Polyaromatic Layers Research Articles

Chemical Structure Transformations in Kerogen from Longmaxi Shales in Response to Tectonic Stress as Investigated by HRTEM, FTIR, and 13C NMR

Kerogen molecular structure controls the micropore (<2 nm diameter) evolution in shale and exerts a significant impact on shale gas adsorption, desorption, and diffusion. However, the influence of tectonic deformation on kerogen structure and organic micropores needs intensive study. Our study mainly focuses on the transformations in the extracted kerogen structure and organic micropores of Longmaxi shale during tectonic deformation. Vitrinite reflectance measurement (VRM) and Raman spectroscopy (RS) were utilized to determine the maturity of organic matter. Organic pore network attributes of kerogen samples were estimated using CO2 adsorption experiments. High-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), and 13C nuclear magnetic resonance (13C NMR) were utilized to interpret the kerogen molecular structures of these samples. VRM and RS results show that Longmaxi shale has reached the wet gas window. Adsorption analyses of CO2 indicate that kerogen samples in shale with strong deformation have larger micropore volume and surface area (<2 nm). 13C NMR and FTIR results reveal that the tectonic stress may promote the shedding of aliphatic carbon. HRTEM images exhibit that aromatic rings with a size of 3 × 3 account for the largest proportion in all kerogen samples, which indicates that the kerogen samples have reached a high thermal evolution level, consistent with the Raman experiment. For weakly deformed shale samples, 66.5 and 88.8% of the total number of aromatic rings in LZ-1 and LZ-4 kerogen belong to the major direction (within a 45° range). In the most strongly deformed sample, LZ-2, distribution orientations of aromatic fringes are dispersed and primarily concentrated at 15–105°. Such disorientation of nanometer-sized polyaromatic layers in the strongly deformed sample creates a nanopore network in organic matter (OM) that increases the micropore volume and surface area. These findings from integrated approaches can provide a new perspective of adsorbed gas enrichment in the complex tectonic areas.

Investigation of the structural characteristics of vitrinites of some coals of the Kuznetsk Basin

In this work, the structural parameters of vitrinites of coal of various degrees of metamorphism were investigated by X-ray diffraction methods. Vitrinite concentrates were obtained from coal of the Kuznetsk Basin by the method of fractional analysis of coals, according to which the studied fuel is stratified into fractions in liquids of different densities. The following X-ray structural parameters were analyzed: the number of carbon atoms in the lamellae (natC), the longitudinal size of the lamellae, the height of their stacking (La and Lc), the number of polyaromatic layers in the stack (N), and the packing density of the lamellae (ρ). It was shown that in vitrinite concentrates, an increase in all analyzed structural parameters (Lc, La, natC, N, ρ) is observed with an increase in the degree of metamorphism, at the same time, a decrease in the value of the interplanar distance (d002) is observed. The performed X-ray diffraction studies showed that the average number of layers in a package and carbon atoms per monolayer in the samples of vitrinite concentrates of bituminous coals of high stages of metamorphism (Ro, r = 1.41%) varies from 7 to 8 and 14-15, respectively. A correlation was found between the linear nature of the number of arene layers and the height of their packing. The results obtained are in good agreement with the literature data given for coals of various deposits.

Resonant Raman scattering of anthracene‐based carbons in the secondary carbonization stage

AbstractThe Raman spectra of graphene‐based matter exhibit a set of defect/disorder‐induced bands. The D band, which exhibits a strong dispersion up to ~50 cm−1/eV, comes from transverse optical phonons around K or K′ in the first Brillouin zone and involves an intervalley double resonance (DR) Raman process. In the present work, resonant Raman scattering (lines ranging from 1.58 to 3.81 eV) is used to study the unusual behavior of the one‐phonon Raman band of a carbonaceous material (anthracene‐based carbon which is one of the graphitizable carbons) upon its secondary carbonization stage (450°C–1000°C). While the G band appears to be nondispersive, the D band exhibits a change in both position and intensity. Its dispersion progressively rises from ~6 cm−1/eV to values close to what is usually observed in defected graphene‐based systems when anthracene‐based carbon becomes almost pure. This evolution appears to be correlated with a release of hydrogen (fixed on the edges of polyaromatic layers) questioning their role in changing the D band resonance conditions.

