Antiferromagnetism is relevant to high-temperature (high-Tc) superconductivity because copper oxide and iron arsenide superconductors arise from electron- or hole-doping of their antiferromagnetic ...parent compounds. There are two broad classes of explanation for antiferromagnetism: in the 'local moment' picture, appropriate for the insulating copper oxides, antiferromagnetic interactions are well described by a Heisenberg Hamiltonian; whereas in the 'itinerant model', suitable for metallic chromium, antiferromagnetic order arises from quasiparticle excitations of a nested Fermi surface. There has been contradictory evidence regarding the microscopic origin of the antiferromagnetic order in iron arsenide materials, with some favouring a localized picture and others supporting an itinerant point of view. More importantly, there has not even been agreement about the simplest effective ground-state Hamiltonian necessary to describe the antiferromagnetic order. Here, we use inelastic neutron scattering to map spin-wave excitations in CaFe2As2, a parent compound of the iron arsenide family of superconductors. We find that the spin waves in the entire Brillouin zone can be described by an effective three-dimensional local-moment Heisenberg Hamiltonian, but the large in-plane anisotropy cannot. Therefore, magnetism in the parent compounds of iron arsenide superconductors is neither purely local nor purely itinerant, rather it is a complicated mix of the two. PUBLICATION ABSTRACT
Here, mechanical property-microstructure relationships of an X70 pipeline steel were evaluated at temperatures up to 400 °C using tensile testing, scanning and transmission electron microscopy, and ...synchrotron wide-angle X-ray scattering characterization techniques. The X70 steel had a bainitic microstructure consisting of quasi-polygonal ferrite, retained austenite, martensite-austenite islands, and carbide/nitride microconstituents. Results are compared to an X52 steel with a ferrite-pearlite microstructure. Both steels exhibited dynamic strain aging (DSA) as evidenced by serrated yielding, reductions in strain rate sensitivity, increased strengths, and reduced dutilities in the approximate temperature ranges of 100–250 °C. For temperatures above the DSA range, the X70 steel exhibited unique properties of an increase in strength simultaneously with an increase in uniform strain, both features interpreted due to microstructural changes during testing due to dynamic tempering, indicated by decomposition of the retained austenite and associated cementite and transition carbide nucleation and coarsening, i.e. microstructural changes normally associated with static tempering at temperatures above 400 °C. However, if the X70 steel was tempered at the test temperature prior to testing, dynamic microstructural changes were absent and the steel exhibited behavior similar to that observed for the X52 steel, i.e. a decrease in strength and increase in ductility at temperatures above the DSA range. New alloying strategies are suggested to improve microstructure stability during isothermal holds at elevated temperature, while maintaining the strength benefits from strain assisted bainitic tempering during plastic deformation.
Titanium alloys are advanced lightweight materials, indispensable for many critical applications
. The mainstay of the titanium industry is the α-β titanium alloys, which are formulated through ...alloying additions that stabilize the α and β phases
. Our work focuses on harnessing two of the most powerful stabilizing elements and strengtheners for α-β titanium alloys, oxygen and iron
, which are readily abundant. However, the embrittling effect of oxygen
, described colloquially as 'the kryptonite to titanium'
, and the microsegregation of iron
have hindered their combination for the development of strong and ductile α-β titanium-oxygen-iron alloys. Here we integrate alloy design with additive manufacturing (AM) process design to demonstrate a series of titanium-oxygen-iron compositions that exhibit outstanding tensile properties. We explain the atomic-scale origins of these properties using various characterization techniques. The abundance of oxygen and iron and the process simplicity for net-shape or near-net-shape manufacturing by AM make these α-β titanium-oxygen-iron alloys attractive for a diverse range of applications. Furthermore, they offer promise for industrial-scale use of off-grade sponge titanium or sponge titanium-oxygen-iron
, an industrial waste product at present. The economic and environmental potential to reduce the carbon footprint of the energy-intensive sponge titanium production
is substantial.
