iron carbide

The Mössbauer spectroscopy of iron carbides (α-Fe, γ'-FeC, η-Fe2C, ζ-Fe2C, χ-Fe5C2, h-Fe7C3, θ-Fe3C, o-Fe7C3, γ'-Fe4C, γ''-Fe4C, and α'-Fe16C2) is predicted utilizing the all electron full-potential linearized augmented plane wave (FLAPW) approach across various functionals from LDA to GGA (PBE, PBEsol, and GGA + U) to meta-GGA to hybrid functionals. To validate the predicted MES from different functionals, the single-phase χ-Fe5C2 and θ-Fe3C are synthesized in experiment and their experimental MES under different temperature (from 13 K to 298 K) are determined. The result indicates that the GGA functional (especially, the PBEsol) shows remarkable success on the prediction of Mössbauer spectroscopy of α-Fe, χ-Fe5C2 and θ-Fe3C with delocalized d electrons. From the reliable simulations, we propose a linear relationship between Bhf and μB with a slope of 12.81 T/μB for iron carbide systems and that the proportionality constant may vary from structure to structure.

Les fibres naturelles sous leurs formes traditionnelles ou sous de nouvelles formes (fibres/films/ composites régénérés) offrent une alternative aux fibres synthétiques. La soie du Bombyx mori présente de très bonnes propriétés mécaniques moyennes, mais une très grande variabilité. Afin de mieux comprendre cette variabilité des soies de différentes sources (vers à soie ou araignées) sont analysées par plusieurs techniques (absorption Infrarouge et diffusion Raman in situ-in vivo, calorimétrie, traction uniaxiale) pour caractériser simultanément la structure et la mécanique des monofilaments, en fonction de leur âge, depuis le précurseur de fibroïne dans la glande jusqu'aux fibres chimiquement traitées (décreusage, teintures) en passant par des fibres prélevées in vivo. Cinq comportements sont identifiés et discutés en fonction des changements structuraux (transition hélices α - feuillets β), des interactions avec l'eau à la lumière de l'analyse des modes Amide I & II ain...

The Fe 5 PB 2 compound offers tunable magnetic properties via the possibility of various combinations of substitutions on the Fe and P-sites. Here, we present a combined computational and experimental study of the magnetic properties of (Fe 1-x Cox) 5 PB 2 . Computationally, we are able to explore the full concentration range, while the real samples were only obtained for 0 ≤ x ≤ 0.7. The calculated magnetic moments, Curie temperatures, and magnetocrystalline anisotropy energies (MAEs) are found to decrease with increasing Co concentration. Co substitution allows for tuning the Curie temperature in a wide range of values, from about six hundred to zero kelvins. As the MAE depends on the electronic structure in the vicinity of Fermi energy, the geometry of the Fermi surface of Fe 5 PB 2 and the k-resolved contributions to the MAE are discussed. Low temperature measurements of an effective anisotropy constant for a series of (Fe 1-x Cox) 5 PB 2 samples determined the highest value of 0.94 MJ m -3 for the terminal Fe 5 PB 2 composition, which then decreases with increasing Co concentration, thus confirming the computational result that Co alloying of Fe 5 PB 2 is not a good strategy to increase the MAE of the system. However, the relativistic version of the fixed spin moment method reveals that a reduction in the magnetic moment of Fe 5 PB 2 , by about 25%, produces a fourfold increase of the MAE. Furthermore, calculations for (Fe 0.95 X 0.05 ) 5 PB 2 (X = 5d element) indicate that 5% doping of Fe 5 PB 2 with W or Re should double the MAE. These are results of high interest for, e.g., permanent magnet applications, where a large MAE is crucial.

and Astronomy-The magnetotransport properties of C-Fe films formed by e-beam vapor deposition onto glass substrates are presented in the temperature region of 2 K to 300 K. Hall effect measurements exhibit a significant anomalous Hall voltage whose magnitude increases with increasing temperature. Measurements of the ordinary Hall coefficient in 10 nm-thick films give a charge carrier density ranging from n ∼ 3.0 x 10 29 m −3 at 2 K to approximately half that value at 290 K. A comparison between anomalous Hall effect and parallel field magnetooptic Kerr effect measurements reveal a highly anisotropic coercive field with the easy direction lying in the plane of the film. The films have an isotropic linear positive magnetoresistance (LPMR) beyond their saturation magnetization.

