Molten Iron Alloys Research Articles

Development of Wet Chemical Analysis Technique for Tramp Elements (M = As, Pb, Sb, and Sn) in Silver-M Alloys

Wet chemical analysis techniques for four elements (M = As, Pb, Sb, and Sn) in Ag – M binary alloys were investigated with emphasis on the choice of solvent acid and the characteristic wavelength used in the ICP-AES (Inductively-Coupled Plasma Atomic Emission Spectrometer) analysis. The elements are representative tramp elements in ferrous scrap. The activity of these elements needs to be increased to remove them efficiently during the molten scrap refining process. The activity of these elements in the molten scrap (molten iron alloy) is usually measured by a chemical equilibration technique with molten Ag. Therefore, performing an accurate and reliable chemical analysis of these elements in the molten iron alloy and the molten Ag alloy is important. Preliminary tests using conventional acids (hydrochloric acid, nitric acid) resulted in unreliable results. In the present study, the proper choice of acids as solvents was investigated for each element M in the Ag-M alloys. Several synthesized Ag-M alloys of known compositions were analyzed using two ICP-AES systems independently, for cross-checking. As and Pb in Ag alloys could be successfully dissolved in the nitric acid-based solution. On the other hand, Sb and Sn in Ag alloys did not dissolve in the nitric acid-based solution completely, leaving some precipitates. It was found that the addition of hydrofluoric acid could resolve this problem. In addition to this, the effect of the mass of the Ag-M alloy and wavelength selection during ICP-AES analysis on the accuracy and the reproducibility were investigated. An optimized procedure for the wet chemical analysis of these elements in Ag-M alloys is reported.

Role of liquid and solid particles in solid-liquid mixed fluxes on sulfur removal from molten iron under centrifugal stirring by an impeller

Process for removal of S from molten iron alloy is successfully established process in these days, e.g. Kanbara Reactor (KR) process. However, its operating mechanism needs to be understood in a more clear manner. A series of laboratory-scale experiments using lime–fluorspar flux, which is a solid particle-liquid mixture at the reaction temperature, were carried out in order to find out effects of composition, total mass, the liquid fraction (fL), order of injection of the flux, and centrifugal stirring on the reaction performance. Theoretical calculations for the phase diagram of the flux system, flux-molten iron reaction equilibria, and the reaction rate considering flux detachment/aggregation in case of the centrifugal stirring were carried out. It was concluded that (1) major S-absorbing phase should be the liquid phase in the flux, (2) increasing the fL enhances the reaction performance when the molten iron was desulfurized without the stirring, (3) the centrifugal mechanical stirring enhances the reaction rate, but it was not effective when fL is high, (4) the centrifugal mechanical stirring for solid particle-liquid mixed flux significantly affects the interfacial reaction area: enlarging the area by the detachment of the flux and contracting the area by aggregation. The fL, therefore, influences not only the volume of the S-absorbing part of the flux, but also the degree of detachment/aggregation, which depends on the physico-chemical properties of the flux. Optimum fL may be determined by the physico-chemical properties and degree of the stirring. An index for assessing DeS performance was used to reveal the role of fL and the mechanical stirring. It shows that the mechanical stirring could enhance the DeS performance without the unnecessary increase of liquid fraction of the flux, by adding fluorspar in the present case.

New glass‐based binders from engineered mixtures of inorganic waste

AbstractAluminum is one of the most important strategic resources, but the Bayer process, typically applied for the purification of ores, leads to vast amounts of alkaline slurry waste, known as red mud. Though interesting for potential reprocessing, red mud is still predominantly stored in big slurry pools, due to high levels of toxic metals. Toxic ions can be easily immobilized by vitrification, but the high costs of this solution need to be balanced by the reuse of the obtained glass. The present paper is dedicated to the transformation of waste‐derived glass into new binders for the construction industry, according to both “conventional melting” and “smelting” approaches. In the first case, red mud was included in a mixture of waste, designed to yield a reactive glass (CMG), that is, forming stable gels after activation in an alkaline aqueous solution. In the second approach, red mud was subjected to a thermal treatment in a reductive atmosphere, implying the separation of molten iron alloy. The remaining glassy slag, according to its chemical composition (CaO and Al2O3‐rich) underwent gelation by simple interaction with pure water, without any alkaline activator, thus configuring a new “glass cement.”

