Graphitization Process Research Articles

Thermal conductivity and heat transfer mechanism of epoxy composites constructing by carbon fiber felt with three‐dimensional layered structure

AbstractThe preparation of lightweight polymer‐based composites with high thermal conductivity is an urgent requirement for thermal management applications. In this work, carbon fiber felt (CFF) with three‐dimensional (3D) layered structure was firstly prepared based on papermaking method. Then, high in‐plane thermal conductivity (TC) Epoxy resin/graphitized carbon fiber felt (Epoxy/G‐CFF) composites were prepared by graphitized CFF with different layers under vacuum assistance. The effect of graphitization on the thermal property was investigated, and the practical heat transfer behavior was analyzed. The results show that the Epoxy/G‐CFF composites exhibit the highest in‐plane thermal conductivity of 1.88 W/mK at 8.5 wt% loading, which is 889.47% higher than that of pure Epoxy. It represents the achievement of enhancing the thermal performance of polymer‐based composites with low additions. More importantly, the composites still exhibit low density and strong thermal management capability. This suggests that Epoxy/G‐CFF composites have promising applications in the thermal management field.Highlights The carbon fiber felt (CFF) with three‐dimensional (3D) layered structure was firstly prepared based on papermaking method. The graphitization process significantly increases the grain size and shortens the layer spacing, contributing to the comprehensive properties of G‐CFF. The Epoxy/G‐CFF composites exhibit the highest in‐plane thermal conductivity of 1.88 W/mK at 8.5 wt% loading.

Effect of Pyrolysis Temperature on the Carbon Sequestration Capacity of Spent Mushroom Substrate Biochar in the Presence of Mineral Iron.

The preparation of biochar typically involves the pyrolysis of waste organic biomass. Iron-rich magnetic biochar not only inherits the characteristics of high specific surface area and porous structure from biochar but also possesses significant advantages in easy separation and recovery, which has shown great application potential in various fields such as soil improvement and water resource remediation. This study aims to explore the influence of mineral iron on the carbon sequestration capability of biochar during the pyrolysis process. Experiments were conducted by using spent mushroom substrates as raw materials to prepare biochar at different temperature intervals (300 to 600 °C). The addition of exogenous iron has been found to significantly enhance the carbon retention rate (12.2-44.5%) of biochar across various pyrolysis temperatures and, notably, improves the carbon stability of biochar at 300 °C, 400 °C, and 600 °C. Through the analysis of thermogravimetric mass spectrometry (TG-MS) and X-ray photoelectron spectroscopy (XPS), we discovered that iron catalyzes the thermochemical reactions and inhibits the release of organic small molecules (C2-C5) through both physical blocking (FexOx) and chemical bonding (C=O and O-C=O). The results of Raman spectroscopy and infrared spectroscopy analyses indicate that the addition of iron significantly promotes the graphitization process of carbon and enhances the thermal stability of biochar within the temperature range of 300 to 500 °C. When exploring the retention and stability of carbon during pyrolysis, it was found that under the conditions of 600 °C and the presence of iron, the maximum carbon sequestration rate of biochar can reach 60.6%. Overall, this study highlights the critical role of iron and pyrolysis temperature in enhancing the carbon sequestration capacity of biochar.

Synthesis of biochar and its metal oxide composites and application on next sustainable electrodes for energy storage devices

Biochar materials have been applied in energy storage due to their unique properties, such as high storage of ions, high conductivity, chemical stability and ease of production. Combining it with the high specific capacitance could be a promising strategy to develop devices and improve the properties. Through a hydrothermal technique the biochar powders were synthesized from sugarcane biomass. An acid pretreatment was carried out before and after the graphitization process aiming to obtain carbon materials with high surface area and porosity. The morphological characterization reveals powders with pores of submicrometer diameter. For the pure biochar it was determined a superficial area of 477.66 m2.g−1 with a median pore size of 42.92 Å and a pore volume of 0.21 cm3.g−1. A carbon-based paste was then prepared to deposit on nickel foam and obtain the electrodes. In a 3-electrode system characterization, biochar has showed higher specific capacitance than the metal oxide composites due to higher surface area and higher medium pore diameter. It was calculated a resistance of 2.7 Ω, a capacitance of 446 mF.g−1, a power density of 46.2 W.kg−1 and an energy density of 1.8 W.h.kg−1. These results indicate the potential use of biochar-based electrodes with high electrical conductivity and improved surface area to obtain higher capacitance properties for development of advanced devices.

Effects of High-Temperature Treatments in Inert Atmosphere on 4H-SiC Substrates and Epitaxial Layers.