We report a tunable organometallic synthesis of monodisperse iron carbide and core/shell iron/iron carbide nanoparticles displaying a high magnetization and good air-stability. This process based on the decomposition of Fe(CO) 5 on Fe(0) seeds allows the control of the amount of carbon diffused and therefore the tuning of nanoparticles magnetic anisotropy. This results in unprecedented hyperthermia properties at moderate magnetic fields, in the range of medical treatments.

The magnetotransport properties of C-Fe films formed by e-beam vapor deposition onto glass substrates are presented in the temperature region of 2 K to 300 K. Hall effect measurements reveal a significant anomalous Hall voltage whose magnitude increases with increasing temperature. Measurements of the ordinary Hall coefficient in 10 nm-thick films reveal a charge carrier density ranging from n ≅ 3.0 × 10 29 m −3 at 2 K to approximately half that value at 290 K. A comparison between anomalous Hall effect and parallel field magneto-optic Kerr effect measurements reveals a highly anisotropic coercive field with the easy direction lying in the plane of the film. Magnetoresistance measurements show that the films posses isotropic linear positive magnetoresistance beyond their saturation magnetization. The presence of carbon nanotubes formed during the e-beam process is confirmed via atomic force microscopy.

Recent efforts towards developing novel lead electrodes involving carbon and lead composites have shown potential for increasing the cycle life of lead–acid (LA) batteries used to store energy in various applications. In this study, first-principles calculations are used to examine the structural stability, defect formation energy, and migration barrier of C in Pb for LA batteries. Density functional theory with the GGA-PBE functional performed the best out of various functionals used for structural stability calculations. Furthermore, with the complete incorporation of C in the Pb matrix, the results show that C is energetically preferred to be at the octahedral interstitial (CiOcta) site in the FCC structure of Pb. Additionally, climbing-image nudged elastic band calculations show a minimum energy pathway for C diffusing from a stable octahedral site to the adjacent octahedral site assisted by a tetrahedral intermediate site. Therefore, the minimum energy pathway for C migration i...

Near-phase-pure nanoparticle iron carbides (Fe3C and Fe5C2) were synthesised. Debye model calculations were used with hyperfine parameters gathered by 57 Fe Mössbauer spectroscopy within a temperature range of 10 K to 293 K, with analysis providing Debye temperatures of 422 K and 364 K for two Fe sites in Fe5C2 and 355 K for ferromagnetic Fe3C. The intrinsic isomer shifts were calculated as 0.45 mm s −1 and 0.43 mm s −1 for iron sites 1 and 2 respectively in Fe5C2 and 0.42 mm s −1 for Fe3C. Recoil-free fractions for the two iron sites were also calculated at f300 0.785 and 0.726 for site 1 and 2 respectively.

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Recent efforts towards developing novel lead electrodes involving carbon and lead composites have shown potential for increasing the cycle life of lead–acid (LA) batteries used to store energy in various applications. In this study, first-principles calculations are used to examine the structural stability, defect formation energy, and migration barrier of C in Pb for LA batteries. Density functional theory with the GGA-PBE functional performed the best out of various functionals used for structural stability calculations. Furthermore, with the complete incorporation of C in the Pb matrix, the results show that C is energetically preferred to be at the octahedral interstitial (CiOcta) site in the FCC structure of Pb. Additionally, climbing-image nudged elastic band calculations show a minimum energy pathway for C diffusing from a stable octahedral site to the adjacent octahedral site assisted by a tetrahedral intermediate site. Therefore, the minimum energy pathway for C migration i...