The etching of iron alloy items in a Hsub.3POsub.4 solution is used in various human activities (gas and oil production, metalworking, transport, utilities, etc.). The etching of iron alloys is ...associated with significant material losses due to their corrosion. It has been found that an efficient way to prevent the corrosion of iron alloys in a Hsub.3POsub.4 solution involves the formation of thin complex compound films consisting of the corrosion inhibitor molecules of a triazole derivative (TrzD) on their surface. It has been shown that the protection of iron alloys with a mixture of TrzD + KNCS in a Hsub.3POsub.4 solution is accompanied by the formation of a thin film of coordination polymer compounds thicker than 4 nm consisting of TrzD molecules, Fesup.2+ cations and NCSsup.−. The layer of the complex compound immediately adjacent to the iron alloy surface is chemisorbed on it. The efficiency of this composition as an inhibitor of iron alloy corrosion and hydrogen bulk sorption by iron alloys is determined by its ability to form a coordination polymer compound layer, as experimentally confirmed by electrochemical, AFM and XPS data. The efficiency values of inhibitor compositions 5 mM TrzD + 0.5 mM KNCS and 5 mM TrzD + 0.5 mM KNCS + 200 mM Csub.6Hsub.12Nsub.4 at a temperature of 20 ± 1 °C are 97% and 98%, respectively. The kinetic parameters of the limiting processes of hydrogen evolution and permeation into an iron alloy in a Hsub.3POsub.4 solution were determined. A significant decrease in both the reaction rate of hydrogen evolution and the rate of hydrogen permeation into the iron alloy by the TrzD and its mixtures in question was noted. The inhibitor compositions 5 mM TrzD + 0.5 mM KNCS and 5 mM TrzD + 0.5 mM KNCS + 200 mM Csub.6Hsub.12Nsub.4 decreased the total hydrogen concentration in the iron alloy up to 9.3- and 11-fold, respectively. The preservation of the iron alloy plasticity in the corrosive environment containing the inhibitor under study was determined by a decrease in the hydrogen content in the alloy bulk.
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•Nix-Gao model combined with pileup corrections are critical to improve the accuracy of bulk equivalent hardness from nanoindentation testing.•Evaluating bulk hardness by hardness ...ratio or changes at a reference depth will cause quantitative errors as large as 60%.•Constant strain rate and constant loading rate tests result in comparable hardness for materials with a weak strain rate sensitivity.•The curvature in Nix-Gao fitting is not simply caused by nanoindentation testing procedures.•Size dependent dislocation obstacle strengths are essential for accurate microstructure- and nanoindentation-predicted strength change.
Estimations of bulk hardness from nanoindentation are frequently subject to considerable uncertainties due to indentation size effects (ISE), pileup effects, and potential influence of surface quality or test methods. This study examined materials science principles of nanoindentation test methods to enable accurate prediction of bulk hardness for a series of high purity Fe and Fe-(3–25 wt%) Cr alloys. These materials were tested in as-annealed and thermally aged (100–900 h at 475 ℃ to produce Cr-rich α’ precipitates) conditions. Nanoindentation with a Berkovich indenter at constant strain rate (0.05–0.5 /s) and constant loading rate conditions provided comparable bulk equivalent hardness (H0) extracted by Nix-Gao model, indicating a weak strain rate sensitivity at room temperature. Results from electropolished and fine mechanically polished samples gave comparable measured hardness. Pileup corrections produced a 5–14% correction to H0 which agreed with the experimental bulk Vickers hardness within ∼10% for most tested materials. The microstructural model-predicted and measured strength values agreed for aged samples. A derived analytic expression demonstrates that an ISE error, associated with inappropriate methods such as hardness ratios or changes at a reference depth, would be as large as 60% in estimated bulk hardness for the investigated Fe-Cr alloys.
The conduction of heat through minerals and melts at extreme pressures and temperatures is of central importance to the evolution and dynamics of planets. In the cooling Earth's core, the thermal ...conductivity of iron alloys defines the adiabatic heat flux and therefore the thermal and compositional energy available to support the production of Earth's magnetic field via dynamo action. Attempts to describe thermal transport in Earth's core have been problematic, with predictions of high thermal conductivity at odds with traditional geophysical models and direct evidence for a primordial magnetic field in the rock record. Measurements of core heat transport are needed to resolve this difference. Here we present direct measurements of the thermal conductivity of solid iron at pressure and temperature conditions relevant to the cores of Mercury-sized to Earth-sized planets, using a dynamically laser-heated diamond-anvil cell. Our measurements place the thermal conductivity of Earth's core near the low end of previous estimates, at 18-44 watts per metre per kelvin. The result is in agreement with palaeomagnetic measurements indicating that Earth's geodynamo has persisted since the beginning of Earth's history, and allows for a solid inner core as old as the dynamo.
