The lead-lead isochron age of chondrules in the CR chondrite Acfer 059 is 4564.7 +/- 0.6 million years ago (Ma), whereas the lead isotopic age of calcium-aluminum-rich inclusions (CAIs) in the CV ...chondrite Efremovka is 4567.2 +/- 0.6 Ma. This gives an interval of 2.5 +/- 1.2 million years (My) between formation of the CV CAIs and the CR chondrules and indicates that CAI- and chondrule-forming events lasted for at least 1.3 My. This time interval is consistent with a 2- to 3-My age difference between CR CAIs and chondrules inferred from the differences in their initial 26Al/27Al ratios and supports the chronological significance of the 26Al-26Mg systematics.
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•Electronic structure of oxidized nitrogen-doped carbon nanoflakes is studied.•Narrow and broad components are detected in absorption EPR spectra.•Narrow line follows Curie-Weiss law ...and it is attributed to localized electrons.•Broad line follows Pauli law and it is associated with mobile electrons.•Long-time storage and thermocycling does not significantly affect the structure.
Being widely used in many applications the oxidized nitrogen-doped graphene nanoflakes (N-GNFox) are subjected to chemical composition change due to the aging, thermal and oxygen treatment. These processes were studied for the first time by electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The 3.5 years aging of the sample increased the oxygen and decreased the carbon contents, reduces the dispersion of atom around the paramagnetic centers and causes a change in the surrounding of the centers. The EPR spectra consist of the narrow and broad components which exhibit the Curie-Weiss and Pauli behaviors. The assignment of the EPR spectrum lines to localized and mobile electrons is discussed in connection with the temperature dependence of the intensity of paramagnetic response and conduction mechanism. The results of this work can be useful in explanation of the properties of carbon nanomaterials when used in modern devices and processes.
Ca, Al-rich inclusions (CAIs) are believed to have formed by evaporation, condensation, and melting of the pre-existing solids during the earliest stages of the solar system evolution. Most CAIs in ...unmetamorphosed chondrites contain detectable excesses of super(26)Mg( super(26)Mg*), a decay product of the short-lived radionucllde super(26)Al (T sub(1/2) similar to 730.000 yr), that correspond to an initial super(26)Al/ super(27)Al ratio of similar to (4-7) x 10 super(-7). It is suggested that super(26)Al was injected into the protosolar molecular cloud or protoplanetary disk by a nearby core-collapse supernova (SN Type II) and uniformly distributed in the solar system; CAI formation started shortly after injection of super(26)Al and lasted less than 20,000 yr. Here we show that CAIs from the metal-rich carbonaceous chondrites Acfer 214 (CH) and Isheyevo (CH/CB-like) have a bimodal distribution of super(26)Mg*. Most CAIs composed of grossite (CaAl sub(4)O sub(7)), hibonite (CaAl sub(12)O sub(19)), Al-rich pyroxene, perovsklte (CaTiO sub(3)), and gehlenitic melilite (Ca sub(2)Al sub(2)SiO sub(7)-Ca sub(2)MgSl sub(2)O sub(7)) show either unresolvable or small super(26)Mg* corresponding to an initial super(26)Al/ super(27)Al ratio of similar to 4 x 10 super(-7). Some of the grossite-rich CAIs and the less refractory inclusions composed of melilite, spinel (MgAl sub(2)O sub(4)), Al, Ti-pyroxene, and anorthite (CaAl sub(2)Si sub(2)O sub(8)) have large super(26)Mg* corresponding to the initial super(26)Al/ super(27)Al ratio of similar to 5 x 10 super(-5). The super(26)Al-poor and super(26)Al-rich CAIs are characterized by super(16)O-rich ( Delta super(17)O < -20 %o) compositions typical of CAIs. We suggest that the super(26)Al-poor and super(26)Al-rich CAIs represent samples of at least two generations of CAIs formed before and after injection of super(26)Al into the solar system, respectively. Model yields of super(16)O, super(17)O, and super(18)O for SN wind prior to explosion, during explosion, and in total, combined with the observations that both super(26)Al-poor and super(26)Al-rich CAIs plot on a three-isotope oxygen diagram ( delta super(17)O vs. delta super(18)O) along a single line with a slope of similar to 1 are consistent with injection of super(26)Al with the SN wind into the protosolar molecular cloud rather with the SN explosion into the disk.