Исследование структурных характеристик витринитов некоторых углей Кузнецкого бассейна

The article is devoted to research of the main structural parameters of vitrinites of bituminous coals of various metamorphism degrees carried out by methods of X-ray phase and X-ray structural analysis. Vitrinite concentrates were obtained from coal of the Kuznetsk Basin. The main X-ray structural parameters were estimated: the number of carbon atoms in the lamellae (natC), the longitudinal size of the lamellae, and the height of their stacking (La and Lc), the number of polyaromatic layers in the package (N), and the packing density of the lamellae (ρ). It is shown in the work that in vitrinite concentrates, an increase in all analyzed structural parameters (Lc, La, natC, N, ρ) is observed with an increase in the degree of metamorphism, at the same time, a decrease in the value of the interplanar distance (d002) is observed. The XRD analysis showed that for the average number of layers in a package and carbon atoms per monolayer, in the samples of vitrinite concentrates of bituminous coals of high stages of metamorphism (Ro, r = 1.41%) varies from 7 to 8 and 14-15, respectively. It was found a correlation between the linear nature of the number of polyarene-layers and the height of their stacking. The results obtained were in good agreement with the literature data given for coals of various deposits.

X-Ray Structural Analysis of Vitrinites in Coal at Different Metamorphic Stages

By X-ray structural analysis, the following structural parameters of vitrinite concentrates from coal of different metamorphic stages are determined: the number of carbon atoms in each lamella (nC), the width of the lamellas (La), their stacking height (Lc), the number of polyaromatic layers in each stack (N), and the packing density of the lamellas (ρ). Later metamorphic stages are associated with increase in Lc, La, nC, N, and ρ in the vitrinite concentrates, with symbatic decrease in the interplane distance (d002). For vitrinite samples from coal of later metamorphic stages (Ro,r = 1.41%), the mean number of layers in a stack is 7–8, and the number of carbon atoms per layer is 14–15. The number of arene layers is linearly related to the stack height. These results are in good agreement with literature data for coal of different metamorphic stages.

Effect of CO2 on the characteristics of soot derived from coal rapid pyrolysis

The present work aims to investigate the effects of a CO2-rich atmosphere on the characteristics of coal-derived soot. The rapid pyrolysis of Shenfu bituminous coal was conducted in a Drop tube furnace (DTF) in N2 and CO2 atmospheres with a wall temperature of 1073–1473 K and residence time below 700 ms. The yields and microstructure characteristics of N2-soot and CO2-soot were analysed by using a series of techniques (elemental analysis, HRTEM, Raman, XRD, FT-IR and thermogravimetry techniques). CO2 enhanced the soot formation and proceeded the dehydrogenation. CO2 improved the order of internal carbon lattices, enhanced the lateral extension of carbon nanostructures, decreased the interplanar spacing of the graphene layers and also promoted the stack of polyaromatic layers. The variations of the SOLO, DUO, TRIO and QUARTO structures were also analysed, and the contribution of CO2 was found to reduce the defects of the basic structure units (BSU). The defects of soot were an important indication of the initial gasification reactivity. Overall, CO2-soot was more mature and low active than N2-soot.

