White Inclusions Research Articles

Electrochemical dissolution of simulated "white inclusions" in nitric acid. Linear voltammetry study with Mo, Re, Ru metals and their alloys electrodes

Summary The process of electrochemical dissolution of pure Mo, Re and Ru metals, as well as their alloys 52.5 at. Mo – 47.5 at. Re and 90 at. Mo – 10 at. Ru in 0.5-6.0M HNO3 was studied using the linear voltammetry technique. The dissolution potentials of the pure metals were found to increase from 0.39 to 0.48V/SCE (Mo), from 0.7 to 0.81V/SCE (Re) and from 1.15 to 1.25V/SCE (Ru) with the augmentation of HNO3 concentration in the electrolyte. The dissolution potentials of the alloys 52.5 at. Mo + 47.5 at. Re and 90 at. Mo + 10 at. Ru were found to change from 0.49 to 0.58 (Mo-Re) and from 0.92 to 1.09 (Mo-Ru) when HNO3 concentration in the electrolyte increased from 0.5 to 6.0M. The secondary passivation of Mo-containing electrodes was observed in the solutions 2.0-6.0M HNO3 at the potentials from 1.4 to 1.9V/SCE, decreasing their dissolution rate in this range of potentials. The maximum electrochemical dissolution rate constants of pure Mo, Re, Ru metals and Mo-Re, Mo-Ru alloys have been estimated using the data of linear voltammetry. The obtained values (1.85-2.20g/cm2 h for Mo-Re and 0.58-0.64g/cm2 h for Mo-Ru alloys electrochemical dissolution) are found to be thousand times greater, than reported for the process of chemical dissolution of corresponding alloys in boiling HNO3.

S‐asteroids 387 Aquitania and 980 Anacostia: Possible fragments of the breakup of a spinel‐bearing parent body with C03/CV3 affinities

Abstract— Asteroids 387 Aquitania and 980 Anacostia are anomalous members of the S‐class. Their reflectance spectra exhibit a strong broad absorption feature longwards of 1.5 μm and no significant feature near 1 μm. Their spectra indicate the presence of spinel, an aluminum‐magnesium oxide mineral commonly present in inclusions in CV3 and CO3 meteorites. Spinel probably makes up only a small percentage of the surface assemblages of these asteroids, but its spectral effect may be enhanced by its presence in fine‐grained white inclusions in immature asteroid regoliths. It is speculated that Aquitania and Anacostia represent material formed in the same nebular zone as the CV3 and CO3 chondrites but either: A) at an earlier time in the nebula when such inclusions might have been a relatively larger fraction of the nebular grain population, or B) in local regions where nebular processes (e.g., settling to the midplane) had concentrated such inclusions. The close similarity of two orbital elements (a, i) suggests that Aquitania and Anacostia may be members of a partially dispersed asteroid family produced by the early disruption of a spinel‐bearing parent body.

Formation of crystalline tripalmitin-rich spicules in isolated hepatocytes.

Conditions were developed for rapid deposition of triglyceride in isolated rat hepatocytes. Liver cells from fasted rats were incubated for 90 min at 37 degrees C with 3.0 mM palmitic or oleic acid, 4% bovine serum albumin, 20 mM glucose, 10 mM lactate, and 1 mM pyruvate. When oleic acid was used, numerous cytoplasmic lipid droplets were produced. When hepatocytes were incubated with palmitic acid, similar amounts of triglyceride were synthesized but instead of lipid droplets, a vast accumulation of peculiar spicules permeated the cytoplasm. These inclusions appeared in myriads of swirled threads, thick elongated angular plates, and needles, some of which exhibited longitudinal osmiophilic bands of 250 A thickness. These structures were associated with smooth endoplasmic reticulum. The cells appeared otherwise normal. Polarized light microscopy at 37 degrees C revealed a multiplicity of brilliant white inclusions between crossed polars in cells incubated with palmitic acid. These birefringent structures exhibited 90 degrees periodicity between both maximum brilliance and extinction, indicative of anisotropic crystalline deposits. Molecular species analysis of triglycerides in cells incubated with palmitic acid, together with data on [1-14C]palmitic acid incorporation, demonstrated an almost exclusive synthesis of tripalmitin. Spicules isolated from homogenized hepatocytes displayed needles containing longitudinal single and double osmiophilic bands of 110 A and 260 A thickness, respectively, and lipid spicular aggregates. The isolated spicules were almost pure tripalmitin by analysis. These observations document the formation and development of crystalline triglyceride in living cells and may provide a unique system for the study of cellular lipid synthesis, transport and deposition.

