Iron Phases Research Articles

New evidences in CO oxidation and selective chemisorption of carbon oxides on different alkaline ferrite crystal phases (NaFeO2 and LiFeO2)

Different thermogravimetric and CO oxidation analyses were performed on sodium and lithium ferrites (NaFeO2 and LiFeO2) to study CO-CO2 sorption selectivity and mechanism, in presence and absence of oxygen. In both phases, CO is chemisorbed producing the corresponding alkaline carbonate and secondary iron phases with reduced oxidation states. In all the cases, NaFeO2 showed better sorption and oxidation properties than the Li-based ferrite. The sorption and catalytic behavior observed between the alkaline ferrites studied are associated to the crystal structures and alkali composition. Although Li and Na chemical affinity to these gases is similar, their availability changes based on the ferrite crystal structure. Additionally, on CO oxidation properties, the ferrite with tetrahedrally coordinated Fe3+ ions presented better efficiency against CO oxidation than the ferrite with octahedrally coordinated Fe3+ ions.

Density and thermal expansion coefficients of liquid and austenite phase in lamellar cast iron

Volume change related defects formation mechanisms are an important detracting phenomenon in production of complex shaped cast components. Among different technical alloys, cast iron behaves in a complex manner due to the combined volume change of the formed phases. The liquid and the austenitic phase are contracting while the graphite phase is expanding during the solidification. The complex volume change in combination with complex casting shapes causes a considerable deviation from isotropy in the solidification domain. The mentioned difficulties are considered the main reason why an extensive research work is condensed in the literature within this topic. The multitude of reported experimental set up and the various efforts to interpret the volume change phenomena in terms of density and thermal expansion coefficients makes the results difficult to compare from different sources. With these difficulties in mind, the present paper presents a broad experimental series and measures unidirectional linear deformation of an industrially spread lamellar cast iron alloy system (Fe-C-2Si) using the push-rod based dilatometer technique. The measurements are divided into two major groups with respect to the liquid iron deformation over the liquidus temperature line, and the austenite deformation below the solidus temperature line. The obtained results are interpreted as thermal expansion coefficients, density variation slopes, and density data at the liquids and solidus temperature. The obtained results are compared with literature data and with calculated values by the Thermo Calc software.

Recovery of Molybdenum, Chromium, Tungsten, Copper, Silver, and Zinc from Industrial Waste Waters Using Zero-Valent Iron and Tailored Beneficiation Processes

Zero-valent iron (ZVI) has been used for water treatment for more than 160 years. However, passivation of its surface often constituted a problem which could only be tackled recently by the innovative Ferrodecont process using a fluidized bed reactor. In this study, pilot scale experiments for the removal of Mo, Cr, W, Cu, Ag and Zn from two industrial waste water samples and lab-scale experiments for the beneficiation of the abrasion products are presented to integrate the Ferrodecont process into a complete recycling process chain. Firstly, 38.5 % of Cu was removed from sample A, yielding abrasion products containing 33.1 wt% Cu as metallic copper (Cu) and various Cu compounds. The treatment of sample B removed 99.8 % of Mo, yielding abrasion products containing 17.8 wt% of Mo as amorphous phases or adsorbed species. Thermal treatment (1300 °C) of the abrasion product A indicated a reduction of delafossite to metallic Cu according to differential scanning calorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD), which was successfully separated from the magnetic iron phases. Hydrometallurgical treatment (1.5 M NaOH, 3 d, liquid:solid ratio (L:S) = 15:1) of sample B yielded aqueous extracts with Mo concentrations of 5820 to 6300 mgL−1. In conclusion, this corresponds to an up to 53-fold enrichment of Mo during the entire process chain.

Spatially Resolved Organomineral Interactions across a Permafrost Chronosequence.

