Iron Shell Research Articles

Monte-Carlo simulation of the kinetics of nuclear and radiative processes upon fast ignition of the fusion target in a `double liner' system

A laser ignition scheme is considered for a fusion target placed in the cavity of a radiating plasma liner produced in a `double liner' system. It is shown that this scheme can be employed to realise an efficient thermonuclear burst. The precompression and heating of a deuterium — tritium target with an iron shell by a thermal radiation pulse was simulated using the TRITON mathematical code for the parameters of the Z-generator at the Sandia National Laboratories (USA). Laser and target parameters were optimised for the ignition of the deuterium — tritium fuel by protons accelerated by laser radiation. The propagation of the thermonuclear burning wave during the fast ignition was calculated employing the TERA mathematical code, which involves Monte-Carlo simulation of the kinetics of fast thermonuclear particles and hard gamma-ray quanta at each time step of hydrodynamic calculations. The dependence of the fusion energy gain G on the ignition energy is theoretically explained. The laser parameters required to obtain G ≫ 1 are determined.

Existence of Critical Wavelength for Gap Nucleation in Solidification on a Rigid Mold

Previous theoretical models of pure metal solidification on a patterned mold surface neglected either the thermal capacitance of the solidifying shell material (which is equivalent to assume that thermal diffusivity is infinitely large) or interfacial coupling between the thermal and mechanical fields along the mold-shell interface. In the present work, however, we examine the combined effects of thermomechanical coupling at the mold-shell interface and non-negligible thermal capacitance (or finite thermal diffusivity) of the solidifying shell material during solidification of pure aluminum and iron shells on a rigid, perfectly conducting mold. It is assumed that the mold surface has a sinusoidal corrugation with a small aspect ratio, and the surface is perfectly wet by the molten metal which is initially at its melting temperature. The undulatory geometry of the mold surface lead to nonuniform heat extraction and hence initiated a nonuniform evolving distortion of the metal shell. This distortion produces a critical wavelength that corresponds to the situation where both the contact pressure and its time derivative simultaneously fall to zero. This critical mold surface wavelength serves as a cutoff between those wavelengths that lead to gap nucleation in the troughs and those that lead to gap nucleation in the crests. The conditions for gap nucleation in the mold surface troughs are examined since a corresponding increase in contact pressure at the crests signals the possibility of a growth instability in the metal shell at later stages in the process. Gap nucleation times, associated mean shell thicknesses, and critical wavelengths are calculated for pure aluminum and pure iron shells under identical process conditions. It is found that the iron shell nucleates gaps faster than an aluminum shell, with the associated critical wavelengths of iron being substantially larger than those for aluminum.

Iron (III)-silica interactions in aqueous solution: insights from X-ray absorption fine structure spectroscopy

The influence of aqueous silica on the hydrolysis of iron(III) nitrate and chloride salts in dilute aqueous solutions ( m Fe ∼ 0.01 mol/kg) was studied at ambient temperature using X-ray absorption fine structure (XAFS) spectroscopy at the Fe K-edge. Results show that in Si-free iron nitrate and chloride solutions at acid pH (pH < 2.5), Fe is hexa-coordinated with 6 oxygens of H 2O- and/or OH-groups in the first coordination sphere of the metal, at an Fe-O distance of 2.00 ± 0.01 Å. With increasing pH (2.7 < pH < 13), these groups are rapidly replaced by bridging hydroxyls (-OH-) or oxygens (-O-), and polymerized Fe hydroxide complexes form via Fe-(O/OH)-Fe bonds. In these polymers, the first atomic shell of iron represents a distorted octahedron with six O/OH groups and Fe-O distances ranging from 1.92 to 2.07 Å. The Fe octahedra are linked together by their edges (Fe-Fe distance 2.92–3.12 Å) and corners (Fe-Fe distance ∼3.47 ± 0.03 Å). The Fe-Fe coordination numbers ( N edge = 1–2; N corner = 0.5–0.7) are consistent with the dominant presence of iron dimers, trimers and tetramers at pH 2.5 to 2.9, and of higher-polymerized species at pH > 3. At pH > 2.5 in the presence of aqueous silica, important changes in Fe(III) hydrolysis are detected. In 0.05- m Si solutions (pH ∼ 2.7–3.0), the corner linkages between Fe octahedra in the polymeric complexes disappear, and the Fe-Fe distances corresponding to the edge linkages slightly increase (Fe-Fe edge ∼ 3.12–3.14 Å). The presence of 1 to 2 silicons at 3.18 ± 0.03 Å is detected in the second atomic shell around iron. At basic pH (∼12.7), similar structural changes are observed for the iron second shell. The Fe-Si and Fe-Fe distances and coordination numbers derived in this study are consistent with (1) Fe-Si complex stoichiometries Fe 2Si 1-2 and Fe 3Si 2-3 at pH < 3; (2) structures composed of Fe-Fe dimers and trimers sharing one or two edges of FeO 6-octahedra; and (3) silicon tetrahedra linked to two neighboring Fe octahedra via corners. At higher Si concentration (0.16 m, polymerized silica solution) and pH ∼ 3, the signal of the Fe second shell vanishes indicating the destruction of the Fe-Fe bonds and the formation of different Fe-Si linkages. Moreover, ∼20 mol.% of Fe is found to be tetrahedrally coordinated with oxygens in the first coordination shell ( R Fe-O = 1.84 Å). This new finding implies that Fe may partially substitute for Si in the tetrahedral network of the silica polymers in Si-rich solutions. The results of this study demonstrate that aqueous silica can significantly inhibit iron polymerization and solid-phase formation, and thus increase the stability and mobility of Fe(III) in natural waters. The silica “poisoning” of the free corner sites of iron-hydroxide colloids should reduce the adsorption and incorporation of trace elements by these colloids in Si-rich natural waters.

