Liquid Fe Alloys Research Articles

Iron isotope fractionation between metal and silicate during core-mantle differentiation in rocky bodies

Fe isotope variations in rocky bodies reveal fundamental information about planetary evolution. However, experimental results have come to contradictory conclusions on the equilibrium Fe isotope fractionation between metal and silicate during core-mantle differentiation. Many different processes, including evaporation, core formation, partial melting and disproportion of mantle silicate, have been consequently proposed to explain the observed Fe isotope variations in rocky solar system bodies. Here we perform ab initio molecular dynamics simulations and find that the anharmonicity in iron strongly decreases the force constant of Fe at low pressures (<∼50 GPa), which even reverses the equilibrium Fe isotope fractionation between metal and silicate. We conclude that pyrolitic melt is always enriched in heavy Fe isotopes relative to liquid Fe-alloys, no matter what pressure. Therefore core-mantle differentiation will play a significant role in explaining the heavy Fe isotope compositions of the mantles of some rocky bodies (e.g., Earth, the ureilite parent body, and possibly the asteroid Vesta). As all previously proposed processes for Fe isotope fractionation can only enrich the mantle-derived rocks in heavy Fe isotopes, the near/sub-chondritic Fe isotope signatures of Mars and the aubrite parent body thus imply that iron sulfide enriched in light Fe isotopes may significantly contribute to the iron components of those meteoritic samples.

Electrical resistivity of liquid Fe-8wt%S-4.5wt%Si at high pressures with implications for heat flux through the cores of Io and sub-earth exoplanets

Potentially resulting in magnetic dynamo action, the heat flow through the outer cores of small terrestrial planetary bodies depends on the thermal conductivity of liquid Fe alloys at high pressures. The electrical resistivity of liquid Fe-8wt%S-4.5wt%Si was measured at 2–5 GPa and 295–1800 K in a 1000-ton cubic anvil press with a sample volume of a few cubic millimeters. Resistivity values of 220–270 μΩ·cm were measured, and a range of thermal conductivity values of 15–19 W/m/K were calculated using the Wiedemann-Franz law. The adiabatic heat flux at the top of a terrestrial exoplanet's Fe-8wt%S-4.5wt%Si core as a function of radius is calculated. The core of Io, if liquid, could have a convective heat flow density of a few μW/m2 without generating a magnetic dynamo powered by thermal convection.

Metals extraction on Mars through carbothermic reduction

In situ resource utilization (ISRU), and specifically the extraction and production of structural metals from Martian soil, is important for supporting further exploration, habitat and industrial developments on Mars. Considering Mars's atmospheric conditions and soil compositions, systematic analyses (supported by thermodynamic calculations) on possible metal extraction processes have been carried out. The analyses suggest that carbothermic reduction of Martian regolith would be the preferable starting point considering the abundance of carbon in the form of CO2 in the Martian atmosphere. It was proposed that carbon would be sourced from the cooling of carbon monoxide produced from CO2 electrolysis (MOXIE) from the Martian atmosphere. An Ellingham diagram showing the relative stability of oxides at Mars's atmospheric pressure of 7 mbar has been constructed; detailed equilibrium calculations to evaluate the carbothermic reduction of Martian regolith have also been carried out. The thermodynamic calculations predicted the formation of liquid Fe alloy with 99.9% conversion when the regolith was reacted with carbon (at approximately 10 wt% addition) at 1120 °C and 7 mbar. The impurities in the liquid Fe alloy were predicted to be mainly Si, C, Cr, and P. The hot gas produced from the process was predicted to be rich in CO (91%) and could be used for the preheating of the regolith. The CO could also be recycled and condensed to produce C (that could be re-used for the carbothermic reduction). The minimum energy requirement for the carbothermic reactor was calculated to be 3.37 MWh/tonne of liquid iron alloy (while the total energy requirement including MOXIE and agglomeration was calculated to be 15.51 MWh/tonne of liquid iron alloy). A generic process flowsheet has been developed considering these results.

