Solid Iron Research Articles

Experimental Study of Iron Losses Generated by a Uniform Rotating Field

This paper introduces a mock-up with a solid iron cylinder rotating in a fixed excitation frame powered by dc current. A uniform field is created in the rotating cylinder, which is driven by an external motor. The braking torque is measured, allowing the study of iron losses generated by a uniform rotating field. The aim is to advance toward a vector iron loss model that takes into account different magnetization directions and their interdependency. The eddy current losses are the dominant loss source in the mock-up, rendering it easier to model. A standard eddy currents model is proposed. It models well the losses at low and medium magnetic flux density, but lower losses are measured near saturation levels. This could be due to the high thickness to radius ratio changing the eddy current paths near the edges of the rotor, which can be later analyzed by a full 3-D finite-element method analysis. A 2-D finite-element method simulation is performed, which estimates the magnetic flux heterogeneity in the rotor. Several lessons are drawn from this mock-up, which prepares a second version with a higher speed and a longer laminated stack rotor. A higher air gap will decrease the voltage fluctuation in the primary winding, a smaller angular opening of the excitation frame will improve the uniformity of the flux in the rotor.

Reactivity of suspended iron oxide particles in low temperature alkaline electrolysis

Electrolysis of iron ore is a promising CO2-free iron production route based on the electrolytic reduction of solid iron oxide particles suspended in 110 °C concentrated alkaline electrolyte. The reactivities of different iron compounds during their reduction into iron through this process have been compared using a model laboratory cell. Chronoamperometry experiments were performed on suspensions containing hematite (α-Fe2O3), magnetite (Fe3O4) or goethite (α-FeOOH) at a cell voltage of 1.66 V. Current density response, anode and cathode electrochemical potentials, faradaic efficiency and iron deposit morphology were compared. Hematite reduces to iron at 1100 A/m2 with current yield near 85%. For goethite, the current density response was 33% lower and current efficiency dropped by 20% compared to hematite. Magnetite reactivity proved to be extremely low with eight-time lower current density and tenfold lower current efficiency than hematite. The weaker reactivity of goethite and magnetite particles could be ascribed to their more difficult adsorption on the cathode surface partly covered with metal iron, the far higher viscosity of goethite suspensions, although at the same solid concentrations as the other oxide particles and the occurrence of opposite electrode reactions with dissolved Fe(OH)3 − and Fe(OH)4 − ions.

Evidence of Coupled Carbon and Iron Cycling at a Hydrocarbon-Contaminated Site from Time Lapse Magnetic Susceptibility.

Conventional characterization and monitoring of hydrocarbon (HC) pollution is often expensive and time-consuming. Magnetic susceptibility (MS) has been proposed as an inexpensive, long-term monitoring proxy of the degradation of HC. We acquired repeated down hole MS logging data in boreholes at a HC-contaminated field research site in Bemidji, MN, USA. The MS data were analyzed in conjunction with redox conditions and iron availability within the source zone to better assess whether MS can serve as a proxy for monitoring HC contamination in unconsolidated sediments. The MS response at the site diminished during the sampling period, which was found to coincide with depletion of solid phase iron in the source zone. Previous geochemical observations and modeling at the site suggest that the most likely cause of the decrease in MS is the transformation of magnetite to siderite, coupled with the exhaustion of ferrihydrite. Although the temporal MS response at this site gives valuable field-scale evidence for changing conditions of iron cycling and stability of iron minerals it does not provide a simple proxy for long-term monitoring of biodegradation of hydrocarbons in the smear zone.