Excitation of Ar15+ and Fe23+ for diagnostic application to fusion and astrophysicalplasmas

Electron-impact excitation collision strengths for transitions among doubly excited levels up to then = 3 shell (excluding the1s 3l3l'configurations) of lithium-like argon and iron have been calculated using aradiation- and Auger-damped, intermediate-coupling frame transformation,R-matrix approach.Collision strengths have also been calculated for transitions between all singly excited levelsup to the n = 5shell for the same systems. The Maxwell-averaged effective collision strengthsare estimated to be accurate to within 20% at temperatures 5 × 104–5 × 108 K forAr15+and 105–109 K for Fe23+.These results are of substantially improved precision compared to previousstudies. The data relate to the analysis of soft x-ray helium-like spectra in bothastrophysical and fusion thermal plasmas. We summarize the sensitivity to thenew data of the spectral simulations which are matched to experiment in currentspectral analysis procedures. Also, we present some brief results of modellingusing the presented data.

A New Investigation of Iron Cross Sections via Spherical-Shell Transmission Measurements and Particle Transport Calculations

We are engaged in a multi-year project to study neutron scattering interactions in iron, the principal objective of which is to investigate the well-known deficiency that exists in reactor pressure vessel neutron fluence determinations. Specifically, we are using the spherical-shell transmission method, employing iron shells with different thicknesses, and neutron time-of-flight measurements of the scattered neutrons, in an effort to precisely determine specific energy regions over which deficiencies in the non-elastic scattering cross section for neutron scattering in iron appear to exist. The analysis of the experimental data involves correlating the data with theoretical calculations of neutron transport through the iron spheres in order to evaluate the degree to which the calculated neutron spectra predict the measured spectra relative to different types of particle interactions. In doing so, we have developed new methodologies for performing neutron transport calculations that will be useful to a range of transport problems. Preliminary results show good agreement between the experimental data and the calculated distribution of neutron flight times over much of the data range, except for the contribution due to breakup neutrons.

New Particle Transport Methods for Design and Optimization of Spherical-Shell Transmission Measurements

This paper discusses new particle transport methods developed for accurate investigation of iron non-elastic scattering cross sections using the spherical-shell transmission method, employing iron shells with different thicknesses, and neutron time-of-flight spectroscopy of the scattered neutrons. New calculational techniques based on the deterministic and Monte Carlo methods have been developed for design and optimization of the experiment, and for identification and reduction of experimental uncertainties. The new methods include a new tallying option for the MCNP code and new quadrature sets for the 3-D parallel Sn code PENTRAN. The new tallying option is used to determine the optimum source energy versus target thickness, and among the new quadrature sets, the Pn-Tn with ordinate-splitting technique has resulted in accurate flux distributions as compared to Monte Carlo prediction.