First-principles investigation of equilibrium iron isotope fractionation in Fe1−xSx alloys at Earth's core formation conditions

Iron is one of the most abundant non-volatile elements in the solar system. As a major component of planetary metallic alloys, its immiscibility with silicates plays a major role in planetary formation and differentiation. Information about these processes can be gained by studying the equilibrium Fe isotope fractionation between metal alloys and molten silicates at conditions of core formation. In particular, recent attention has been paid to 56Fe/54Fe equilibrium isotope fractionation at conditions relevant to Earth's core formation and the influence that light elements (O, H, C, Ni, Si and S) have had in this process. Most of these experimental studies relied on the measurement of Fe isotope fractionation from quenched phases of silicate melts and molten iron alloys. The experimental works are extremely challenging, and may suffer different drawbacks. To overcome this, we use ab-initio computational methods to perform a systematic study of the 56Fe/54Fe equilibrium isotope fractionation in molten and solid Fe1−xSx alloys at conditions of the core formation (60 GPa, 3000 K). We show for the first time, that equilibrium isotope fractionation factors from solid systems can be used as proxies for molten systems with differences between these two methods less than 0.01‰ at the relevant P-T conditions. Additionally, we discuss the effect of sulphur concentration on the equilibrium Fe isotope fractionation and show that although there are some structural changes due to atom substitutions, the wide range of studied concentrations produces β-factors that are constant within ∼0.02‰. Finally, we discuss the implications of our results for the interpretation of recent experiments and the understanding of core crystallisation processes.

Evidence for Fe-Si-O liquid immiscibility at deep Earth pressures

Seismic observations suggest that the uppermost region of Earth's liquid outer core is buoyant, with slower velocities than the bulk outer core. One possible mechanism for the formation of a stably stratified layer is immiscibility in molten iron alloy systems, which has yet to be demonstrated at core pressures. We find immiscibility between liquid Fe-Si and Fe-Si-O persisting to at least 140 GPa through a combination of laser-heated diamond-anvil cell experiments and first-principles molecular dynamics simulations. High-pressure immiscibility in the Fe-Si-O system may explain a stratified layer atop the outer core, complicate differentiation and evolution of the deep Earth, and affect the structure and intensity of Earth's magnetic field. Our results support silicon and oxygen as coexisting light elements in the core and suggest that [Formula: see text] does not crystallize out of molten Fe-Si-O at the core-mantle boundary.

Penetration of molten iron alloy into the lower mantle phase

The core–mantle boundary is the only interface where the metallic core and the silicate mantle interact physically and chemically. Many geophysical anomalies such as low shear velocity and high electrical conductivity have been observed at the bottom of the mantle. Perturbations in the Earth's rotation rate at decadal time periods require the existence of a thin conductive layer with a conductance of 108 S. Substantial additions of molten iron from the outer core into the mantle may produce these geophysical anomalies. Although iron enrichment by penetration has only been observed in (Mg,Fe)O, the second dominant mineral in the lower mantle, the penetration process leading to iron enrichment in the silicate mantle has not been experimentally confirmed. In this study, high-pressure and high-temperature experiments were conducted to investigate the penetration of molten iron alloy into lower mantle phases; postspinel, polycrystalline bridgmanite and polycrystalline (Mg,Fe)O. At the interface between (Mg,Fe)O aggregate and molten iron alloy, liquid metal penetrated the (Mg,Fe)O aggregate along grain boundaries and formed a thin layer containing metal-rich blobs. In contrast, no penetration of molten iron alloy was observed at the interface between molten iron alloy and silicate phases. Penetration of liquid iron alloy into the (Mg,Fe)O aggregate is caused by the capillarity phenomenon or Mullins–Sekerka instability. Neither mechanism occurs at the boundary of pure polycrystalline MgO, indicating that the FeO in (Mg,Fe)O plays an essential role in this phenomenon. Infiltration of molten iron alloy along grain boundaries (capillarity phenomenon) is the dominant process and precedes penetration due to the Mullins–Sekerka instability. The capillarity phenomenon is governed by the balance of forces between surface tension and gravity. In the case where the ultralow velocity zone (ULVZ) with a low shear velocity is composed of Fe-rich (Mg,Fe)O, the maximum penetration distance of molten iron alloy by capillary rise is limited to 20m. The addition of iron-rich melt to the base of the mantle is therefore unlikely to be the main cause of the high conductance of the CMB region predicted from decadal variation of the length of day. Furthermore, the absence of molten iron alloy penetration into silicate phases does not allow an extensive modification of the chemical composition of the mantle by core–mantle interaction.