The origin of the ‘FUN’ anomalies and the high temperature inclusions in the allende meteorite

The discovery of isotopic anomalies in white inclusions of the meteorite Allende has led to fundamental questions concerning the origin of these anomalies and of the white inclusions themselves. An analysis of the ‘FUN’ anomalies in the inclusions C1 and EK1-4-1 demonstrates that these isotopic anomalies may be decomposed into individual nucleosynthetic components, which have been subjected to separate mass and component fractionations. There is no evidence that any freshlysynthesized material injected into the primitive solar nebula was of abnormal isotopic composition, or that the FUN anomalies were due to an injection of unusual material. Rather, they show the effects of form of interstellar grains whose size or chemistry served as a memory for the nucleosynthetic origins of their constituent atoms. Giant gaseous protoplanets, as described for the early solar nebula by Cameron (1978), are a potential site for achieving both mass and component fractionations, and for producing white inclusions in general.

40Ar 39Ar ages of Allende

KAr and/or 40Ar 39Ar plateau ages of Allende samples—whole rock, matrix, chondrules, white inclusions–range from 3.8 AE for matrix of ≳5 AE for some white inclusions, but cluster strongly near 4.53 AE. This age marks the dominant KAr resetting of Allende materials. Age spectra show disturbances due to 39Ar recoil or some other argon redistribution processes. Possible explanations for the apparent presolar ages (>4.6 AE) include: ≳20% loss of 39Ar; ≳40% loss of 40K ∼3.8 AE ago with no loss of 40Arl trapped argon of unique 40Ar/ 36Ar isotopic composition; admixture of “very old” presolar grains.

Allende meteorite—old age but normal isotopic composition of potassium

The extensive investigation of the Allende meteorite has provided much new information on the early history of our Solar System. The findings include small but significant anomalies of the isotopic composition for several elements which are clearly not due to any of the processes hitherto known to cause such variations (see ref. 1 for review). These anomalies seem to confirm the reality of astrophysical concepts developed since the classical paper of Burbidge et al.2 on the different modes of origin of the nuclei. Evidence has also been found which points to the possible presence in Allende of pre-solar condensates. Jessberger and Dominik3 have presented data to support an earlier result4 according to which the 40Ar gas retention ages of some white inclusions from Allende exceed the canonical age of the Solar System. These gas retention ages were obtained by 40Ar–39Ar dating, however, and are therefore based on the assumption that the 39K/40K ratio in the inclusions is identical to that used in the reference standard. In view of the far-reaching implications of finding in meteorites solid matter pre-dating by roughly 500 Myr the condensation of the Solar System we have attempted to verify this assumption. This is especially important because the Allende inclusions contain elements with an anomalous isotopic composition.

87Rb- 87Sr chronology of enstatite meteorites

A 87Rb- 87Sr analysis of some enstatite meteorites has been made. Whole rocks plot on an isochron of age 4.508 ± 0.037b.y. and strontium initial ratio 0.69880 ± 0.00044 (2σ errors; λ 87Rb= 1.42 × 10 −11yr −1) . If the Norton County results are joined, we get an age of 4.516 ± 0.029b.y. and initial ratio of 0.69874 ± 0.00022. This result is indistinguishable from the whole rock isochron for H chondrites. It is interpreted as the age of condensation from the solar nebula. The identity of the 87Sr/ 86Sr initial ratio with the ones for Allende white inclusions shows that this ratio was homogeneous in the solar nebula, and that the Rb-Sr fractionations observed between the different chondrite groups appeared only shortly before or during condensation accretion. Internal studies of the type-I enstatite chondrites Abee and Indarch and the intermediate-type Saint Mark's and Saint Sauveur have been done. Abee data scatter in the 87Rb- 87Sr diagram. For Indarch, Saint Mark's and Saint Sauveur, we obtained well-defined straight lines of “age” ( T) and “initial ratio” ( I): Indarch, T = 4.393 ± 0.043b.y. I = 0.7005 ± 0.0009; Saint Mark's, T = 4.335 ± 0.050b.y. I = 0.69979 ± 0.00022; Saint Sauveur, T = 4.457 ± 0.047b.y. I = 0.6993 ± 0.0014. Our result on Indarch agrees with the former result of Gopalan and Wetherill [5]. A careful examination of the data shows that these straight lines are neither due to leaching effects by heavy liquids, nor result from terrestrial weathering. The “isochrons” for Indarch and Saint Sauveur can be mixing lines between enstatite and feldspar. The results are interpreted in terms of cosmochemical secondary effects: type-I and intermediate-type enstatite chondrites have been shocked 60–200 m.y. after their formation. This agrees with the idea of an early generalized bombardment of the inner solar system; this also indicates that type-I enstatite chondrites were rather situated in the outershells of their parent body and might be at the origin of the scatter of I-Xe ages of enstatite meteorites. Whole rock and enstatite from Bishopville, Cumberland Falls and Mayo Belwa have also been analysed. In these three aubrites, the 87Rb- 87Sr system is perturbed. Our Bishopsville sample might not be fresh and this makes the significance of our results uncertain. Cumberland Falls and Mayo Belwa probably suffered relatively recent shocks and open-system redistribution of Rb and Sr.