Estimation of Activity Coefficient of Solute in Infinite Dilute Liquid Iron Based on Surface Tension of Binary Liquid Fe Alloys

Estimation of Activity Coefficient of Solute in Infinite Dilute Liquid Iron Based on Surface Tension of Binary Liquid Fe Alloys

TiC-MgO composite: an X-ray transparent and machinable heating element in a multi-anvil high pressure apparatus

ABSTRACTTiC-MgO composite was developed as a heating element for X-ray study in the multi-anvil high pressure apparatus. We synthesized TiC-MgO blocks (50–70 wt.% of TiC) by compression in a cold isostatic press followed by baking in a gas flow furnace. Heaters of tubular shape were manufactured from the synthesized blocks either by lathe or numerically controlled milling machine. The so-produced heating elements have been proved to generate temperatures up to 2250 K at 10 GPa, condition where classical graphite heaters are not suitable anymore due to graphite-diamond transition. These new heaters have been successfully used for in situ X-ray radiography and diffraction measurements on liquid Fe alloys, exploiting excellent X-ray transparency.

化学反応による溶鉄-溶融スラグ間の界面張力の動的変化

化学反応による溶鉄-溶融スラグ間の界面張力の動的変化

Short- and Intermediate-Range Structure and Dynamics of Fe-Ni-C Liquid Under Compression

Properties of liquid Fe alloys under high-pressure conditions are crucial for understanding the composition, thermal state, and dynamics of Earth’s core. Experiments on such liquids, however, are often performed under pressures far below those of the outer core, necessitating long extrapolations of experimental results to core conditions. Such estimates can be complicated by light elements possibly forming pressure-dependent molecular clusters that can significantly affect the physical properties of liquids as core conditions are approached. First-principles molecular dynamics simulations were employed to compute the properties of an Fe-Ni-C liquid with a composition of Fe3.7Ni0.37C at 1673 K and pressures from 0 to 67 GPa to benchmark computational methods on pressure effects on the structure and properties of the liquid relative to low pressure experimental results. The short-range structure is manifested by the coordination number (CN) of Fe/Ni-Fe/Ni being around 12, indicative of a nearly close-packed structure in the pressure range, and the CN of C-Fe/Ni gradual increasing from 6.5 to 8.5, indicative of an approximately octahedral to cubic transition as pressure increases. The Fe/Ni-Fe/Ni bond distance, however, is found to be 10 times more compressible than the C-Fe/Ni distance. The intermediate-range structure of Fe/Ni-Fe/Ni and C-Fe/Ni subsystems, described by a partial configurationally-decomposed distribution function, undergoes substantial changes, characterized by a significant increase of the number of polyhedra that share 3 atoms with each other. Such dense configurations are related to an increased bulk modulus, decreased diffusion coefficient, decreased activation volume for diffusion, and increased shear viscosity. Reproducing the experimental observations at low pressures provides important support for modeling the liquid under the conditions relevant to the outer core.

Heat Flow in Earth's Core From Invariant Electrical Resistivity of Fe‐Si on the Melting Boundary to 9 GPa: Do Light Elements Matter?

AbstractThe electrical resistivity and thermal conductivity of liquid Fe alloys are the least constrained parameters in Earth's outer core (OC). These parameters are important as they modulate energy budget available for the geodynamo and affect the spatiotemporal evolution of the core. We report results of electrical resistivity measurements on solid and liquid Fe‐4.5 wt%Si from 3–9 GPa using a large volume multianvil press. The internally modified 18/11 octahedron cell was used to maintain the geometry of the liquid sample and to delay the onset of contamination. Electrical resistivity of solid Fe‐4.5Si decreases steadily with pressure and is very sensitive to increasing temperature‐driven onset of phase transitions. Along the melting boundary and within error, electrical resistivity remains constant and assumes the same value of 120 μΩcm as observed in pure liquid Fe. The results are interpreted in the context of icosahedral short‐range order (ISRO) structures that exhibit higher concentration with increasing pressure. Along the melting line, the increasing concentration of ISROs reduces charge carrier mean free path and prevents decrease of electrical resistivity with increasing pressure as seen in liquid metals, Cu, Ag, and Au, which do not have ISROs. In light of recent developments in understanding of the structure and dynamics of liquid transition metals and alloys, we postulate that our findings are applicable to other Fe alloys in the OC with small light element (C, S, and O) content. We calculated an adiabatic heat flow of 9.4–12 TW at the OC‐CMB interface, which admits thermal convection.