Carbon materials have attracted increasing attention as supports for metal catalysts. Ironcontaining carbon nanotubes often promoted with copper have found application in Fischer-Tropsch synthesis, which provides an alternative way for conversion of renewable feedstocks to chemicals and fuels. In carbon nanotubes, the active phase can be nanoconfined inside the channels or localized on the outer surface. In most of previous work, the distribution of metal nanoparticles inside or outside carbon nanotubes is considered to be immobile during the catalyst activation or catalytic reaction. In this paper, we uncovered remarkable mobility of both iron and copper species in the bimetallic catalysts between inner carbon nanotube channels and outer surface, which occurs in carbon monoxide and syngas, while almost no migration of iron species proceeds in the monometallic catalysts. This mobility is enhanced by noticeable fragility and defects in carbon nanotubes, which appear on their impregnation with the acid solutions of metal precursors and precursor decomposition. Remarkable mobility of iron and copper species in bimetallic catalysts affects the genesis of iron active sites, and enhances interaction of iron with the promoter. In the bimetallic iron-copper catalysts, the major increase in the activity was attributed to higher reaction turnover frequency over iron surface sites located in a close proximity with copper.

Using theoretical quantum chemical methods, we investigate the dearth of ordered alloys involving thorium and titanium. Whereas both these elements are known to alloy very readily with various other elements, for example with oxygen, current experimental data suggests that Th and Ti do not alloy very readily with each other. In this work, we consider a variety of ordered alloys at varying stoichiometries involving these elements within the framework of density functional theory using the generalized gradient approximation for the exchange and correlation functional. By probing the energetics, electronic, phonon and elastic properties of these systems, we confirm the scarcity of ordered alloys involving Th and Ti, since for a variety of reasons many of the systems that we considered were found to be unfavorable. However, our investigations resulted in one plausible ordered structure: We propose ThTi 3 in the Cr 3 Si structure as a metastable ordered alloy. 1 I. INTRODUCTION Thorium, a heavy metal, combined with various elements such as boron, carbon, nitrogen and oxygen has been studied both theoretically 1-3 and experimentally 4-6 in relation 2 to a range of physical, chemical, electronic, and thermophysical properties, often exhibiting high density, good thermal conductivity and good mechanical properties. The applications of Th-based alloys are wide-ranging. These include uses in nuclear reactors and in the aerospace industry because of its good corrosion resistant properties and high melting points. Th binary systems exist in various ordered alloys such thorium monocarbide (ThC), 7 mononitride (ThN) 8 and monoxide ThO. 9 ThO crystallizes in the rock salt structure, while ThO 2 crystallizes in the fluorite structure. ThB 4 10 and ThB 6 exist in the ThB 4 and CaB 6 structures. Titanium, a relatively light metal is strong, has excellent corrosion resistant properties and a high melting point. Given its relatively small atomic size, Ti can be easily impregnated into materials without radically altering the host crystal structure. Therefore, Ti is a versatile element for alloying and modifying the properties-especially the strength properties-of materials. Applications range from additives in paints to metals for aerospace and industry. In this way, Ti is useful for engineering the properties of materials. Ti-based oxides are very well known, for example TiO 2 exists in the equilibrium rutile, and the metastable anatase and brookite structures, and the high pressure monclinic and orthorhombic forms. Ti also combines very readily with other metals, such as Pt in a variety of crystallographic forms and stoichiometries. It would seem, then, that ordered alloys involving Th and Ti should form readily when in fact this is not the case. Experimental evidence by Carlson et al. 11 dating back to 1956 still appears to be the only authoritative view on this subject, although similar results were found by Pedersen et al. in 1980. 12 Carlson et al. discovered that Th-Ti forms a simple eutectic at 1190 o C and at 12 wt % Ti, with no intermediate phases. Pedersen et al. found the eutectic composition to be 13.26 wt % Ti. The solid phases at the eutectic are α-Th (cubic) and β-Ti (hexagonal). Carlson et al. concluded that solid solubilities at room temperatures are negligible. They argued that since the atomic radii of Th and Ti differ by about 22%, and because the Hume-Rothery rules for alloying suggest that extensive solid solubility should not occur between metals differing in size by more than 15%, the dearth of compounds (ordered or not) should not be surprising. Furthermore, they argued that since there is a marginal difference in the electronegativity of these two elements (the electronegativities are 1.3 for Th and 1.5 for Ti), compound phases should not form readily.

