304 Stainless Steel

An effective and low-cost method for applying polysilazane-based barrier coating on stainless steel is presented. A SiN (PHPS) precursor has been used for applications of polymeric and ceramic-like coating material. With precursor solution in dibutyl ether, AISI 304 stainless steel substrates were coated by means of a simple dip coating technique. After pyrolysis stage at 800 °C, the efficiency of the PHPS-based coating has been proved, and oxidation tests were done at 900 °C in air. By measuring the weight gain, and by using analytical techniques as in situ X-Ray Diffraction and Scanning Electron Microscopy, it has been shown that an amorphous silica layer formed from the initial PHPS-based coating and acts as a protective glass which provides complete separation of the AISI 304 steel surface from the oxidizing environment. This protective silica layer appears to be a very good diffusion barrier by preventing iron-containing oxide formation.

Effect of the sequence of chemical transformations on the spatial segregation of components and formation of periclase-spinel nanopowders in the MgO–Fe2O3–H2O System

Specific features of the process in which oxide nanopowders are formed in a hydrothermal treatment of coprecipitated magnesium and iron oxides were studied. It was shown that the rate at which oxide nanoparticles are formed increases when reagents structurally close to the final product are used. It was found that, with the hydrothermal treatment of coprecipitated magnesium and iron hydroxides at 450°C combined with the subsequent thermal treatment in air at temperatures of 400–600°C, it is possible to obtain a homogeneous mixture of nanocrystalline powders based on an iron-containing spinel phase and magnesium oxide.

Use of conditioning time to investigate the mechanisms of interactions of selected fatty acids on hematite Part II laboratory investigations

It is the aim of this paper to examine the effects of conditioning time on the flotation of hematite using three technical grade fatty acid reagents as providing additional evidence on their mechanism of interaction with the hematite surface. Various mechanisms have been postulated as occurring as conditioning time is increased. Both physical (e.g. conditioning time and power input) and chemical (nature, dispersion and solubility of the adsorbing species) contribute to the mechanisms of attachment of collector. In this paper, the mechanism of attachment of oleate to hematite can be readily explained by chemisorption, but the mechanism of attachment of lauric acid appears to be physical adsorption at neutral pH. The flotation of hematite with a mixture of tallow-type fatty acids (palmitic, stearic and oleic acids) is very sensitive to conditioning time, and suggests that, even though flotation is very effective at short conditioning times, it is very susceptible to the presence of fines and their associated high surface areas. It is therefore obvious that both the physical and chemical conditions contribute to the mechanisms of adsorption of fatty acids on iron-containing oxide minerals and must be understood in order to optimise the flotation of these minerals in an industrial situation.