Estimation of Activity Coefficient of Solute in Infinite Dilute Liquid Iron Based on Surface Tension of Binary Liquid Fe Alloys

Estimation of Activity Coefficient of Solute in Infinite Dilute Liquid Iron Based on Surface Tension of Binary Liquid Fe Alloys

Early episodes of high-pressure core formation preserved in plume mantle.

The decay of short-lived iodine (I) and plutonium (Pu) results in xenon (Xe) isotopic anomalies in the mantle that record Earth's earliest stages of formation. Xe isotopic anomalies have been linked to degassing during accretion, but degassing alone cannot account for the co-occurrence of Xe and tungsten (W) isotopic heterogeneity in plume-derived basalts and their long-term preservation in the mantle. Here we describe measurements of I partitioning between liquid Fe alloys and liquid silicates at high pressure and temperature and propose that Xe isotopic anomalies found in modern plume rocks (that is, rocks with elevated 3He/4He ratios) result from I/Pu fractionations during early, high-pressure episodes of core formation. Our measurements demonstrate that I becomes progressively more siderophile as pressure increases, so that portions of mantle that experienced high-pressure core formation will have large I/Pu depletions not related to volatility. These portions of mantle could be the source of Xe and W anomalies observed in modern plume-derived basalts. Portions of mantle involved in early high-pressure core formation would also be rich in FeO, and hence denser than ambient mantle. This would aid the long-term preservation of these mantle portions, and potentially points to their modern manifestation within seismically slow, deep mantle reservoirs with high 3He/4He ratios.

Formation of N–С–О–Н molecules and complexes in the basalt–basaltic andesite melts at 1.5 Gpa and 1400°C in the presence of liquid iron alloys

The contents and speciation of nitrogen, carbon, and hydrogen were determined in basalt–basaltic andesite melts in equilibrium with liquid Fe alloys at 1.5 Gpa, 1400°C, and oxygen fugacity (fO2) 1.4–1.9 log units below that of the Fe–FeO buffer (ΔlogfO2(IW) =–1.4 …–1.9). Experiments were carried out on a piston- cylinder type apparatus using welded Pt capsules in the presence of excess С (graphite). Starting mixture consisted of natural ferrobasaltic glass and silicon nitride (Si3N4) as nitrogen source in the system. Experimental quench products representing glasses with spherical inclusions of iron alloy were analyzed using electron microprobe, Raman, and IR spectroscopy. With increase of Si3N4 in the starting mixture and, respectively, decrease of fO2, silicate melt forming during experiments became depleted in FeO and enriched in SiO2. It was established that the nitrogen content in the glasses increases from 0.13 to 0.44 wt % with decrease of ΔlogfO2(IW) from–1.4 to–1.9, whereas C content in the first approximation remains constant within 1.18–1.13 wt %, while the total water content (ОН– + Н2О) determined by IR spectroscopy decreases from 4.91 to 1.20 wt %. The N (0.13–0.48 wt %) and C (0.75–2.26 wt %) contents determined in the Fe alloy show no clear correlation with fO2. The IR and Raman spectroscopic study of the glasses indicates the formation of molecules and complexes with bonds N–H (NH3, NH2−, NH2+, NH4+), Н–О (Н2О, OH–), С–Н (СН4) as well as N2 and Н2 molecules in silicate melts. IR spectra also reveal the presence of complexes with С=О, С–N bonds and СО2 molecules. Obtained data are compared with results of previous studies on the solubility and speciation of N, С, and Н in the model FeO–Na2O–SiO2–Al2O3 melts in equilibrium with liquid iron alloys at 1.5 GPa (1400°C) and 4 GPa (1550°C) (Kadik et al., 2011, 2015).

Infiltration, interface microstructure and the dry sliding wear behavior of network ceramics/Fe-alloy composites

Three types of ceramic/Fe alloy composites were successfully fabricated by a pressureless infiltration. The network ceramic/ferroalloy interface was analyzed by SEM, EDS and the room temperature sliding wear behaviors of the composites were investigated by an optimal SRV testing machine. The results showed that the liquid Fe alloy can infiltrate Ni-doped alumina ceramics and the surface metallization of the ceramics enhances the wettability and promotes the spontaneous infiltration process. The abrasion loss increased with the rising of load and friction frequency and the network ceramic/spheroidal graphite iron had a better wear behavior than those network ceramics reinforced with abrasion-resistant steel and high chromium iron. However, for the three composites, the high-chromium iron matrix composite with higher hardness has a higher abrasive resistance than the others.

