Metal Nodules Research Articles

Effect of pretreatments on the metal–ceramic bonding strength of a Pd–Ag alloy

ObjectivesThe purpose of this study was to evaluate the efficacy of surface treatments on the bonding properties between a metal and ceramic. MethodsSixty metal specimens were divided equally into four groups of 15 samples each. These groups received different treatments (Gr1: 250μm Al2O3+preoxidation; Gr2: 250μm Al2O3+degassing; Gr3: 120μm Al2O3+preoxidation; Gr4: 120μm Al2O3+degassing). Bond strengths were evaluated using a three-point bending test. The results were analyzed using 2-way ANOVA and Tukey's test. Scanning electron microscopy and energy dispersive spectroscopy were used to observe the microscopic features, elemental compositions and distributions, and diffusion in the specimens. Mechanical profiler was used to measure the roughness of metal surface. ResultsThe bond strengths of the four groups ranged from 45.00±3.63MPa to 51.61±5.91MPa, with significant differences (P<.05). The specimen that received the pretreatment of 250μm Al2O3 air-particle abrasion+degassing had the highest bond strength. Heating under different oxygen partial pressures caused the final Pd–Ag alloys to have varying degrees of internal oxidation and different quantities of metallic nodules. None of the elements in either the ceramic or the Pd–Ag alloy layer diffused into the other layer. ConclusionsThe metal–ceramic specimen subjected to air-particle abrasion with 250μm Al2O3 and degassed before porcelain firing had significantly higher bond strength than specimens treated differently.

Opaque assemblages in CR2 Graves Nunataks (GRA) 06100 as indicators of shock‐driven hydrothermal alteration in the CR chondrite parent body

AbstractWe have studied the petrologic characteristics of sulfide‐metal lodes, polymineralic Fe‐Ni nodules, and opaque assemblages in the CR2 chondrite Graves Nunataks (GRA) 06100, one of the most altered CR chondrites. Unlike low petrologic type CR chondrites, alteration of metal appears to have played a central role in the formation of secondary minerals in GRA 06100. Differences in the mineralogy and chemical compositions of materials in GRA 06100 suggest that it experienced higher temperatures than other CR2 chondrites. Mineralogic features indicative of high temperature include: (1) exsolution of Ni‐poor and Ni‐rich metal from nebular kamacite; (2) formation of sulfides, oxides, and phosphates; (3) changes in the Co/Ni ratios; and (4) carbidization of Fe‐Ni metal. The conspicuous absence of pentlandite may indicate that peak temperatures exceeded 600 °C. Opaques appear to have been affected by the action of aqueous fluids that resulted in the formation of abundant oxides, Fe‐rich carbonates, including endmember ankerite, and the sulfide‐silicate‐phosphate scorzalite. We suggest that these materials formed via impact‐driven metamorphism. Mineralogic features indicative of impact metamorphism include (1) the presence of sulfide‐metal lodes; (2) the abundance of polymineralic opaque assemblages with mosaic‐like textures; and (3) the presence of suessite. Initial shock metamorphism probably resulted in replacement of nebular Fe‐Ni metal in chondrules and in matrix by Ni‐rich, Co‐rich Fe metal, Al‐Ti‐Cr‐rich alloys, and Fe sulfides, while subsequent hydrothermal alteration produced accessory oxides, phosphates, and Fe carbonates. An extensive network of sulfide‐metal veins permitted effective exchange of siderophile elements from pre‐existing metal nodules with adjacent chondrules and matrix, resulting in unusually high Fe contents in these objects.

Elemental composition and history of metal in the Pesyanoe and Norton County enstatite achondrites

The composition (determined by INAA) of the Fe,Ni phase of the Norton County and Pesyanoe enstatite achondrites (aubrites) indicates that the fractionation trends of elements in the metal phase of aubrites are different from those predicted using the purely condensation or magmatic models for the genesis of aubrites. Metal nodules in aubrites with chemical composition similar to that of the metal of enstatite chondrites are relics of the primary condensates of the protoplanetary nebula. The matrix metal, which is depleted in refractory Ir relative to moderately volatile elements, underwent magmatic differentiation. The positive Ni-Au, Ni-As, and Au-As correlations in the metal of the Pesyanoe and Norton County aubrites and the negative Ir-Ni (Au) correlations in the matrix metal and nodules with low Ir concentrations testify to genetic relationship between these metal fractions. The matrix metal was produced by the partial melting of the nodules, which are the primary metal of the parent planetesimal body that had an enstatite chondrite composition. Its melting and differentiation produced the aubrite material. The composition of the aubrite Fe,Ni phase is consistent with the model of aubrite origin in two stages during the early evolution of the Solar System as a result of gravitational agglomeration of fragments that were ejected from different depths of a primary planetesimal with following formation of an asteroidal size body.

