Partitioning Behavior Of Elements Research Articles

Liquid immiscibility in the CaF2-granite system and trace element partitioning between the immiscible liquids

The recent discoveries of Ca-fluoride melt in magmatic systems, especially in peralkaline granites with rare earth element enrichment, has raised questions about the presence and nature of liquid immiscibility in CaF2-granite systems, as well as the partitioning behavior of trace elements between such immiscible liquids. We have experimentally explored the immiscibility in this system using natural granite-fluorite starting materials at fast-and slow-cooling rates, temperatures from 500 °C to 1200 °C and 1 atmosphere pressure. Our experiments confirm the presence of a miscibility gap in the CaF2-granite system over a wide range of temperatures. The two immiscible liquids are a mafic fluorosilicate melt (fm) with high CaO and F and a felsic oxysilicate melt (sm) with high SiO2 and alkalis. Immiscibility is encountered when the bulk F-content exceeds approximately 4.4 wt% at 1200 °C and then rapidly decreases to only 0.75 wt% at low temperature (below 900 °C). This indicates that calcic magmas are able to evolve to the liquid immiscibility domain by the residual enrichment of fluorine resulting from fractional crystallization, and that liquid immiscibility should be common. The peritectic reaction fm = sm + fluorite removes the fluorosilicate liquid around 600 °C and could explain the absence of fluorosilicate observations in natural granites. The compositions of the liquids in fast-cooling experiments show a significantly larger miscibility gap which is characterized by, compared to slow-cooling runs, similar sm compositions but higher Ca and F content in fm. This difference is caused by suppression of fluorite nucleation and is interpreted as a metastable extension of the high temperature liquid immiscibility. Immiscibility results in strong fractionation of trace elements which is primarily governed by melt structure and the ionic potential (Z/r) of the elements. The behavior of trace elements can be categorized into three groups: 1. Network formers (Si, Al, Ga, Pb, B) partition into the oxysilicate melt; 2. The partitioning of the alkalis and alkali earths is strongly dependent on the ionic potential, with the partitioning coefficients (D fm/sm) in the order DCs < DRb < DK < DNa < DLi < DBa < DSr < DCa ≤ DMg; 3. High field strength elements (Ti, Zr, Hf, Nb, Ta, Th, U) and rare earth elements (REE) strongly partition into the fluorosilicate melt. The D values vary with the size of the miscibility gap, which is in turn controlled by temperature with more pronounced fractionation as the miscibility gap widens. The fluorosilicate melt effectively sequesters the REE especially at the lower temperatures relevant for granite magmatism and, given its higher density and lower viscosity compared to the coexisting oxysilicate melt, fractionates the REE from the host silicate melt, suggesting a potential REE-mineralising process.

Microstructure, phase stability and element partitioning of γ-γ′ Co-9Al-9W-2X alloys in different annealing conditions

The phase stability, γ′ precipitate morphology and element partitioning behavior in dependence on temperature and alloying composition have been systematically investigated in Co-9Al-9W-2X alloys using electron microscopy, energy-dispersive X-ray spectroscopy (EDX) and high-energy X-ray diffraction (HEXRD). The results show that the decomposition of the γ′ phase is promoted by adding some quaternary elements which increase the γ′ solvus temperature (except V). A larger lattice misfit in the Mo, V, Ti, Nb or Ta containing alloys can explain that coarser γ′ particles with a more cuboidal morphology were found in these alloys. Additional alloying elements and the annealing temperature show a stronger influence on the partitioning behavior of W between the γ and γ′ phases compared to that of Co and Al. The partitioning tendency towards the γ′ phase decreases with increasing temperature for all investigated alloying elements except Cr.