Raman microspectroscopy characterization of carbon blacks: Spectral analysis and structural information

The aim of this paper is to describe carbonisation and partial graphitization of carbon blacks (CB). Raman spectrometry is used to investigate a series of five CB grades during heat treatment (up to 2600°C). Obtained results are discussed by comparing Raman data with X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) observations. For Raman spectra interpretation, the usual curve fitting method proposed by Sadezky et al. for soot and disordered carbonaceous material is applied. As the same procedure can be applied over all the heat-treatment temperature range, the determination of band parameters from five band decompositions appears to be the most convenient to follow the CB’s structural improvement. We demonstrate that only a partial graphitization takes place and the graphitizability is limited by the diameter of the primary particles. Our observations generalize the results obtained for cokes: graphitization degree of carbonaceous materials after the heat-treatment is limited by the diameter of the volumes within polyaromatic layers are oriented in parallel.

Evolution of Barnett Shale organic carbon structure and nanostructure with increasing maturation

The organic nanopore network of shales is believed to be the location of hydrocarbon trapping in source rocks. Better understanding of organic carbon structure and nanostructure constitutes a key point for estimating the oil and gas in-place at the local and basinal scale. Here we characterize, a maturation series from Mississippian Barnett Shale at multiple scales down to the nanometer scale. Organic petrography, Rock–Eval pyrolysis and Raman microspectroscopy are used to determine the organic matter properties (e.g. maturity, type, TOC content). Organic pore network attributes (e.g. pore size distribution, surface area, polyaromatic layers characteristics) are estimated using low pressure gas adsorption analyses and direct imaging by high-resolution transmission electron microscopy (HRTEM). Based on Raman data we show that Barnett Shale organic matter has only reached the level of carbonization, even within overmature samples; graphitization has not yet been triggered. Interestingly, the investigated samples exhibit an additional broad Raman band centered at about 1480cm−1, likely due to the presence of retained hydrocarbons within the organic matter nanoporosity. Low pressure gas adsorption analyses evidence a positive correlation between surface areas, mesopores (pores of about 2–50nm of diameter) and maturity level. HRTEM images confirm Raman data: even the overmature organic matter remains disordered. Such disorientation of nanometer sized polyaromatic layers creates a nanoporosity network in organic matter that appears most developed in samples of gas window maturity. Furthermore, carbon nanoparticles of concentric nanostructures, known to result from the thermal cracking of hydrocarbons, are detected in overmature samples.

D-depleted organic matter and graphite in the Abee enstatite chondrite

A combination of NanoSIMS and High resolution transmission electron microscopy (HRTEM) imaging along with Raman spectroscopy was used to characterize the carbonaceous phases in HF/HCl residue of the Abee enstatite chondrite. This acid residue hosts a very D-depleted component (δD=−480‰). This residue is a mixture of graphite and highly disordered insoluble organic matter. The latter exhibits a significant mesoporosity (i.e., 200–500nm scale), and also shows concentric and elongated stacks of polyaromatic layers. Insoluble organic matter is shown to be the most D-depleted component in Abee. We also determined, by using NanoSIMS, carbon isotopic composition of graphite and insoluble organic matter in the acid residue (δ13C=−11.3±2.9‰ and −28.4±2.2‰, respectively).We identified graphite in metal-rich clasts and in the matrix of Abee, associated with enstatite, sulfide and metal, but we could not localize highly disordered organic matter in our section. Regardless, given the vulnerability of organic matter to thermal degradation, we suggest that it was added to Abee parent body during the latest stage of its formation, after any thermal metamorphism or partial melting of Abee parent body.A genetic link between organic matter and graphite in Abee is excluded based on our HRTEM and carbon isotopic data. The differences in carbon isotopic compositions between these phases are consistent with previous data obtained by stepwise heating experiments and indicate that graphite is not derived from a pure thermal solid-state graphitization of the organic matter. Rather, we suggest that graphite precipitated from a melt rich in C during the partial melting of the Abee parent body. Insoluble organic matter in Abee has the lowest D/H ratio among the extraterrestrial organics. Organics in most carbonaceous and ordinary chondrites are believed to have been subjected to irradiations in low temperature environments, resulting in a dramatic isotopic fractionation through exchange and reaction with gaseous molecular hydrogen during their synthesis. In contrast, Abee organic matter was likely synthesized in a neutral (i.e., not ionized) environment where thermodynamic processes at equilibrium most likely controlled its isotopic composition.This organic matter could have been accreted in a minor component of Abee like the dark inclusions without (or prior to) exposure to the radiation responsible for D enrichments in other meteoritic organics. During the last brecciation events that have affected the Abee parent body, these inclusions could have been mixed with other Abee components. The properties of this organic matter can be interpreted as an indication that thermodynamic processes acted in the synthesis of organic matter in the protosolar disk, in addition to ion/molecule and gas/grains reaction witnessed by the D-rich insoluble organic matter contained in carbonaceous chondrites.

