Fe-C Systems Research Articles

First principles and molecular dynamics simulations of effect of dopants on properties of high strength steel for hydrogen storage vessels

High-pressure gaseous hydrogen storage is an important way of hydrogen energy storage and transport at present, while high-strength steel material is one of the main materials used for hydrogen storage vessels. However, their internal doping elements and inherent defects often lead their mechanical properties to decrease, thus reducing the pressure-bearing capability and storage life of the vessel. At present, the mechanism of doping elements influencing the mechanical properties of high-strength steels is still unclear. In this work, a first-principles approach is used to study the influence of elemental doping (Cr, Mn, Mo, As, Sb, Bi, Sn, Pb) on the mechanical properties of Fe single crystals and Fe-C systems. The results show that among the above elements, Mn doping can increase the elastic modulus, bulk modulus, and shear modulus compared with those of pure Fe, while the doping by remaining elements will reduce the three moduli above, with the non-transition metal elements having a greater effect on the three moduli than the transition metal elements. Electronic structure analysis shows that the transition metal elements have better compatibility with the Fe lattice. Molecular dynamics results further show that the injection of H atoms significantly disrupts the lattice ordering of the Fe polycrystalline doped by C, Cr, and Mn elements, while the doping of Cr elements can significantly enhance the dislocation density of the system. The effects of doping elements on the mechanical properties of single-crystal and polycrystalline Fe, which are studied in this work, are of great significance in guiding the mechanistic study of the effects of doping and defects on the strength of Fe-based materials.

Peculiarities of Fe penetration into the matrix of CaCO<sub>3</sub> ± olivine ± serpentine at a pressure of 4 GPa and temperature of 1400-1500°C (experimental data)

Research subject. We present the first results on modeling of the interaction of CaCO3 with metallic Fe in the presence of olivine and serpentine at high P-T parameters in comparison with the CaCO3-Fe system. The relevance of the study is related to the need to study decarbonatization reactions during subduction of crustal matter into the Earth's reduced mantle within the context of the global carbon cycle. Methods. The experiment was carried out using a BARS high-pressure apparatus at a pressure of 4.0 GPa and temperatures of 1400-1500°С with a subsequent study of the obtained samples on a scanning electron microscope equipped with a chemical microanalysis system. Results. CaCO3 was found to be unstable under the implemented conditions. The reaction products were iron carbide and Ca-wustite or Ca-magnesiowustite in the presence of silicate phases. Conclusions. The interaction of CaCO3 with metallic Fe at high pressure occurs even if the components are in the solid state. High reaction rates during interaction are provided by the appearance of liquid metal due to the relatively low melting temperature of the eutectic in Fe-C systems. The influence of gravity on the penetration of Fe into the carbonate matrix, which consists in the predominant infiltration of liquid metal between carbonate grains, was established. The presence of H2O significantly reduces the melting point of carbonate, which leads to an increase in the diffusion of components and decarbonization reaction rate, while the effect of gravity also takes place due to the difference in the density of liquid Fe in comparison with other components in a highly fluidized environment.

The influence of carbon atoms on the magnetic moment in the Fe-C system: calculation from the first principles

From the first principles, the influence of carbon content on the magnetic moment of theBCC- and BCC Fe-C systems was evaluated. The systems Fe-0.40C, Fe-0.79C and Fe-1.19C mass% with mass% were considered. It is shown that the tetragonality of the Fe-C system increases linearly with increasing carbon content and is in good agreement with experimental results. The average magnetic moment on Fe atoms also increases linearly with increasing carbon content. At the same time, the magnetic moment of Fe atoms located in the immediate vicinity of carbon atoms is less than in pure iron, and the atoms of the second coordination sphere, on the contrary, have more. It is shown that this is primarily due to the magneto-volume effect, whereas the effect of tetragonal distortion of the lattice is secondary. Keywords: computer simulation, Fe-C, magnetic moment, tetragonality, magneto-volume effect.

Влияние атомов углерода на магнитный момент в системе Fe-C: расчет из первых принципов

From the first principles, the influence of carbon content on the magnetic moment of the BCC and BCC Fe-C systems was evaluated. The systems Fe-0.40 C, Fe-0.79 C and Fe-1.19 with mass% were considered. It is shown that the tetragonality of the Fe-C system increases linearly with increasing carbon content and is in good agreement with experimental results. The average magnetic moment on Fe atoms also increases linearly with increasing carbon content. At the same time, the magnetic moment of Fe atoms located in the immediate vicinity of carbon atoms is less than in pure iron, and the atoms of the second coordination sphere, on the contrary, have more. It is shown that this is primarily due to the magneto-volume effect, whereas the effect of tetragonal distortion of the lattice is secondary