Incorporation of Fe2+and Fe3+in bridgmanite during magma ocean crystallization

Using large volume press, samples of bridgmanites (Bg) in equilibrium with both silicate melt and liquid Fe-alloy were synthesized to replicate the early period of core-mantle segregation and magma ocean crystallization. We observe that the Fe partition coefficient between Bg and silicate melt ![Formula][1] varies strongly with the degree of partial melting (F). It is close to 1 at very low F and adopts a constant value of ~0.3 for F values above 10 wt%. In the context of a partially molten mantle, a larger F (closer to liquidus) should yield Fe-depleted Bg grains floating in the liquid mantle. In contrast, a low F (closer to solidus) should yield buoyant pockets of silicate melt in the dominantly solid mantle. We also determined the valence state of Fe in these Bg phases using X-ray absorption near-edge spectroscopy (XANES). Combining our results with all available data sets, we show a redox state of Fe in Bg more complex than generally accepted. Under the reducing oxygen fugacities ![Formula][2] of this study ranging from IW-1.5 and IW-2, the measured Fe3+ content of Bg is found moderate (Fe3+/ΣFe = 21 ± 4%) and weakly correlated with Al content. When ![Formula][3] is comprised between IW-1 and IW, this ratio is correlated with both Al content and oxygen fugacity. When ![Formula][4] remains between IW and Re/ReO2 buffers, Fe3+/ΣFe ratio becomes independent of ![Formula][5] and exclusively correlated with Al content. Due to the incompatibility of Fe in Bg and the variability of its partition coefficient with the degree of melting, fractional crystallization of the magma ocean can lead to important chemical heterogeneities that will be attenuated ultimately with mantle stirring. In addition, the relatively low-Fe3+ contents found in Bg (21%) at the reducing conditions (IW-2) prevailing during core segregation seem contradictory with the 50% previously suggested for the actual Earth’s lower mantle. This suggests the presence of 1.7 wt% Fe3+ in the lower mantle, which reduces the difference with the value observed in the upper mantle (0.3 wt%). Reaching higher concentrations of trivalent Fe requires additional oxidation processes such as the late arrival of relatively oxidized material during the Earth accretion or interaction with oxidized subducting slabs. [1]: /embed/mml-math-1.gif [2]: /embed/mml-math-2.gif [3]: /embed/mml-math-3.gif [4]: /embed/mml-math-4.gif [5]: /embed/mml-math-5.gif

Towards a consensus on the pressure and composition dependence of sound velocity in the liquid Fe–S system

Recent advances in techniques for high-pressure and high-temperature experiments enable us to measure the velocity of sound in liquid Fe alloys. However, reported velocities in liquid Fe–S differ among research groups (e.g., by >10% at 5GPa), even when similar methods are used (i.e., the ultrasonic pulse–echo overlap method combined with a large volume press). To identify the causes of the discrepancies, we reanalyzed previous data and conducted additional sound velocity measurements for liquid Fe–S at 2–7GPa, and evaluated the potential error sources. We found that the discrepancy cannot be explained by errors in the sound velocity measurements themselves, but by inaccuracies in determining the temperature, pressure, and chemical composition in each experiment. Of particular note are the significant errors introduced when determining pressures from the unit-cell volume of MgO, which is a temperature-sensitive pressure standard, using inaccurate temperatures. To solve the problem, we additionally used h-BN as a pressure standard, which is less sensitive to temperature. The pressure dependence of the sound velocity became smaller than that of the original data because of the revised pressure values. Our best estimate for the seismic velocity of the Moon’s liquid outer core is 4.0±0.1km/s, given a chemical composition Fe83S17.

