PRESOLAR SiC GRAINS OF TYPE C
نویسندگان
چکیده
منابع مشابه
Nanosims Studies of Presolar Graphite Grains: Are C-isotopic Ratios Grain-size- Dependent?
Introduction: After silicon carbide (SiC), graphite is the best studied presolar mineral. A wealth of information exists on the isotopic compositions of C and of many minor/trace elements in micrometer-sized grains [e.g., 1-5]. Presolar graphite grains exhibit large C-isotopic anomalies with C/C ratios between 2 and 7000. Although this range is compatible with what is observed for SiC [6, 7], t...
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Introduction: Transmission electron microscopy (TEM) studies of sub-μm presolar SiC grains showed that 3C-SiC is the dominant polytype (~80%) [1]. Although TEM is the most effective technique to determine the crystal structure and disorder, TEM is destructive and time-consuming, and may not be representative of the bulk sample. On the other hand, Raman spectrometry investigates matter at the sc...
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A 28 g sample of the Qingzhen enstatite (EH3) chondrite was subjected to chemical and physical separation procedures to yield several grain-size residues. Ion mapping of isotopes of Si, O, and C in the ion microprobe of two size fractions (QZR4: 0.4–0.8 lm; QZR5: 0.8–2 lm) identified 55 30Si-depleted candidates out of 37,917 Si-rich grains and six 18O-depleted grains out of 54,410 oxides. Subse...
متن کاملCoordinated Tem/nanosims Microanalysis of Structurally or Isotopically Rare Presolar Silicon Carbides
Introduction: Submicron-to micron-sized grains of SiC originating from asymptotic giant branch (AGB) stars and supernovae (SN) can be ubiquitous in the matrices of primitive chondrites. Previous work has shown that presolar SiC occurs as three fundamental polytypes or stacking sequences (cubic 3C, hexagonal 2H, and one-dimensionally disordered hexagonal structure designated here ∞H) along with ...
متن کاملPresolar Grain Inventories of the Ungrouped C3 Adelaide and the Cv3 Rbt 04133
Introduction: Presolar grains are particularly abundant in primitive extraterrestrial materials such as IDPs [e.g. 1-3] and the matrices of the least altered chondrites [4-6]. To date, the presolar silicate and oxide inventories of the primitive chondrites Acfer 094 [4-7] and ALHA 77307 [7] have been reported extensively. More recently, the search for presolar silicates and oxides has been exte...
متن کاملSupernova mixing to reproduce isotopic ratios of presolar grains
Presolar grains are considered to have traces in their birth before the solar system formation in their isotopic and elemental features. Most of silicon carbide type X (SiC X) and low density graphite grains show the excesses of 12C and 28Si. These isotopic features suggest that SiC X and low density graphite are originating from supernovae. On the other hand, elemental signatures of the grains...
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