87Rb [sbnd]87Sr chronology of H chondrites: Constraint and speculations on the early evolution of their parent body

A precise 87Rb- 87Sr whole-rock isochron for H chondrites and an internal isochron for Tieschitz (H3) have been determined. The age and 87Sr/ 86Sr initial ratio of the whole rocks are 4.52 ± 0.05 b.y. and 0.69876 ± 0.00040 (λ( 87Rb) = 1.42 × 10 −11yr −1) . For Tieschitz, whereas handpicked separates plot on a well-defined line, heavy liquid separates scatter in the 87Rb/ 86Sr vs. 87Sr/ 86Sr diagram. Leaching experiments by heavy liquids indicate that they might have a sizeable effect on Tieschitz minerals. The age and 87Sr/ 86Sr initial ratio as determined by handpicked separates are 4.53 ± 0.06 b.y. and 0.69880 ± 0.00020, indistinguishable from the whole-rock isochron. These results are interpreted as “primitive isochrons” dating the condensation of chondrites from the solar nebula. The best value of this event is given by joining both isochrons together at 4.518 ± 0.026 b.y. and 87Sr/ 86Sr= 0.69881 ± 0.00016 . The near identity of this initial ratio with the one of Allende white inclusions argues in favor of a sharp isochronism of condensation from a 87Sr/ 86Sr homogeneous nebula. Data from Guaren˜a [11] and Richardton [48] are interpreted as secondary internal isochrons, 100 m.y. after the condensation of the whole rocks. The data are then used to constrain a thermal evolution model of the H chondrite parent body. This body might have a 150–175 km radius, and might have been heated by 26Al. An 26Al/ 27Al ratio of 4–6 × 10 −6 is enough for heating such a body. Further tests for this model are proposed.

Gerontology of the Allende meteorite

IN the Allende meteorite several elements are found to have an isotopic composition that cannot be due to radioactive or spallation or fractionation processes1. These isotope anomalies are mostly confined to white inclusions enriched in refractory elements2 (Ca–Al-rich inclusions) and are thought to be introduced into the Solar System by precondensed grains3. We have previously reported an anomalously high K–Ar age of a composite sample of five white inclusions from the Allende meteorite4; no direct verification of this lone-standing result of 4,800 Myr was possible because, with the exception of a small chip of one of the inclusions used for a thin section, the material was fused in the 40Ar–39Ar experiment. We therefore began a search for old material in other Ca–Al-rich inclusions. Three different samples from a new type of inclusion proved to be no older than most of Allende's constituents, 4,510 Myr (ref. 5). A small white inclusion gave a well developed 40Ar/39Ar plateau over almost the entire 39Ar release, with an age of 4,500±20 Myr (ref. 6). We report here on the 40Ar–39Ar analysis of two further coarsegrained Allende inclusions that showed ages in excess of 4,550 Myr.

Wollastonite whiskers in the Allende meteorite and their bearing on a possible post-condensation process.

The fine-grained white inclusions in the Allende meteorite have been studied by the scanning electron microscope with non-dispersive and dispersive X-ray detector, and a transmission electron microscope. The white inclusions consist almost entirely of the aggregates of losely packed semi-euhedral crystals rich in Ca and Al on the whole. Whisker crystals 0.5-5 microns in width and 10-50 microns long are found in cavities about 0.1 mm in diameter. These whisker crystals are wollastonite (CaSiO3) whose formation process has not been fully elucidated with the equilibrium condensation. On the basis of the evidence that a portion of the wall of the wollastonite-filled cavity is rich in Al2O3, we presumed some possible formation processes of these wollastonite whiskers. In conjunction with a finding of layered rims enclosing Ca-Al rich inclusions in carbonaceous chondrites, the growth of wollastonite whiskers in the inclusions also provide an evidence that some post-condensation processes took place within the inclusions as well as at the rims.