The Earth's core is about ten per cent less dense than pure iron (Fe), suggesting that it contains light elements as well as iron. Modelling of core formation at high pressure (around 40-60 ...gigapascals) and high temperature (about 3,500 kelvin) in a deep magma ocean predicts that both silicon (Si) and oxygen (O) are among the impurities in the liquid outer core. However, only the binary systems Fe-Si and Fe-O have been studied in detail at high pressures, and little is known about the compositional evolution of the Fe-Si-O ternary alloy under core conditions. Here we performed melting experiments on liquid Fe-Si-O alloy at core pressures in a laser-heated diamond-anvil cell. Our results demonstrate that the liquidus field of silicon dioxide (SiO
) is unexpectedly wide at the iron-rich portion of the Fe-Si-O ternary, such that an initial Fe-Si-O core crystallizes SiO
as it cools. If crystallization proceeds on top of the core, the buoyancy released should have been more than sufficient to power core convection and a dynamo, in spite of high thermal conductivity, from as early on as the Hadean eon. SiO
saturation also sets limits on silicon and oxygen concentrations in the present-day outer core.
Water contamination with chlorinated hydrocarbons such as chloroform (CHCl
3
), carbon tetrachloride (CCl
4
) and trichloroethylene (TCE) is one of the major public health concerns. In this study, we ...explored the use of aluminum-iron alloys particles in millimeter scale for rapid removal of CHCl
3
, CCl
4
and TCE from water. Three types of Al-Fe alloy particles containing 10, 20 and 58 wt% of Fe (termed as Al-Fe10, Al-Fe20 and Al-Fe58) were prepared and characterized by electrochemical polarization, X-ray diffraction and energy dispersive spectrometer. For concentrations of 30-180 μg/L CHCl
3
, CCl
4
and TCE, a removal efficiency of 45-64% was achieved in a hydraulic contact time of less than 3 min through a column packed with 0.8-2 mm diameter of Al-Fe alloy particles. The concentration of Al and Fe ions released into water was less than 0.15 and 0.05 mg/L, respectively. Alloying Al with Fe enhances reactivity towards chlorinated hydrocarbons' degradation and the enhancement is likely the consequence of galvanic effects between different phases (Al, Fe and intermetallic Al-Fe compounds such as Al
13
Fe
4
, Fe
3
Al and FeAl
2
) and catalytic role of these intermetallic Al-Fe compounds. The results demonstrate that the use of Al-Fe alloy particles offers a viable and green option for chlorinated hydrocarbons' removal in water treatment.
Mixtures of high-purity elemental powders of Al with an Fe content of 10wt% were consolidated at room temperature by means of High-Pressure Torsion (HPT) and subsequently deformed to high levels of ...strain. Relative density of the consolidated disks was >99% even at low strains. The microstructure observation by transmission electron microscopy revealed that the alloy consisted of an ultrafine grained Al matrix with an average grain size of 145nm. Supersaturation of Fe was estimated in the matrix to a maximum of ∼1wt% Fe by X-ray diffraction. The dispersion of secondary Fe-rich particles was quantified by scanning electron microscopy and image processing techniques. Hardness and tensile strength were improved significantly with straining by HPT, in direct correlation with grain refinement and potentiated by dissolution of Fe particles in the matrix. Excellent compromise of strength and ductility was achieved at intermediate levels of imposed strain.
Density and surface tension of liquid Ni –Cu –Fe alloys have been measured over a wide temperature range, including the undercooled regime. A non-contact technique was used, consisting of an ...electromagnetic levitator, an optical densitometer, and an oscillating drop tensiometer.
At temperatures above and below the liquidus point, density and surface tension are linear functions of temperature. The concentration dependence of the density is significantly influenced by a third-order (ternary) parameter in the volume, while the surface tensions can be derived from the thermodynamic potentials
of the binary phases alone.
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