Recent efforts towards developing novel lead electrodes involving carbon and lead composites have shown potential for increasing the cycle life of lead–acid (LA) batteries used to store energy in various applications. In this study, first-principles calculations are used to examine the structural stability, defect formation energy, and migration barrier of C in Pb for LA batteries. Density functional theory with the GGA-PBE functional performed the best out of various functionals used for structural stability calculations. Furthermore, with the complete incorporation of C in the Pb matrix, the results show that C is energetically preferred to be at the octahedral interstitial (CiOcta) site in the FCC structure of Pb. Additionally, climbing-image nudged elastic band calculations show a minimum energy pathway for C diffusing from a stable octahedral site to the adjacent octahedral site assisted by a tetrahedral intermediate site. Therefore, the minimum energy pathway for C migration i...

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

We present an approach to study the transferability of molecular dynamics (MD) interatomic potentials (IPs) for materials modeling during metal additive manufacturing (MAM) processes, which involves rapid and cyclic melting, solidification, vaporization, and solid phase transformations. We apply the approach to the ten available IPs of titanium (Ti) as an example, which resembles the MAM process modeling of commercially pure Ti and Tibase alloys. We consider the capability to produce solid phase change behavior of the alloy in equilibrium and nonequilibrium thermodynamics as the primary required characteristics of an IP for the MAM process modeling. Two-phase α-β, β-liquid, and liquid-vapor coexistence properties are used as the secondary criteria. Finally, we use other relevant single-phase properties as the tertiary criteria, such as the elastic constants at high temperatures, liquid structure factor, self-diffusivity, and shear viscosity. We show there are only three IPs that demonstrate reasonable characteristics for MAM process modeling.

Abstract—Fischer–Tropsch technology has gathered renewed interest in the energy industry in recent times for synthesis of diesel and gasoline. The synthesis of linear hydrocarbon diesel fuel (having high cetane number) through Fischer–Tropsch synthesis (FTS) reaction requires syngas with high H2/CO molar ratio. Producer gas obtained from biomass gasification has low H2/CO ratios, with significant content of CO2, and hence, is not suitable as feed for FT synthesis using conventional transition metal (usually cobalt and nickel) based catalysts. Catalysts having high water gas shift reaction (WGS) activity are suitable for FT synthesis with biomass derived producer gas, as WGS reaction can compensate for H2 deficiency. Iron catalysts are wellknown for their FTS as well as WGS activity. In this study, co-precipitated Fe-catalysts with different metal promoters have been synthesized and characterized In this work, we have attempted to identify different intermediate phases involved durin...

Methane has long captured the world's spotlight for being the simplest and yet one of the most notorious hydrocarbon. Exploring its potential to be converted into value added products has raised a compelling interest. In the present work, we have studied the efficiency of Single-Atom Catalysts (SACs) for methane activation employing Density Functional Theory (DFT). The Climbing Image-Nudged Elastic Bond (CI-NEB) method is used in tandem with the Improved Dimer (ID) method to determine the minimum energy pathway for the first C-H bond dissociation of methane. Our study reported that the transition-metal doped Cu(111) surfaces enhance adsorption, activate C-H bond, and reduce activation barrier for first C-H bond cleavage of methane. The results suggest Ru/Co/Rh doped Cu(111) as promising candidates for methane activation with minimal activation barrier and less endothermic reaction. For these SACs, the calculated activation barriers for first C-H bond cleavage are 0.17 eV, 0.24 e...