A Study on the Formation Mechanism of the Interfacial Layer Between Solid CaO and Molten Iron Alloys

The present study aims to clarify the formation mechanism of the interfacial layer between solid CaO and molten iron through SEM–EDS analysis. The interfacial layer formed between CaO and molten iron is observed by SEM–EDS for different compositions of molten iron (CaO/Fe–C–S interface: CaS layer; CaO/Fe–C–Si–S interface: CaS and Ca2SiO4 layers; CaO/Fe–C–Si interface: no interfacial layer; CaO/Fe–S–Si interface: Ca2SiO4 and CaS layers). The effect of S and Si concentrations on layer formation is discussed using the following proposed mechanism. $$ {\text{CaO}}\left( s \right) + \underline{\text{S}} = {\text{CaS}}\left( s \right) + \frac{1}{2}{\text{O}}_{2} $$ $$ 2{\text{CaO}}\left( s \right) + \underline{\text{Si}} + {\text{O}}_{2} = {\text{Ca}}_{2} {\text{SiO}}_{4} \left( s \right) $$ In the case of the Fe–C–Si–Al–S/CaO interface, CaS and Ca3Al2O6 layers are observed. The formation mechanism of a reaction layer for Al-containing iron melts is also proposed as below. $$ {\text{CaO}}\left( s \right) + \underline{\text{S}} = {\text{CaS}}\left( s \right) + \frac{1}{2}{\text{O}}_{2} $$ $$ 3{\text{CaO}}\left( s \right) + \underline{{2{\text{Al}}}} + \frac{3}{2}{\text{O}}_{2} = {\text{Ca}}_{3} {\text{Al}}_{2} {\text{O}}_{6} \left( {\text{s}} \right) $$

Interface Structure and Elements Diffusion of As-Cast and Annealed Ductile Iron/Stainless Steel Bimetal Castings

Bimetal casting is considered to a promising technique for the production of high performance function materials. Heat treatment process for bimetal castings became an essential tool for improving interface structure and metallurgical diffusion bond. Molten iron alloy with carbon equivalent of 4.40 is poured into sand mold cavities containing solid 304 stainless steel strips insert. Specimens are heated to 7200C in an electrical heating furnace and holded at 720 0C for 60min and 180min. For as-cast specimens, a good coherent interface structure of ductile cast iron/304 stainless bimetal with four layers interfacial microstructure are obtained. Low temperature annealing at 720oC has a significat effect on the interface layers structure, where, three layers of interface structure are obtained after 180min annealing time because of the complete dissolving of thin layer of ferrite and multi carbides (Layer 2). Low temperature annealing shows a significant effect on the diffusion of C and otherwise shows slightly effect on the diffusion of Cr and Ni. Plearlite phase of Layer 3 is trsformed to spheroidal shape instead of lamallar shape in as-cast bimetals by low tempeature annealing at 720oC. The percent of the performed spheroidal cementit increases by increasing anneaaling time. Hardness of interface layers is changed by low temperauture annealing due to the significant carbon deffussion.

