Fe Shell Research Articles

$L1_{0}$ FePt/Fe Exchange Coupled Composite Structure on MgO Substrates

A core-shell type exchange-coupled composite (ECC) structure is developed with an L10 phase FePt core and an Fe shell. Coercivity decreases from 30.6 kOe for the FePt granular film with a very thin thickness of 3.2 nm, to 7.85 kOe for the FePt/Fe core-shell type granular film with a 3-nm-thick Fe. The energy barriers of the FePt/Fe films are measured by using Sharrock equation. A modified formula of gain factor considering the effect of films' thickness is proposed. Core-shell type FePt/Fe ECC granular film has a large advantage over a conventional granular film for media application.

Removal of arsenate from water by using an Fe–Ce oxide adsorbent: Effects of coexistent fluoride and phosphate

The Langmuir two-site equation, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure spectroscopy have been employed to study the competitive behaviors of fluoride (F) and phosphate (P) in relation to arsenate adsorption on an Fe–Ce adsorbent as well as the mechanisms involved. The two-site isotherm revealed the presence of two kinds of adsorption sites with different binding affinities for arsenate. Both the total and low-binding-energy maximum adsorption capacities ( Q and Q 1) of arsenate decreased significantly even at a molar ratio of As/P = 1:0.1. The coexistence of F, only influenced the total Q of arsenate at high simultaneous F concentrations. The fact that Fe–Ce released 0.15–0.24 mmol sulfate for every mmol arsenate adsorbed suggested that, while sulfate groups might have played a role for adsorption, surface hydroxyl groups should be the major active sites. The XPS results indicated that arsenate and P are mainly adsorbed through the substitution of Fe surface active sites, while F is mainly adsorbed through substitution of Ce surface active sites. The As k-edge EXAFS data show that the second peak of Fe–Ce after arsenate adsorption is As–Fe shell, which further supported that arsenate adsorption occurs mainly at the Fe surface active sites.

Effects of snail shell and iron filings on properties of green moulding sand

This paper presents the report of a research on the adaptation of green moulding sand. This was done by addition of iron filings and snail shell to standard silica sand. The objective is to evaluate the compatibility of iron filings and snail shell with green moulding sand in order to know their usability with green moulding sand. Twenty-five sand samples were prepared with different Fe and snail shell contents ranging from 1 wt% to 5 wt%. A control sand sample which had no iron and snail shell content was also prepared. The properties of the sand samples were tested. The results show that addition of Fe filing does not have any adverse effects on the properties of green moulding sand; however, the snail shell content show some effects on some of the properties of the moulding sand.

Interfacial Reactions between Oxygen Containing Fe and Al at the Onset of Liquid Fe Deoxidation by Al Addition

The phenomena taking place at the early stage of Al deoxidation were investigated with specific attention on the formation of Al2O3 inclusions. In a quartz tube, Al was exposed to liquid Fe containing different amounts of dissolved oxygen ((O) under bar) for 1, 5, 30 and 60s. In this paper, quenched microstructures of the diffusion couple were examined to identify the interactions and the nature of the phases at the experimental temperature. They revealed that the reaction zone was composed of successive layers of Fe-Al intermetallic compounds, as predicted by the phase diagram of the system, i.e. alpha Fe(Al), FeAl, FeAl2, Fe2Al5 and FeAl3. Based on the microstructure, the concentration profiles, diffusion processes in solid and liquid phases, and the behavior of Al2O3 inclusions in the reaction zone, it was demonstrated that the reaction zone was completely liquid and that the solid Fe shell melted for the samples with holding time of 30 and 60 s.

Interfacial Reactions During Titanium Dissolution in Liquid Iron: A Combined Experimental and Modeling Approach

The dissolution behavior of Ti in liquid Fe has been investigated experimentally and theoretically within the framework of inclusion formation in steel. In the experimental study, Ti cylinders have been immersed into liquid Fe and, subsequently, water-quenched. Macroscopic observation of quenched samples shows the initial solidification of an Fe shell around the Ti. Microstructural analysis of the Fe-Ti interfacial area with a scanning electron microscope equipped with an energy dispersive X-ray spectrometer reveals that a reaction zone develops in a three-step process: formation of a first liquid eutectic layer rich in Ti, formation of a second eutectic layer rich in Fe, and then mixing of both layers. The reaction zone grows in thickness up to 40 pct of the original sample radius and dissolves both parts of the Ti sample and the Fe shell. A simplified, one-dimensional, implicit finite volume model has been used to describe these phenomena theoretically. Good qualitative agreement is achieved between experiment and model. The model has been used to estimate the influence of original addition size, preheating, convection, and superheating on the required melt-back time.