SOLIDIFICATION OF A PURE METAL WITH FINITE THERMAL CAPACITANCE ON A SINUSOIDAL MOLD SURFACE

Previous models of mold microgeometry-induced gap nucleation during pure metal solidification neglected the thermal capacitance of the solidifying shell: this is equivalent to the assumption that the shell has a small Stefan number. Although this assumption leads to steady heat conduction in the shell, and hence simplifies the solution for the thermal field, the corresponding assumption of a small Stefan number material is generally not appropriate for metals. In the present work, we remove the small Stefan number restriction used in a previous model for solidification of a pure metal on a rigid, perfectly conducting mold. The mold has a sinusoidal surface microgeometry for which the ratio of the amplitude to the wavelength is much less than one. This makes the aspect ratio a convenient perturbation parameter. Molten metal initially at its fusion temperature is assumed to wet the mold surface perfectly, which is held a constant temperature below the fusion temperature. The temperature field in the growing metal shell is numerically evaluated, and the instantaneous temperature field is incorporated into an analytical solution for the stress field in the shell. The evolving thermomechanical distortion of the shell is modeled assuming that the shell material follows a thermohypoelastic constitutive law that is a rate formulation of thermoelasticity. The contact pressure profile at the shell/asperity interface, which is indicative of shell distortion due to the asperity geometry, is obtained from the stress field. The effects of the mold wavelength and shell thermal capacitance on the contact pressure, temporal and spatial evolution of gap nucleation at the shell/mold interface, and mean shell thickness are examined for pure aluminum and iron shells.

Mechanisms of arsenic uptake from aqueous solution by interaction with goethite, lepidocrocite, mackinawite, and pyrite: an X-ray absorption spectroscopy study.

The mechanisms whereby As(III) and As(V) in aqueous solution (pH 5.5-6.5) interact with the surfaces of goethite, lepidocrocite, mackinawite, and pyrite have been investigated using As K-edge EXAFS and XANES spectroscopy. Arsenic species retain original oxidation states and occupy similar environments on the oxyhydroxide substrates, with first-shell coordination to four oxygens at 1.78 A for As(III) and 1.69 A for As(V). In agreement with other workers, we find that inner sphere complexes form, apparently involving bidentate (bridging) arsenate or arsenite. Interaction of As(III) and As(V) with the sulfide surfaces shows primary coordination to four oxygens (As-O: 1.69-1.76 A) with further sulfur (approximately 3.1 A) and iron (3.4-3.5 A) shells suggesting outer sphere complexation. Arsenic species were also coprecipitated with mackinawite (pH 4.0), and these samples were further studied following oxidation. At high As(III) or As(V) concentrations, arsenate or arsenite species form, probably as sorption complexes, along with poorly crystalline arsenic sulfide (the only product at low As(V) concentrations). All oxidized samples show primary coordination to four oxygens at 1.7 A, indicating As(V); these arsenates may show both outer sphere complexation with residual mackinawite and inner sphere complexation with new oxyhydroxides. These experiments help to clarify our understanding of As mobility in near-surface environments.

Mössbauer investigations and molecular orbital calculations on epidote

The electronic structure of iron-rich epidote has been investigated by cluster molecular orbital calculations in local spin density approximation. Calculated quadrupole splittings for Fe(III) at both the M1 and M3 sites are in quantitative agreement with the experimental values obtained by Mossbauer spectroscopy. A detailed analysis of the theoretical results shows that a strong tetragonal compression of the M3 octahedron is responsible for the unusually large value of the quadrupole splitting of FeM3(III). The corresponding electric field gradient (efg) is dominated by the anisotropy of the valence shell of iron, whereas the ligands contribute only about 15% to the efg. The calculations emphasize that rather large clusters, extending beyond the second coordination sphere of iron, are necessary for a reliable description. Small clusters including only the first coordination sphere of iron generally yield misleading results due to unsaturated oxygen bonds and relatively large cluster charges.

Hot rolling mill roll microstructure interpretation: A computational thermodynamics study

The microstructure of the interface of a high chromium cast iron/ductile cast iron composite hot rolling mill roll has been interpreted with the help of Fe-Cr-Si-C laboratory alloys and thermodynamic calculations of their solidification paths. It has been shown that the mill roll presents two limiting microstructures: the ductile cast iron core and the white cast iron shell. While the core is heavily contaminated with chromium, originating from the partial dissolution of the shell during core pouring, the shell shows a typical high chromium white cast iron micro-structure, since it remains solid during processing. The high chromium contents in the core originate a typical “mottled” cast iron microstructure, combining nodular graphite and ledeburite. The region between the two limiting microstructures is called interface. As the distance from the core toward the shell increases in the interface, the content of chromium increases but that of silicon decreases. The resulting microstructural gradient shows ledeburitic M3C, hexagonal-section M3C, duplex M3C/M7C3 carbides, and M7C3 carbide, which could be well correlated with the calculated solidification paths of the laboratory samples.