Effects of electron correlations on transport properties of iron at Earth's core conditions.

Earth's magnetic field has been thought to arise from thermal convection of molten iron alloy in the outer core, but recent density functional theory calculations have suggested that the conductivity of iron is too high to support thermal convection, resulting in the investigation of chemically driven convection. These calculations for resistivity were based on electron-phonon scattering. Here we apply self-consistent density functional theory plus dynamical mean-field theory (DFT+DMFT) to iron and find that at high temperatures electron-electron scattering is comparable to the electron-phonon scattering, bringing theory into agreement with experiments and solving the transport problem in Earth's core. The conventional thermal dynamo picture is safe. We find that electron-electron scattering of d electrons is important at high temperatures in transition metals, in contrast to textbook analyses since Mott, and that 4s electron contributions to transport are negligible, in contrast to numerous models used for over fifty years. The DFT+DMFT method should be applicable to other high-temperature systems where electron correlations are important.

Core–mantle boundary landscapes

The molten-iron alloy of the core meets the mantle's silicate rock at Earth's core–mantle boundary. Seismological images reveal hummocks of iron-enriched material above the boundary, highlighting the heterogeneous nature of the mantle.

GEOMAGNETIC MEASUREMENTS IN LATVIA

The knowledge of the Earth's magnetic field elements and their dynamic fluctuations over the area concerned are important and can be used for many practical purposes in various fields, including Geodesy and Cartography. Earth's magnetic field tends to vary over time. Unlike the field of a bar magnet, Earth's field changes over time because it is really generated by the motion of molten iron alloys in the Earth's outer core. Long-term magnetic field changes are caused mainly by processes in the Earth's interior, particularly the iron-rich core. Short-term changes of the magnetic field are mainly caused by the currents in the ionosphere and magnetosphere generated by Solar activity. The Latvian Geospatial Information Agency (LGIA) has monumented repeat stations and started periodical Earth's magnetic field declination and inclination measurements in Latvia in 2004. The Network of 6 repeat stations is regularly distributed over the territory of Latvia. The repeat stations of Latvia are: Aglona; Ozolaine; Mikeltornis; Velena; Nigrande; Vilkene. In every repeat station the D, I and F values were determined. Declination on territory of Latvia changes from 4° till 8° in the West – East direction. Magnetometer LEMI – 203 together with theodolite 3T2KP and proton magnetometer PMP 5 were used for measurements. Coordinates of the stations were determined by double frequency (L1/L2) GPS receivers. Determined coordinates were used to obtain geographical azimuth. For reduction the data from Toravere (Estonia) observatory were used, where a variometer from the Nurmijarvi Geophysical Observatory is located. Repeat station points are fixed with benchmarks. Benchmarks are non-magnetic. All the data were sent to the British Geological Survey National Geoscience Data Centre.

ChemInform Abstract: Anisotropic Hexagonal Boron Nitride Nanomaterials: Synthesis and Applications

AbstractReview: 176 refs.

Potassium partitioning into molten iron alloys at high-pressure: Implications for Earth's core

The partition coefficients of potassium, D K, between molten sanidine, KAlSi 3O 8, and molten roedderite, K 2Mg 5Si 12O 30, with FeS-rich alloy and pure Fe metal liquids have been investigated in a multi-anvil press, between 5 and 15 GPa, at a temperature of 2173 K, and at an oxygen fugacity between 0.5 and 3 log units below the iron-wüstite (IW) buffer. No pressure dependence of the D K coefficients in sulphur-free and sulphur-bearing systems was found within the investigated pressure range. We also observed minor effect of the silicate melt composition for an nbo/t (non-bridging oxygen to tetrahedral cation ratio) higher than 0.8 ± 0.4. In contrast, the partitioning of potassium varies strongly with the metallic phase composition, with an increase of K-solubility in the metallic liquid for high sulphur and oxygen contents. We review all available high-pressure data to obtain reliable D K coefficients for the interaction between molten silicates and Fe-alloy liquids at pressures and temperatures relevant to those of core formation in a terrestrial magma ocean. The dominant controlling parameters appear to be the temperature and the chemical composition of the metallic phase, with D K coefficients significantly increased with temperature, and with the sulphur and oxygen contents of the Fe-alloy liquid. Our considerations distinguish two extreme cases, with an S-free or S-bearing iron core, which yield K contents of ∼25 or ∼250 ppm, respectively. These two extreme values have very different consequences for thermal budget models of the Earth's core since its formation.