Permafrost contains a large (1700 Pg C) terrestrial pool of organic matter (OM) that is susceptible to degradation as global temperatures increase. Of particular importance is syngenetic Yedoma permafrost containing high OM content. Reactive iron phases promote stabilizing interactions between OM and soil minerals and this stabilization may be of increasing importance in permafrost as the thawed surface region ("active layer") deepens. However, there is limited understanding of Fe and other soil mineral phase associations with OM carbon (C) moieties in permafrost soils. To elucidate the elemental associations involved in organomineral complexation within permafrost systems, soil cores spanning a Pleistocene permafrost chronosequence (19,000, 27,000, and 36,000 years old) were collected from an underground tunnel near Fairbanks, Alaska. Subsamples were analyzed via scanning transmission X-ray microscopy-near edge X-ray absorption fine structure spectroscopy at the nano- to microscale. Amino acid-rich moieties decreased in abundance across the chronosequence. Strong correlations between C and Fe with discrete Fe(III) or Fe(II) regions selectively associated with specific OM moieties were observed. Additionally, Ca coassociated with C through potential cation bridging mechanisms. Results indicate Fe(III), Fe(II), and mixed valence phases associated with OM throughout diverse permafrost environments, suggesting that organomineral complexation is crucial to predict C stability as permafrost systems warm.

Investigation of the effects of selected bio-based carburising agents on mechanical and microstructural characteristics of gray cast iron

The mechanism of graphite formation on gray cast iron metal during carburisation process using organic nano-carbon (ONC) was investigated at 900 °C for a holding time of three (3) hours. TEM and XRD were employed to characterize the pulverised nano-carbon to determine their phases and bonding potentials. Also, SEM/EDS, XRD and Vickers’ hardness tester were employed to determine the microstructure, phase compositions as well as hardness and wear properties of the carburised material. The microstructural result showed that, there was uniform carbon diffusion into the substrate material which led to layers of graphite formation and subsequent surface modifications for each of the selected nano-carbon used. Also, the XRD results revealed variations in the peak patterns for each of the substrate carburised with different organic carbon with substrates showing graphite and iron phases as observed in that carburised in pulverised palm kernel shell having broad peaks at 35.50o, 44.4o, 65.12o and 82.395o. This is traceable to amorphous properties and crystalline behaviour of the organic carbon. Further to this, the micro-hardness measurement showed that substrate carburised using pulverised palm kernel shell performed better compared to other substrates in other media with a micro hardness value of 355.8 (HV) against as-received which is 116.9 (HV). Thus, this is a novel and possible method of improving the properties of grey cast iron to meet the increasing demand in gear applications.

Combined Haber-Weiss and vacancy mechanism: Ce4+ used as intelligent isomorphic ions in iron oxides

Cerium is known for its good ability to transition between the Ce3+ and Ce4+ forms, which modulates its ability to incorporate oxygen into different material structures. Therefore to promote the slow phase characterize by oxidative processes, related to phase of regenerating the reduced metallic sites, iron oxide-based catalysts partially replaced by cerium were synthesized, and their physical, textural and morphological properties were evaluated. The catalysts were prepared by synthesizing the magnetite phase and doping with cerium (Ce4+), such that the isomorphic ion content in the FeCex formula was 0.05> x> 0.2 mol. The X-ray diffraction (XRD) results of the oxide after Ce was incorporated exhibited peaks corresponding to magnetite, which is less crystalline than bulk iron, suggesting that the isomorphic ion was incorporated into the iron oxide crystal lattice. Furthermore, incorporating the rare earth element also favored the appearance of diffraction peaks corresponding to the formation of other iron phases, such as goethite. The results suggest a strong interaction between the metals, because even after the single addition of Ce4+, X-ray photoelectron spectrometry (XPS) analysis shows the presence of the +3 and +4 oxidation states. The materials obtained after incorporating cerium had a high catalytic capacity for removing a reactive red dye. The dye removal was significant, and the materials demonstrated a remarkable chemical stability and remained active for seven consecutive reaction cycles without the need for regenerating the active centers. The dye removal essentially occurs by a heterogeneous process, in which the active phase leaching rates are not significant.