Surface-related properties of γ-Fe 2O 3 nanoparticles

Surface/interface effects on static magnetic properties of γ-Fe 2O 3 nanoparticles of average diameter 3–10 nm, have been investigated by magnetisation measurements (0–55 kOe, 4.2–300 K) as a function of the field and temperature and by in-field (60 kOe) Mössbauer spectroscopy experiments. The comparison of the results between particle dispersions with different concentrations in polyvinylic alcohol and phosphate-coated particles provides evidence for the interplay between surface anisotropy, intraparticle exchange coupling between surface and core, and interparticle interactions. Enhanced local surface anisotropy and surface spin disorder at low temperature have been found in both systems. In the dispersions, the existence of a canted surface spin structure below ≈85 K is evidenced by in-field Mössbauer experiments and by magnetisation measurements showing a strong increase of the high-field magnetisation with decreasing temperature as the field increases, more and more important with decreasing particle size. In the phosphate-coated particles, consisting of a γ-Fe 2O 3 core surrounded by a disordered phosphated iron shell, the surface spins are paramagnetic down to ≈30 K, below which they freeze in a speromagnetic-like structure.

Mössbauer study of RF-sputtered Fe xN( x≈2) film

Fe x N (1.6<x<2.2) is produced by RF-sputtering of pure iron under high purity argon and nitrogen atmosphere. Abundances of Fe, N, O and C are analyzed by proton deep elastic scattering, while X-ray photoelectron spectroscopy (XPS) is used to detect the oxidation of iron. Mössbauer spectroscopy was used to characterize the samples as-sputtered and after annealing at 200°C, 250°C and 300°C for 30 minutes, respectively. X-ray diffraction and Mössbauer results show that for the chemical ratio of iron in Fe x N approaching 2, orthorhombic ζ-Fe 2N will transform into hcp ε-Fe x N or quasi-ZnS type structure with an increase of nitrogen content in the sputtering atmosphere or after annealing. The first neighbor shell of iron is either rich or depleted of nitrogen in ε-Fe 2N.

Morphology and reduction kinetics of fluxed iron ore pellets

The present paper describes studies of the reduction and sintering behaviour, followed by examination of the structural changes taking place, during direct reduction of fluxed composite (ore plus coal) pellets. The kinetics and morphological aspects of the direct reduction of fluxed composite pellets are compared with those for the gaseous reduction of fluxed ore pellets without carbon addition. It is shown that the chemical reaction is the rate limiting factor for fluxed composite pellets, and the mass transport of reactant gas through the reaction product iron layer governs the overall reduction process in the case of fluxed ore pellets. Microscopic analysis of the fluxed composite pellets has indicated no tendency to form a reduction inhibition iron shell towards the end of the reduction, as found in the case of gaseous reduction of fluxed ore pellets under identical reduction process conditions. The effects of basicity, Fe/C, temperature, and other variables on morphological and microstructural changes in the directly reduced fluxed composite pellets have been experimentally investigated in the present work.

Shielding Benchmarks Analysis for Transport/Storage Casks

The dose rate measurements of the TN 12/2, TN 28 VT and FS 65 has been used to evaluate the calculational procedures of Transnucléaire (TN). The three-dimensional (3D) Monte Carlo code TRIPOLI-3.4 which is used to optimize the shielding of TN casks, is applied to the analysis of a series of benchmarks. In the same cases the one-dimensional (1D) Sn code SN1D and the point kernel code MERCURE-V (3D) used for the more simplified calculations, are checked by the comparison with the measurements. The multi-group approximation used by the above codes, in order to reduces nulear data, introduces errors due to the neutron cross-sections resonance treatment and the repartition of the gamma-ray spectrum (discrete) into an energy group structure. For a cask consisting of an iron shell of 250 mm of thickness, neutron dose rates can been underestimated of 50% if the resonances of the iron cross sections for high energy (above 1 MeV) are not taken into account. Also, depending on the energy group structure, gamma-ray dose rates can be over-estimated or under-estimated by the repartition of the gamma rays. The comparisons between measured and calculated dose rates are closer than 20% for the Monte Carlo calculations, 50% for the Sn calculations (1D) and a factor of 2 for the point kernel calculations.

