Graphite Crystallite Size Research Articles

Unveiling the microscopic compression failure behavior of mesophase-pitch-based carbon fibers for improving the compressive strength of their polymer composites

Mesophase-pitch-based carbon fiber (MPCF) reinforced polymer (MPCFRP) composites show great potential for aerospace applications due to their excellent thermal conductivity and dimensional stability. However, the low compressive strength severely limits their application in high load-bearing areas. To address this issue, MPCF-A with a split-radial structure and MPCF-B with a skin-core structure were meticulously prepared by fiber structure regulation. The compression failure behavior of MPCFs at the monofilament and the microregion levels was investigated using the tensile recoil method and in-situ micropillar compression technique. MPCF-A exhibits the failure mode of petal-like lamellar separation due to axial crack penetrating along the (002) crystal plane of graphite layers, with the compressive strength of the core region (391 MPa) being higher than that of the skin region (360 MPa). Conversely, MPCF-B demonstrates a large transverse fracture in the skin region during damage, along with uniform microcracks in the core region. Notably, the compressive strength of the core region (547 MPa) significantly exceeds that of the skin region (456 MPa). Furthermore, the compressive strength of MPCF-B monofilaments (583 MPa) is higher than that of MPCF-A (462 MPa), attributed to factors such as the smaller graphite crystallite size (La = 36.54 nm, Lc = 26.75 nm), lower crystallite orientation (Z = 10.21°, R = 0.25), smaller pore size (Rg = 9.56 nm), and higher amorphous carbon content (g = 69.77%, K = 20.38). Consequently, the compressive strength of MPCFRP-B (232 MPa) is enhanced by 30.3% compared to MPCFRP-A.

Role of sodium sulfate in electrical conductivity and structure of lignin-derived carbons

Lignin is a promising renewable alternative to fossil fuels for producing carbon materials such as carbon fibers, activated carbons, or carbon black. Despite extensive research, lignin-derived carbon materials show limited graphitization relative to comparable petroleum-derived carbons. Further, lignin-derived carbons show high variation in graphitization and electrical conductivity depending on the source of the lignin. Herein, nine lignins, derived from various feedstocks and isolation procedures, are pyrolyzed to produce biochar at 1100∘C. These lignins have a range of chemical compositions, carbon structures, and particle sizes. As a result, the pyrolysis behavior of these lignins varies, with powdered, clumped powder, and “foam” biochar morphologies resulting from finely powdered lignin. The produced biochars vary widely in both electrical conductivity, from 0.19 to 19 S/cm, and in-plane graphitic crystallite size, from 3.4 to 41.2Å. A significant decrease in electrical conductivity is identified when Na2SO4 is removed from lignin, accompanied by an increase in graphitic crystallite size. Based on this finding, a quadratic relationship between biochar graphitic crystallite aspect ratio and electrical conductivity is proposed that builds on established quasi-percolation models for biochar electrical conductivity.

The effect of co-pyrolysis of bamboo waste and polypropylene on biomass deoxygenation and carbonization processes

While numerous research studies have delved into the co-pyrolysis of biomass and plastic waste, limited attention has been devoted to comprehending the interaction mechanism that impacts biomass deoxygenation and carbonization. Therefore, this study explores the co-effect of temperature and polypropylene blending ratio on co-pyrolysis reaction kinetics, distribution of oxygenates/hydrocarbons, as well as the evolution of biochar structure. At a blending ratio of 0.5, the co-pyrolysis exhibits the lowest activation energy (146 kJ/mol), approximately 25.1 % lower than that required for individual pyrolysis. The interaction between bamboo waste with polypropylene increases the O-abstraction process, resulting in the creation of O-containing free radicals and hydrocarbon compounds. The peak proportion of aromatic compounds, reaching approximately 69.5 %, is observed at 700 °C when the blending ratio is 0.5. The H-abstraction process converts large-molecular alkanes into H free radicals and tiny-molecular unsaturated hydrocarbons. The aliphatic functional group content diminishes as the polypropylene ratio increases. The maximum specific surface area (7.70 m2/g) and pore volume (21.7 mm3/g) are achieved at a blending ratio of 0.75. Notably, polypropylene exerts minimal influence on the graphite crystallite size and graphitization degree of biochar. This research significantly contributes to advancing our understanding of the interaction mechanisms between biomass and plastic waste.