Microscopy characterization of metallurgical production evidences from Vila Nova de São Pedro (Azambuja, Portugal)

The Castro de Vila Nova de São Pedro (VNSP) is an emblematic settlement located at Azambuja (Portugal), occupied predominantly during the Chalcolithic period. A large and diversified metallurgical collection was recovered from this settlement which includes artefacts, crucibles and other metallurgical production remains, like slags and droplets. The chemical and microstructural characterization of this metallic collection aims to contribute to a better comprehension of the early copper-based metallurgy on the Portuguese Estremadura, the degree of knowledge of the ancient metallurgists and the role of the metallurgical activities in Chalcolithic societies.A group of 53 selected copper-based fragments of artefacts plus metallurgical production remains (12 crucibles and 20 slags and droplets), all belonging to VNSP, were characterized by using different analytical techniques: EDXRF and micro-EDXRF spectrometry, optical microscopy (OM) and SEM-EDS. The EDXRF and micro-EDXRF spectrometry gives the elemental composition of the artefacts and metallic nodules. The microscopy techniques play a fundamental role in the chemical and microstructural characterization of artefacts and metallurgical remains. The OM allows the identification of different phases, inclusions and thermomechanical processes applied during the shaping of the artefacts. The SEM-EDS plays an important role in the determination of main chemical phases present in the metal alloy and slags, and also in the distribution of chemical elements and minerals in the inclusions. The combination of these two microscopy techniques gives indication of the processes used in the reduction of minerals in order to obtain the metal and also allows the characterization of the operation chain, regarding the production of artefacts.The research that has been carried out by us offer indications concerning the provenance of the arsenic, the technological choices involved in the production of an arsenical copper alloy and how it was recognized by ancient metallurgists. Results obtained on the elemental composition of the metallurgical production remains are consistent with copper and arsenical copper (As &gt; 2 %) artefact production. Crucibles and slags analysed indicate melting and smelting operations (of copper ores or copper/arsenic ores). A statistically significant association was found between copper alloyed with arsenic and artefacts classified as tools/weapons (arrowheads, daggers and knives). In several cases, the presence of arsenic rich phases in the microstructure, resulting from an inverse segregation phenomenon, shows no evidence of chemical homogeneity control during the artefact manufacture. Microstructural analyses also show that the majority of the artefactual group was shaped with forging plus annealing operation cycles and 23 % of the artefacts received a final forging treatment. This final treatment was associated to artefacts presenting higher arsenic contents.This research work has been financed by the Portuguese Science Foundation (FCT-MCTES) through the EarlyMetal project (PTDC/HIS-ARQ/110442/2008) and the PhD Grant SFRH/BD/78107/2011 (FP). The financial support of CENIMAT/I3N through the Strategic Project-LA25-2011-2012 (PEst-C/CTM/LA0025/2011) is also acknowledged.

Structure, composition, and location of organic matter in the enstatite chondrite Sahara 97096 (EH3)

