Iron Lattice Research Articles

A facile and novel approach to magnetic Fe@SiO2and FeSi2@SiO2nanoparticles

Fe@SiO2 and FeSi2@SiO2 nanoparticles with core@shell structure have successfully been synthesized by direct silane silicification of Fe2O3 nanoparticles. The as-prepared samples were characterized by N2 physisorption, X-ray diffraction, transmission electron microscopy, temperature programmed reduction of H2, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and superconducting quantum interference magnetometry. It was found that the amorphous SiO2 shell was formed to protect the core against oxidation when the reduced Fe2O3 nanoparticles were silicified by silane. When the reduced Fe2O3 nanoparticles were exposed to air, a Fe2O3 layer was formed. The structure of the core changed from cubic Fe to orthorhombic FeSi2 with increasing silicification temperatures from 350 to 550 °C, due to the dissolution of Si atoms into the iron lattice. The magnetic characterization showed that all samples have ferromagnetic nature and the saturation magnetization values drastically decreased with increasing silicification temperature. This novel methodology can be applied to synthesis of Co@SiO2 and Ni@SiO2 with core@shell structure. The as-prepared Fe@SiO2 and FeSi2@SiO2 nanoparticles with core@shell structure can find applications in magnetically separable catalysts, biomedicines, and magnetically recording materials.

Three-sublattice model that takes into account the spin density anisotropy, short-range order, and dimensioned factor for the binary Fe-Cr(V, Mo) systems

The diffusion properties of the elements entering into the composition of austenitic and ferritic steels are analyzed as functions of the temperature and the time evolution of induced radioactivity. As compared to austenitic steels, ferritic steels are shown to have better diffusion properties and swelling resistance during operation at temperatures up to 650°C under irradiation conditions and can be used as structural materials in the core of a fast neutron reactor. Experimental and calculated (Calphad method) data on the Fe-Cr phase diagram and the thermodynamic properties and the experimental data on the short-range order in Fe-Cr alloys are analyzed, and it is concluded that they are conflicting and that models taking into account the short-range order should be developed. The results of quantum-mechanical calculations of the average magnetic moment for ferromagnetic (FM) iron as a function of the volume are analyzed and used to introduce a concept of partial magnetic moments of the iron atoms located in the first four coordination spheres (1–4 CS). The values of these moments are calculated. The concept of the partial magnetic moments of iron atoms agrees qualitatively with the experimental data on the spin-density anisotropy of the bcc lattice of pure iron. This concept is used to formulate a three-sublattice model for binary FM alloys of Fe-M systems (M is an alloying paramagnetic element). An extended cell whose sites contain 8 bcc cells and 16 atoms per cell and that is isomorphic to a DO3-type crystal lattice is considered. A functional is constructed for the internal energy on the extended 16-atom cell. The dimensioned factor is taken into account in a self-consistent manner, by the expansion of the interaction energies of atoms of both components located in different CSs in the atom displacement with respect to ideal lattice sites. The dimensioned factor is taken into account in the three-sublattice model to obtain a set of equations of state for bcc FM binary iron-rich alloys in a 1–3 CS approximation. The obtained estimates demonstrate that the anisotropy of the distribution of magnetic moments in the bcc iron lattice is responsible for the appearance of a short-range order in bcc FM iron-rich Fe-Cr (V, Mo) binary alloys.

THE STRUCTURAL DESIGN OF THE HEAD OFFICE OF GUNZE RAW SILK MFG. CO., LTD.

The head office of GUNZE Raw Silk Mfg. Co., Ltd. was built in 1933. It was designed by the engineers of the company’s construction section. The features of the construction and the design were as follows:The building had the appearance of RC due to the use of wooden lattice pillars. They were used for the entrance and large spans in the hall. The engineers, who had experience using RC, applied the concept of iron lattice frames to this wooden building. In addition, the most of the walls, doors, trim and furniture of the interior were made of lauan plywood.These results suggest that the new development happened to wooden structure and material by the influence of the economic depression.