Causes of formation of white flaky inclusions in products for illumination engineering

Causes of formation of white flaky inclusions in products for illumination engineering

Isotopic composition of lithium in the Allende meteorite.

An anomaly in the isotopic composition of lithium has been searched for in the Allende meteorite. White inclusions, a chondrule and the matrix of Allende were analysed and compared with terrestrial standard rocks and with the meteoritic standards of St. Severin, Peace River and Bruderheim. No anomaly of 7Li/6Li was observed in any of the Allende samples.

GROSSULAR IN THE ALLENDE (TYPE III CARBONACEOUS) METEORITE*

Grossular garnet has been observed in several white inclusions in the Allende meteorite. Compositions range from Gro9sPy5 to Gro88Py12 in five inclusions. Its mottled appearance indicates that it crystallized from a glass of near‐grossular composition and not by a solid state reaction between wollastonite, anorthite and melilite. These grossular‐bearing inclusions either condensed directly as metastable liquids from the solar nebula or if initial solid condensates were liquefied by some subsequent heating process. In either case, a prolonged residence time in a thermal blanket appears necessary to effect crystallization of the grossular.

Chromium and phosphorus enrichment in the metal of type II (C2) carbonaceous chondrites

Electron microprobe analyses of metal grains in nine C2 meteorites show consistently high Cr and P contents, with large grain to grain variations within individual meteorites. Cr ranges from 0.16 to 1.0 wt.% (average 0.6 per cent for 43 analyses). P ranges from 0.00 to 3.2 wt.% (average 0.42 per cent). In addition, metal grains in seven C3 meteorites show a lesser enrichment of Cr, 0.00 to 0.7 per cent (average 0.13 per cent for 59 analyses), with no P present. Both of these elements, Cr and P, are generally below detection in the metal of other chondrite groups, equilibrated and unequilibrated. C2 metal grains occur typically as spherical to ovate blebs contained within single, euhedral forsterite crystals or crystal fragments that are either isolated in the black C2 matrix or are in clusters making up white inclusions. Metal is rare within true chondrules. Calculations of the expected Cr contents in metal condensing directly from a solar nebular gas agree remarkably well with the observed values. Unfortunately, no calculation is possible for P because of insufficient data at the present time. The composition and the textural relationships indicate this Cr, P rich metal, and the enclosing forsterite are direct condensates from a cooling solar nebula. Cr and P, in the quantities reported here, characterize C2 metal.

129I and 244Pu abundances in white inclusions of the Allende meteorite

Data are presented for thermal-release xenon analysis of a neutron-irradiated sample of white inclusions from the carbonaceous chondrite Allende. The best-fit high-temperature 129Xe/ 132Xe vs. 128Xe/ 132Xe isochron defines an iodine-xenon age 2.4 ± 1.3 my before that of the chondrite Bjurböle, well within the previously observed range of meteoritic iodine-xenon ages. The high-temperature data are not strictly consistent with the linear isochron model, however, and are best interpreted as defining a spread of about 4 my, corresponding either to slow cooling or to separate formation of phases before aggregation. The high-temperature data also define a good correlation between 130Xe/ 132Xe and 134Xe/ 132Xe, determining a ratio 244Pu/ 238U = 0.087 ± 0.011 at the time the sample began to retain xenon. This ratio is nearly six times higher than that found in the chondrite St. Severin. Comparison with the iodine chronology indicates that this result cannot be interpreted as very early gas retention, but must be ascribed to chemical fractionation between Pu and U in the formation of these inclusions. Results are also presented for a partial thermal-release xenon analysis of the neutron-irradiated carbonaceous chondrite Karoonda. Agreement of these results with those of a previous experiment is significant because Karoonda is the first case in which it has been possible to test the reproducibility of the I-Xe method by comparison of duplicate analyses.

Luminescence, Electron Paramagnetic Resonance, and Optical Properties of Lunar Material

Dust samples have been found to luminesce weakly under proton excitation, but not under ultraviolet. Damage, recovery, and heating effects have been investigated. Chips of breccia show luminescence, from white inclusions only, under ultraviolet and protons. Some rock chips show general luminescence, mainly from plagioclase. No natural or excited thermoluminescence has been found for dust or chips. The electron paramagnetic resonance spectrum shows the same broad Fe(3+) dipole resonance for dust and for some chips; other chips show no response. The polarization characteristics of dust are found to be identical to those of the Sea of Tranquillity, independently of proton damage. Chips show characteristics unlike any part of the lunar surface.