A novel carbon-based solid acid catalyst with high acidity for the hydration of α-pinene to α-terpineol: Effect of graphite crystallite size and synergistic effect of defects

This work, for the first time, highlights that small-sized graphite crystallite and highly defective carbon-based catalysts can effectively increase the −SO3H density of the catalysts and modulate the surface electronic properties of the catalysts, which further facilitates the α-pinene hydration reaction. Hydrothermal phosphoric acid modulation of graphite crystallite size and defects in carbon-based catalysts systematically revealed the correlation between −SO3H density, catalytic activity, graphite crystallite size, and defects in biomass carbon. The characterization results demonstrate that small-size graphite crystallites and high structural defects provide more sp2 hybridized carbon edges, contributing to the catalyst's increase of −SO3H density. The −SO3H group density of the catalyst increased from 0.89 to 1.20 mmol/g after hydrothermal phosphoric acid treatment. The catalyst has the highest efficiency in the α-pinene hydration to α-terpineol among the reported catalysts, in which 87.06 % of α-pinene was converted and reached a maximum α-terpineol selectivity (55.38 %) time only 22 h. Density functional theory calculations show that the lattice defects of graphite crystallites in catalysts lead to the polarization of the electron cloud around the catalyst, which further leads to the reduction of electrostatic resistance between α-pinene and the active catalytic sites. The apparent activation energy of hydration by the catalyst is 1.74 times lower than that of conventional biomass carbon-based solid acids. The reduction of graphite crystallite size is considered a critical step in improving the selectivity of α-terpineol attributed to the effective reduction of α-terpineol adsorbed on the catalyst.

Effect of Synthesis Conditions on Capacitive Properties of Porous Carbon Derived from Hemp Bast Fiber

A systematic study of the influence of synthesis conditions on the structural, morphological, and electrical properties, as well as the electrochemical performance of hemp fiber-derived carbon materials was performed. An analysis of the capacitive response of carbons obtained under various activation conditions with additional treatment with HNO3 and annealing was completed. The contribution of the formation of an electrical double layer at the outer electrode–electrolyte interface, as well as on surfaces inside micropores, has been studied and analyzed in terms of the effect of the turbostratic carbon properties (average lateral size of graphite crystallites, pore size distribution, BET surface area).

Effect of boron content on the microstructure and electromagnetic properties of SiBCN ceramics

Electromagnetic wave (EMW) absorbing materials have excellent potential for various applications in civil engineering and the military. In this study, siliconboron carbonitride (SiBCN) ceramics with excellent EMW absorption capability and oxidation resistance were obtained by adjusting the boron content. The results revealed that the graphite crystallite size in the SiBCN ceramics increased from 3.42 to 3.78 nm, whereas the thickness of the oxide layer decreased from 16.6 to 8.2 μm. The highest electrical conductivity and permittivity for the SiBCN ceramics were obtained when the boron content was 5%. The minimum reflection loss was −35.25 dB at 10.57 GHz and a ceramic thickness of 2.0 mm. At a temperature of 600 °C, the SiBCN ceramic exhibited excellent EMW attenuation ability; particularly, the minimum reflection loss reached −29.18 dB at 9.65 GHz and a ceramic thickness of 2.5 mm. The superior EMW absorption properties of the SiBCN ceramics at high temperatures can be ascribed to the synergistic effect of relaxation and conductivity. The results suggest that boron could enhance the transformation of amorphous carbon into crystalline graphite and increase the number of heterointerfaces and conductive paths. This work provides a method for obtaining SiBCN ceramics with excellent EMW absorption properties.

Correlation between structural properties and electrical conductivity of porous carbon derived from hemp bast fiber

A comprehensive study of the correlation between the structural and morphological parameters and the frequency-temperature dependences of the conductivity of porous carbon materials obtained by carbonization of hemp fibers has been carried out. The effect of treatment with nitric acid and additional annealing on the transport of charge carriers in carbon materials carbonized in the temperature range of 500–1000 °C has been established. Porous carbon materials have been described as a heterophase system, in which highly conductive graphitized particles are separated by low conductivity amorphous carbon, from the standpoint of the effect of carbonization temperature and changes in the morphology of materials due to acid treatment and annealing on the formation of conduction channels with the simultaneous implementation of fluctuation-assisted tunneling between graphitic clusters separated by low conductive barriers and the formation of conduction channels as a result of contact of individual graphitized carbon clusters. A model has been constructed that relates the results of measuring the specific surface area and pore size distribution, changes in the size of graphite crystallites, and changes in conductivity with temperature. The possibility of applying the theory of percolation conductivity to describe the charge transport has been analyzed and the percolation threshold has been established.