La2O3 nanoparticles stabilized on carbon nanoflake (CNF) matrix were synthesized and graphitized to produce core-shell structures La2O3/CNFs@C. Further oxidation of these structures by nitric acid ...vapors for 1, 3 or 6 h was performed, and surface-oxidized particles La2O3/CNFs@C_x (x = 1, 3, 6) were produced. Bulk and surface compositions of La2O3/CNFs@C and La2O3/CNFs@C_x were investigated by thermogravimetric analysis and X-ray photoelectron spectroscopy. With increasing the duration of oxidation, the oxygen and La2O3 content in the La2O3/CNFs@C_x samples increased. The electronic structures of samples were assessed by electron paramagnetic resonance. Two paramagnetic centers were associated with unpaired localized and mobile electrons and were registered in all samples. The correlation between bulk and surface compositions of the samples and their electronic structures was investigated for the first time. The impact of the ratio between sp2- and sp3-hybridized C atoms, the number and nature of oxygen-containing groups on the surface and the presence and proportion of coordinated La atoms on the EPR spectra was demonstrated.
– Detailed petrologic and oxygen isotopic analysis of six forsterite‐bearing Type B calcium‐aluminum‐rich inclusions (FoBs) from CV3 chondrites indicates that they formed by varying degrees of ...melting of primitive precursor material that resembled amoeboid olivine aggregates. A continuous evolutionary sequence exists between those objects that experienced only slight partial melting or sintering through objects that underwent prolonged melting episodes. In most cases, melting was accompanied by surface evaporative loss of magnesium and silicon. This loss resulted in outer margins that are very different in composition from the cores, so much so that in some cases, the mantles contain mineral assemblages that are petrologically incompatible with those in the cores. The precursor objects for these FoBs had a range of bulk compositions and must therefore have formed under varying conditions if they condensed from a solar composition gas. Five of the six objects show small degrees of mass‐dependent oxygen isotopic fractionation in pyroxene, spinel, and olivine, consistent with the inferred melt evaporation, but there are no consistent differences among the three phases. Forsterite, spinel, and pyroxene are 16O‐rich with Δ17O ∼ −24‰ in all FoBs. Melilite and anorthite show a range of Δ17O from −17‰ to −1‰.
Coarse-grained igneous Ca,Al-rich inclusions (CAIs) in CV (Vigarano group) carbonaceous chondrites have typically heterogeneous O-isotope compositions with melilite, anorthite, and high-Ti (>10 wt% ...TiO2) fassaite being 16O-depleted (Δ17O up to ∼ − 3 ± 2‰) compared to hibonite, spinel, low-Ti (<10 wt% TiO2) fassaite, Al-diopside, and forsterite, all having close-to-solar Δ17O ∼ − 24 ± 2‰. To test a hypothesis that this heterogeneity was established, at least partly, during aqueous fluid-rock interaction, we studied the mineralogy, petrology, and O-isotope compositions of igneous CAIs CG-11 (Type B), TS-2F-1, TS-68, and 818-G (Compact Type A), and 818-G-UR (davisite-rich) from Allende (CV > 3.6), and E38 (Type B) from Efremovka (CV3.1–3.4). Some of these CAIs contain (i) eutectic mineral assemblages of melilite, Al,Ti-diopside, and ± spinel which co-crystallized and therefore must have recorded O-isotope composition of the eutectic melt; (ii) isolated inclusions of Ti-rich fassaite inside spinel grains which could have preserved their initial O-isotope compositions, and/or (iii) pyroxenes of variable chemical compositions which could have recorded gas–melt O-isotope exchange during melt crystallization and/or postcrystallization exchange controlled by O-isotope diffusivity. If these CAIs experienced isotopic exchange with an aqueous fluid, O-isotope compositions of some of their primary minerals are expected to approach that of the fluid.