Modes of occurrence and partitioning behavior of trace elements during coal preparation—A case study in Guizhou Province, China

Coal preparation technology is expected to play an important role in trace elements removal before coal combustion. The modes of occurrence of five trace elements (As, Se, Pb, Be, and Hg) in two coal cleaning plants in Guizhou, China, designated WJZ and ZZC, were studied using screening and float-and-sink tests. The behaviors of these trace elements when coal was cleaned were also investigated via sampling and analysis of raw coal, coal products, fresh water, and circulating water in two coal cleaning plants. Screening tests show that the content of trace elements is highest in 3–1 mm or 1–0.5 mm size fraction and they distributed mainly (more than 50%) in the +0.5 mm size fractions. Float-and-sink tests indicate that trace elements have a strong inorganic affinity and are significantly enriched, distributed in high-density fraction (+1.8 g/cm3). Over 50% of trace elements could be removed when pre-gangue removal is done with separation density of 1.8 g/cm3. The analysis of solid samples (raw coal, coal products) demonstrates that trace elements migrated mainly into gangue, and slime, enrichment of trace elements in middlings was also observed in ZZC plant. Results of water samples analysis suggest that Se, and As in coal are more likely to be released into water during coal cleaning while Be and Hg are present in a highly insoluble form in coal.

Partition Behavior of Alloying Elements in Nickel-Based Alloys and Their Activity Interaction Parameters and Infinite Dilution Activity Coefficients

Abstract The partition behavior of alloying elements between the γ’ and γ phases in Nickel-based alloys was investigated by using infinite dilution activity coefficient and activity interaction parameter. The results showed that the preferential partition behavior of elements in the γ’ and γ phases is related to its infinite dilution activity coefficient ( ln γ i 0 \ln \gamma _i^0 ). When ln γ i 0 ≪ 0 \ln \gamma _i^0 \ll 0 , the element i has a strong tendency to partition in the γ’ phase; When ln γ i 0 \ln \gamma _i^0 approaches to zero, the element i has preferentially partition to the matrix γ phase. In addition, the partition behavior of element i in the γ’ and γ phases is also affected by the third element j in Nickel-based alloys, and this effect can be distinguished by the sign of the second-order activity interaction parameter ρ i i j \rho _i^{ij} .

Elemental Phase Partitioning in the γ-γ″ Ni2CoFeCrNb0.15 High Entropy Alloy

The partitioning of the alloying elements into the γ″ nanoparticles in a Ni2CoFeCrNb0.15 high entropy alloy was studied by the combination of atom probe tomography and first-principles calculations. The atom probe tomography results show that the Co, Fe, and Cr atoms incorporated into the Ni3Nb-type γ″ nanoparticles but their partitioning behaviors are significantly different. The Co element is much easier to partition into the γ″ nanoparticles than Fe and Cr elements. The first-principles calculations demonstrated that the different partitioning behaviors of Co, Fe and Cr elements into the γ″ nanoparticles resulted from the differences of their specific chemical potentials and bonding states in the γ″ phase.

γ’-(L12) precipitate evolution during isothermal aging of a Co[sbnd]Al[sbnd]W[sbnd]Ni superalloy

The coarsening kinetics and elemental partitioning behavior of γ’-(L12) precipitates in a γ(f.c.c.)-matrix for a model quaternary Co-8.8Al-8.9W-9.9Ni at.% superalloy are investigated utilizing isothermal aging conditions at 650, 800 and 900 °C. The γ′-precipitate mean radius, number density, and volume fraction, at 800 and 900 °C, were studied using scanning electron microscopy; the calculated temporal exponents associated with coarsening of γ′-precipitates display good agreement with model predictions for quasi-stationary coarsening. An atom probe tomographic (APT) investigation of the aged γ/γ′ microstructure at 650 °C demonstrates that the compositions and volume fractions of both phases vary continuously up to 4096 h. The aged microstructure at 650 °C consists of interconnected nanoscale γ′-precipitates, corroborated utilizing SEM for the 4096 h aged-specimen. The activation energy for coarsening is estimated for the temperature range 650–900 °C to be 283 kJ mol−1, in reasonable agreement with activation energies for diffusion of Al, W, and Ni in Co, suggesting that coarsening of γ′-precipitates is limited by bulk-diffusion. APT measurements of specimens aged for 1024 h at 800 and 900 °C demonstrate that the isothermal aging temperature has a significant effect on the compositions and partitioning behavior of Co, Al, W and Ni between the γ- and γ′-phases. The partitioning ratio of the concentrations between the γ′- and γ-phases is largest for W, decreasing linearly from 5.3 ± 0.1 at 650 °C to 2.1 ± 1.2 at 900 °C, and smallest for Co, decreasing from 0.86 ± 0.01 at 650 °C to 0.73 ± 0.01 at 900 °C.