Sustained molecular oxygen activation by solid iron doped silicon carbide under microwave irradiation: Mechanism and application to norfloxacin degradation

Sustained molecular oxygen activation by iron doped silicon carbide (Fe/SiC) was investigated under microwave (MW) irradiation. The catalytic performance of Fe/SiC for norfloxacin (NOR) degradation was also studied. Rapid mineralization in neutral solution was observed with a pseudo-first-order rate constant of 0.2239 min−1 under 540 W of MW irradiation for 20 min. Increasing Fe/SiC rod and MW power significantly enhanced the degradation and mineralization rate with higher yield of reactive oxygen species (ROS). Fe shell corrosion and subsequent Fe0/II oxidation by molecular oxygen with MW activation was the key factor for NOR degradation through two-electron-transfer by Fe0 under acidic conditions and single-electron-transfer by FeII under neutral-alkaline solution. Removal rate of NOR was significantly affected by solution pH, showing higher degradation rates at both acidic and alkaline conditions. The highest removal efficiencies and rates at alkaline pH values were ascribed to the contribution of bound FeII species on the Fe shell surface due to the hydroxylation of Fe/SiC. ·OH was the main oxidizing specie for NOR degradation, confirmed by density functional theory (DFT) calculations and radical scavenger tests. DFT calculations were conducted on the reaction/activation energies of the transition/final states of NOR/degradation products, combined with intermediate identification with high performance liquid chromatography coupled with a triple-quadruple mass spectrometer (HPLC-MS/MS), the piperazinyl ring was the most reactive site for ·OH attack, followed by further ring-opening and stepwise oxidation. In this study, Fe/SiC were proved to be an excellent catalyst for the treatment of fluoroquinolone antibiotics with MW activation.

(Invited) Growth and Characterization of Bulk Hvpe-GaN. Pathway to Highly Conductive and Semi-Insulating GaN Substrates

Development of GaN-based optoelectronic and electronic devices is closely linked to ongoing work devoted to crystallizing bulk GaN. Hydride vapor phase epitaxy (HVPE) is the most popular method for obtaining commercial-grade substrates. Significant advantages of HVPE are high growth rate and high purity of new-grown GaN. Using ammonothermal GaN substrates of high crystallographic and structural quality as seeds enables growth of HVPE-GaN of the same high quality [1]. Without intentional doping the material has a very low concentration of impurities and n-type conductivity comes from silicon with concentration close to 1×1017 cm-3. Free carrier concentration is at the level of 3-5×1016 cm-3. Controllable doping of HVPE-GaN to prepare substrates of specific parameters is still a challenge. In this work influence of different dopants on optical and electrical properties of GaN is presented. Results showing highly conductive n-type HVPE-GaN doped with silicon and germanium and semi-insulating material doped with carbon and iron with manganese will be presented. Characterization of the crystals includes their structural (X-ray diffraction, defect selective etching), optical (Raman spectroscopy, photoluminescence) and electrical (Hall measurements, Capacitance–voltage profiling) properties. Concentrations of dopants will be examined by Secondary Ion Mass Spectrometry (SIMS). Detailed characterization of the grown GaN:Si and GaN:Ge will be presented. The way of introducing precursors to the HVPE reactor and details of crystallization process will be demonstrated. A difference between concentration of Si, which is always higher, and free electron concentration is observed in GaN:Si. This suggests that part of Si donors is compensated by an acceptor state. The strong yellow luminescence (YL) peaks suggest that this acceptor is gallium vacancy (VGa) or its complexes. The assumption is in good agreement with theoretical calculations of energy of VGa formation decreasing for highly n-type material [2]. However, when we incorporate Ge into our HVPE-GaN we observe no YL in the PL spectra and there is no significant difference between concentration of Ge and the free carrier concentration. This is probably connected to lack of VGa in GaN:Ge. Uniformity, in terms of free carrier concentration, of GaN:Si and GaN:Ge on c-plane and m-plane of crystals will be studied. It will be shown that highly conductive n-type material can be used as substrates for building laser diodes on them. When C is introduced to HVPE-GaN, using CH4 as a precursor, a strong YL peak is observed in PL spectra of crystallized material. The crystals are highly resistive (>108 Ωcm) at room temperature. Hall measurements performed up to 1000 K showed p-type conductivity with hole concentration 4×1015 cm-3. Activation energy of ~1 eV was calculated from Arrhenius plot. This is an experimental confirmation of DFT calculations performed for C substituted for N [3]. It is also an explanation for strong yellow luminescence (YL) present in PL spectra for GaN:C in this case not related to VGa but to C. Gallium nitride crystals can also be grown using solid iron as a source of dopants. Then, no yellow luminescence and only weak near band edge luminescence are visible in the crystals. A sharp peak is observed at 1.3 eV. This was shown before as an intrinsic transition of Fe impurity in GaN [4]. The grown crystals are highly resistive at room temperature. High-temperature Hall effect measurements revealed n-type conductivity with activation energy equal to 1.8 eV. Secondary ion mass spectrometry indicated the presence of manganese in the samples. The concentration of manganese was always higher than concentration of iron in the doped GaN. [1] T. Sochacki et al., Appl. Phys. Express 6, 075504 (2013). [2] J. Neugebauer et al., Appl. Phys. Lett. 69 (4), 503 (1996). [3] J. L. Lyons et al., Appl. Phys. Lett. 97, 152108, (2010). [4] R. P. Vaudo, et al., Phys. Stat. Sol. (a) 200, No. 1, 18– 21 (2003)