Iron mineralogy and speciation of sediment iron-bearing minerals in mangrove forest: Case study of Zhangjiang estuary, China

Few investigations of iron speciation exist in intertidal conditions with little attention given to understanding the geochemical behavior of Fe3+–Fe2+ and its biogeochemical processes. Here, one sediment core was collected in Yunxiao mangrove forests, Zhangjiang estuary, China and iron mineralogy was determined by magnetic methods and Mössbauer spectroscopy. Changes in magnetic susceptibility, susceptibility of anhysteretic remanent magnetization, and saturation isothermal remanent magnetization were linked to changes of pseudo-single domain soft coercive components with minor antiferromagnetic fractions and the presence of minimal concentrations of superparamagnetic particles was confirmed by the no frequency dependent of AC magnetization. A positive correlation between L-ratio and hard isothermal remanent magnetization is congruent with the distribution of high-coercivity antiferromagnetic minerals. At 295 K, the Mössbauer spectrum of specimens was well fitted with a single magnetic sextet, hematite and two magnetic doublets, paramagnetic Fe2+ and paramagnetic Fe3+. The usefulness of magnetic data and Mössbauer spectroscopy could offer valuable analytical tools for tracking changes of iron speciation and phase in the intertidal conditions.

Unraveling the Mineralogical Complexity of Sediment Iron Speciation Using Sequential Extractions

AbstractIron speciation is one of the most widely applied proxies used to reconstruct oxygen levels and redox conditions in past aqueous environments. The iron speciation proxy estimates proportions of different reactive iron species in fine‐grained sedimentary rocks, which are mapped to redox conditions based on empirical calibrations from modern sediments. It is based on a standardized extraction technique of sequentially applying acetate, hydroxlamine‐HCl, dithionite, and oxalate solutions to a powdered sample in order to dissolve iron phases and quantify the amount of iron carried by carbonates, “easily reducible” oxyhydroxides, ferric iron (oxyhydr)oxides, and magnetite, respectively. Although tested on pure minerals and mixtures, assessments of whether this sequential extraction process accurately dissolves the targeted minerals in natural sediments and sedimentary rocks are lacking. In our study, residues from each sequential extraction step were analyzed using rock magnetic and X‐ray diffraction experiments to identify and quantify the iron‐bearing minerals that were dissolved. The dithionite extraction robustly removes the targeted mineralogy as magnetic data show it to solubilize nearly all of the goethite. However, magnetic quantification of magnetite was orders of magnitude less than the iron measured in the oxalate extraction; X‐ray diffraction data suggest that dissolution of iron‐bearing clays, specifically berthierine/chamosite, could explain this disparity. Our data compilation shows higher values of iron from the oxalate extraction in Precambrian sedimentary rock samples, suggesting a significant temporal shift in iron cycling. Recognition of heterogeneity in chemical extraction efficiency and targeting is vital for holistic multiproxy interpretation of past oxygen levels and communication between disciplines.

The Influence of Remelting on the Properties of AlSi9Cu3 Alloy with Higher Iron Content.

This article aims to evaluate the influence of remelting on the experimental Al-Si-Cu type alloy with higher iron content on mechanical properties in relation to the resulting structure. The remelting or recycling process is one of the means of reducing the production costs of the forge plant. The experimental part deals with the analysis of the results of mechanical properties, structural analysis, and the process of crystallization of structural components and their changes due to the increased iron content caused by remelting at different states of the examined alloy. The effect of remelting and ageing on microstructure was observed using a combination of different analytical techniques (light microscopy, scanning electron microscopy (SEM), and upon deep etching and energy dispersive X-ray analysis (EDX)). Tensile strength and elongation tests point to the negative effect of alloying, a gradual increase in wt% Fe and a change in the morphology of the iron phases, which began to manifest significantly after the fourth remelting. The process of natural ageing has been shown to be effective only on alloys with a lower number of remelting cycles, whereas the application of artificial ageing has resulted in improved mechanical properties in all the test alloys.

Evaluation of carbothermal reduction for processing of banded hematite quartzite iron ore

ABSTRACTThis study evaluates iron recovery from low grade banded hematite quartzite iron ore. The ore was found susceptible to microwaves and hence carbothermal reduction was pursued. The susceptibility of iron phases to microwave exposure and their selective absorption assists in the liberation of iron values. It was observed that ferrite balls were formed when a small fraction of ore-charcoal mixture was microwave irradiated. The adequate presence of bonded silica content leads to an easy formation of the fayalite phase which leads to fall in the iron grade. Microwave carbothermal reduction at the varying charcoal dosage (6–11%) yielded FeG 45–48% at FeR 40–70%. However, at higher charcoal dosage (11%), ferrite ball formation was observed. Taguchi L9 statistical design revealed the formation of ferrite ball at the higher charcoal dosage (9–12%) and higher power (720–900 W) which accounts for 8–10% of total iron values contained.