On the microstructural evolution and partitioning behavior of L12-structured γ′-based Co-Ti-W alloys upon Cr and Al alloying

We report on the effects of Cr and Al on the microstructure and elemental partitioning behavior of γ/γ′ forming Co-Ti-W-based alloys. Additions of Cr to a Co-15Ti-3W (at.%) base alloy at the expense of Ti led to a decrease in γ′ volume fraction, whereas Al additions at the expense of Co led to substantially increased γ′ volume fractions. Such alloy modifications resulted in reduced γ/γ′ lattice misfits. Using atom probe tomography, we could show that Ti and W strongly partitioned to the γ′ phase, whereas Al and Cr partitioned to γ. While Cr appeared to have only minor effects on the partitioning behavior of the other alloying elements, Al enhanced partitioning of Ti and in particular W to γ′, thus causing the observed increases in γ′ volume fraction.

Strengthened Cr-Si-base alloys for high temperature applications

The microstructural development of CrSi alloys with Cr ≥ 89 at.% has been studied. As well as silicon, up to 2 at.% germanium, molybdenum, and platinum were used as alloying elements. All alloys consist of only two phases, Crss and A15. The phase fraction of primary A15 precipitates present in the arc melted condition and fine secondary A15 precipitates formed after a heat treatment (100 h at 1200 °C) were determined. EPMA and SEM measurements show that the alloying elements partition in different ways: Molybdenum is homogeneously dissolved in both phases, while platinum, germanium, and silicon predominantly act as A15 phase formers. Additionally, molybdenum refines the A15 precipitates, germanium increases the amount of secondary precipitates, and platinum coarsens the microstructure. The lattice parameters of both phases were determined using XRD. The results were found to be in accordance to the elemental partitioning behavior of the constituent phases and can be correlated to the respective covalent atomic radii of the respective alloying element. Microhardness measurements confirmed the alloy's ability of precipitation hardening. Using nanohardness measurements the A15 phase was found to be around 18GPa harder compared to Crss offering a way to design mechanical properties depending on alloying element additions, A15 phase fraction, and distribution.

Timescales of collisional metamorphism from Sm-Nd, Lu-Hf and U-Pb thermochronology: A case from the Proterozoic Putumayo Orogen of Amazonia