High resolution TEM of chondritic carbonaceous matter: Metamorphic evolution and heterogeneity

Abstract– The insoluble carbonaceous matter from 12 chondrites (CI, CM, CO, CV, EH, and UOC), was characterized by high resolution transmission electron microscopy (HRTEM). Besides ubiquitous nanoglobules, the insoluble organic matter from petrologic type 1 and 2 chondrites and Semarkona (LL 3.0) is composed of a highly disordered polyaromatic component. No structural differences were observed between these IOMs, in agreement with the limited thermal metamorphism they all experienced. In chondrites of petrologic type &gt;3.0, the evolution of the IOM is controlled by the extent of thermal metamorphism. The polyaromatic layers, shorter than 1 nm in petrologic type ≤3.0 chondrites, grow up to sizes between 5 and 10 nm in petrologic type &gt;3.6 chondrites, contributing to the increase of the degree of structural order. In addition, we find rare, but ubiquitous onion‐like carbons, which may be the product of nanodiamond graphitization. The insoluble carbonaceous matter of the enstatite chondrite Sahara 97096 (EH 3) is different from the other meteorites studied here. It is more heterogeneous and displays a high abundance of graphitized particles. This may be the result of a mixture between (1) the disordered carbon located in the matrix, and (2) catalytic graphitized phases associated with metal, potentially originating from partial melting events. The structural and nanostructural evolution are similar in all IOMs. This suggests that the structure of the accreted precursors and the parent body conditions of their secondary thermal modifications (temperature, duration, and pressure) were similar. The limited degree of organization of the most metamorphosed IOMs compared with terrestrial rocks submitted to similar temperature suggests that the conditions are not favorable to graphitization processes, due to the chemical nature of the precursor or the lack of confinement pressure.

Nano structure of low crystallinity carbon materials analyzed by using high energy X-ray diffraction

Abstract In this study, we tried to characterize a kind of low crystallinity carbon materials. The structure of polyparaphenylene(PPP)-based carbon was analyzed by means of high energy X-ray diffraction using the apparatus of SPring-8. The experimental results revealed the existence of basic structural units (BSU) in the highly disordered materials like PPP-based carbon. It is thought that the PPP-based carbons consist of small turbostratic particles, which have a few piled up poly-aromatic layers. The structure of the PPP-based carbon which seemed to be amorphous was estimated to have hexagonal carbon layers with the size of up to 1 nm. The pores in the PPP-based carbon seem to be clearances formed among the BSUs and amorphous carbon. The pore size of PPP-based carbon was estimated from the result of N2 absorption measurement. The experimental results suggested that the lithium ion charge mechanism in the PPP-based carbon differs from that in graphite.

High-Resolution Transmission Electron Microscopy Studies of Graphite Materials Prepared by High-Temperature Treatment of Unburned Carbon Concentrates from Combustion Fly Ashes