Crystallization of semi-insulating HVPE-GaN with solid iron as a source of dopants

Gallium nitride crystals were grown by hydride vapor phase epitaxy using solid iron as a source of dopants. Three crystal growth processes were performed at constant HCl flow over the solid iron and with different gallium chloride flows. High structural quality ammonothermal GaN was used as seed material. No yellow luminescence and only weak near band edge luminescence were visible in all grown crystals. A sharp peak was observed at 1.298eV. This was shown before as an intrinsic transition of Fe impurity in GaN. The grown crystals were highly resistive at room temperature. High-temperature Hall effect measurements revealed n-type conductivity with activation energy equal to 1.8eV. Secondary ion mass spectrometry indicated the presence of manganese in all three samples. The concentration of manganese was always higher than concentration of iron in the doped GaN.

Tidal constraints on the interior of Venus

AbstractAs a prospective study for a future exploration of Venus, we compute the tidal response of Venus' interior assuming various mantle compositions and temperature profiles representative of different scenarios of Venus' formation and evolution. The mantle density and seismic velocities are modeled from thermodynamical equilibria of mantle minerals and used to predict the moment of inertia, Love numbers, and tide‐induced phase lag characterizing the signature of the internal structure in the gravity field. The viscoelasticity of the mantle is parameterized using an Andrade rheology. From the models considered here, the moment of inertia lies in the range of 0.327 to 0.342, corresponding to a core radius of 2900 to 3450 km. Viscoelasticity of the mantle strongly increases the potential Love number relative to previously published elastic models. Due to the anelasticity effects, we show that the possibility of a completely solid metal core inside Venus cannot be ruled out based on the available estimate of k2 from the Magellan mission (Konopliv and Yoder, 1996). A Love number k2 lower than 0.27 would indicate the presence of a fully solid iron core, while for larger values, solutions with an entirely or partially liquid core are possible. Precise determination of the Love numbers, k2 and h2, together with an estimate of the tidal phase lag, are required to determine the state and size of the core, as well as the composition and viscosity of the mantle.

Modernization of ferrate (VI) technology from the iron hydroxides

As an alternative of the solid iron salts to improve the ferrate(VI) technology it is proposed to use Fe(II) or F(III) hydroxides that are synthesized using special technique. The patterns of Fe(VI) compounds production from iron hydroxides by hypochlorite method are studied in the article. The effect of the main factors (OH - and Cl – ions concentration, temperature, duration of the synthesis, the molar ratio of the reactants [ClO − ]/[Fe(II)] or [ClO − ]/[Fe(III)]) to yield of the desired product is studied. It is shown that conversion degree of iron hydroxides into ferrates reaches 80-86 %. It is found that using the Fe(OH) 2 , except ferrate anions , byproduct (F e3 O 4 magnetite) is formed in an amount not exceeding about 4 % of total Fe. It is found that ferrate(VI) yield is reduced with increasing temperature, therefore for reducing the rate of FeO 4 2 – decomposition it is recommended to carry out the synthesis at low temperatures. It is found that conversion degree (α) of hydroxides into ferrates is also increased with increase of [ClO − ]/[Fe(II)] or [ClO − ]/[Fe(III)] values . Therefore, it should be maintained 2-3 fold excess oxidant to ensure the optimal values of α. The practical guidelines of ferrate(VI) production from Fe(II) and Fe(III) hydroxides are developed on the basis of experiments.