Inelastic wrinkling and collapse of tubes under combined bending and internal pressure

The problem of inelastic bending and collapse of tubes in the presence of internal pressure is investigated using experiments and analyses. The experiments involve 1.5-inch diameter, D/ t=52 stainless steel tubes bent to failure at fixed values of pressure. The moment–curvature response is governed by the inelastic characteristics of the material. Bending induces some ovalization to the tube cross section while, simultaneously, the internal pressure causes the circumference to grow. Following some inelastic deformation, small amplitude axial wrinkles appear on the compressed side of the tube, and their amplitude grows stably as bending progresses. Eventually, wrinkling localizes, causing catastrophic failure usually in the form of an outward bulge. Internal pressure stabilizes the structure, it increases the wavelength of the wrinkles and can increase significantly the curvature at collapse. The onset of wrinkling is established by a custom bifurcation buckling formulation. The evolution of wrinkling and its eventual localization are simulated successfully using a FE shell model. The material is represented as an anisotropic elastic–plastic solid using the flow theory, while the models are assigned initial geometric imperfections with the wavelength of the wrinkling bifurcation mode. It is demonstrated that successful prediction of collapse requires very accurate representation of the material inelastic properties including yield anisotropies, and that as expected, the collapse curvature is sensitive to the imperfection amplitude and wavelength imposed.

Structural characterization of poorly-crystalline scorodite, iron(III)–arsenate co-precipitates and uranium mill neutralized raffinate solids using X-ray absorption fine structure spectroscopy

X-ray absorption fine structure (XAFS) is used to characterize the mineralogy of the iron(III)–arsenate(V) precipitates produced during the raffinate (aqueous effluent) neutralization process at the McClean Lake uranium mill in northern Saskatchewan, Canada. To facilitate the structural characterization of the precipitated solids derived from the neutralized raffinate, a set of reference compounds were synthesized and analyzed. The reference compounds include crystalline scorodite, poorly-crystalline scorodite, iron(III)–arsenate co-precipitates obtained under different pH conditions, and arsenate-adsorbed on goethite. The poorly-crystalline scorodite (prepared at pH 4 with Fe/As = 1) has similar As local structure as that of crystalline scorodite. Both As and Fe K-edge XAFS of poorly-crystalline scorodite yield consistent results on As–Fe (or Fe–As) shell. From As K-edge analysis the As–Fe shell has an inter-atomic distance of 3.33 ± 0.02 Å and coordination number of 3.2; while from Fe K-edge analysis the Fe–As distance and coordination number are 3.31 ± 0.02 Å and 3.8, respectively. These are in contrast with the typical arsenate adsorption on bidentate binuclear sites on goethite surfaces, where the As–Fe distance is 3.26 ± 0.03 Å and coordination number is close to 2. A similar local structure identified in the poorly-crystalline scorodite is also found in co-precipitation solids (Fe(III)/As(V) = 3) when precipitated at the same pH (pH = 4): As–Fe distance 3.30 ± 0.03 Å and coordination number 3.9; while at pH = 8 the co-precipitate has As–Fe distance of 3.27 ± 0.03 Å and coordination number about 2, resembling more closely the adsorption case. The As local structure in the two neutralized raffinate solid series (precipitated at pH values up to 7) closely resembles that in the poorly-crystalline scorodite. All of the raffinate solids have the same As–Fe inter-atomic distance as that in the poorly-crystalline scorodite, and a systematic decrease in the As–Fe coordination is observed when pH is progressively increased; the basic poorly-crystalline scorodite structural feature remains in the raffinate solid up to pH 7.

Interfacial Reactions during the Dissolution of Titanium in Liquid Iron

The interfacial reactions between a solidified Fe shell and Ti were investigated within the framework of steel alloying. Ti cylinders were immersed into liquid Fe for various durations and subsequently water-quenched. An Fe shell solidifies around the Ti. At the interface between Fe and Ti a reaction zone is formed. Initially it consists of a liquid eutectic layer, though in later stages all stable phases at elevated temperature can be found in the quenched microstructure. The larger part of this reaction zone is fluid at high temperature and both Ti and Fe dissolve into it. Moreover, intermetallic compound formation and mixing of Fe and Ti generate extra heat, shortening the time required for shell melt-back. The reaction zone reaches thicknesses up to 40 % of the initial sample’s radius and when the shell has completely remolten, a discontinuity in the thickness-time profile is expected. The exact morphology of the reaction zone at high temperature remains to be determined: presence of a solid layer of Fe2Ti may impede mixing in the initial stages.