Enhanced reduction of Cr(VI) in iron-carbon micro-electrolysis constructed wetlands: Mechanisms of iron cycle and microbial interactions

The increased pollution of Cr(VI) poses a major threat to public health and the ecological environment. Iron-carbon (Fe-C) micro-electrolysis was a potential sustainable strategy for improving Cr(VI) reduction in constructed wetlands (CWs). This study explored the performance and mechanisms of Cr(VI) removal in Fe-C based CWs that established with iron oxide and biochar, especially the microbial-driven Fe cycle. Efficient removal of total Cr (49%) and Cr(VI) (65%) was detected in Fe-C systems, which was 377% and 34% greater than that of the control group without Fe-C, respectively. As a vital sink for Cr, the Fe-C substrate presented better capacity for reducing Cr(VI), which showed a 20.5% lower Cr(VI) content than the control. Moreover, the Fe cycle along substrate depths were highly concurrent with Cr(VI) reduction, which was driven by the enhanced microbial function of electron transport (improved electron transport chain) and Fe oxidation or reduction microbes (such as Geobacter, Desulfovibrio, Pseudomonas, and Ferrovibrio). The relative abundances of some strains of Betaproteobacteriales and Comamonadaceae were increased in the Fe-C system, which was highly related to chrA, sdhA, mtrC, and nemA that associated with Cr(VI) reduction and transformation enzyme-encoding genes. Our results may be helpful for understanding the processes and mechanisms of Cr(VI) removal in Fe-C mediated CWs.

OKMC simulation of matrix defect evolution of Fe-C Alloy under irradiation

The effects of carbon traps in Fe-C alloys on matrix defects and the evolutions of matrix defects in Fe-C alloys under irradiation are investigated in this paper. The object kinetic Monte Carlo (OKMC) modeling is used to establish a bridge between the micro-computational simulation data and the macro-experimental data. The simulation results verify the evolution of the carbon (C)-vacancy (Vac) complex under ideal conditions, and at relatively low temperatures, the complex is mainly C-Vac<sub>2</sub>. Under the assumption of complex traps, the evolution of matrix defects in Fe-C systems under irradiation is simulated in this work. It is verified that the carbon vacancy complex has an obvious trapping effect on matrix defects, and the simulation results of evolution simulation of matrix defects in the Fe-C system under irradiation are consistent with the experimental results. Furthermore, the effective approximate parameters used in the simulation are compared and discussed. The present research can provide a basic support for the research on the evolution of iron-based alloy irradiation defects.

Genome placement of alpha-haemolysin cluster is associated with alpha-haemolysin sequence variation, adhesin and iron acquisition factor profile of Escherichia coli.

Since the discovery of haemolysis, many studies focused on a deeper understanding of this phenotype in Escherichia coli and its association with other virulence genes, diseases and pathogenic attributes/functions in the host. Our virulence-associated factor profiling and genome-wide association analysis of genomes of haemolytic and nonhaemolytic E. coli unveiled high prevalence of adhesins, iron acquisition genes and toxins in haemolytic bacteria. In the case of fimbriae with high prevalence, we analysed sequence variation of FimH, EcpD and CsgA, and showed that different adhesin variants were present in the analysed groups, indicating altered adhesive capabilities of haemolytic and nonhaemolytic E. coli . Analysis of over 1000 haemolytic E. coli genomes revealed that they are pathotypically, genetically and antigenically diverse, but their adhesin and iron acquisition repertoire is associated with genome placement of hlyCABD cluster. Haemolytic E. coli with chromosome-encoded alpha-haemolysin had high frequency of P, S, Auf fimbriae and multiple iron acquisition systems such as aerobactin, yersiniabactin, salmochelin, Fec, Sit, Bfd and hemin uptake systems. Haemolytic E. coli with plasmid-encoded alpha-haemolysin had similar adhesin profile to nonpathogenic E. coli, with high prevalence of Stg, Yra, Ygi, Ycb, Ybg, Ycf, Sfm, F9 fimbriae, Paa, Lda, intimin and type 3 secretion system encoding genes. Analysis of HlyCABD sequence variation revealed presence of variants associated with genome placement and pathotype.