Redox controls on arsenic enrichment and release from aquifer sediments in central Yangtze River Basin

More than 100 million people in Asia are presently exposed to groundwater with arsenic (As) concentrations exceeding the World Health Organization standard of 10μgL−1. Arsenic contaminated groundwater within basins of the central portion of the Yangtze River has recently been reported, but the processes controlling arsenic concentrations have yet to be resolved. We examined the hydrologic and geochemical factors controlling arsenic within the Jianghan Plain, an inland sedimentary basin of the Yangtze River, where arsenic concentrations exhibit strong seasonal variability driven by surface and groundwater mixing (Schaefer et al., 2016). Hydrologic fluctuations alter redox conditions in the aquifer, leading to oscillations between arsenic/iron reduction and oxidation. Here we investigate the depth-distribution of solid and aqueous phase iron and arsenic species and, through a series of laboratory manipulations, constrain the biogeochemical processes controlling seasonal changes in groundwater arsenic concentrations. In sediment incubations from ∼20m below the surface, where solid-phase arsenic concentrations exceed 100mgkg−1, both unamended and glucose-amended sediment samples result in arsenic release to the aqueous phase. In situ carbon was capable of promoting As release in the sediment. In contrast, sediment batch incubations from other depths resulted in limited As release. Solid phase arsenic in the enriched zone was relatively oxidized but may become reduced over short time periods. In sediments below the As-enriched zone, glucose amendment resulted in arsenic reduction, but arsenic release to the aqueous phase was restricted by the subsequent formation of arsenic sulfide minerals. Buried sedimentary arsenic coupled with anaerobic microbial respiration of subsurface organic carbon within the Jianghan Plain aquifer leads to rapid release of As to groundwater. Arsenic release from sediments at ∼20m depth is sufficient to explain arsenic concentrations throughout the aquifer, and provides a mechanism to explain how shifts in hydrology result in seasonally variable arsenic concentrations in groundwater.

Theoretical analysis and numerical simulation of electromagnetic parameters of Fe-C coaxial single fiber

Based on the Maxwell equation, the electromagnetic model in the coaxial fiber was described. The interaction with electromagnetic wave was analysed and the theoretical formula of axial permeability (μ∥), axial permittivity (ε∥), radial permeability (μ⊥) and radial permittivity (ε⊥) of Fe-C coaxial fiber were derived, and the demagnetization factor (N) of fibrous material was revised. Calculation results indicate that the composite fiber has stronger anisotropy and better EM dissipation performance than the hollow carbon fiber and solid iron fiber with the same volume content. These properties can be enhanced through increasing aspect ratio and carbon content. The μ‖ is 5.18-4.46i, μ⊥ is 2.58-0.50i, ε∥ is 7.63-6.97i, and ε⊥ is 1.98-0.15i when the electromagnetic wave frequency is 5GHz with the outer diameter of 0.866μm, inner diameter of 0.500μm, and length of 20μm. The maximum of the imaginary part of μ∥ and ε∥ are much larger than that of μ⊥ and ε⊥ when the structural parameters change, and the maximum of μ∥ and ε∥ can reach 6.429 and 23.59. Simulation results show that greater conductivity, larger aspect ratio, thin iron shell play important roles to improve the electromagnetic matching ability and microwave attenuation for the Fe-C coaxial fibers.

How does the universe store iron?