Dynamic Changes in Interfacial Tension between Liquid Fe Alloy and Molten Slag Induced by Chemical Reactions

Dynamic Changes in Interfacial Tension between Liquid Fe Alloy and Molten Slag Induced by Chemical Reactions

Predicting macroscopic thermal expansion of metastable liquid metals with only one thousand atoms

Results of thermal expansion prediction from atomic scale for metastable liquid metals are reported herein. Three pure liquid metals Ni, Fe, and Cu together with ternary Ni60Fe20Cu20 alloy are used as models. The pair distribution functions were employed to monitor the atomic structure. This indicates that the simulated systems are ordered in atomic short range and disordered in long range. The thermal expansion coefficient was computed as functions of temperature and atom cutoff radius, which tends to maintain a constant when the cutoff radius increases to approximately 15 A. In such a case, slightly more than 1000 atoms are required for liquid Ni, Cu, Fe and Ni60Fe20Cu20 alloy, that is, the macroscopic thermal expansion can be predicted from the volume change of such a tiny cell. Furthermore, the expansion behaviors of the three types of atoms in liquid Ni60Fe20Cu20 alloy are revealed by the calculated partial expansion coefficient. This provides a fundamental method to predict the macroscopic thermal expansion from the atomic scale for liquid alloys, especially in the undercooled regime. thermal expansion, liquid metal, undercooling, metastable state

Electrical resistivity and thermal conductivity of liquid Fe alloys at high P and T, and heat flux in Earth's core.

Earth's magnetic field is sustained by magnetohydrodynamic convection within the metallic liquid core. In a thermally advecting core, the fraction of heat available to drive the geodynamo is reduced by heat conducted along the core geotherm, which depends sensitively on the thermal conductivity of liquid iron and its alloys with candidate light elements. The thermal conductivity for Earth's core is very poorly constrained, with current estimates based on a set of scaling relations that were not previously tested at high pressures. We perform first-principles electronic structure computations to determine the thermal conductivity and electrical resistivity for Fe, Fe-Si, and Fe-O liquid alloys. Computed resistivity agrees very well with existing shock compression measurements and shows strong dependence on light element concentration and type. Thermal conductivity at pressure and temperature conditions characteristic of Earth's core is higher than previous extrapolations. Conductive heat flux near the core-mantle boundary is comparable to estimates of the total heat flux from the core but decreases with depth, so that thermally driven flow would be constrained to greater depths in the absence of an inner core.

Partitioning of Ru, Rh, Pd, Re, Ir and Pt between liquid metal and silicate at high pressures and high temperatures - Implications for the origin of highly siderophile element concentrations in the Earth’s mantle

The apparent overabundance of the highly siderophile elements (HSEs: Pt-group elements, Re and Au) in the mantles of Earth, Moon and Mars has not been satisfactorily explained. Although late accretion of a chondritic component seems to provide the most plausible explanation, metal–silicate equilibration in a magma ocean cannot be ruled out due to a lack of HSE partitioning data suitable for extrapolations to the relevant high pressure and high temperature conditions. We provide a new data set of partition coefficients simultaneously determined for Ru, Rh, Pd, Re, Ir and Pt over a range of 3.5–18GPa and 2423–2773K. In multianvil experiments, molten peridotite was equilibrated in MgO single crystal capsules with liquid Fe-alloy that contained bulk HSE concentrations of 53.2–98.9 wt% (XFe=0.03–0.67) such that oxygen fugacities of IW−1.5 to IW+1.6 (i.e. logarithmic units relative to the iron-wüstite buffer) were established at run conditions. To analyse trace concentrations of the HSEs in the silicate melt with LA-ICP-MS, two silicate glass standards (1–119ppm Ru, Rh, Pd, Re, Ir, Pt) were produced and evaluated for this study. Using an asymmetric regular solution model we have corrected experimental partition coefficients to account for the differences between HSE metal activities in the multicomponent Fe-alloys and infinite dilution. Based on the experimental data, the P and T dependence of the partition coefficients (D) was parameterized.The partition coefficients of all HSEs studied decrease with increasing pressure and to a greater extent with increasing temperature. Except for Pt, the decrease with pressure is stronger below ∼6GPa and much weaker in the range 6–18GPa. This change might result from pressure induced coordination changes in the silicate liquid. Extrapolating the D values over a large range of potential P–T conditions in a terrestrial magma ocean (peridotite liquidus at P⩽60–80GPa) we conclude that the P–T-induced decrease of D would not have been sufficient to explain HSE mantle abundances by metal–silicate equilibration at a common set of P–T-oxygen fugacity conditions. Therefore, the mantle concentrations of most HSEs cannot have been established during core formation. The comparatively less siderophile Pd might have been partly retained in the magma ocean if effective equilibration pressures reached 35–50GPa. To a much smaller extent this could also apply to Pt and Rh providing that equilibration pressures reached ⩾60GPa in the late stage of accretion. With most of the HSE partition coefficients at 60GPa still differing by 0.5–3 orders of magnitude, metal–silicate equilibration alone cannot have produced the observed near-chondritic HSE abundances of the mantles of the Earth as well as of the Moon or Mars. Our results show that an additional process, such as the accretion of a late veneer composed of some type of chondritic material, was required. The results, therefore, support recent hybrid models, which propose that the observed HSE signatures are a combined result of both metal–silicate partitioning as well as an overprint by late accretion.