An artificial neural network model for the unary description of pure substances and its application on the thermodynamic modelling of pure iron

The aim of this work is to introduce a novel approach for the universal description of the thermodynamic functions of pure substances on the basis of artificial neural networks. The proposed approximation method is able to describe the thermodynamic functions (C_{p}(T), S(T), H(T)-H(T_{mathrm{ref}}), G(T)) of the different phases of unary material systems in a wide temperature range (between 0 and 6000 K). Phase transition temperatures and the respective enthalpies of transformation, which are computationally determined by the minimization of the Gibbs free energy, are also approximated. This is achieved by using artificial neural networks as models for the thermodynamic functions of the individual phases and by expressing the thermodynamic quantities in terms of the free network parameters. The resulting expressions are then optimized with machine learning algorithms on the basis of measurement data. A physical basis for the resulting approximation is given by the use of, among others, Planck–Einstein functions as activation function of the neurons of the network. This article provides a description of the method and as an example of a specific application the approximation of the thermodynamic functions of the different phases of pure iron. The article focuses on the problem of the representation of thermodynamic data and their practical application.

Features of the interfacial zone structure formation during thermal diffusion metallization of diamond by transition metals

The paper studies morphology, chemical, structural and phase composition of the diamond-metal interphase zone, formed in the process of thermal diffusion metallization of diamond with chromium, titanium, iron, nickel and cobalt powders with the same temperature-time mode that corresponds to the sintering of diamond-containing WC-Co-matrices with copper impregnation. In the process of thermal diffusion metallization of chromium and titanium, a metalized coating is formed on the surface of the diamond, consisting of a mixture of carbides, metals and graphite of variable composition phases. The insignificant content of graphite formations and their intermittent nature of the diamond-metal interfacial zone ensure a strong adhesion of the metalized coating to the diamond through the carbides of the corresponding metals. When thermal diffusion metallization of diamond with iron occurs at the diamond-metal interfacial zone, the formation of an intermediate layer strongly adhered to the diamond also takes place. The intermediate layer has a complex structural phase composition comprising a mixture of iron phases, a solid solution of carbon in iron and graphite of variable composition. An intermediate layer on the surface of diamond could be formed by solidification of the liquid phase with the eutectic composition resulting from the eutectic melting of the diamond-iron contact pairs. However, this assumption requires additional research to confirm it, and special experiments using highly sensitive research methods. Under the heating conditions specified in the experiment samples of nickel-diamond and cobaltdiamond cause intense catalytic graphitization of diamond with the formation of numerous traces of erosion on its surface. The observed weak adhesive interaction of these metals with diamond is probably due to the high melting temperatures of the Ni-C and Co-C eutectics, which does not allow the metals to react with diamond under given experimental conditions.

Magnetic phase diagram of ɛ′ -FeH

Iron hydrides attract significant interest as candidates for the main constituents of the Earth's core in geophysics and planetary science. However, their basic physical properties are still not well known. Here, we combined high-pressure transport, synchrotron radiation M\ossbauer, and Fe $K\ensuremath{\beta}$ x-ray emission spectroscopy measurements on ${\ensuremath{\varepsilon}}^{\ensuremath{'}}$-FeH to map out a detailed magnetic phase diagram of this hydride phase of iron. In contrast to our original expectations, we found two magnetic phase transitions at high pressure due to two inequivalent iron sites existing in the ${\ensuremath{\varepsilon}}^{\ensuremath{'}}$-FeH structure. Our results account for the previous large pressure difference on the loss of ferromagnetism between experiment and theoretical calculations. The discovery of an unexpected complex magnetic phase diagram in ${\ensuremath{\varepsilon}}^{\ensuremath{'}}$-FeH has implications for a better understanding of the magnetic and physical properties of the iron-hydrogen compounds, important for the conditions of planetary interiors.