A Japanese research team launched a rocket loaded with lasers and a nucleation chamber more than 300 km above Earth’s surface to investigate how the universe might stow its solid iron. Although the mission didn’t discover interstellar iron troves, the researchers did find one form the element is unlikely to take: pure iron granules (Sci. Adv. 2017, DOI: 10.1126/sciadv.1601992). Iron-rich particles floating in the expanses between stars likely play a role in catalyzing the universe’s chemical evolution, but scientists are uncertain about the forms solid iron takes in interstellar space. Pure iron particles now seem an unlikely option, according to the research team led by Yuki Kimura of Hokkaido University. The team evaporated iron atoms within a nucleation chamber that allowed researchers to control temperature and pressure. Flying the chamber in parabolic patterns aboard a rocket allowed the team to emulate the microgravity of space. The famed “vomit comet” aircraft

Precipitation Mechanism of Copper Sulfides in Solid Iron

Precipitation Mechanism of Copper Sulfides in Solid Iron

The influence of carbon on the seismic properties of solid iron

AbstractThe mechanical properties of C‐doped hexagonal close‐packed (hcp) iron are studied at high pressure from first‐principles calculations. The energy required for doping with C as an interstitial impurity is 246 meV/1 wt % C at 120 GPa for one unit cell of hcp Fe and increases almost linearly with pressure. The density deficit of the inner core can be matched for 1 to 2.5 wt % in hcp Fe, depending on the thermal profile. Carbon doping in hcp iron increases the compressional seismic wave velocity, decreases the shear wave velocity, while increasing the shear wave splitting and seismic anisotropy. In general, the presence of C in the inner core helps in explaining the observed seismic properties, though it cannot be considered the only light element.

MOF-derived iron as an active energy storage material for intermediate-temperature solid oxide iron-air redox batteries.

We here demonstrate that the iron derived from an iron-based metal-organic framework (MOF), with exposed high-density Fe-atom planes, exhibits improved reduction activity, enabling good rechargeability of solid oxide iron-air redox batteries at 500 °C. The discharge mass specific energies are 226.5 W h kg-1-Fe and 214.8 W h kg-1-Fe at C/4 and C/3, respectively, at a constant Fe-utilization of 20%.

Magnetic behavior of Bi5Nb3–3xFe3xO15–δ solid solutions

Most bismuth compounds with layered perovskite-like structure, analogs of Aurivillius phases, exhibit ferroelectric properties and are of interest from both practical and theoretical points of view. In this study, we carried out magnetochemical measurements of an electronic state and exchange interactions between iron atoms in the solid solutions Bi5Nb3O15, obtained by heterovalent substitution of niobium by atoms of iron (III). The iron-containing solid solutions were obtained in a narrow concentration range at x≤0.06. The iron-containing solid solutions at concentrations x> 0.005 are characterized by monoclinic distortion of the tetragonal cell (P2/m). The measurements of magnetic susceptibility of the solid solutions were carried out by the Faraday method in the temperature range of 77 - 400 K. The isotherms of a paramagnetic component of magnetic susceptibility of iron atoms are typical of antiferromagnets. The effective magnetic moment of single iron atoms increases with increasing temperature from 6.87 mB (90 K) to 6.92 mB (320 K). The study of the iron-containing Bi5Nb3O15 solid solutions has shown that, in the solid solutions iron (III) atoms aggregate to form dimers and tetramers with antiferromagnetic and ferromagnetic types of exchange. The values of antiferromagnetic and ferromagnetic exchange in dimers, Jdim = - 60 cm-1 and Jdim = 40 cm-1, and tetramers, Jtetr = - 40 cm-1 and Jtetr = 25 cm-1 correspondently.

Key Parameters on the Microwave Assisted Synthesis of Magnetic Nanoparticles for MRI Contrast Agents.