Formation of Ferromagnetic Iron Core-Shell Nanocubes on a H-Terminated Si(100) Surface by Electrodeposition

Near-monosized and uniformly distributed cubic Fe core-shell nanoparticles (with an average side length of ) were electrodeposited on H-terminated in a solution. X-ray photoelectron spectroscopy analysis indicates chemical states of the Fe nanocubes characteristic of predominant ferromagnetic metallic Fe cores covered by shells. Glancing-incidence X-ray diffraction analysis reveals a body-centered cubic (bcc) lattice structure. A nanometer-thick film consisting of 2–3 layers of cuboidal nanoparticles of the same bcc Fe core and shell can be obtained when the amount of charge transfer is increased. The prominent magnetic domains of these nanocubes can be illustrated by magnetic force microscopy.

Speciation and characterization of arsenic in gold ores and cyanidation tailings using X-ray absorption spectroscopy

The knowledge of mineralogy and molecular structure of As is needed to better understand the stability of As in wastes resulting from processing of gold ores. In this study, optical microscopy, scanning electron microscopy, electron microprobe, X-ray diffraction and X-ray absorption fine structure (XAFS) spectroscopy (including both XANES and EXAFS regimes) were employed to determine the mineralogical composition and local coordination environment of As in gold ores and process tailings from bench-scale tests designed to mimic a common plant practice. Arsenic-bearing minerals identified in the ores and tailings include iron (III) oxyhydroxides, scorodite (FeAsO 4·2H 2O), ferric arsenates, arseniosiderite (Ca 2Fe 3(AsO 4) 3O 2·3H 2O), Ca-Fe arsenates, pharmacosiderite (KFe 4(AsO 4) 3(OH) 4·6–7H 2O), jarosite (K 2Fe 6(SO 4) 4(OH) 12) and arsenopyrite (FeAsS). Iron (III) oxyhydroxides contain variable levels of As from trace to about 22 wt% and Ca up to approximately 9 wt%. Finely ground ore and tailings samples were examined by bulk XAFS and selected mineral grains were analyzed by microfocused XAFS (micro-EXAFS) spectroscopy to reconcile the ambiguities of multiple As sources in the complex bulk EXAFS spectra. XANES spectra indicated that As occurs as As 5+in all the samples. Micro-EXAFS spectra of individual iron (III) oxyhydroxide grains with varying As concentrations point to inner-sphere bidentate-binuclear arsenate complexes as the predominant form of As. There are indications for the presence of a second Fe shell corresponding to bidentate-mononuclear arrangement. Iron (III) oxyhydroxides with high As concentrations corresponding to maximum adsorption densities probably occur as nanoparticles. The discovery of Ca atoms around As in iron (III) oxyhydroxides at interatomic distances of 4.14–4.17 Å and the coordination numbers suggest the formation of arseniosiderite-like nanoclusters by coprecipitation rather than simple adsorption of Ca onto iron (III) oxyhydroxides. Correlation of Ca with As in iron (III) oxyhydroxides as determined by electron microprobe analysis supports the coprecipitate origin for the presence of Ca in iron (III) oxyhydroxides. The samples containing higher abundances of ferric arsenates released higher As concentrations during the cyanidation tests. The presence of highly soluble ferric arsenates and Ca-Fe arsenates, and relatively unstable iron (III) oxyhydroxides with Fe/As molar ratios of less than 4 in the ore and process tailings suggests that not only the tailings in the impoundment will continue to release As, but also there is the potential for mobilization of As from the natural sources such as the unmined ore.

Evaluation of energy release rate for delamination defects at the skin/stringer interface of a stiffened composite panel

This paper deals with numerical investigation on a stiffened composite panel under longitudinal compression load, in presence of artificial delamination defects between skin/stringer interface layers. At first, both the experimental and numerical non-linear equilibrium paths were determined, until the failure load value of the structure was reached. Then local evaluation of the energy release rate parameter was performed at defect front, by means of a hybrid (FEM/analytical) procedure based on a particularized virtual crack closure technique. The same FE shell model was used to perform both global and local calculations by means of a single analysis.