Mold Surface Wavelength Effect on Gap Nucleation in Solidification

A theoretical model that predicts the time and position of gap nucleation along the metal-shell interface during solidification of a pure metal on a sinusoidal mold surface is presented. The ratio of the mold surface amplitude to its wavelength is assumed to be much less than one and hence it is used as a perturbation parameter in the analysis. The molten metal perfectly wets the mold surface prior to the beginning of solidification, and this leads to a corresponding undulation of the metal shell thickness. A nonuniform distortion develops in the shell due to the lateral temperature gradient induced by the modest spatial variation of the mold surface. This causes a variation in the contact pressure so that the growing shell pushes harder on the mold in some places, but in other places it starts to pull away from the mold. Gap nucleation is assumed to occur when the contact pressure falls to zero. The conditions for gap nucleation in the surface troughs are examined since a corresponding increase in pressure at the crests signals the possibility of a growth instability in the shell at later stages of the process. A series expansion for the contact pressure is presented which is appropriate for early solidification times. This reveals how the contact pressure varies with the mold surface wavelength. This solution is compared with a numerical solution for the contact pressure that is not limited to early solidification times. Gap nucleation times are calculated for pure aluminum and iron shells for selected mold surface wavelengths. The associated mean shell thicknesses are calculated as a function of wavelength at selected mean molten metal pressures. [S0021-8936(00)02901-9]

Mathematical modelling of alloy melting in steel melts

en

A Theoretical Investigation of Kinetics and Mechanisms of Iron Ore Reduction in an Ore/Coal Composite.

In this heterogeneous multi-reaction system, kinetic steps in each group of heat transfer, mass transfer and chemical reactions are investigated first to identify the slowest step based on a validated mathematical model of 19 independent equation.2, 3) They are conductive heat transfer, convective mass transfer and carbon gasification by CO2 and H2O. The overall reaction of metallization of iron ore by coal with heat supplied by an external source is largely limited by the conduction of heat though the sponge iron shell of an ore/coal composite.

Transmission Electron Microscopy Study of Gold-Coated Iron Core-Shell and Au/Fe/Au Onion-Like Nanoparticles Synthesized using Reverse Micelles

ABSTRACTGold-coated iron core-shell structure and Au/Fe/Au onion-like nanoparticles synthesized using reverse micelles were characterized by transmission electron microscopy (TEM). The average nanoparticle size of the core-shell structure is about 8 nm, with about 6 nm diameter core and 2 nm shell. The gold shell structure can be resolved from both high resolution electron microscopy (HREM) image and energy dispersive X-ray spectrum (EDS). Even though the gold and iron electron diffraction rings overlap a little bit, they can still be identified due to the slight mismatch of the diffraction rings. The Au/Fe/Au onion-like nanoparticles were also observed. The nanoparticles were formed with about 6 nm diameter gold core, 1 nm iron interlayer and 2 nm gold shell. The shell structure coated on the core appeared unhomogeneous, however, in both cases the iron core and interlayer iron shell stay air-stable.

Interplay between ferritin metabolism, reactive oxygen species and nitric oxide

The biological relevance of each of the three inorganic species – iron, oxygen, and nitric oxide (NO) – is crucial. Moreover, their metabolic pathways cross each other and thus create a complex network of connections responsible for the regulation of many essential biological processes. The iron storage protein ferritin, one of the main regulators of iron homeostasis, influences oxygen and NO metabolism. Here, examples are given of the biological interactions of the ferritin molecule (ferritin iron and ferritin shell) with reactive oxygen species (ROS) and NO. The focus is the regulation of ferritin expression by ROS and NO. From these data, ferritin emerges as an important cytoprotective component of the cellular response to ROS and NO. Also, by its ability to alter the amount of intracellular "free" iron, ferritin may affect the metabolism of ROS and NO. It is proposed that this putative activity of ferritin may constitute a missing link in the regulatory loop between iron, ROS, and NO.

A boundary element formulation for thin shell problems

With time harmonic eddy current problems, surface impedance approaches have been successfully applied. The surface impedance techniques are warranted in eddy current applications due to the fact that the rate of change of the field normal to the conductor is guaranteed to dominate over the tangential gradients. The analysis of thin iron shells has classically been problematic due to cancellation errors across the thickness of the shells. A boundary element formulation is developed which eliminates the volume of the shell. The collapsed interface is assumed to contain both single and double layer surface currents to represent their field contribution in all of space. The double layer currents accurately simulate the channeling of flux into the shell. The single layer surface currents accurately reflect the thin shell's perturbation to the field far from the shell. A thin shell cylinder and sphere serve as the test body against which the formulation's predictions are compared for a variety of element densities.