Abstract– The insoluble organic matter (IOM) of an unequilibrated enstatite chondrite Sahara (SAH) 97096 has been investigated using a battery of analytical techniques. As the enstatite chondrites are thought to have formed in a reduced environment at higher temperatures than carbonaceous chondrites, they constitute an interesting comparative material to test the heterogeneities of the IOM in the solar system and to constrain the processes that could affect IOM during solar system evolution. The SAH 97096 IOM is found in situ: as submicrometer grains in the network of fine‐grained matrix occurring mostly around chondrules and as inclusions in metallic nodules, where the carbonaceous matter appears to be more graphitized. IOM in these two settings has very similar δ15N and δ13C; this supports the idea that graphitized inclusions in metal could be formed by metal catalytic graphitization of matrix IOM. A detailed comparison between the IOM extracted from a fresh part and a terrestrially weathered part of SAH 97096 shows the similarity between both IOM samples in spite of the high degree of mineral alteration in the latter. The isolated IOM exhibits a heterogeneous polyaromatic macromolecular structure, sometimes highly graphitized, without any detectable free radicals and deuterium‐heterogeneity and having mean H‐ and N‐isotopic compositions in the range of values observed for carbonaceous chondrites. It contains some submicrometer‐sized areas highly enriched in 15N (δ15N up to 1600‰). These observations reinforce the idea that the IOM found in carbonaceous chondrites is a common component widespread in the solar system. Most of the features of SAH 97096 IOM could be explained by the thermal modification of this main component.

IRON-60 HETEROGENEITY AND INCOMPLETE ISOTOPE MIXING IN THE EARLY SOLAR SYSTEM

Short-lived radionuclides (e.g., 26Al, 53Mn, 60Fe, 182Hf) are widely used to refine the chronology of the early solar system. They provide chronological information, however, only if they were homogeneously distributed in the source region of the objects under scrutiny at the time of their formation. With the high level of precision now achieved on isotopic measurements, very short time intervals can in principle be resolved and a precise evaluation of the initial homogeneity degree becomes increasingly crucial. High-precision nickel isotope data for differentiated meteorites (angrites, ureilites) and chondritic (CB) components allow us to test the initial distribution of radioactive 60Fe and stable Ni isotopes. Although these meteorites appear to have formed nearly contemporaneously, they yield variable initial 60Fe/56Fe ratios. Besides, the CB metal nodules and ureilite silicates show nucleosynthetic anomalies. The new data presented here do not confirm the recently inferred late injection of 60Fe into the protoplanetary disk. Instead, live 60Fe was present, but heterogeneously distributed, from the start of the solar system, revealing an incomplete mixing of material from various nucleosynthetic sources and restricting the use of the 60Fe-60Ni system as a chronometer.

Great Balls of Fire?

Metallic nodules found in the Siyalk II settlement and in Iron Age III tombs in Luristan, Iran, were identified by the excavators as meteorites. However, these identifications must be questioned. The Siyalk nodules could be of telluric origin. The four Luristan specimens are identified as pyrite nodules. It is suggested that such nodules were used for fire-making, although other functions such as a use as sling balls are not to be excluded either.

A Novel Scheme for Wide Bandwidth Chip-to-Chip Communications

Quilt Packaging (QP), a novel chip-to-chip communication paradigm for system-in-package integration, is presented. By forming protruding metal nodules along the edges of the chips and interconnecting integrated circuits (ICs) through them, QP offers an approach to ameliorate the I/O speed bottleneck. A fabrication process that includes deep reactive ion etching, electroplating, and chemical-mechanical polishing is demonstrated. As a low-temperature process, it can be easily integrated into a standard IC fabrication process. Three-dimensional electromagnetic simulations of coplanar waveguide QP structures have been performed, and geometries intended to improve impedance matching at the interface between the on-chip interconnects and the chip-to-chip nodule structures were evaluated. Test chips with 100 μm wide nodules were fabricated on silicon substrates, and s-parameters of chip-to-chip interconnects were measured. The insertion loss of the chip-to-chip interconnects was as low as 0.2 dB at 40 GHz. Simulations of 20 μm wide QP structures suggest that the bandwidth of the inter-chip nodules is expected to be above 200 GHz.

Transition from External to Internal Oxidation of Single Phase Binary Alloys

It is shown from the oxidation results that, for Fe-Cr, Ni-Cr, Co-Cr binary alloys with and without internal Cr2O3 precipitations after exposure, continuous external Cr2O3 scales formed on their surfaces, especially at the initial stage. It is therefore suggested that the transitions of oxidation for these alloys take place from externally to internally. There are two types of transitions for alloys: (1) the transition from temporary external oxidation to internal oxidation; and (2) the transition from permanent external oxidation to internal oxidation. The thermodynamic conditions for these transitions have been analyzed, and the criterion for prediction of the minimum solute concentration of a binary solid solution alloy required for the second transition has been derived. It is also suggested that the external oxide scale is an important factor to determine the formation of pure solvent metal nodules on the surfaces.