A study of nonisothermal tempering kinetics in plain 9Cr 1Mo steel

The present study elaborates the behavior of tempering reaction of nuclear grade plain 9Cr 1Mo martensitic steel investigated under a constant heating rate imposed by a high temperature heat flux differential scanning calorimeter (DSC). The heating rate imposed is varied from 1 to 30 K min−1. The inflection in the baseline which occurs during the tempering reaction namely, martensite (α′) to ferrite (α) + chromium carbide (M23C6) around 873 K is identified in the DSC profile as the typical tempering onset temperature. The DSC profiles are used to characterize the extent of carbide precipitation under different heating rates. The analysis of the kinetics of tempering reaction is performed using Kolmogorov-Johnson-Mehl-Avrami (KJMA) model to extract the kinetic parameters. In addition, the Kissinger method of obtaining apparent activation energy (Qeff) is also attempted. The value of the Qeff obtained using both of the models are in good agreement and suggest that bulk diffusion of chromium in iron lattice could be the rate controlling mechanism in the tempering of 9Cr-steels. The effect of tempering reaction is also supported by metallographic studies.

Modelling radiation damage effects on a bcc iron lattice containing phosphorous impurity atoms near symmetrical tilt boundaries

The effects of radiation on phosphorous impurity atoms present in a bcc iron lattice and their interactions with primary radiation-induced defects have been investigated by means of molecular dynamics simulations. In this work symmetrical tilt boundaries, with two different CSL relationships, have been inserted in 110,000 atom computational cells. The simulations provided information about the effects of PKA energy (between 0.5 and 6keV), PKA position, PKA direction and grain boundary on the evolution of the collision cascades. The results have shown marked difference between collisions occurring near grain boundaries and those occurring in the bulk. A large number of defects accumulate at GBs, which act as traps for defect propagation. The mobility of single P interstitial atoms and mixed dumbbells has been investigated at four different temperatures of 673, 783, 873 and 973K. The system evolution was then observed during simulation times as long as 1ns. This allowed the investigation of the effects of temperature and primary defects on the migration of the P atoms.

Theory of the valley-density wave and hidden order in iron pnictides

In the limit of perfect nesting, the physics of iron-pnictides is governed by the density wave formation at the zone-edge vector M. At high energies, various spin- (SDW), charge- (CDW), orbital/pocket- (PDW) density waves, and their linear combinations, all appear equally likely, unified within the unitary order parameter of U(4)XU(4) symmetry. Nesting imperfections and low-energy interactions reduce this symmetry to that of real materials. Nevertheless, the generic ground state preserves a distinct signature of its highly symmetric origins: a SDW along one axis of the iron lattice is predicted to coexist with a perpendicular PDW, accompanied by weak charge currents. This "hidden" order induces the structural transition in our theory, naturally insures T_s >= T_N, and leads to orbital ferromagnetism and other observable consequences.

Recoilless fraction of cobalt-doped magnetite

Hydrothermally-synthesized Fe 3− x Co x O 4 ( x = 0–0.9) samples were analyzed by transmission Mössbauer spectroscopy in order to determine the recoilless fraction of the tetrahedral (A) and octahedral (B) sites as a function of the cobalt content x. Our results provided direct evidence for the presence of the Co substitution in the B sublattice, which was found to be accompanied by a systematic increase of the hyperfine field at these sites. The recoilless fractions of the two sublattices were determined using our recently-developed dual absorber method. The recoilless fraction of the tetrahedral sites is practically constant, while that of the octahedral sites steadily decreases with increasing the Co content. These results tend to suggest that only the iron lattice participates in the recoilless process.

Sampling Iron for Radiocarbon Dating: Influence of Modern Steel Tools on 14C Dating of Ancient Iron Artifacts

Before the 17th century, charcoal was regularly used in the production of iron (smelting and forging) and some of this charcoal carbon was incorporated into the iron. Depending on the age of the wood used to produce the charcoal, the age of the carbon incorporated in the iron lattice can reflect the age of manufacture of the iron artifacts. A reliable preparation method allowing for the routine dating of iron artifacts would permit the dating of numerous objects for which now the age can only be estimated. In an earlier work (Hüls et al. 2004), we tested the extraction of carbon from iron samples by closed-tube combustion. The samples were cut in small pieces to ease the release of the carbon from the lattice. During the tests, it became clear that the steel tools used to cut the samples can add contamination at the surface. As modern steel is made using coal, this leads to erroneously old ages. We have tested ways to reduce or eliminate this surface contamination from the sampling tools using iron artifacts of known ages. In order to quantify the contamination, we produced standard test materials from pure iron (99.998% Fe) melted with carbon of known 14C content and prepared samples using different cutting tools. The results of these tests indicate that the proper choice of cutting technique and tool, combined with an additional cleaning of the freshly cut surface, reduces sample contaminations to low levels; measured sample 14C concentrations are close to the 14C content of the charcoal used to produce these standard iron samples.