High-resolution transmission electron microscopy (HRTEM) has been used in this work to study the microstructural (structure and microtexture) changes occurring during the high-temperature treatment of the unburned carbon concentrates from coal combustion fly ashes. Emphasis was placed on two aspects: (i) the development of graphitic carbon structures and (ii) the disordered carbon forms remaining in the graphitized samples. In addition, by coupling HRTEM with energy-dispersive spectroscopy, the transformations with the temperature of the inorganic matter (mainly iron- and silicon-based phases) of the unburned carbon concentrates were evidenced. The HRTEM results were compared to the averaged structural order of the materials as evaluated by X-ray diffraction (XRD) and Raman spectroscopy. As indicated by XRD and Raman parameters, more-ordered materials were obtained from the unburned carbon concentrates with higher mineral/inorganic matter, thus inferring the catalytic effect of some of their components. However, the average character of the information provided by these instrumental techniques seems to be inconclusive in discriminating between carbon structures with different degrees of order (stricto sensu graphite, graphitic, turbostratic, etc.) in a given graphitized unburned carbon. Unlike XRD and Raman, HRTEM is a useful tool for imaging directly the profile of the polyaromatic layers (graphene planes), thus allowing the sample heterogeneity to be looked at, specifically the presence of disordered carbon phases.

Multiscale organisation of organic matter associated with gold and uranium minerals in the Witwatersrand basin, South Africa

Abstract Organic matter from the northern part of the Early Proterozoic Witwatersrand basin (Carbon Leader reef) was investigated using optical (OM) and transmission electron (TEM) microscopes, completed by XRD analysis. The multiscale organization (texture, microtexture, structure) of the organic matter was observed in order to gain information about the processes which affected organic material after its deposition in sediments. In the micrometre scale (optical microscope), the shape and size of the Reflectance Indicating Surface (RIS) of the organic matter were determined. The organic matter reveals a prevailing biaxial symmetry. The size of RIS is generally dependent on uranium and increases with increasing uranium concentration. Furthermore, it appears that more than one RIS is present within the scale of a single sample, each with a different symmetry and size. The presence of domains differing in organisation of the aromatic framework was confirmed by TEM observation in the DF mode. The aromatic skeleton of organic matter is composed of short, often crumpled, mostly isolated (non-stacked) polyaromatic layers whose fringe length corresponds to 3–16 aromatic rings. The data indicate reorganization of the polyaromatic organic matter structure under stress in high pressure and relatively low temperature conditions. The organic matter was in a solid state within the rocks before the pressure event.

Bone mineral density of spine and femur in healthy Taiwan adolescents

A combination of NanoSIMS and High resolution transmission electron microscopy (HRTEM) imaging along with Raman spectroscopy was used to characterize the carbonaceous phases in HF/HCl residue of the Abee enstatite chondrite. This acid residue hosts a very D-depleted component (δD = −480‰). This residue is a mixture of graphite and highly disordered insoluble organic matter. The latter exhibits a significant mesoporosity (i.e., 200–500 nm scale), and also shows concentric and elongated stacks of polyaromatic layers. Insoluble organic matter is shown to be the most D-depleted component in Abee. We also determined, by using NanoSIMS, carbon isotopic composition of graphite and insoluble organic matter in the acid residue (δ13C = −11.3 ± 2.9‰ and −28.4 ± 2.2‰, respectively).We identified graphite in metal-rich clasts and in the matrix of Abee, associated with enstatite, sulfide and metal, but we could not localize highly disordered organic matter in our section. Regardless, given the vulnerability of organic matter to thermal degradation, we suggest that it was added to Abee parent body during the latest stage of its formation, after any thermal metamorphism or partial melting of Abee parent body.A genetic link between organic matter and graphite in Abee is excluded based on our HRTEM and carbon isotopic data. The differences in carbon isotopic compositions between these phases are consistent with previous data obtained by stepwise heating experiments and indicate that graphite is not derived from a pure thermal solid-state graphitization of the organic matter. Rather, we suggest that graphite precipitated from a melt rich in C during the partial melting of the Abee parent body. Insoluble organic matter in Abee has the lowest D/H ratio among the extraterrestrial organics. Organics in most carbonaceous and ordinary chondrites are believed to have been subjected to irradiations in low temperature environments, resulting in a dramatic isotopic fractionation through exchange and reaction with gaseous molecular hydrogen during their synthesis. In contrast, Abee organic matter was likely synthesized in a neutral (i.e., not ionized) environment where thermodynamic processes at equilibrium most likely controlled its isotopic composition.This organic matter could have been accreted in a minor component of Abee like the dark inclusions without (or prior to) exposure to the radiation responsible for D enrichments in other meteoritic organics. During the last brecciation events that have affected the Abee parent body, these inclusions could have been mixed with other Abee components. The properties of this organic matter can be interpreted as an indication that thermodynamic processes acted in the synthesis of organic matter in the protosolar disk, in addition to ion/molecule and gas/grains reaction witnessed by the D-rich insoluble organic matter contained in carbonaceous chondrites.