Identification and characterization of sorbed lutetium species on 2-line ferrihydrite by sorption data modeling, TRLFS and EXAFS

The Lu(III) sorbed species onto synthetic hydrous ferric oxide (HFO), commonly called ferrihydrite, has been identified. Characterization of the synthetic 2-line HFO shows that its synthesis is reproducible. Potentiometric titration of freshly synthesized HFO, modeled using the constant capacity model (κ1=0.5 F/m2) in the FITEQL code, yields a specific surface area S a of 360±35 m2/g (N2-BET), a site density N d of 2.86 sites/nm2 (concentration of hydroxyl groups, N s=1.71×10-3 mol sites/g HFO), and acidity constants pK a1}int=6.37 and pK a2}int=9.25. Evaluation of chemical sorption data reveals the presence of two different Lu surface sorbed species, dependent on pH; a monodendate species forms at low pH and a polydentate species at pH>5. Satisfactory fits to the sorption data are obtained using a combination of monodentate and bidentate surface species. The combination of species is chosen, based on extended X-ray absorption fine structure (EXAFS) results. The sorption constants obtained from these fits are pK s=-1.89(±0.1) and pK s=-1.69(±0.1) for the monodentate species ≡FeOLu(H2O)5 2+ for fits to the pH edge and to the isotherm at pH°5.9, respectively. A value of pK s=3.69(±0.01) is found for the bidentate species ≡ Fe(O)2Lu(H2O)5 + for both fits. EXAFS analysis of sorption samples prepared at 4.5<pH<8 shows that Lu is surrounded by a single first shell of 7±1 oxygen atoms, at a distance of (2.30±0.01) Â in all samples. A second coordination shell of Fe neighboring atoms at a distance of (3.38±0.01) Â is observed for sorption samples pH≥5.5. This distance is associated with the formation of a bidendate complex with bonding via edge sharing to iron octahedra. The samples prepared at pH<5.1 show no Fe shell, as expected for monodentate coordination. No evidence for surface precipitation and no noticeable difference between wet paste and dried powder samples is found.

Reactions of copper and cadmium ions in aqueous solution with goethite, lepidocrocite, mackinawite, and pyrite

The uptake of Cu and Cd in aqueous solution by interaction with the surfaces of carefully synthesized finely sized particles of goethite, lepidocrocite, mackinawite, and pyrite was measured as a function of initial metal concentration in solution. The results show how reactions between metal ions in solution and mineral surfaces depend in a subtle way on the nature of the surfaces and, in certain cases, on the initial concentration of metal in solution. The uptake curves fall into two groups; type I in which the efficiency of uptake decreases with increasing concentration (Cu and Cd on goethite and lepidocrocite, Cd on pyrite), and type II in which it remains constant (Cu on mackinawite and pyrite, Cd on mackinawite). The total uptake is an order of magnitude greater for the latter group. X-ray absorption spectroscopies (XANES and EXAFS) were used to define the local environments of the metals taken up at the mineral surfaces. All examples showing the type I behavior yield information on local environments consistent with their being bound to the surfaces by an inner sphere complex formation mechanism. Thus, Cu on goethite appeared to form a Jahn-Teller distorted octahedral complex (four O atoms at 1.94 Aa; two O atoms at 2.41 Aa) but with evidence for interaction with two further Fe (or Cu) at 2.92 Aa. On lepidocrocite, the first coordination sphere was essentially identical to that on goethite but with a second Cu or Fe shell at 3.04 Aa and, for the highest Cu loadings, a third shell (2 Cu or Fe) at 3.67 Aa. The Cd on goethite showed best fits for sixfold coordination to O (at 2.26 Aa) but with evidence for a second shell of Fe atoms at 3.75 Aa. On lepidocrocite, the first shell was essentially the same as for goethite, but a second shell of Fe atoms appeared to occur at the shorter distance of 3.31 Aa. For Cd-loaded pyrite, best fits were given by a single shell of six O atoms at 2.27 to 2.28 Aa and with no evidence for a second shell of metal atoms. The systems exhibiting the type II behavior yielded spectra consistent with the formation of new phases on the surfaces, either by precipitation or replacement reactions. In the case of Cu interaction with mackinawite, a chalcopyrite phase appeared to form, whereas interaction with pyrite seemed to produce binary Cu sulfides--covellite at lower loadings and chalcocite at higher loadings. Cd interaction with mackinawite seemed to produce a CdS phase.