Connectivity of molten Fe alloy in peridotite based on in situ electrical conductivity measurements: implications for core formation in terrestrial planets

The connectivity of molten Fe–S in peridotite has been experimentally investigated by means of in situ electrical conductivity measurements at high temperatures and 1 GPa. Starting materials were powdered mixtures of peridotite KLB-1 with various amounts (0, 3, 6, 13, 19, 24 vol.%) of the 1 GPa eutectic composition in the Fe–FeS binary system. At temperatures above the eutectic point in the Fe–FeS system (∼980 °C) and below the solidus of KLB1 (∼1200 °C), molten Fe–S in a solid silicate matrix interconnects when the volume fraction is over ∼5%. Conductivity–temperature paths indicate that in the presence of partial silicate melting the connectivity of molten Fe–S in a peridotite matrix is inhibited. Based on observations of retrieved samples, the percolation threshold of Fe–S melts in the presence of low to moderate degrees of silicate melt is estimated at 13±2 vol.%. These results indicate that if the volume fraction of Fe-alloy in a planetesimal was initially greater than 5%, and if early heating by decay of radionuclides raised the temperature of the interior above the Fe-alloy melting point, initial metal segregation was controlled by permeable flow of molten iron alloy in a solid silicate matrix. These conditions were likely met by many terrestrial objects in the early solar nebula. Efficient removal of residual Fe-alloy (5 vol.%) from silicate requires high-degree melting of silicate so that metal can segregate as droplets. Giant impacts during the final stage of accretion of large planetary objects could supply the energy required for high-degrees of melting. Alternatively, if initial metal segregation were delayed until a planetary object grew to large size (∼1000 km in diameter), release of gravitational potential energy due to metal segregation could contribute enough heat to form a magma ocean.

Connectivity of molten Fe alloy in peridotite based on in situ electrical conductivity measurements: implications for core formation in terrestrial planets

The connectivity of molten Fe–S in peridotite has been experimentally investigated by means of in situ electrical conductivity measurements at high temperatures and 1 GPa. Starting materials were powdered mixtures of peridotite KLB-1 with various amounts (0, 3, 6, 13, 19, 24 vol.%) of the 1 GPa eutectic composition in the Fe–FeS binary system. At temperatures above the eutectic point in the Fe–FeS system (∼980 °C) and below the solidus of KLB1 (∼1200 °C), molten Fe–S in a solid silicate matrix interconnects when the volume fraction is over ∼5%. Conductivity–temperature paths indicate that in the presence of partial silicate melting the connectivity of molten Fe–S in a peridotite matrix is inhibited. Based on observations of retrieved samples, the percolation threshold of Fe–S melts in the presence of low to moderate degrees of silicate melt is estimated at 13±2 vol.%. These results indicate that if the volume fraction of Fe-alloy in a planetesimal was initially greater than 5%, and if early heating by decay of radionuclides raised the temperature of the interior above the Fe-alloy melting point, initial metal segregation was controlled by permeable flow of molten iron alloy in a solid silicate matrix. These conditions were likely met by many terrestrial objects in the early solar nebula. Efficient removal of residual Fe-alloy (5 vol.%) from silicate requires high-degree melting of silicate so that metal can segregate as droplets. Giant impacts during the final stage of accretion of large planetary objects could supply the energy required for high-degrees of melting. Alternatively, if initial metal segregation were delayed until a planetary object grew to large size (∼1000 km in diameter), release of gravitational potential energy due to metal segregation could contribute enough heat to form a magma ocean.