Temperature dependence for the frequency position of the low-frequency dielectric dispersion in the polyacenequinone spectrum and quantum measurements

The current state of the art in the physics of mesoscopic and strongly correlated electron systems [1] necessitates an appeal to the conceptual tenets of quantum mechanics [2, 3]. We associate the low-frequency (LF) dispersion region in the dielectric spectrum of polyacenequinone (PAQ) synthesized by polycondensation of pyrene with pyromellitic dianhydride at 300 ° C with the phenomenon of quantum coherence in a system of donor‐acceptor (D‐A) complexes. We imply a system of atmospheric oxygen intercalated into graphite-like fragments of the surface-layer structure of PAQ granules and two-dimensional polyaromatic layers [4]. In the present paper, the temperature behavior of the LF maximum in the frequency dependence of the tangent δ ( ν ) of the dielectric-loss angle δ ( ν ) is interpreted on the basis of a scheme of quantum measurements that was recently proposed [3]. For definiteness, we assume that the intercalated oxygen interacts with the π -conjugate system of only one of the adjacent polyaromatic layers. The problem of possible elementary mechanisms of the relaxation polarization is beyond the scope of the present discussion. In the temperature dependence of the position ν m LF

Quantitative high-resolution transmission electron microscopy: a promising tool for carbon materials characterization

Carbon materials usually exhibit a multiscale organization from the subnanometric to the millimetric scales. Such an organization is the fingerprint of the conditions of formation and is responsible for numerous properties. High-resolution transmission electron microscopy (HRTEM) is a relevant tool to image directly the profile of the polyaromatic layers forming the skeleton of these carbons. Quantitative data are required to accurately describe such multiscale organization, to decipher the formation conditions and to foresee industrial properties. In this respect, an in-house image analysis procedure was developed based on the skeletonization of the HRTEM images, followed by the extraction of structural and microtextural data. Thanks to these quantitative data, the organization of disordered carbons can be relevantly revisited. Some applications of this approach are presently tested in the field of carbon characterization, in relation with environment problems, earth or universe sciences, or industrial carbon materials.

In situ X-ray diffraction performed on mesophase formation during the carbonization of acenaphtylene

The principal steps of mesophase formation which appear during the acenaphtylene carbonization were studied by in situ X-ray diffraction. Additional information about the process was also obtained by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and infrared spectroscopy. We observed firstly the melting of acenaphtylene between 90 and 100°C which undergoes a polymerization process from 200°C/230°C to 350°C/380°C. Then cracking of polyacenaphtylene at 400°C leads to a liquid phase containing principally decacyclene molecules. The liquid recrystallizes by cooling in a structure that we have previously identified as the high-temperature crystalline φ 2 phase of decacyclene. In the case of acenaphtylene pyrolysis, the φ 2 phase melting point is depressed due to the other molecular species which constitute the final cracking blending. At 420°C the liquid pitch turns into a new phase which we call φ 2′ which would have a discotic type structure with a short range order. The high amount of free radicals in the acenaphtylene pitch at such a temperature facilitates the linkage of decacyclene molecules through the φ 2′ phase. This process promotes the formation of polyaromatic layers which leads to the ordering existing in the Brooks and Taylor mesophase spheres.