The construction of mountain belts by continent-continent collision is a fundamental phase of the supercontinent cycle and an inevitable consequence of subduction-driven plate tectonics on Earth. Yet, quantitative estimation of the rate and duration of prograde orogenic metamorphism in high-grade collisional belts has proven elusive to constrain. Differences in the chemical partitioning and diffusive behavior of elements associated with the 147Sm-143Nd and 176Lu-176Hf isotopic systems in metamorphic garnet can provide valuable insights on the time scales over which this mineral grows and cools in regionally metamorphosed terranes. Here, we present new Sm-Nd and Lu-Hf isotopic results from multiple garnet and whole-rock aliquots from a granulite-grade metasedimentary rock from the Proterozoic Putumayo Orogen of South America. Using a combination of internal isochron dating by these two decay systems, combined with apatite U-Pb dating and pressure-temperature-time (P-T-t) constraints from mineral equilibria and chemical diffusion geospeedometry, we provide first-order insights into the time scales of a Proterozoic continent-continent collisional metamorphic event in Amazonia associated with its incorporation to the Supercontinent Rodinia. Our results indicate that these metasediments attained peak granulite-grade metamorphic conditions of nearly 0.62 GPa and 680 °C at approximately 1035 Ma, and started to cool slowly, presumably during exhumation, at a rate of ∼5 K/Myr. Simple diffusion scaling relationships and numerical modeling of Sm-Nd and Lu-Hf in garnet indicate that, while Sm and Nd were both fully re-equilibrated at peak temperatures and therefore date cooling, Lu and Hf underwent diffusive decoupling due to incomplete Hf re-equilibration. By modeling the impact of this differential re-equilibration in the development of the Sm-Nd and Lu-Hf isochrons, we constraint the duration of the prograde metamorphic path and argue that garnet growth in this sample took place over millions of years—approximately 25 Myr according to our preferred interpretation. The determined apatite U-Pb date vs. grain-size relationship cannot be reconciled with the thermal history described above when modeled using the existing experimental diffusion data, and instead suggest that much slower Pb diffusivities in this mineral compared to those predicted by the existing experimental data may have inhibited its resetting. We note that the inferred temperature-time history for the metamorphic loop of this segment of the Putumayo basement is comparable to that proposed for the metamorphism and exhumation of metasediments in the India-Asia collision zone, suggesting that similar tectonic processes and rates likely operated during the Mesoproterozoic Putumayo orogeny.

Characterization of resistance spot welded transformation induced plasticity (TRIP) steels with different silicon and carbon contents

This research work examines the influence of chemical composition and microstructure of 6 different transformation induced plasticity (TRIP) steels on the mechanical behavior of resistance spot weldments. The microstructure of the spot welds was characterized by means of scanning electron microscopy and X-ray diffraction techniques. The mechanical properties were assessed under lap-shear tensile and hardness testing. Results indicated that the nugget width is strongly correlated with the type of failure mode of the spot welds. The mechanical properties exhibited by the spot weldments are related with the partitioning behavior of chemical elements specially Si and C present in the steels during the cooling stage of the resistance spot welding process. X-ray diffraction study indicated traces of retained austenite in the heat affected zones of the spot welds of those steels with Si-enriched chemical composition where intercritical annealing temperatures were closer to Ac1.

Element partitioning in magnetite under low-grade metamorphic conditions – a case study from the Proterozoic Belt Supergroup, USA

The distribution and partitioning of elements in igneous rocks is well established for various melt–(fluid)–solid pairs and provides important insights into the petrogenesis of these rocks. Studies of the partitioning behavior of elements under metamorphic conditions are scarce and commonly focus on high-grade metamorphic facies. Little is known about the partitioning behavior of elements under low-grade metamorphic conditions. Greenschist-facies metasedimentary rocks of the North American Belt Supergroup host magnetite that displays equilibrium features with co-existing mineral phases such as quartz and carbonate. Magnetite is an ideal target for geochemical investigations because it can incorporate a large number of cations and is sensitive to changes in temperature, oxygen fugacity, pressure, whole-rock composition, and cooling trends. Whole-rock major and trace element analyses have been undertaken on representative samples from Belt Supergroup metasedimentary rocks using X-ray fluorescence. Electron microprobe and laser ablation ICP-MS were used to obtain major and trace element concentrations for magnetite hosted in these rocks. Stable-isotope geothermometry of magnetite–quartz and magnetite–carbonate pairs constrain metamorphic temperatures to ca . 390 °C. Partition coefficients ( D ) for magnetite–matrix pairs presumably reflect equilibrium at these low-grade metamorphic conditions. Except for Mn and Ni, which show comparable partition coefficients, the calculated values are one to two orders of magnitude lower than those for igneous magnetite. Aluminum displays the lowest calculated partition coefficient with a value of 0.006 and Ni and Fe the highest values with 6.3 and 20.9, respectively. Of the elements that commonly occur in spinel-group minerals, two groups can be distinguished: (1) elements that preferentially partition into the host rock ( D D > 1): Zn, Mn, Cr, V, Ni, and Fe.