The I-Xe record of alteration in the allende CV chondrite

Complex I-Xe and mineralogical studies have been performed on four heavily-altered Allende fine-grained spinel-rich Ca, Al-rich inclusions (CAIs) and four Allende dark inclusions (DIs) showing various degrees of iron-alkali metasomatic alteration. The CAIs are largely composed of Fe-rich spinel, Al-diopside, and secondary nepheline and sodalite. The DIs consist of chondrules and Allende-like matrix composed of lath-shaped fayalitic olivine, nepheline, sodalite, and Ca, Fe-rich pyroxene ± andradite ± FeNi-sulfide nodules. Chondrule phenocrysts are extensively or completely replaced by fayalitic olivine, nepheline, and sodalite; metal nodules are replaced by FeNi-sulfides, andradite and Ca, Fe-rich pyroxenes. The chondrules and matrices are crosscut by Ca, Fe-rich pyroxene ± FeNi-sulfide ± fayalitic olivine veins. DIs are surrounded by continuous Ca-rich rims composed of andradite, wollastonite, kirschsteinite, and Ca, Fe-rich pyroxenes, whereas the outer portions of the inclusions are depleted in Ca. Three CAIs yield well-defined I-Xe isochrons with ages 3.1 ± 0.2, 3.0 ± 0.2 and 3.7 ± 0.2 Ma younger than the Shallowater internal standard (4566 ± 2 Ma). Similar release profiles suggest the same iodine carrier (most probably sodalite) for all four CAIs. The Allende DIs yield I-Xe ages from 0.8 ± 0.3 to 1.9 ± 0.2 Ma older than Shallowater. Based on the petrographic observations, we infer that the DIs experienced at least two-stage alteration. During an early stage of the alteration, which took place in an asteroidal setting, but not in the current location of the DIs, chondrule silicates were replaced by secondary fayalitic olivine, nepheline, and sodalite. Calcium lost from the chondrules was redeposited as Ca, Fe-rich pyroxene veins and Ca, Fe-rich pyroxene ± andradite nodules in the matrix. The second stage of alteration resulted in mobilization of Ca from the DIs and its re-deposition as Ca-rich rims composed of Ca, Fe-rich pyroxenes, andradite, and wollastonite, around the DIs. We interpret I-Xe ages of the DIs as time of their alteration prior incorporation into Allende. The younger I-Xe ages of the fine-grained spinel-rich CAIs may reflect hydrothermal alteration of the Allende host, which could have occurred contemporaneously with the second stage of alteration of the Allende DIs. The lack of evidence for the disturbance of I-Xe system in the Allende DIs may suggest that fluid responsible for the alteration of the Allende CAIs was in equilibrium with the I- and Xe-bearing phases of the DIs.

Composition of impact melt debris from the Eltanin impact strewn field, Bellingshausen Sea

The impact of the km-sized Eltanin asteroid into the Bellingshausen Sea produced mm- to cm-sized vesicular impact melt-rock particles found in sediment cores across a large area of the ocean floor. These particles are composed mainly of olivine and glass with minor chromite and traces of NiFe-sulfides. Some particles have inclusions of unmelted mineral and rock fragments from the precursor asteroid. Although all samples of melt rock examined have experienced significant alteration since their deposition in the late Pliocene, a significant portion of these particles have interiors that remain pristine and can be used to estimate the bulk composition of the impact melt. The bulk composition of the melt-rock particles is similar to the composition of basaltic meteorites such as howardites or mesosiderite silicates, with a contribution from seawater salts and a siderophile-rich component. There is no evidence that the Eltanin impact melt contains a significant terrestrial silicate component that might have been incorporated by mixing of the projectile with oceanic crust. If terrestrial silicates were incorporated into the melt, then their contribution must be much less than 10 wt%. Since excess K, Na, and CI are not present in seawater proportions, uptake of these elements into the melt must have been greatest for K and least for CI, producing a K/CI ratio about 4 times that in seawater. After correcting for the seawater component, the bulk composition of the Eltanin impact melt provides the best estimate of the bulk composition of the Eltanin asteroid. Excess Fe in the impact melt, relative to that in howardites, must be from a significant metal phase in the parent asteroid. Although the estimated Fe:Ni:Ir ratios (8:1:4 x 10(exp -5)) are similar to those in mesosiderite metal nodules (10:1:6 x 10(exp -5), excess Co and Au by factors of about 2 and 10 times, respectively, imply a metal component distinct from that in typical mesosiderites. An alternative interpretation, that siderophiles have been highly fractionated from a mesosiderite source, would require loss of about 90% of the original metal from the impact melt and the sediments, and is unsupported by any observational data. More likely, the excess Fe in the melt rocks is 'representative of the amount of metal in the impacting asteroid, which is estimated to be 4+/- 1 wt%.