Two-dimensional FeC compound with square and triangle lattice structure – Molecular dynamics and DFT study

The stability, electronic structure and magnetic behaviors of the two-dimensional (2D) FeC compounds with square and triangle lattice structure are studied by the density functional theory (DFT) calculations. We find that both forms of 2D FeC, one with a flat square lattice structure denoted as t-FeC and another with a puckered triangle lattice structure denoted at tr-FeC, are stable after DFT optimization. However, calculations of the phonon dispersion and binding energy show that the puckered 2D FeC with a triangle lattice structure is the most stable form. We find that both forms of the 2D FeC compounds are metallic and ferromagnetic materials, however, the mean atomic magnetic moment of Fe in the puckered 2D tr-FeC is significantly smaller than that of the flat 2D t-FeC. We check various interatomic potentials for the Fe-C systems implemented in the LAMMPS package and find that only 2D t-FeC can be formed ‘naturally’ from the melt while it does not occur for the 2D tr-FeC. The crystallization temperature (TX≈2600K) and mean interatomic distance for the Fe-C pair of the flat 2D t-FeC have reasonable values. Various structural defects and mechanical behaviors of the flat 2D t-FeC compound are found and discussed.

The characteristics of diamonds crystallized using Fe-C-H at high pressure and temperature

Diamond crystallization in an Fe–C system with C10H10Fe additive(collectively called the Fe-C-H system) has been studied at 5.0–6.0GPa and temperatures ranging from 1400 to 1700°C. Both spontaneous diamond nucleation and growth were studied. The results showed that the stable form of diamond growth is octahedral in Fe-C-H systems, which is similar to pure Fe-C systems. However, the diamond morphologies changed from high quality octahedral to aggregated octahedral as the amount of C10H10Fe increased, accompanied by a deterioration of the surfaces. The FTIR results indicated that hydrogen-doped diamonds with less than 1ppm nitrogen are easily synthesized in this system. The crystallization of diamonds in the Fe-C-H system was not only affected by the pressure and temperature conditions, but also by the amount of C10H10Fe additive. This was attributed to changes in the pure Fe catalyst caused by the elemental hydrogen produced by the decomposition of C10H10Fe.

Stability and crystal structures of iron carbides: A comparison between the semi-empirical modified embedded atom method and quantum-mechanical DFT calculations

Iron carbides play a crucial role in steel manufacturing and processing and to a large extent determine the physical properties of steel products. The modified embedded atom method (MEAM) in combination with Lee's Fe-C potential is a good candidate for molecular dynamics simulations on larger Fe-C systems. Here, we investigate the stability and crystal structures of pure iron and binary iron carbides using MEAM and compare them with the experimental data and quantum-mechanical density functional theory calculations. The analysis shows that the Fe-C potential gives reasonable results for the relative stability of iron and iron carbides. The performance of MEAM for the prediction of the potential energy and the calculated lattice parameters at elevated temperature for pure iron phases and cementite are investigated as well. The conclusion is that Lee's MEAM Fe-C potential provides a promising basis for further molecular dynamics simulations of Fe-C alloys and steels at lower temperatures (up to 800 K).

A structural and functional analysis of type III periplasmic and substrate binding proteins: their role in bacterial siderophore and heme transport

In Escherichia coli the Fhu, Fep and Fec transport systems are involved in the uptake of chelated ferric iron-siderophore complexes, whereas in pathogenic strains heme can also be used as an iron source. An essential step in these pathways is the movement of the ferric-siderophore complex or heme from the outer membrane transporter across the periplasm to the cognate cytoplasmic membrane ATP-dependent transporter. This is accomplished in each case by a dedicated periplasmic binding protein (PBP). Ferric-siderophore binding PBPs belong to the PBP protein superfamily and adopt a bilobal type III structural fold in which the two independently folded amino and carboxy terminal domains are linked together by a single long α-helix of approximately 20 amino acids. Recent structural studies reveal how the PBPs of the Fhu, Fep, Fec and Chu systems are able to bind their corresponding ligands. These complex structures will be discussed and placed in the context of our current understanding of the entire type III family of Gram-negative periplasmic binding proteins and related Gram-positive substrate binding proteins.

1027 水素ガス環境におけるFe, Fe-C, Fe-N系の粒界凝集エネルギーの第一原理計算(OS10. 電子・原子・マルチシミュレーションに基づく材料特性評価,OS11. 材料の組織・強度に関するマルチスケールアナリシス 合同ポスターセッション,オーガナイズドセッション講演)

1027 水素ガス環境におけるFe, Fe-C, Fe-N系の粒界凝集エネルギーの第一原理計算(OS10. 電子・原子・マルチシミュレーションに基づく材料特性評価,OS11. 材料の組織・強度に関するマルチスケールアナリシス 合同ポスターセッション,オーガナイズドセッション講演)

Thermodynamic re-assessment of the Fe-Al-C system based on the Fe-rich experimental data

The influence of C and Al content on phase transformation temperatures, i.e., the A1 and A3 of Fe-rich alloys is investigated by dilatometric analysis. With the new set of experimental data, an updated thermodynamic description of the Fe-Al-C system is presented, by using the thermodynamic data of the Fe-C, Fe-Al and Al-C systems, as well as the parameters for the Fe-Al-C ternary system optimized in this study. The good compatibility of the thermodynamic parameters with experimental data is demonstrated by several calculated vertical sections. A well reproduced vertical section of the Fe-Mn-Si-Al-C system is also presented according to the thermodynamic description of the lower order systems.