Rare earth element partitioning and subsolidus exchange behaviour in olivine

The systematics of the rare earth element (REE) abundances in olivine are poorly understood and this undermines their usefulness in deciphering petrogenetic processes. Here we report a novel REE dataset for olivine spanning a wide range in Mg number (Mg# 1–59) from the Skaergaard Layered Intrusion.Olivine La and Lu concentrations vary from 0.68 to 56ppb and 66 to 571ppb, respectively. Apparent olivine/melt partition coefficients for the heavy to middle REE define near-symmetrical parabolas, consistent with lattice strain theory, indicating that these elements are structurally bound within the olivine lattice. The parabolas define peaks with variable optimal radii (ro). This suggests that the Fe-content of olivine exerts a strong influence on REE partitioning, as fayalitic olivines display more open parabolas (higher apparent Young's modulus, E) than forsteritic olivines. The greater site elasticity is manifest as higher REE concentrations in the fayalitic samples. The observation that E and ro are not constant accross a range of Mg# has implications for predictive models for olivine REE.The CI chondrite-normalised olivine REE patterns show smooth trends from the heavy to the middle REE, with greater variation amongst the light REE (LREE). Variation and enrichment of the LREE are ubiquitous within published data for natural olivine, yet are not predicted by experimental results. This study also presents two-dimensional REE maps illustrating the behaviour of the REE in olivine in unprecedented detail. Mapping of magnesian olivine shows core to rim increase in Al, LREE, and Eu and the development of a positive Eu anomaly in olivine, resulting from solid-state, likely diffusive re-equilibration with adjacent plagioclase. We propose that secondary redistribution is the principal cause of elevated LREE patterns in natural olivine.The results from the present investigation show that from a petrological point of view, MREE to HREE systematics of olivine hold promise for study of olivine petrogenesis and that the LREE in olivine may be further developed to understand diffusion time scales and cooling rates in magmatic systems.

Cu partitioning behavior and its effect on microstructure and mechanical properties of 0.12C-1.33Mn-0.55Cu Q&amp;P steel

Cu, as an austenitic stable element, is added to steel in order to suppress the adverse effects of high content of C and Mn on welding. Based on C partitioning, Cu and Mn partitioning can further improve the stability of retained austenite in the intercritical annealing process. A sample of low carbon steel containing Cu was treated by the intercritical annealing, then quenching process (I&Q). Subsequently, another sample was treated by the intercritical annealing, subsequent austenitizing, then quenching and partitioning process (I&Q&P). The effects of element partitioning behavior in intercritical region on the microstructure and mechanical properties of the steel were studied. The results showed that after the I&Q process ferrite and martensite could be obtained, with C, Cu and Mn enriched in the martensite. When intercritically heated at 800 degrees C, Cu and Mn were partitioned from ferrite to austenite, which was enhanced gradually as the heating time was increased. This partitioning effect was the most obvious when the sample was heated at 800 degrees C for 40 min. At the early stage of alpha -> gamma transformation, the formation of. was controlled by the partitioning of carbon, while at the later stage, it was mainly affected by the partitioning of Cu and Mn. After the I&Q&P process, the partitioning effect of Cu and Mn element could be retained. C was assembled in retained austenite during the quenching and partitioning process. The strength and elongation of I&Q&P steel was increased by 5 305 MPa% compared with that subjected to Q&P process. The volume fraction of retained autensite was increased from 8.5% to 11.2%. Hence, the content of retained austenite could be improved significantly by Mn and Cu partitioning, which increased the elongation of steel.