Core formation in planetesimals triggered by permeable flow.

The tungsten isotope composition of meteorites indicates that core formation in planetesimals occurred within a few million years of Solar System formation. But core formation requires a mechanism for segregating metal, and the 'wetting' properties of molten iron alloy in an olivine-rich matrix is thought to preclude segregation by permeable flow unless the silicate itself is partially molten. Excess liquid metal over a percolation threshold, however, can potentially create permeability in a solid matrix, thereby permitting segregation. Here we report the percolation threshold for molten iron-sulphur compounds of approximately 5 vol.% in solid olivine, based on electrical conductivity measurements made in situ at high pressure and temperature. We conclude that heating within planetesimals by decay of short-lived radionuclides can increase temperature sufficiently above the iron-sulphur melting point (approximately 1,000 degrees C) to trigger segregation of iron alloy by permeable flow within the short timeframe indicated by tungsten isotopes. We infer that planetesimals with radii greater than about 30 km and larger planetary embryos are expected to have formed cores very early, and these objects would have contained much of the mass in the terrestrial region of the protoplanetary nebula. The Earth and other terrestrial planets are likely therefore to have formed by accretion of previously differentiated planetesimals, and Earth's core may accordingly be viewed as a blended composite of pre-formed cores.

Effect of Surface Concentration of Alloying Elements on Nitrogen Dissolution Rate in Molten Iron Alloys.

The effects of alloying elements, such as Mn, Cu and Mo, on the rate of nitrogen dissolution in the molten iron alloys are investigated by an isotope exchange technique at 1 973 K. The rate constant of nitrogen dissolution increases with increasing the content of Mn or Mo, which has stronger affinity with nitrogen than iron. On the other hand, the rate constant decreases with increasing the Cu content, which has a repulsive force against nitrogen in iron. The mole fractions of the alloying elements in the surface phase are estimated, and the reaction mechanism is discussed by investigating the dependence of the rate constant on the mole fraction in the surface phase. The effect of alloying elements on the nitrogen dissolution rate depends on the affinity of the solute element with nitrogen in molten iron and the mole fraction in the surface phase.

高圧地球科学のフロンティア 高圧下における鉄合金メルトの物性

In order to understand the formation, evolution and dynamic processes of the molten core of the terrestrial planets, knowledge of the physical properties, such as viscosity and density, of the molten iron alloy is required. Recent progress in the high-pressure technology combined with synchrotron radiation allows us to measure such properties at high-temperature and high-pressure. In this article, recent advances in the high-pressure research of molten iron alloys are reviewed.

Effects of aluminum, silicon, and boron on the dissolution rate of nitrogen into molten iron

An isotope exchange technique is employed as a method for measuring the nitrogen dissolution rate into molten iron alloys, and the effects of Al, Si, and B addition have been studied at temperatures ranging from 1873 to 2023 K. The results are compared with those of other elements such as Ti, Zr, V, and Cr. The rate of nitrogen dissolution into molten iron is shown to decrease by the addition of Al, Si, and B due to a weaker affinity for nitrogen than Fe, which is contrary to the case of Ti, Zr, V, and Cr. Among them, B shows the largest effect when their contents are lower than 1 mass pct. A reasonable correlation of the rate constant with an interaction parameter between nitrogen and each element has been observed, which can be explained by the change in the activity of the vacant site on the surface of the molten alloy.

Percolation of core melts at lower mantle conditions

Experiments at high pressure and temperature to determine the dihedral angle of core melts in lower mantle phases yielded a value of approximately 71 degrees for perovskite-dominated matrices. This angle, although greater than the 60 degrees required for completely efficient percolation, is considerably less than the angles observed in mineral matrices at upper mantle pressure-temperature conditions in experiments. In other words, molten iron alloy can flow much more easily in lower mantle mineralogies than in upper mantle mineralogies. Accordingly, although segregation of core material by melt percolation is probably not feasible in the upper mantle, core formation by percolation may be possible in the lower mantle.