Oceanic Hydrates: More Questions Than Answers

From an oil industry standpoint, methane hydrate is known as a major problem because it plugs casing and pipelines. From a media standpoint, hydrates provide an almost inexhaustible supply of articles concerning greenhouse effects, landslides, global warming and mysterious events such as the loss of aircraft in the "Bermuda Triangle". From a scientific standpoint, they provide much scope for academic research projects. Oceanic hydrates have been recovered in some of the thousands of ODP/Joides boreholes, from which a total of over 250 km of core have been taken. Unfortunately, hydrates dissociate when brought on deck, and few samples were preserved for further analysis. Most of the oceanic hydrates are reported to be of biogenic origin, except where they overlie petroleum reservoirs, as in the Caspian Sea and Gulf of Mexico. The hydrates in the cores are found mostly as dispersed grains or thin laminae. Massive pieces of hydrate, greater than 10 cm thick, have been found only at three sites. Downhole logs...

A clast of Bali‐like oxidized CV material in the reduced CV chondrite breccia Vigarano

Abstract— The CV (Vigarano‐type) chondrites are a petrologically diverse group of meteorites that are divided into the reduced and the Bali‐like and Allende‐like oxidized subgroups largely based on secondary mineralogy (Weisberg et al., 1997; Krot et al., 1998b). Some chondrules and calcium‐aluminum‐rich inclusions (CAIs) in the reduced CV chondrite Vigarano show alteration features similar to those in Allende: metal is oxidized to magnetite; low‐Ca pyroxene, forsterite, and magnetite are rimmed and veined by ferrous olivine (Fs40–50); and plagioclase mesostases and melilite are replaced by nepheline and sodalite (Sylvester et al., 1993; Kimura and Ikeda, 1996, 1997, 1998).Our petrographic observations indicate that Vigarano also contains individual chondrules, chondrule fragments, and lithic clasts of the Bali‐like oxidized CV materials. The largest lithic clast (about 1 times 2 cm in size) is composed of opaque matrix, type‐I chondrules (400–2000 μm in apparent diameter) surrounded by coarse‐grained and fine‐grained rims, and rare CAIs. The matrix‐chondrule ratio is about 1.1. Opaque nodules in chondrules in the clast consist of Cr‐poor and Cr‐rich magnetite, Ni‐ and Co‐rich metal, Ni‐poor and Ni‐rich sulfide; low‐Ni metal nodules occur only inside chondrule phenocrysts. Chromium‐poor magnetite is preferentially replaced by fayalite. Chondrule mesostases are replaced by phyllosilicates; low‐Ca pyroxene and olivine phenocrysts appear to be unaltered. Matrix in the clast consists of very fine‐grained (&lt;1 μm) ferrous olivine, anhedral fayalite grains (Fa80–100), rounded objects of porous Ca‐Fe‐rich pyroxenes (Fs10–50Wo50), Ni‐poor sulfide, Ni‐ and Co‐rich metal, and phyllosilicates; magnetite is rare.On the basis of the presence of the Bali‐like lithified chondritic clast—in addition to individual chondrules and CAIs of both Bali‐like and Allende‐like materials—in the reduced CV chondrite Vigarano, we infer that (1) all three types of materials were mixed during regolith gardening on the CV asteroidal body, and (2) the reduced and oxidized CV materials may have originated from a single, heterogeneously altered asteroid.