Titanium “irons” and titanium “steels”

Special features of the structure and properties of promising structural alloys based on the Ti-Si system are described. The similarity of the diagrams of phase equilibria of the Fe-Si and Fe-C systems makes it possible to classify the alloys of the Ti-Si system into titanium “steels” and “irons” depending on the silicon content. Results of studies of the effects of alloying, heat treatment, and thermomechanical treatment on the phase and structural transformations and on some properties of alloys based on the Ti-Si system are presented.

Concentration dependence of the dispersity of dendrite structure in alloys of binary systems

The dendrite structure of binary alloys of the Fe-C, Fe-P, Fe-Si, and Fe-Mn systems is studied. The distances between second-order dendrite arms are determined as a function of the concentration of the second component and of the type of the phase diagram. The results obtained are analyzed from the standpoint of thermodynamics.

Performance Comparison of MLSE and Iterative Equalization in FEC Systems for PMD Channels With Respect to Implementation Complexity

Advanced electronic signal processing for high-bit-rate lightwave systems has become available recently. Adaptive receiver concepts are proposed to mitigate dynamic changes in the optical channel response. In particular, two different approaches are under discussion: independent equalization and decoding, e.g., by maximum-likelihood sequence estimation followed by a separate error-correction decoder, and a combined approach by iterative decoding of the channel correlations and the error-correction code. The authors compare the two concepts with respect to their mitigation capabilities in the presence of polarization mode dispersion. Special attention is paid to hardware implementation aspects, since the application of the concepts is severely limited by memory and signal processing requirements

Modeling structure parameters of irregular eutectic growth: Modification of Magnin-Kurz theory

A new approach to irregular eutectic growth (faceted/nonfaceted crystallization) in Fe-C and Al-Si alloys has been presented in this article. The results of unidirectional crystallization of the irregular eutectic in the Fe-C, Al-Si, and Al-Fe systems were used for the experimental verification of the resulting model. For the oriented graphite, α(Al)-Si and α(Al)-Al3Fe eutectics, a decrease of the interlamellar spacing λ and in protrusion δβ of the nonfaceted phase (austenite, α(Al)) by the leading faceted phase (graphite, silicon, and Al3Fe), the increase of growth rate v was observed. The Magnin-Kurz theory of irregular eutectic growth has been modified in order to better understand the physical mechanisms driving the crystallization process. A comparison of the measured and calculated average λ values has revealed good agreement for the (γ)Fe-graphite, α(Al)-Si, and α(Al)-Al3Fe eutectics. The developed model also considered the influence of the material constants of the examined alloys on the interlamellar spacing and protrusion of the leading phase—graphite, silicon, and Al3Fe. It has been found that material constants such as the wetting angle, diffusion coefficient, and Gibbs-Thomson coefficient are of great importance in this eutectic growth.

Deformation-induced dissolution of the Fe2B boride in nanocrystalline α-Fe

Structural-phase transformations in the α-Fe+Fe2B composite with a total boron content of 15 at. % during mechanical grinding in a planetary ball mill have been studied using X-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. It has been established that dissolution of the Fe2B boride with the formation of an amorphous phase and segregations of boron atoms at grain boundaries occur after the grain size reaches 3 nm. In this work a comparative analysis of the deformation-induced dissolution of Fe2B and Fe3C in the Fe-B and Fe-C systems has been made and the possible mechanisms of the structural-phase transformations have been discussed.

Synthesis and characterisation of new sputtered metastable carbides

This paper describes part of a work carried out to develop new ternary M–M1–C systems (M=metal of the Groups IV–VI and M1=Group VIII element) by sputtering. The results obtained in this study on Ti–Fe–(C) and Mo–Fe–(C) systems showed that, depending on the type and content of iron, the obtained materials are structurally metastable, formed either by structures with enlarged solubility domains or amorphous structures. The amorfisation was verified in the Ti–Fe and Mo–Fe-C systems, as a result of the introduction of iron. The Ti–Fe–C system shows better resistance to amorphisation than the Mo–Fe–C system.

On re-configurable methods and gate array based solutions of fast forward error correction systems for software radio and set-top-box applications

Existing communication systems and the corresponding interfaces differ with respect to bandwidth, carrier frequency and modulation patterns. The investigation of digital receivers for processing of multiple standards and modulation schemes within a single system are one of the research topics today. In this paper fast forward error correction units, required for broadband receivers and software radio solutions have been investigated. The proposed FEC systems are based on a radix-2/radix-4 decoding approach and have been verified within high density FPGAs.