Processing of Banded Hematite Quartzite Ore for Recovery of Iron Values

This study investigates upgrading of low-grade banded hematite quartzite iron ore (Fe ~31%). Conventional beneficiation was found to be futile. The susceptibility of iron phases to microwave exposure and their selective absorption assists in the liberation of iron values. Microwave exposure of coarse particles at 540 W for 10 min yielded a concentrate with Fe 56.30% and recovery of 50.68%. Conventional carbothermic reduction at 500 °C, 60 min and 9% charcoal yielded a concentrate with Fe 57.6% and iron recovery of 68%. The presence of sufficiently bonded silica leads to an easy formation of a fayalite phase. The microwave reduction design yielded FeG of 57.6%, FeR of 47% and a yield of 24% at an optimal condition of 540 W, 8 min and 6% charcoal. It was found that a small fraction of microwave-irradiated ore-charcoal mixture melted rapidly, and pure ferrite balls were observed within 8 min. An optical micrograph of a ferrite ball reveals the retained austenite and martensite phase.

New Magnetic Fe Oxide-Carbon Based Acid Catalyst Prepared from Bio-Oil for Esterification Reactions

In this work, bio-oil (an organic matrix rich in oxygen functionalities) was used to efficiently dissolve and disperse Fe3+ which upon thermal treatment produced a carbon containing dispersed and encapsulated Fe oxide magnetic nanoparticles. These materials were prepared by dissolution of 8, 16 and 24 wt.% Fe3+ salt in bio-oil followed by treatment at 400, 450, 500 or 600 oC in N2 atmosphere. X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopies (TEM), elemental analysis, thermogravimetric-mass spectrometry (TG-MS), potentiometric titration, Raman and Mossbauer spectroscopies showed that Fe3+ species in bio-oil is reduced to produce magnetic nanoparticles phases: magnetite Fe3O4 and maghemite γ-Fe2O3. At low temperatures, the iron phases were less protected, and the carbon matrix was more reactive, while in temperatures above 500 oC, the iron phases were more stable, however, the carbon matrix was less reactive. Reaction of these magnetic carbon materials with concentrated H2SO4 produced surface sulfonic acidic sites (ca. 1 mmol g-1), especially for the materials obtained at 400 and 450 oC. The materials were used as catalysts on esterification reaction of oleic acid with methanol at 100 oC and conversions of 90% were reached, however, after 2 consecutive uses, the conversion decreased to 30%, being required more studies to improve the material stability.

Effect of vibration frequency on primary phase and properties of grey cast iron fabricated by lost foam casting

The properties of gray cast iron (GCI) are affected by density of matrix, size of flake graphite and primary austenite. In this paper, the Y-type specimen of GCI was prepared by lost foam casting (LFC) with and without vibration, and the influence of vibration frequency on the density of matrix, size of primary phase, and properties of the GCI was studied. The results show that the length of the flake graphite and the size of the primary austenite in GCI firstly decrease and then increase with the increase of the vibration frequency. With a vibration frequency of 35 Hz, the length of the flake graphite is the shortest, the primary austenite is the finest and the density of the matrix is the highest. In addition, the tensile strength, elongation and hardness of the GCI firstly increase and then decrease with the increase of the vibration frequency, due to the refinement of the primary phase and the increase of the matrix density. In order to analyze the refinement mechanism of the primary phase of the GCI fabricated by the LFC with vibration, the solidification temperature fields of the GCI fabricated by the LFC with the vibration frequency of 0 and 35 Hz were measured. The results show that the vibration reduces the eutectic point of the GCI and increases the supercooling degree during the eutectic transformation. As a result, the length of the flake graphite and the size of the primary austenite in GCI fabricated by LFC with the vibration frequency of 35 Hz decrease.