A multidisciplinary approach to assess history, environmental risks, and remediation feasability of soils contaminated by metallurgical activities. Part B: direct metal speciation in the solid phase.

Three soils contaminated by industrial smelting activities previously characterized using chemical and physical approaches (Part A, Venditti et al. [2000] Arch Environ Contam Toxicol [in press]) were further investigated through a complementary mineralogical approach. X-ray diffraction allowed identification of the main mineral components: carbonates (calcite, siderite) and iron oxides (magnetite, hematite, goethite) prevailed in both siderurgical soils, and siliceous compounds were more abundant in the agricultural soil. Scanning electron microscopy coupled with energy dispersive x-ray microanalysis showed that carbonates and oxides contained low amounts of heavy metals (HMs), but the potential solubility of such species under acidic conditions associated to their abundance may result in a high mobility of associated contaminants. Microanalysis also revealed peculiar minor mineral forms (metallic nodules, alloys, ore residues) that were highly informative about the history of soil contamination. Small metal-rich particles were observed (brass, lead and zinc oxides). In such compounds, HMs showed high chemical stability and were consequently poorly mobile and toxic, but also poorly removable through chemical leaching. A risk of mechanical dispersion was suggested for these particles, particularly after the chemical and/or mechanical disruption of carbonate cements. These features allowed completion and confirmation of the conclusions achieved after chemical and physical investigations, providing accurate information about the history, environmental risks and remediation feasability of industrial soil contamination.

Formation of large metal nodules in ordinary chondrites

Literature data show that many large (2–30 mm) metallic Fe‐Ni nodules in ordinary chondrites are depleted in refractory siderophiles (e.g., Re, Os, Ir, Ru, Pt, and Rh) and Cu relative to fine‐grained metal but are not depleted in (normally refractory) W and Mo, common siderophiles (e.g., Ni and Co) and volatile siderophiles (e.g., Au, As, and Sb). It was recently proposed that metamorphic diffusion could form the metal nodules and that partitioning of siderophile elements between kamacite and taenite could account for the nodules' unusual compositions. However, the nodules have the same compositional trends as metal nodules and veins in shocked meteorites that clearly formed by impact‐related processes. If large metal nodules formed during metamorphism, type 6 chondrites should contain abundant large nodules. Instead, the mean metal grain size in H6 chondrites is 0.12±0.15 mm, far smaller than any of the nodules. It seems likely that the metal nodules formed by impact vaporization, oxidation of W and Mo to form volatile oxides, concomitant partial oxidation of Re and Os, rapid fractional condensation of refractory siderophiles, transport of the residual vapor, condensation of Cu, S, and Se into vugs and fractures to form sulfide, and condensation of the remaining siderophiles to form metal nodules and veins. During vapor cooling and condensation (or during subsequent parent body annealing) W, Mo, Re, and Os oxides were reduced.

Reevaluation of formation of metal nodules in ordinary chondrites

Abstract— Compositions of four metal nodules from two ordinary chondrites, WIS91627 (H3.7) and Juin (H5), were determined by instrumental and radiochemical neutron activation analyses. Compared with bulk metal fractions, the metal nodules are characterized by strong and variable depletion of the refractory siderophile elements Re, Os, Ir, Ru, Pt and Rh but normal W and Mo, some fractionation of Co from Ni, and low Cu concentrations. These characteristics are difficult to explain by shock‐induced vaporization followed by fractional condensation, a mechanism suggested by Widom et al. (1986). We propose formation of metal nodules during metamorphism in the parent body. Refractory siderophile elements, such as Ir, Os, Rh, etc., are partly locked up in noble metal nuggets and cannot participate in kamacite formation. The occurrence of metal nodules in both equilibrated and unequilibrated ordinary chondrites suggests that diffusion along grain boundaries was important in the development of kamacite and taenite in ordinary chondrites.