We find that in the eutectic melt regions composed of highly-åkermanitic melilite (Åk65−71), anorthite, low-Ti fassaite, and spinel of E38, spinel, fassaite, and anorthite are similarly 16O-rich (Δ17O ∼ − 24‰), whereas melilite is 16O-poor (Δ17O ∼ − 1‰). In the eutectic melt regions of CG-11, spinel and low-Ti fassaite are 16O-rich (Δ17O ∼ − 24‰), whereas melilite and anorthite are 16O-poor (Δ17O ∼ − 3‰). In TS-2F-1, TS-68, and 818-G, melilite and high-Ti fassaite grains outside spinel have 16O-poor compositions (Δ17O range from − 12 to − 3‰); spinel is 16O-rich (Δ17O ∼ − 24‰); perovskite grains show large variations in Δ17O, from − 24 to − 1‰. Some coarse perovskites are isotopically zoned with a 16O-rich core and a 16O-poor edge. Isolated high-Ti fassaite inclusions inside spinel grains are 16O-rich (Δ17O ∼ − 24‰), whereas high-Ti fassaite inclusions inside fractured spinel grains are 16O-depleted: Δ17O range from − 12 to − 3‰. In 818-G-UR, davisite is 16O-poor (Δ17O ∼ − 2‰), whereas Al-diopside of the Wark-Lovering rim is 16O-enriched (Δ17O < − 16‰). On a three-isotope oxygen diagram, the 16O-poor melilite, anorthite, high-Ti fassaite, and davisite in the Allende CAIs studied plot close to O-isotope composition of an aqueous fluid (Δ17O ∼ − 3 ± 2‰) inferred from O-isotope compositions of secondary minerals resulted from metasomatic alteration of the Allende CAIs.
We conclude that CV igneous CAIs experienced post-crystallization O-isotope exchange that most likely resulted from an aqueous fluid-rock interaction on the CV asteroid. It affected melilite, anorthite, high-Ti fassaite, perovskite, and davisite, whereas hibonite, spinel, low-Ti fassaite, Al-diopside, and forsterite retained their original O-isotope compositions established during igneous crystallization of CV CAIs. However, we cannot exclude some gas–melt O-isotope exchange occurred in the solar nebula. This apparently “mineralogically-controlled” exchange process was possibly controlled by variations in oxygen self-diffusivity of CAI minerals. Experimentally measured oxygen self-diffusion coefficients in CAI-like minerals are required to constrain relative roles of O-isotope exchange during aqueous fluid–solid and nebular gas–melt interaction.
Electronic structure of carbon nanotube network Ulyanov, Alexander N.; Suslova, Evgeniya V.; Savilov, Serguei V.
Mendeleev communications,
January-February 2023, 2023-01-00, Letnik:
33, Številka:
1
Journal Article
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Covalently cross-linked carbon nanotube network has been synthesized using spark plasma sintering followed by nitric acid treatment. EPR investigation of its electronic structure in ...comparison with pristine carbon nanotubes has revealed that the covalent cross-linking leads to a decrease in the number of paramagnetic centers, while the oxidation results in an increase in their number. The oxidation affects the cross-linked and pristine materials in a different manner
— Fine‐grained, spinel‐rich inclusions in the reduced CV chondrites Efremovka and Leoville consist of spinel, melilite, anorthite, Al‐diopside, and minor hibonite and perovskite; forsterite is very ...rare. Several CAIs are surrounded by forsterite‐rich accretionary rims. In contrast to heavily altered fine‐grained CAIs in the oxidized CV chondrite Allende, those in the reduced CVs experienced very little alteration (secondary nepheline and sodalite are rare). The Efremovka and Leoville fine‐grained CAIs are 16O‐enriched and, like their Allende counterparts, generally have volatility fractionated group II rare earth element patterns. Three out of 13 fine‐grained CAIs we studied are structurally uniform and consist of small concentrically zoned nodules having spinel ± hibonite ± perovskite cores surrounded by layers of melilite and Al‐diopside. Other fine‐grained CAIs show an overall structural zonation defined by modal mineralogy differences between the inclusion cores and mantles. The cores are melilite‐free and consist of tiny spinel ± hibonite ± perovskite grains