Оксидно-металлические гетерогенные радиопоглощающие в средней и ближней ИК-областях покрытия, содержащие магнитоактивные фазы никеля, кобальта и железа, сформированные методом импульсного микроплазменного оксидирования

Оксидно-металлические гетерогенные радиопоглощающие в средней и ближней ИК-областях покрытия, содержащие магнитоактивные фазы никеля, кобальта и железа, сформированные методом импульсного микроплазменного оксидирования

Influence of dispersity on local physical, structural, magnetic and thermodynamic properties of bcc Fe and its binary alloys

The model was proposed for iron nano-particles (and solid solutions based on bcc-Fe) containing a core and a surface layer coherent with each other in the form of a two-phase stratifying parts (“surface” and bulk) system with different local physical properties. Using the results of measurements of the experimental temperature dependence of the heat capacity and the application of the Debye models for both the “core”-phase and the surface layer (“surface”-phase) as two-phase heat capacity components for Fe nanoparticles, it was shown by calculations that the local elastic modulus for the surface layer is nano-particles are approximately 2 times smaller than for the “core”-phase of the nano-particle iron. The purpose of the research is to establish the relationship between local physical properties (bulk modulus of elasticity, static displacements of iron atoms surrounding an impurity atom, magnetic moments) for the core part and the surface layer of nanoparticles. From the condition of local mechanical equilibrium it was shown that static displacements of Fe atoms around an impurity atom in various coordination spheres on the surface of nanoparticles of Fe-rich binary BCC solutions of Fe - (Cr, V, Mo, W) with nano-particles increase significantly (compared to static displacements of Fe atoms “core” of nano-particles).

Synthesis and structural characterization of iron-cementite nanoparticles encapsulated in carbon matrix

Carbon-encapsulated iron-cementite (Fe-Fe3C) nanoparticles, promising nanomaterials for medicine due to their valuable magnetic properties, were synthesized by a single-step solid-state pyrolysis of iron phthalocyanine. To obtain required magnetic characteristics of such nanoparticles by governing of the pyrolysis conditions one needs reliable structural information of the atomic architecture of the obtained nanoparticles of composition (Fe-Fe3C), in which Fe atoms have different types of the local surrounding. The latter complicates the structural characterization of samples, which was performed using the complementary methods of TEM, SAXS, XRD, XANES, and EXAFS and the results of simulations by the method of reactive force field molecular dynamics (ReaxFF MD). The size of the particles is on the order of 10 nm with cementite concentration of about 60–70 wt%. The simulations enabled to reveal that the most plausible combinations of the local structures of Fe atoms in (Fe-Fe3C) nanoparticle result in the difference of corresponding atomic pair radial distribution functions relatively to iron (RDF), which can be further filtered through the comparison with experimentally obtained RDF for iron atoms in the studied sample. Such RDF was derived from experimental Fe K-edge EXAFS in the sample by Fourier transform multi-shell processing within harmonic approximation and using the results of the analysis of SAXS, XRD, and XANES. The used approach, based on the filtering of ReaxFF MD-calculated RDFs via comparison with the EXAFS derived RDF, revealed that for particles of composition (Fe-Fe3C) with XRD derived iron:cementite ratio of $\sim 40$:60 wt% and sizes bigger than 4 nm, the architecture with iron in core region of particle and cementite in its shell (Fe@Fe3C) is the most probable for the mean nanoparticle comparing with architectures of the inverted core-shell (Fe3C@Fe) or the mixture of iron and cementite phases (Fe+Fe3C).

Investigations of the effective parameters on the synthesis of monodispersed magnetic Fe3O4 by solvothermal method for biomedical applications

Monodispersed magnetite nanoparticles were obtained by investigating the different synthesis parameters of the solvothermal method. The morphology and chemical structure of the Fe3O4 nanoparticles were characterized by Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), Dynamic Light Scattering (DLS) and Vibrating sample magnetometer (VSM). Results indicated that without the addition of water, it forms the minor phase of iron instead of magnetite. Furthermore, the size of nanoparticles is tunable in the range of 117.7 to 217.6 nm by changing the amounts of water, PSSMA and NaOH. The amount of PSSMA restricts the growth of the nanoparticles and narrow the size distribution and a hydrophilic surface was obtained. Synthesized magnetite nanoparticles were successfully conjugated with carbon dots. The resulting nanoparticles exhibited good fluorescence characteristics. Cytotoxicity tests confirmed that nanoparticles are non-toxic. Both magnetite and C-dots/Fe3O4 nanoparticles are good potential candidates for biomedical applications specifically for bioimaging and biosensing in the future.