Fe Mössbauer spectroscopy was used to study the effect of iron concentration on the oxidation state and microenvironments of iron in Fepolygalacturonate compounds prepared by a novel method from pectin. The iron concentration of the coordination compounds was determined by inductively coupled plasma optical emission spectrometry analysis. The Mössbauer spectra of the studied compounds could be decomposed into three markedly different quadrupole doublets referring to three microenvironments. Two of these have ferrous and one has ferric oxidation state. In the applied concentration range the relative occurrence of the ferric component was found to increase considerably with iron concentration. At the same time, with increasing iron concentration the relative occurrence characteristic of the three components showed saturation behaviour up to the iron concentration at which for each pair of galacturonic acid units there is on average one

Fe Mössbauer spectroscopy was used to study the effect of iron concentration on the oxidation state and microenvironments of iron in Fepolygalacturonate compounds prepared by a novel method from pectin. The iron concentration of the coordination compounds was determined by inductively coupled plasma optical emission spectrometry analysis. The Mössbauer spectra of the studied compounds could be decomposed into three markedly different quadrupole doublets referring to three microenvironments. Two of these have ferrous and one has ferric oxidation state. In the applied concentration range the relative occurrence of the ferric component was found to increase considerably with iron concentration. At the same time, with increasing iron concentration the relative occurrence characteristic of the three components showed saturation behaviour up to the iron concentration at which for each pair of galacturonic acid units there is on average one

Spin polarized density functional theory computations were performed to elucidate electronic effects based on first-row transition metal doped Fe(100) and Fe 5 C 2 IJ100) surfaces for CO dissociation. Both Mn and Cr doped Fe(100) and Fe 5 C 2 IJ100) surfaces can enhance the dissociation of CO, while the Co, Ni and Cu doped ones are unfavorable for the dissociation of CO. Besides the BEP relationship, a linear relationship between activation energy and the electronegativity of the dopant atom is established. It can be deduced that the metals with lower electronegativity are favorable for the activation of CO. The reason has been analyzed by density of states and crystal orbital Hamilton population. The metals with lower electronegativity relative to Fe could donate electrons to doped sites and then activate CO with a more delocalized O 2p orbital. The electronic effects revealed herein are helpful for the understanding of the CO activation process and for the design of catalysts with desired activity.

The morphology change is crucial to the catalysis performance of catalyst nanoparticles in heterogeneous cat-alysis. Iron and iron carbide nanoparticles are used as high temperature heterogeneous catalyst, such as Fischer-Tropsch synthesis and carbon nanotube growth. Here we have investigated the effect of temperature and entropy on the surface free energy and morphology of the iron and iron carbide (θ-Fe 3 C, χ-Fe 5 C 2 , and o-Fe 7 C 3) nano-particles using molecular dynamics. The free energies of all the bulk and most of the surface systems drop following a parabolic curve with elevating temperature due to entropic effect. The nanoparticles are covered by low index surfaces at low temperature. At low temperature, the surface free energies of all surfaces usually decrease with a similar slope with increasing temperature. However, a critical temperature exists at which the high-index surfaces starts to dominate the catalyst particles. Fe 7 C 3 shows an unusual minimum surface free energy at 400 K in all the surfaces. This study provides fundamental insights into the modulation of iron-based nanocatalysts morphologies with desired catalytic performance.

First-principle calculations are carried out to interpret the experimental observations and to generate the mechanisms of CO and CH 4 conversion with Fe 2 O 1-3. The stabilization of FeAC bonding involves p ⁄ (CAO) and electron donating from oxygens' LP. The FeAO bond activation is rate-limiting step of conversions. Stabilization and activation are affected by number of oxygens at the iron active site. Low ORBs are identified for CO + Fe 2 O 1-3 reaction pathways. Significant ORBs are calculated for Fe 2 O 3 + CH 4 , and the competing mechanism of reduction by H 2 is shown. DFT calculations suggest favorable formation of Fe 3 C in atmosphere of CH 4 and its oxidation in atmosphere of CO.