Microstructure of high thermal conductivity mesophase pitch-based carbon fibers

The microstructural characteristics of high thermal conductivity mesophase pitch-based carbon fibers were investigated by XRD, Raman spectroscopy, SEM and TEM. The relationship between microstructural characteristics and thermal conductivity is discussed. Results show that the radial structure is always accompanied by a splitting structure. La has more significant impact on the thermal conductivity than Lc. The Raman spectroscopy ID/IG value of the cross section was used as an essential index to evaluate the thermal conductivity of the carbon fibers. The microstructural characteristics including large graphite crystallite size, high preferred orientation along the fiber axis, and few defects contribute to the high thermal conductivity of the carbon fibers.

Roles of Ion-Exchangeable Sodium in the Conversion Process of Tar to Soot during Rapid Pyrolysis of Two Brown Coals in a Drop-Tube Reactor.

In this work, two series of brown coals (including acid-washed coal and ion-exchangeable Na-loaded coal) were pyrolyzed in a drop-tube reactor. The experimental results revealed that soot and tar yields of Na-loaded coals were significantly lower than that of acid-washed coals. Gasified Na can reduce the formation of big soot agglomerates. During coal primary pyrolysis, ion-exchangeable Na can reduce the amount and aromaticity of primary tar. Na released with volatiles can catalyze the cracking of aliphatic and aromatic compounds, inhibit the polymerization between aromatic rings, and promote the combination of soot/tar with oxygen-containing substances, resulting in the decrease of graphite crystallite size and the increase of amorphous carbon content. Na can also reduce the organization degree of soot by forming intercalation compounds.

Interfacial reactions in graphene oxide/polyacrylonitrile composite films

ABSTRACT This study investigated the role of polyacrylonitrile (PAN) in graphene macroassemblies. Samples were characterized by differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectrometry. The results show that PAN can be used as a ‘coupling agent’ of graphene oxide (GO). During heat treatment, the carboxyl group (-COOH) on GO sheets nucleophilically attacks the carbon of the cyano group (-CN) to initiate cyclization of the PAN, which in turn connects GO to PAN. Meanwhile, the oxygen in GO promotes PAN dehydrogenation. As the temperature increases continuously, crosslinking occurs between PAN molecules and those PAN connected to GO, and between the edges of GO. This promotes formation of larger conjugate planes. Larger graphite crystallites are formed owing to π–π stacking interaction. The extent of reaction between GO and PAN varies with different PAN content. A low PAN content primarily acts as a coupling agent. The graphite crystallites size increases as the PAN content increases, with the largest crystallite size obtained in the presence of 17 wt% PAN. As PAN content increases further, large amounts of PAN self-react and carbonize to form small graphite crystallites. The average size of graphite crystallites therefore decreases with increasing PAN content.

Effect of Fuel Injection Condition on Graphitic Crystallite Size of PM from Diesel Engine

Effect of Fuel Injection Condition on Graphitic Crystallite Size of PM from Diesel Engine

Microstructure and properties of polyacrylonitrile based carbon fibers

The microstructure of polyacrylonitrile (PAN)-based carbon fibers with different mechanical properties was investigated. It was found that the tensile strength of the PAN-based carbon fibers generally decrease with the increase in the modulus. The properties of PAN-based carbon fiber are mainly controlled by the microstructure and microvoids. The increase in size and orientation of graphite crystallites follows the decrease in interlayer space of graphite sheets, which accompanies the increase in modulus and decrease in tensile strength of the carbon fibers. Simultaneously, the increase in the modulus of the carbon fibers accompanies the merging of the elliptical microvoids along the fiber axis and the turbostratic graphite in the carbon fibers transforms into 3D ordered graphite lamellar structure. This work provides useful information on tailoring the mechanical properties of carbon fibers by adjusting the microstructure.