Density measurements of liquid Fe–Si alloys at high pressure using the sink–float method

The compositional dependence on the density of liquid Fe alloys under high pressure is important for estimating the amount of light elements in the Earth’s outer core. Here, we report on the density of liquid Fe–Si at 4 GPa and 1,923 K measured using the sink–float method and our investigation on the effect of the Si content on the density of the liquid. Our experiments show that the density of liquid Fe–Si decreases from 7.43 to 2.71 g/cm3 non-linearly with increasing Si content (0–100 at%). The molar volume of liquid Fe–Si calculated from the measured density gradually decreases in the compositional range 0–50 at% Si, and increases in the range 50–100 at% Si. It should be noted that the estimated molar volume of the alloys shows a negative volume of mixing between Fe and Si. This behaviour is similar to Fe–S liquid (Nishida et al. in Phys Chem Miner 35:417–423, 2008). However, the excess molar volume of mixing for the liquid Fe–Si is smaller than that of liquid Fe–S. The light element contents in the outer core estimated previously may be an underestimation if we take into account the possible negative value of the excess mixing volume of iron–light element alloys in the outer core.

The effects of nickel and sulphur on the core–mantle partitioning of oxygen in Earth and Mars

Constraints on the partitioning of oxygen between silicates, oxides, and metallic liquids are important for determining the amount of oxygen that may have entered the cores of terrestrial planets and to identify likely reactions at the core–mantle boundary. Several previous studies have examined oxygen partitioning between liquid Fe metal and ferropericlase, however, the cores of terrestrial planets also contain nickel and most likely sulphur. We have performed experiments to examine the effects of both nickel and sulphur on the partitioning of oxygen between ferropericlase and liquid Fe alloy up to pressures of 24.5 GPa in the temperature range 2430–2750 K using a multianvil press. The results show that at a fixed oxygen fugacity the proportion of oxygen that partitions into liquid metal will decrease by approximately 1–2 mol% on the addition of 10–20 mol% nickel to the liquid. The addition of around 30 mol% sulphur will, on the other hand, increase the metal oxygen content by approximately 10 mol%. Experiments to examine the combined effects of both nickel and sulphur, show a decrease in the effect of nickel on oxygen partitioning as the sulphur content of the metal increases. We expand an existing thermodynamic model for the partitioning of oxygen at high pressures and temperatures to include the effects of nickel and sulphur by fitting these experimental data, with further constraints provided by existing phase equilibria studies at similar conditions in the Fe–S and Fe–O–S systems. Plausible terrestrial core sulphur contents have little effect on oxygen partitioning. When our model is extrapolated to conditions of the present day terrestrial core–mantle boundary, the presence of nickel is found to lower the oxygen content of the outer core that is in equilibrium with the expected mantle ferropericlase FeO content, by approximately 1 weight %, in comparison to nickel free calculations. In agreement with nickel-free experiments, this implies that the Earth's outer core is undersaturated in oxygen with respect to plausible mantle FeO contents, which will result in either the depletion of FeO from the base of the mantle or cause the development of an outer core layer that is enriched in oxygen. The oxygen content of the more sulphur-rich Martian core would be in the range 2–4 wt.% if it is in equilibrium with the FeO-rich Martian mantle.