Hydrogen Embrittlement of a Manganese–aluminum High-strength Bainitic Steel for Railway Crossings

The hydrogen embrittlement characteristics of a Mn–Al bainitic steel for railway crossings were studied by means of the slow strain rate test (SSRT), the delayed fracture test and X-ray diffraction (XRD) analysis. The binding energies and hydrogen diffusion barriers of an iron unit cell were tested separately with Al, Si and H, and were evaluated by the first principle calculation. The results showed that the hydrogen embrittlement decreased greatly with increased Al content. Microstructure examinations indicated that the content of retained austenite increased with increased Al content, which was as irreversible hydrogen traps and was not sensitive to hydrogen embrittlement. It is found that the characteristics of hydrogen embrittlement identified by SSRT and the delayed fracture test were different. From the first principle calculation, the binding energy of the iron lattice containing aluminum decreased less as compared to those of the cell containing silicon, but the diffusion barriers increased significantly.

Molecular dynamics study of the ordering of carbon in highly supersaturatedα-Fe

A recently developed Fe-C interatomic potential has been used to investigate carbon in highly supersaturated $\ensuremath{\alpha}$ iron with an emphasis on the possible ways in which carbon can arrange itself on the octahedral sites of the tetragonally distorted $\ensuremath{\alpha}$-iron lattice. Focusing particularly on the composition ${\text{Fe}}_{16}{\text{C}}_{2}$, the embedded atom method potential used gives the same ground-state structure of ${\text{Fe}}_{16}{\text{C}}_{2}$ as density-functional-theory calculations. Moreover, when computing C-C interactions between two carbon atoms at 0 K with energy minimization, the preferred separation distance corresponds exactly to the octahedral site positions expected in ${\text{Fe}}_{16}{\text{C}}_{2}$. It has been shown with molecular dynamics that the carbon atoms in ${\text{Fe}}_{16}{\text{C}}_{2}$ change how they order on octahedral sites during heating and during cooling. Finally, when investigating the interaction energy of ${\text{Fe}}_{1\ensuremath{-}x}{\text{C}}_{x}$ for different carbon compositions, it is found that there is a clear minimum at $x=0.11$ for the fully ordered structure, corresponding to ${\text{Fe}}_{16}{\text{C}}_{2}$ composition. The results of these calculations are discussed with particular reference to carbon ordering in ferrous martensite.

Investigation of different iron sites in ϵ-FeyN (2

Epsilon Iron Nitride has a wide range of nitrogen solubility in its lattice. While the stoichiometric ϵ-Fe3N has an ordered arrangement of nitrogen atoms in the octahedral voids of the hexagonal iron lattice, in non-stoichoimetric ϵ-FeyN (2<y<3) the nitrogen atoms occupy the voids in a disordered manner and the coordination of Fe with nitrogen varies with the number 'y' in the lattice. Mössbauer spectroscopy, which is a nuclear spectroscopic tool, can differentiate the different co-ordination of Fe through its characteristic isomer shift values and is used for identifying the different types of Iron sites. ϵ-FeyN (2<y<3) nanoparticles were prepared by the nitridation of hematite nanoparticles using ammonia at 550°C. Mössbauer spectroscopy at ambient temperature shows a superparamagnetic doublet and a sextet. Spectra at 80 K and 5 K resolve the sextets nicely and thereby the different iron sites present in the ϵ-FeyN (2<y<3) nanoparticles.

American Bridges in New South Wales, 1870–1932

New South Wales Government Railways and the Department of Public Works began with British technology, particularly for rail and road bridges such as the expensive iron lattice girders. Long-serving Engineers-in-Chief, John Whitton and W. C. Bennett, applied their authority to exclude contemporary American bridge technology. However, by 1890 the merits of American bridges were well known and had economic appeal for Government funding. The effect was that in 1894 there was an abrupt and complete change to American Pratt truss bridges, which became the standard for the next 50 years. The first uniform application to railways was for the new standard gauge North Coast Railway, 1911-1932. They are now an historic class of bridges of high heritage significance. For road bridges, American Howe timber trusses were dominant post-1894, and 29 are on the State Heritage Register. Also, steel Pratt truss road bridges from this period are still in-service. This paper details the change to American bridge technology.