Influence of Elevated Temperature Treatment on the Microstructures and Mechanical Properties of Carbon Fibers in Argon Environment

The elevated temperature resistance and fire resistance of carbon fiber-reinforced polymer (CFRP) composites are a critical concern for many applications. The mechanical properties of carbon fiber at elevated temperatures play a crucial role on the mechanical property of CFRP. In many cases, carbon fiber may not directly exposed to air due to the coverage of resin matrix or coatings at elevated temperatures. In the present paper, exposure at 400-700 °C for 30 min, or at 500 °C for 30 min ~ 10 h in argon was simulated in the above case for carbon fibers. The evolution of chemical structural and mechanical properties of carbon fibers at elevated temperatures was investigated. It was found that the tensile strength of the carbon fibers was reduced remarkably, and the tensile modulus was not sensitive to the elevated temperature exposure. Decrease in the shape parameter of carbon fiber after exposure indicated the increase in defects and disordering. Furthermore, elevated temperature exposure does not significantly change the fiber mass, C–C skeleton and graphite crystallite size. However, the micropore size and graphite interlayer spacing increased obviously, leading to the weakened lateral cross-linking between the graphite layers. Finally, the evolution of the tensile strength with the exposed temperatures and time was discussed quantitatively. The contribution factors of van der Waals and amorphous carbon on the tensile strength were found to be 75 and 25%, respectively.

Evidence of magnetism in RF magnetron sputtered deposited carbon films and investigation of its origin

The origin of magnetism in RF magnetron sputtered deposited carbon thin films is reported. Three different carbon thin films were deposited using RF magnetron sputtering of carbon target by Ar ions at RF power of 50 W, 100 W and 150 W, respectively. Microstructural characterization of films using Raman spectroscopy confirms the presence of graphitic crystallites in all three films and the crystallite edges are terminated with the sp3 bonding. However, increasing RF power results in an increase in graphitic crystallite size as well as the sp2/sp3 hybridization ratio, while the average density of the films decreases. The observed magnetization (measured using SQUID-VSM) in all the three-carbon films has a contribution from both superparamagnetic (SPM) particles (due to the interaction between unpaired spins) and the paramagnetic term due to isolated unpaired spins distributed throughout the film. The origin of experimentally observed magnetization in the carbon thin films and their correlation with the change in density and sp2/sp3 hybridization ratio due to variation in RF power is discussed.

Comparison of carbon materials as cathodes for the aluminium-ion battery

Aluminium-ion batteries are of increasing interest as alternatives to lithium-ion batteries, as they use more abundant materials and suffer from fewer safety risks. The limiting factor for battery performance is the capacity of the cathode towards [AlCl4]- intercalation. Although several cathode materials have been used recently, there have been few studies that directly compare the capacity of different cathodes. Graphitic carbon materials have many features that make them ideal for aluminium-ion intercalation: they are electrically conductive, low density and low-cost, and are available in a wide variety of morphologies. This work compares four common forms of graphitic carbon: pyrolytic graphite, carbon paper, carbon cloth and carbon felt as aluminium-ion cathodes. The materials differ in their porosity, average graphite crystallite size, and properties as aluminium-intercalating agents. It was found that of all the materials examined, carbon paper had the highest energy density at 122 Wh.kg−1, and had superior stability compared to pyrolytic graphite as the C-rate of cycling was increased. It also did not undergo crystallographic alteration even after cycling up to the 20C rate. Both carbon paper and pyrolytic graphite have capacities around 70 mAh.g−1 for aluminium intercalation, and carbon cloth and felt have lower capacities of 20–40 mAh.g−1.

Bimodal mesoporous hard carbons from stabilized resorcinol-formaldehyde resin and silica template with enhanced adsorption capacity

Hard carbon powders with hierarchical mesoporous structure from resorcinol-formaldehyde polymer were successfully prepared by use of double pore forming method. Poly-diallyldimethylammonium chloride (pDADMAC) and commercial silica (Sipernat® 50) were used as structuring agent and hard template, respectively. Through the proposed procedure carbon powder with bimodal mesoporous size distribution (around 4–5 nm and 20–40 nm) and different pore volume ratios can be obtained, by changing the ratio pDADMAC/silica used in the synthesis. Pore volumes between 0.70 and 2.10 cm3·g−1, and specific surface areas between 662 and 998 m2·g−1 were obtained.Raman spectroscopy and X-Ray diffraction analysis showed that all the carbons presented a non-ordered mesopore structure, and a hard carbon micro-structure with roughly 40% of single-layer microstructures, an average of 2.6 stacked graphene layers, and an in-plane graphitic crystallite size around 3.4 nm. We have evaluated the adsorption of methylene blue, as a model of a pollutant dye, on the mesoporous carbons with different pore size distribution, and we found that carbons with bimodal pore size distribution exhibit a remarkable and irreversible adsorption capacity. Microporosity can help to enhance the adsorption capacity, provided that micropores are connected to mesopores, allowing the adsorbate to get deep into the carbon structure. The adsorption kinetic is very fast for carbons with such pore architecture, and can be well described by a three-stage intraparticle diffusion model.