Influence of Re/Ru on concentration distribution in the γ/γ′ phases of nickel-based single crystal superalloys

In order to understand the influence of Ru and Re on the concentration distributions of elements in γ′ and γ phases, the partitioning behaviors of elements in various alloy are investigated by means of atom probe tomography (APT). Results show that the elements Al, Ta and Ni are enriched in γ′ phase, while the elements Co, Cr, Mo, W, Re and Ru are enriched in γ matrix phase. Adding Ru may decrease the partitioning ratio of elements in γ and γ′ phases. Wherein, when Ru atoms dissolve into γ′ phase to substitute the Al atoms, some Re, Mo and W atoms adhered in the round of Ru atoms, under the hybridization effect of d orbit, may dissolve into γ′ phase, which is thought to be the main reason of Ru decreasing the partitioning ratios of γ′ and γ phases. When adding Re into the alloy, the Re atoms with low diffusion coefficient may hinder the diffusion of other atoms away from γ′ phase during the growth of γ′ phase, which is thought to be the main reason of decreasing the partitioning ratios of elements in γ and γ′ phase.

Study on the Effect of Mn, Zn, and Sb on Undercooling Behavior of Sn-Ag-Cu Alloys Using Differential Thermal Analysis

Differential thermal analysis (DTA) has been conducted on directionally solidified near-eutectic Sn-3.0 wt.%Ag-0.5 wt.%Cu (SAC), SAC \(+\) 0.2 wt.%Sb, SAC \(+\) 0.2 wt.%Mn, and SAC \(+\) 0.2 wt.%Zn. Laser ablation inductively coupled plasma mass spectroscopy was used to study element partitioning behavior and estimate DTA sample compositions. Mn and Zn additives reduced the undercooling of SAC from 20.4\(^\circ \hbox {C}\) to \(4.9^\circ \hbox {C}\) and \(2^\circ \hbox {C}\), respectively. Measurements were performed at cooling rate of \(10^\circ \hbox {C}\) per minute. After introducing 200 ppm \(\hbox {O}_2\) into the DTA, this undercooling reduction ceased for SAC \(+\) Mn but persisted for SAC \(+\) Zn.

Fluorine and chlorine behaviour during progressive dehydration melting: Consequences for granite geochemistry and metallogeny

AbstractDehydration melting of biotite is the main control on crustal differentiation in the mid to lower continental crust because this reaction produces the most voluminous and most mobile granitic melts. Biotite breaks down over a broad temperature interval, so the partitioning behaviour of elements between biotite and melt is likely to vary. It has been hypothesized that fluorine may stabilize biotite to higher melting temperatures because biotite is typically F‐rich in ultra‐high temperature (UHT) metamorphic rocks. If true, F would be an important influence on crustal differentiation because not only would it broaden the temperature range of melting but also elevated F concentration decreases melt viscosity. Furthermore, ligand partitioning between biotite and melt may be an important influence on the metallogeny of magmas. This study used electron microprobe analysis of biotite in rocks from the Ballachulish and Rogaland metamorphic aureoles to investigate the concentration of F and Cl in biotite heated to 600–1,000°C. Results show a broad increase in biotite F content (up to 5.04% F) with temperature until 850–920°C, beyond which F content decreases (&lt;2.5% F). Chlorine concentrations in biotite are consistently lower (&lt;1% Cl), and show a progressive decrease after the onset of partial melting. It was found that Mg content, and the processes that control Mg distribution, are most strongly correlated with F and Cl concentration in biotite. Calculations based on these results indicate that F‐enriched biotite could be a significant source of F for continental crust‐derived melts. Generation of a hot, F‐rich melt at UHT conditions could be important for transporting lower crustal metals to the upper crust.

Effect of Titanium Addition on the Elemental Partitioning Behavior of Silicon in Ni-19 At. Pct Al-xSi-yTi Alloys

We have investigated the effect of Ti addition on the partitioning behavior of Si in Ni-19 at. pct Al-xSi-yTi alloys (x = 1.0 to 2.5 at. pct and y = 0.0 to 2.0 at. pct). The elemental partition ratios between the γ and γ′ phases were determined by electron probe microanalysis. The results indicate that an increase in the Ti content increases the partitioning tendency of Si in the γ matrix. However, Si was preferentially partitioned in the γ′ phase after 816 hours aging at 1373 K (1100 °C). Interestingly, a CALPHAD-based simulation also predicted the tendency of Si to partition in the γ phase with increasing Ti content. However, Si was predicted to preferentially partition in the γ matrix. First-principles calculations suggest that Ti atoms can replace Si atoms in the γ′ phase and reject Si atoms into the face-centered cubic γ matrix. Furthermore, the partitioning behavior of Si could also be influenced by the presence of point defects and the volume fraction of the γ′ phase.