X-ray absorption spectroscopic studies of the binding of ligands to FeMoco of nitrogenase from Klebsiella pneumoniae

The binding of ligands to the iron-molybdenum cofactor (FeMoco) from Klebsiella pneumoniae nitrogenase has been studied by XANES and EXAFS at the Fe. Mo and Se k-edges and by EPR. Ligands investigated include the anions derived from thiophenol, 2-bromophenylthiol, phenylselenol, a trithiolate ligand, 1, and the cyanate and thiocyanate anions. Evidence has been obtained directly that phenylselenol, and indirectly that thiophenol, 2-bromophenylthiol and ligand, 1, are bound by iron. For FeMoco plus phenylselenol, an iron-selenium distance of 2.36 Å was determined from the Fe k-edge data and 2.38 Å from the Se k-edge data. The results suggest that one selenol (and by analogy thiophenol and 2-bromophenylthiol) is bound in a non-bridging mode by FeMoco. Binding of ligand 1 led to a large splitting of the Fe shell at the Mo k-edge. At the Fe k-edge, binding of ligand 1 led to large decreases in the intensity of the iron-iron contacts. No evidence was found for cyanate or thiocyanate binding to Fe.

EXAFS Study of Zn and ZnEDTA Sorption at the Goethite (α-FeOOH)/Water Interface

EXAFS spectroscopy has been used to compare the sorption mechanism of Zn and ZnEDTA on goethite (α-FeOOH). In the absence of EDTA, Zn is found to form an inner-sphere surface complex. Based on Zn-O and Zn-Fe distances, Zn is inferred to be located in a distorted oxygen octahedron which shares edges and/or comers with surface Fe octahedra. EXAFS spectra of ZnEDTA in solution and sorbed on goethite are similar, indicating that the ZnEDTA complex does not dissociate following its sorption. The absence of an Fe shell within the first 4 A precludes the existence of Zn-O-Fe bonds and allows us to reject a ligand exchange sorption mechanism involving the formation of Zn-O-Fe linkages.

Extended x-ray absorption fine structure studies of IBS Fe–Tb alloy films

We have employed extended x-ray absorption fine structure (EXAFS) analysis to study the compositional dependence of the atomic structure in Fe–Tb alloy films. Fourier transforms of EXAFS data, relative to both the Fe K and the Tb LIII absorption edges, provide information about the local atomic environments relative to each atom. Results indicate the Fe EXAFS data to be dominated by Fe–Fe correlations, and consists of contributions from two Fe atomic shells at radial distances near 2.47 and 2.66 Å and a Tb shell near 2.91 Å. The coordination number of the Fe shells are measured to increase, while radial distances decrease, with increased Fe content. The Tb EXAFS data was found to have an atomic shells of Fe and Tb at 2.91 and 3.47 Å, respectively. Analysis suggests that the Fe shell is very disordered and is comprised of approximately 9.5 atoms while the Tb shell has ≊3 atoms.

Method of obtaining the empirical scattering parameters for the Fe-B pair from the extended x-ray-absorption fine-structure data ofFe2B: Possible limitations

${\mathrm{Fe}}_{2}$B as well as ${\mathrm{Ni}}_{2}$B belong to the ${\mathrm{Al}}_{2}$Cu(C16)-type structure: body-centered tetragonal. When the Fe K-edge extended x-ray-absorption fine structure (EXAFS) for ${\mathrm{Fe}}_{2}$B is Fourier transformed with k weighting, the radial structure function \ensuremath{\Phi}(R) shows two well-separated peaks with a sharp minimum in between. Exactly the same shape of \ensuremath{\Phi}(R) was previously obtained in the case of similarly Fourier-transformed Ni K EXAFS for ${\mathrm{Ni}}_{2}$B, and an approximation was made that the first radial peak in the low-R region comes from the first shell of four B atoms. Thus, for the case of ${\mathrm{Ni}}_{2}$B, the empirical phase shift and envelope functions for the Ni-B pair were obtained by inverse transforming the low-R-side peak region. However, a careful simulation of the Fourier-transform peaks for ${\mathrm{Fe}}_{2}$B shows that the first radial peak has some contribution from the next Fe shell and that the sharp minimum originates from the interference between the contributions of closely spaced shells.

IUE SPECTROSCOPY OF HOT BINARY STARS HD 108,HD 149404 AND HD 163181.

ABSTRACT High-dispersion IUE UV spectra of the hot binaries HD 108, HD 149404 and HD 163181 obtained at several orbital phases is presented in an attempt to assess the influence of the companion on stellar wind outflow. Spectra of HD 108, which has an extreme Of spectrum in the visible, show velocity changes over a range of 40 km/sec in the weak absorption lines, which, however, do not correlate with changes in the wind lines and do not support the binary nature of the object. The double-line O-type spectroscopic binary HD 149404 exhibits a stellar wind in the UV resonance lines which is not phase dependent. HD 163181 shows a clear phase dependence in its stellar wind, with wind phenomena strongest near periastron passage at phase 0.35 in the photometric ephemeris. An expanding Fe shell is indicated in all spectra, with expansion velocities lower than the main wind lines.