surrounded by layers of anorthite and Al‐diopside. The mantles are calcium‐enriched, magnesium‐depleted and coarsergrained relative to the cores; they generally contain abundant melilite but have less spinel and anorthite than the cores. The bulk compositions of fine‐grained CAIs generally show significant fractionation of Al from Ca and Ti, with Ca and Ti being depleted relative to Al; they are similar to those of coarsegrained, type C igneous CAIs, and thus are reasonable candidate precursors for the latter. The finegrained CAIs originally formed as aggregates of spinel‐perovskite‐melilite ± hibonite gas‐solid condensates from a reservoir that was 16O‐enriched but depleted in the most refractory REEs. These aggregates later experienced low‐temperature gas‐solid nebular reactions with gaseous SiO and Mg to form Al‐diopside and ±anorthite. The zoned structures of many of the fine‐grained inclusions may be the result of subsequent reheating that resulted in the evaporative loss of SiO and Mg and the formation of melilite. The inferred multi‐stage formation history of fine‐grained inclusions in Efremovka and Leoville is consistent with a complex formation history of coarse‐grained CAIs in CV chondrites.
— –The CH/CB‐like chondrite Isheyevo consists of metal‐rich (70–90 vol% Fe,Ni‐metal) and metal‐poor (7–20 vol% Fe,Ni‐metal) lithologies which differ in size and relative abundance of Fe,Ni‐metal and ...chondrules, as well as proportions of porphyritic versus non‐porphyritic chondrules. Here, we describe the mineralogy and petrography of Ca,Al‐rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) in these lithologies. Based on mineralogy, refractory inclusions can be divided into hibonite‐rich (39%), grossite‐rich (16%), melilite‐rich (19%), spinel‐rich (14%), pyroxene‐anorthite‐rich (8%), fine‐grained spinel‐rich CAIs (1%), and AOAs (4%). There are no systematic differences in the inclusion types or their relative abundances between the lithologies. About 55% of the Isheyevo CAIs are very refractory (hibonite‐rich and grossite‐rich) objects, 20–240 μm in size, which appear to have crystallized from rapidly cooling melts. These inclusions are texturally and mineralogically similar to the majority of CAIs in CH and CB chondrites. They are distinctly different from CAIs in other carbonaceous chondrite groups dominated by the spinel‐pyroxene ± melilite CAIs and AOAs. The remaining 45% of inclusions are less refractory objects (melilite‐, spinel‐ and pyroxene‐rich CAIs and AOAs), 40–300 μm in size, which are texturally and mineralogically similar to those in other chondrite groups. Both types of CAIs are found as relict objects inside porphyritic chondrules indicating recycling during chondrule formation.
We infer that there are at least two populations of CAIs in Isheyevo which appear to have experienced different thermal histories. All of the Isheyevo CAIs apparently formed at an early stage, prior to chondrule formation and prior to a hypothesized planetary impact that produced magnesian cryptocrystalline and skeletal chondrules and metal grains in CB, and possibly CH chondrites. However, some of the CAIs appear to have undergone melting during chondrule formation and possibly during a major impact event. We suggest that Isheyevo, as well as CH and CB chondrites, consist of variable proportions of materials produced by different processes in different settings: 1) by evaporation, condensation, and melting of dust in the protoplanetary disk (porphyritic chondrules and refractory inclusions), 2) by melting, evaporation and condensation in an impact generated plume (magnesian cryptocrystalline and skeletal chondrules and metal grains; some igneous CAIs could have been melted during this event), and 3) by aqueous alteration of pre‐existing planetesimals (heavily hydrated lithic clasts). The Isheyevo lithologies formed by size sorting of similar components during accretion in the Isheyevo parent body; they do not represent fragments of CH and CB chondrites.
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