Model calculations of edge dislocation defects and vacancies in α-Iron lattice

Two models of defects in perfect α-iron lattice were discussed. In the perfect bcc iron lattice 42×42×42 ao (ao = 2,87 Å) an edge dislocation was created, moving the second half of the bulk on one ao distance. This action generates a little volume in the middle of the bulk witch increases of the positron lifetime (PLT) calculated using the superimposed-atom method of Puska and Nieminen [1]. The result of 118 ps PLT in simple edge dislocation's model is in a good concurrence with earlier publications and experimental data [2]. Through the dislocation line one, two and three vacancies were localized. These models give the results for PLT of 146, 157 and 167 ps respectively. The computer simulations were performed using Finnis–Sinclair (FS) N-body potential.

Kinetic magnetism and orbital order in iron telluride

Iron telluride (FeTe), a relative of the iron-based high-temperature superconductors, displays unusual magnetic order and structural transitions. Here, we explore the idea that strong correlations may play an important role in these materials. We argue that the unusual orders observed in FeTe can be understood from a picture of correlated local moments with orbital degeneracy, coupled to a small density of itinerant electrons. A component of the structural transition is attributed to orbital, rather than magnetic ordering, introducing a strongly anisotropic character to the system along the diagonal directions of the iron lattice. Double exchange interactions couple the diagonal chains leading to the observed ordering wave vector. The incommensurate order in samples with excess iron arises from electron doping in this scenario. The strong anisotropy of physical properties in the ordered phase should be detectable by transport in single domains. Predictions for ARPES, inelastic neutron scattering and hole/electron doping studies are also made.

Cosintering of Powder Injection Molding Parts Made from Ultrafine WC-Co and 316L Stainless Steel Powders for Fabrication of Novel Composite Structures

Sintering response and phase formation during sintering of WC-Co/316L stainless steel composites produced by assembling of powder injection molding (PIM) parts were studied. It is shown that during cosintering a significant mismatch strain (>4 pct) is developed in the temperature range of 1080 °C to 1350 °C. This mismatch strain induces biaxial stresses at the interface, leading to interface delamination. Experimental results revealed that sintering at a heating rate of 20 K/min could be used to decrease the mismatch strain to <2 pct. Meanwhile, WC is decomposed at the contact area and the diffusion of C and Co into the iron lattice results in the formation of a liquid and MC and M6C carbides at 1220 °C. Spreading of the liquid accelerates the reaction, affecting the dimensional stability of the PIM parts. To prevent the reaction, surface oxidation of the cemented carbide followed by hydrogen reduction during sintering was examined. Although the amount of mismatch strain increased, formation of a metallic interface consisting of a W-Co alloy (45 to 50 at. pct Co) and a Co-rich iron alloy (18 at. pct Co) prevented the decomposition of WC and melt formation. It is also shown that the deposition of a thin Ni layer after thermal debinding decreases the mismatch stresses through melt formation, although interlayer diffusion causes pore-band formation close to the steel part.

Hydrogen Embrittlement of High Strength Steels

Hydrogen embrittlement is believed to be one of the main reasons for cracking of structures under stress. High strength steels in these structures often include a ferritic core made of alpha-iron (body centered cubic lattice). We compute the interaction of atomic hydrogen with iron using first principles. The interstitial hydrogen can be placed in two high symmetry positions: octahedral and tetrahedral sites. Our calculations provide diffusion barriers between these sites. These barriers have been analyzed to understand the propagation of hydrogen through the iron lattice. We analyze how these barriers can be modified by the hydrogen concentration. The results show the main site for high and low hydrogen density and they show the diffusion coefficient variation by the hydrogen density.

A Small History to Discovery of Iron Based High Tc Superconductors and Summary

We discovered iron-based layered superconductors: F-doped LaFePnO (Pn=P, As) in 2006. Several superconductors containing square iron lattice have been reported in 2008. Superconducting transition temperature (Tc) of F-doped LnFeAsO (Ln=Nd, Sm, ...) reaches ~55 K. LaFePnO is a 3d transition-metal (TM) based oxypnictides: LnTMPnO. The crystal structure is composed of carrier conducting TM-Pn layer and insulating Ln-O layer. Undoped LnFePO (Ln=La, Sm) shows Tc ~3-5 K, while undoped LnFeAsO shows no Tc. The undoped LnFeAsO takes a orthorhombic crystallographic phase at temperatures below ~160 K, F-doping suppresses the structural transition from tetragonal to orthorhombic phase, stabilizing the tetragonal lattice of LnFeAsO. F-doped LnFeAsO with tetragonal symmetry exhibits Tc.