Uniform iron oxide magnetic nanoparticles have been synthesized using a microwave assisted synthesis method in organic media and their colloidal, magnetic, and relaxometric properties have been analyzed after its transference to water and compared with those nanoparticles prepared by thermal decomposition in organic media. The novelty of this synthesis relies on the use of a solid iron oleate as precursor, which assures the reproducibility and scalability of the synthesis, and the microwave heating that resulted in being faster and more efficient than traditional heating methods, and therefore it has a great potential for nanoparticle industrial production. The effect of different experimental conditions such as the solvent, precursor, and surfactant concentration and reaction time as well as the transference to water is analyzed and optimized to obtain magnetic iron oxide nanoparticles with sizes between 8 and 15 nm and finally colloids suitable for their use as contrast agents on Magnetic Resonance Imaging (MRI). The r2 relaxivity values normalized to the square of the saturation magnetization were shown to be constant and independent of the particle size, which means that the saturation magnetization is the main parameter controlling the efficiency of these magnetic nanoparticles as MRI T2-contrast agents.

Exchange interactions and the state of iron atoms in Bi3Nb1−xFexO7−δ

On the basis of the results of magnetic susceptibility and ESR studies of the Bi3Nb1−xFexO7−δ solid solutions iron atoms in the solid solutions of cubic modification of bismuth niobate were found to exist as Fe(III) monomers and exchange bound Fe(III)-O-Fe(III) dimers with antiferro- and ferromagnetic type of superexchange. The exchange parameters and the distribution of monomers and dimers in the solid solutions were calculated as a function of paramagnetic atom content.

Fe-doped semi-insulating GaN with solid Fe source grown on (110) Si substrates by NH3 molecular beam epitaxy

Iron doped GaN layers were grown on (110) Si substrates by ammonia molecular beam epitaxy (MBE) using solid elemental iron as a source. Specular films with concentrations up to 1×1020cm−3, as determined by secondary ion mass spectroscopy, were grown, unlike a limited incorporation of Fe into GaN by metal-rich rf plasma MBE. The Fe concentration in the film showed an exponential dependence on the inverse of source temperature with an activation energy of 3.4eV, which agrees well to the reported value for the sublimation of Fe. A 1.5µm thick GaN film with a sheet resistance of 1GΩ/sq. was obtained by compensating unintentional residual donors with a small Fe concentration of 1×1017cm−3. X-ray diffraction rocking curves indicated high crystalline quality, very similar to an undoped film, showing that the Fe incorporation required to obtain the semi-insulating film properties did not affect the structural properties of the film. The low-temperature PL spectra of highly resistive and semi-insulating Fe:GaN in the range of 1017~1018cm−3 show dominant exciton emissions and enhanced donor-acceptor-pair (DAP) emissions, implying that Fe ions contribute to the DAP transition between donor levels and Fe-related acceptor levels, possibly compensating the residual donors to achieve the semi-insulating electrical properties.

Structure, magnetic, and electrical properties of bismuth niobates doped with d-elements: XIII. State of iron atoms in the Bi3Nb1–xFexO7–δ solid solutions

From the data of magnetochemical study and ESR spectra of samples of the Bi3Nb1–xFexO7–δ (х ≤ 0.06) solid solutions iron atoms in the solid solutions of cubic modification of bismuth niobate were found to be located as Fe(III) monomers and exchange-bonded Fe(III)–O–Fe(III) dimers with anti- and ferromagnetic exchange types. The exchange parameters and the distribution of monomers and dimers over the solid solution were calculated as functions of the paramagnetic atom fraction.

Indirect determination of equilibrium distribution of V and Cr between liquid slag and solid iron at 1653 K and 101.3 kPa

In the present study, an indirect determination of equilibrium distributions of V and Cr between liquid FeO-SiO2 -MnO-TiO2 -V2 O3 -Cr2 O3 -MgO slag and solid iron was performed at 1653 K and 101.3 kPa. The experimental results were transformed to investigate the distributions of V and Cr between liquid vanadium-chromium slag and liquid iron. It was found that the distribution ratios determinated by indirect equilibrium method are slightly higher than that determinated by direct equilibrium method. Higher FeO content and lower SiO2 content have positive effect on the distribution ratios of V and Cr. However, Cr2 O3 and V2 O3 in slag have little influence on the distribution ratios of V and Cr, respectively. Furthermore, the distribution ratios of V and Cr decrease distinctly with increasing temperature.