The Kaidun meteorite: Composition and origin of inclusions in the metal of an enstatite chondrite clast

Abstract— Metal nodules are one of the major textural components of Kaidun sample #01.3.06 EH3‐4. In terms of structure, the nodules are of three types: (1) globular, (2) zoned with a massive core and globular mantle, and (3) nodules with no internal structure. The size and composition of the globules in the nodules and grains of metal of the matrix are almost identical: no greater than 20 μm and Ni, 5.95; Si, 3.33 wt%. The nodules contain small (usually &lt;5 μm) inclusions of SiO2; albitic glass; enstatite; roedderite; and a mixture of SiO2 and Na2S2. This is the first reported occurrence of a simple sulfide of an alkaline metal in nature. The formation of the inclusions appears to be related to condensation of material onto the surfaces of metal grains. The nodules appear to have formed by aggregation of separate grains (globules) of metal, with conservation of condensates on the grain surfaces as inclusions. The inclusions probably condensed over a significant temperature range from 1400 to 600 K. The aggregation of metal grains and formation of the nodules probably occurred simultaneously with condensation.

Fractionation of refractory siderophile elements in metal from the Rose City meteorite

Abstract— An ∼4 × 9 × 12‐mm concentration of metal (dubbed RC1) situated between silicate melt and a relict chondritic clast in the Rose City H5 impact‐melt breccia is compositionally heterogeneous. Approximately 65 wt% of RC1 is enriched in the refractory siderophile elements, Os and Ir, by 30–40% relative to bulk H chondrite metal; ∼20 wt% is depleted in these elements by 31–35%; and 15 wt% is depleted by a considerably greater amount (75%). Common and volatile siderophile elements are essentially unfractionated in all three regions; W is fractionated to only a moderate degree. The compositions of the different regions of RC1 are similar to those of previously analyzed metal nodules and veins in shocked but unmelted ordinary chondrites. All of these objects probably formed by a complex process involving vaporization of chondritic material, rapidly followed by oxidation of W to form volatile oxides, fractional condensation of refractory siderophile elements, transport of the residual vapor (containing common and volatile siderophile elements as well as W oxide) and condensation of this vapor in fractures and voids or on metallic liquid substrates. The common occurrence of vugs in shock‐heated chondrites and the pervasiveness of vaporization effects recorded in metal masses and veins underscores the important role of superheating in the formation of impact breccias.

Composition of metal in aubrites: Constraints on core formation

Aubrites are differentiated stone meteorites with small amounts of metal. Study of eight aubrites reveals that Fe,Ni grains occur in a variety of textures, from irregular μm-sized particles to rounded nodules of up to 1.5 cm in diameter. The pattern of siderophile element abundances in the silicates is characteristic of igneous metal segregation (the more siderophilic elements are more depleted). Despite large uncertainties in metal/silicate distribution coefficients, the calculated minimum metal content of the aubrite precursor is not unlike that of enstatite chondrites and suggests that metal segregation was an extensive process in the early magmatic evolution of the aubrite parent body. However, the lack of appreciable fractionation in the trace element signature of the metal suggests that the metal now observed in aubrites did not undergo fractional crystallization in a core. We argue instead that the analyzed metal nodules represent a fraction of the iron-nickel that, during partial melting, was not completely segregated from the silicates.

The behavior of Fe-Ni metal during thermal metamorphism of the Jilin Chondrite

1. Under heat influence, the mobility of Fe-Ni metal was relatively high as compared with silicates. During thermal metamorphism of the Jilin meteorite (T ⩽ 800 °C), fine Fe-Ni metal particles in silicate condrules and matrix aggregated into coarse metal grains, which are as large as 5–10 mm in size,in situ or after a short-distance migration and concentration, and some even aggregated into metal nodules as large as 20–30mm in size, but their chemical composition still remains unchanged. 2. High-temperature and high pressure, as well as shock-loading experiments on Jilin meteorite samples provide further evidence that temperature plays an important role in metal /silicate redistribution and differentiation. The variation of temperature exerts great influence on the mode of metal-silicate redistribution. At about 1000 °C or less, metal particles moved and aggregated into rather coarse grains by thermal diffusion, or through the formation of eutectic melts together with FeS. When the temperature reaches about 1300 °C, full melting take place in the meteorite specimens, and at this time metals and metal sulfides play an important role in the immiscibility and gravitational differentiation of metal-silicate melts, thus leading to the rapid separation of metals or metal-sulfides from silicates, followed by the sinking of pure metals and metal-sulfides to the bottom of the experimental products and the formation of silicate melts almostly with no metals and sulfides in the upper parts.