High Temperature Oxidation of Fe-9Cr-1Mo Steel in Liquid Metal

The oxidation mechanism of the T91 martensitic steel in oxygen-saturated Pb-Bi eutectic at 470°C has been investigated to develop a long term predictive model of the steel oxidation kinetic. This work is performed in the frame of life duration studies carried out for the MEGAPIE spallation module demonstrator dedicated to the feasibility demonstration of an hybrid reactor. Our scientific approach has been based on an experimental characterization of the oxide scales and of the T91 steel oxidation kinetics. From these experimental results, an oxidation mechanism has been elaborated and then simulated. The oxide scale formed at the T91 surface has a duplex structure, constituted of an external magnetite scale and an internal Fe-Cr spinel scale. A scale growth mechanism has been proposed: the magnetite scale growth seems to be limited by the iron lattice diffusion inside the duplex oxide scale. At the same time, a self-regulation mechanism seems to govern the Fe-Cr spinel scale growth. This mechanism consists of a non-limiting oxygen diffusion step, which is carried out, across the oxide scale, inside liquid lead nano-channels and a limiting iron oxide lattice diffusion step. Considering the proposed oxidation mechanism, a simulation of the growth of the two oxides scales has been carried out and compared to the experimental oxidation kinetics. The excellent agreement between the experimental results and the simulations supports to accept the proposed mechanism, leading to prediction of kinetics for long oxidation durations.

Dense plasma focus-assisted nitriding of AISI-304

Nitrogen ion implantation into AISI-304 stainless steel is carried out using a dense plasma focus device, operated at a charging voltage of 18 kV (discharge energy=1.45 kJ) with nitrogen filling at optimum pressure of 0.75 mbar. AISI-304 stainless steel samples placed axially above the anode tip are exposed to the ions for 10, 20 and 30 focus shots. X-ray diffraction (XRD), Vickers's micro hardness tester, scanning electron microscopy, and energy dispersive X-ray spectroscopy are used to explore the ion induced changes in the crystallographic structures, surface morphology, elemental composition and surface hardness of the ion irradiated samples. The XRD pattern confirms the formation of an expanded austenite phase, owing to nitrogen incorporated into the existing iron lattice. The results of micro hardness tester show that the hardness is increased about three times at an axial distance of 5 cm for 20 shots.

High-pressure solid/liquid partitioning of Os, Re and Pt in the Fe–S system

Coupled enrichments in 186Os/ 188Os and 187Os/ 188Os in some ocean island basalts have been interpreted to reflect material transfer from Earth's outer core to the base of the mantle. The outer core is a viable source for these coupled enrichments if it is able to maintain sufficiently high Pt/Os and Re/Os ratios for sufficient time. Iron meteorite studies and some experimental data indicate that progressive crystallization of the inner core is a plausible mechanism for generating the required high Pt/Os and Re/Os ratios in the outer core. However, the conditions of the experiments and meteorite parent bodies are far different from those in Earth's core, particularly in terms of pressure. Here we present experimental results on the partitioning of Os, Re and Pt between solid iron and liquid iron sulfide solutions over a wide range of pressures, from 3.3 to 22 GPa. The solid/liquid partition coefficients for these elements decrease, and become more similar to each other, as pressure increases. This behavior is consistent with an increasing misfit of each element in the iron lattice with increasing pressure, due to the small compressibility of Os, Re and Pt relative to iron. The partition coefficients, and differences among them, are too small at the conditions of these experiments to generate the radiogenic Os isotope anomalies observed in some plume-derived lavas. At 22 GPa the partition coefficients are such that inner core crystallization elevates the Pt/Os ratio of the outer core by only 11%, and the Re/Os ratio by only 6%; after 4.5 Gyr, the calculated 186Os/ 188Os ratio of the outer core is only 0.0012% higher than it would be in the absence of inner core crystallization, and the 187Os/ 188Os ratio is only 1.4% higher. If the pressure effect is due to lattice strain, the partition coefficients are expected to decrease further at the pressure and temperature conditions relevant to Earth's core. Thus, the present data set does not support the idea that radiogenic Os isotope anomalies originate in the outer core.