Effect of graphite structures on the productivity and quality of few-layer graphene in liquid-phase exfoliation

Liquid-phase exfoliation (LPE) is a promising technique for commercializing graphene production because of its simplicity and cost-effectiveness. However, the low yield of graphene in laboratory-scale production, less than 10 g/h, necessitates modifications to the process for it to be feasible for commercial applications. Natural graphite has various size distribution, crystallite sizes, and interlayer space, making the choice of initial graphite very important. Five types of natural graphite with different structures were prepared for the experiment. The structural parameters of graphite such as crystallite size and d-spacing were precisely determined based on a standard procedure of X-ray diffraction measurements for carbon materials. The effects of graphite flake size and crystallite size on the productivity and quality of few-layer graphene (FLG) were investigated. The results showed that small graphite was easier to fragment and exfoliate. FLG productivity improvement up to 1500% was attained when graphite with smaller flakes was used instead of graphite with large flakes. The crystallite size of graphite was manipulated by plenary ball milling, and the effect of crystallite on FLG productivity in LPE process was also discussed.

Selecting the Best Graphite for Long-Life, High-Energy Li-Ion Batteries

Most lithium-ion batteries still rely on intercalation-type graphite materials for anodes, so it is important to consider their role in full cells for applications in electric vehicles. Here, we systematically evaluate the chemical and physical properties of six commercially-available natural and synthetic graphites to establish which factors have the greatest impact on the cycling stability of full cells with nickel-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes. Electrochemical data and post-mortem characterization explain the origin of capacity fade. The NMC811 cathode shows large irreversible capacity loss and impedance growth, accounting for much of full cell degradation. However, six graphite anodes demonstrate significant differences with respect to structural change, surface area, impedance growth, and SEI chemistry, which impact overall capacity retention. We found long cycle life correlated most strongly with stable graphite crystallite size. In addition, graphites with lower surface area generally had higher coulombic efficiencies during formation cycles, which led to more stable long-term cycling. The best graphite screened here enables a capacity retention around 90% in full pouch cells over extensive long-term cycling compared to only 82% for cells with the lowest performing graphite. The results show that optimal graphite selection improves cycling stability of high energy lithium-ion cells.

Boron-containing phenolic–siloxane hybrid polymers through facile click chemistry route

Realization of easily processable, tough phenolic functional polymer materials is of high demand for composite applications. Herein, we report the synthesis of boron-containing phenolic–siloxane hybrid polymers through a facile copper-catalysed azide–alkyne click chemistry (CuAAC) approach. For this, phenolic resoles incorporated with boron (PFB) was propargyl-derivatized and then bridged through triazole moieties using telechelic α, ω azidated polydimethylsiloxane (AZ-PDMS). The propargylated boronated PF (PFBPr) resins exhibited high heat of reaction during thermal cure due to the prevalence of multiple reactions. PFBPr-siloxane hybrid co-polymers exhibited glass transitions in the ranges – 100 to – 75 °C and at 25–35 °C corresponding to soft segment and hard segments. Pyrolysed PFBPr-siloxane products showed mixed phase heterogeneous systems of B and SiC. Introduction of boron and silicon improved the degree of graphitization and reduced the graphite crystallite size of the carbonization products. The pyrolysed compounds of silicon and boron formed during high temperature were conducive for creating a layer of void-free graphitic ordered carbon that improved with boron and silicon content, as revealed by SEM images.

Effect of Fuel Injection Timing on Graphitic Crystallite Size of Soot Particles from Diesel Engine

Effect of Fuel Injection Timing on Graphitic Crystallite Size of Soot Particles from Diesel Engine