Characterization, partitioning, and potential ecological risk quantification of trace elements in coal fly ash.

Coal-based thermal power plants are the major source of power generation in India. Combustion of coal gives rise to by-products such as fly ash (FA) in huge quantities. The current study focuses on physico-chemical and mineralogical characterization and risk evaluation of FA, generated from five thermal power plants (TPPs) of India. The coal, and corresponding FA and bottom ash (BA) were further analyzed for trace elements in order to observe the enrichment and partitioning behavior of elements. The environmental risk assessment of trace elements in FA was performed in accordance with geoaccumulation index (I geo) and potential ecological risk index (PERI). The results demonstrated that FA was enriched predominantly in SiO2, Al2O3, and Fe2O3 along with small concentrations of CaO and MgO. The mineral phases identified in FA were quartz, mullite, hematite, and magnetite. Elemental characterization indicated that the metals were more enriched in FA as compared to coal and BA. The concentrations of trace elements, Cr, Pb, Hg, and As in FA (TPPs), varied from 12.59-24.28, 22.68-43.19, <0.0001-2.29, and 0.08-3.39 mg/kg, respectively. Maximum enrichment ratio (ER) was observed for Pb (5.21) in TPP3 FA. Hg in TPP1 showed the highest partition ratio (PR) value. I geo values for metals were mostly below zero. The PERI values indicated moderate risk from TPP4 FA and low risk from TPP1, TPP2, TPP3, and TPP5 FA to the environment, according to the threshold values provided.

Experimental Determination of Partitioning in the Fe-Ni System for Applications to Modeling Meteoritic Metals.

Experimental trace element partitioning values are often used to model the chemical evolution of metallic phases in meteorites, but limited experimental data were previously available to constrain the partitioning behavior in the basic Fe-Ni system. In this study, we conducted experiments that produced equilibrium solid metal and liquid metal phases in the Fe-Ni system and measured the partition coefficients of 25 elements. The results are in good agreement with values modeled from IVB iron meteorites and with the limited previous experimental data. Additional experiments with low levels of S and P were also conducted, to help constrain the partitioning behaviors of elements as a function of these light elements. The new experimental results were used to derive a set of parameterization values for element solid metal-liquid metal partitioning behavior in the Fe-Ni-S, Fe-Ni-P, and Fe-Ni-C ternary systems at 0.1 MPa. The new parameterizations require that the partitioning behaviors in the light-element-free Fe-Ni system are those determined experimentally by this study, in contrast to previous parameterizations that allowed this value to be determined as a best-fit parameter. These new parameterizations, with self-consistent values for partitioning in the end-member Fe-Ni system, provide a valuable resource for future studies that model the chemical evolution of metallic phases in meteorites.

The effect of Ni:Co ratio on the elemental phase partitioning in γ-γ′ Ni-Co-Al-Ti-Cr alloys

Atom probe tomography has been used to characterise the effect of varying Ni:Co ratio on elemental phase partitioning at 800 °C in γ-γ′ alloys derived from the Ni-Co-Al-Ti-Cr system. In all alloys tested, Al and Ti were found to partition preferentially to the γ′ phase, whereas Co and Cr partitioned preferentially to the γ phase. However, above a critical Co content (∼19 at.%), the extent of partitioning of Al and Ti to the γ′ phase reduced. Conversely, Cr partitioned more strongly to the γ phase with Co additions of up to ∼19 at.%, above which this preferential segregation was less pronounced. This non-monotonic trend of elemental partitioning behaviour with increasing Co concentration was attributed to a transition in the chemistry of the L12 γ′ phase from Ni3(Ti, Al) to (Ni, Co)3(Ti, Al) and thus to a change in its solute solubility.