Combining Basin Hopping structure searching algorithm and density functional theory, the iron carbide clusters Fe x C y (x ≤
8; y ≤ 8) and the clusters with various stoichiometry (Fe 2n C n , Fe 3n C n , Fe n C 2n , Fe n C 3n , Fe n C 4n (n = 1 ~ 7), Fe 5n C 2n , Fe 4n C n (n = 1 ~
5)) are predicted. The stable structures of iron rich carbide clusters are composed of C-C dimers or single C atoms on the
surface of clusters, which are remarkably different from their corresponding bulk structures, where the carbon atoms are
atomically distributed in the iron matrix. The most stable carbon rich clusters are highly diverse in topology (bowl, basket,
plane, shoe, necklace, etc.) with long carbon chains. The Bader charge analysis shows that the size effect on iron carbide
clusters is an electronic tuning. The large carbon-rich clusters appears even under low carbon chemical potential, while
small iron-rich clusters are only energetically stable in high carbon chemical potential, indicating that to change the carbon
chemical potential can tune the morphology (size and stoichiometry) of iron carbide clusters. These may help us
understand the catalytic activity of iron and iron carbides in the reactions such as Fischer-Tropsch synthesis and carbon
nanotube formation process.

The Mössbauer spectroscopy of iron carbides (α-Fe, γ'-FeC, η-Fe 2 C, ζ-Fe 2 C, χ-Fe 5 C 2 , h-Fe 7 C 3 , θ-Fe 3 C, o-Fe 7 C 3 , γ'-Fe 4 C, γ''-Fe 4 C, and α'-Fe 16 C 2) is predicted utilizing the all electron full-potential linearized augmented plane wave (FLAPW) approach across various functionals from LDA to GGA (PBE, PBEsol, and GGA + U) to meta-GGA to hybrid functionals. To validate the predicted MES from different functionals, the single-phase χ-Fe 5 C 2 and θ-Fe 3 C are synthesized in experiment and their experimental MES under different temperature (from 13 K to 298 K) are determined. The result indicates that the GGA functional (especially, the PBEsol) shows remarkable success on the prediction of Mössbauer spectroscopy of α-Fe, χ-Fe 5 C 2 and θ-Fe 3 C with delocalized d electrons. From the reliable simulations, we propose a linear relationship between B hf and μ B with a slope of 12.81 T/μ B for iron carbide systems and that the proportionality constant may vary from structure to structure.

Nanophase iron carbides can be obtained by high energy milling (mechanosynthesis). The hydrogenation of CO 2 catalyzed by mechanosynthesized iron carbides (at different milling stages) is studied from the point of view of activity, selectivity and stability during the reaction. The catalytic properties are attractive and competitive with those of other catalytic materials. The catalytic behaviour is shown to be stable during testing for 24 h. Structural characterization of the catalysts after the reaction is also reported.

The aim of this paper is to propose to the scientific community dealing with the adventurous field of the physical metallurgy of steels mechanochemical synthesis in a different perspective. Currently, in fact, mechanochemical synthesis is perceived by the materials community as a technology to synthesize advanced/non-equilibrium materials -such as nanophase powders; the specific goal of this proposal is to help considering it also a tool for synthesizing different iron carbides -as an ancillary technique which could be useful for the synthesis of pure or complex iron carbides; this could substantially aid study of related fundamental and applied properties. So a general framework for the kinetics of mechanochemical synthesis will be presented and applied to the synthesis of pure Fe-C carbides; some recent unpublished data on the mechanochemical synthesis of these carbides will be discussed in this specific framework.