Silicon carbide is a wide-bandgap semiconductor useful in a new class of power devices in the emerging area of high-temperature and high-voltage electronics. The diffusion of SiC devices is strictly related to the growth of high-quality substrates and epitaxial layers involving high-temperature treatment processing. In this work, we studied the thermal stability of substrates of 4H-SiC in an inert atmosphere in the range 1600-2000 °C. Micro-Raman spectroscopy characterization revealed that the thermal treatments induced inhomogeneity in the wafer surface related to a graphitization process starting from 1650 °C. It was also found that the graphitization influences the epitaxial layer successively grown on the wafer substrate, and in particular, by time-resolved photoluminescence spectroscopy it was found that graphitization-induced defectiveness is responsible for the reduction of the carrier recombination lifetime.

Unraveling the Catalytic Graphitization Mechanism of Ni–P Electroless Plated Cokes Via in Situ Analytical Approaches

We have unraveled the mechanism of catalytic graphitization by employing in-situ analytical methods. The process involves the use of a Ni–P electroless plating technique at a modest 1600 °C, ensuring high crystallinity of the produced coke material. Furthermore, we have incorporated ultrasonic waves during the Ni–P electroless plating process to enhance the formation of metallic layers on the carbon material, leading to improved surface characteristics and adhesion . The impact of ultrasonic treatment on the electroless plating process has been confirmed by field emission scanning electron microscopy images and elemental composition analysis. Additionally, our structural analysis using X-ray diffraction and Raman spectroscopy demonstrates that the Ni–P electroless plating significantly accelerates the graphitization process . Lastly, the behavior of graphitization has been illuminated through in situ transmission electron microscopy and XRD analysis . The presence of nickel layers on the surface of the coke material aids in graphite formation by promoting the dissolution and precipitation of amorphous carbons, resulting in effective graphitization at a relatively low temperature. Figure 1

Evaluation of 14C/12C ratio measurements using accelerator mass spectrometry with standard materials under different graphitization conditions

In this study, an evaluation of carbon-beam tuning and 14C/12C ratio measurements is performed to validate the graphitization process in the pre-processing procedure employed at the accelerator mass spectrometry (AMS) facility of Dongguk University in Korea. The AMS isotopic ratio data are analyzed for samples subjected to three different graphitization conditions: (1) the entire process including Fe catalyst pre-heating with a high vacuum, (2) a high vacuum without pre-heating, and (3) a low vacuum without pre-heating. High-quality isotopic ratio measurements are achieved under these conditions. The measured mean isotopic ratio values for the background samples are almost equivalent to the different graphitization condition samples, with a difference in the order of 10−16. Therefore, conducting measurements with or without Fe catalyst pre-heating or high vacuum conditions is equally viable. Furthermore, the simplification of the graphitization process steps reduces the processing time required to produce five samples from 8 to 4 h, thereby enhancing the daily sample throughput by a factor of two, without compromising data quality.

Study on the thermal field material of FZ-Si crystal waste graphite purified by ultrasonic enhanced acid leaching

This study examines the acid-leaching and purification process of waste graphite in the production of Czochralski monocrystalline silicon. The optimal leaching conditions are identified as a liquid-to-solid ratio of 6, a leaching temperature of 70 °C, an acid concentration of 8 mol, and a leaching time of 60 min. The use of hydrofluoric acid, sulfuric acid, and nitric acid in the acid-leaching process increases the fixed carbon content of waste graphite from ∼94 % to ∼98.5 %. To address the low fixed carbon content that cannot be achieved through conventional acid-leaching, a method combining ultrasonic intensification with hydrofluoric and hydrochloric acid leaching is proposed and successfully implemented. Under ultrasonic enhancement conditions, the leaching effect is optimal at a temperature of 60 °C, acidity of 4 mol, and leaching time of 60 min. These results demonstrate that the introduction of ultrasound significantly strengthens the acid-leaching process. The method proposed in this study not only purifies waste graphite through acid-leaching but also elucidates the reaction behavior of various impurity elements during the leaching process. Overall, these findings provide a foundational basis for the recovery of waste graphite in the thermal field.

Synthesis of graphitic carbon from empty palm oil fruit bunches through single-step graphitization process using K2FeO4-KOH catalyst as lithium ion battery anode

This research aims to optimize the graphitization process of carbon derived from Empty Palm Oil Fruit Bunches (EPOFB), a renewable biomass source, using a single-step K₂FeO₄-KOH impregnation-activation method. The results demonstrate that increasing the mass of K₂FeO₄, up to the optimal level, enhances the degree of graphitization, as confirmed by XRD and Raman spectroscopy. Optimal performance is observed with a catalyst mass of 0.11 g K₂FeO₄ in the C_ K₂FeO₄(0.11)KOH_800 sample, which exhibits a d002 spacing of 0.3356 nm, an IG/ID ratio of 2.42, a high surface area of 787.767 m²/g, and clearly defined graphitic layers in TEM images. Electrochemical testing of C_ K₂FeO₄(0.11)_KOH_800 reveals promising results, including the lowest charge transfer resistance (Rct) of 87.18 Ω, a significant area under the curve in cyclic voltammetry, a charging capacity of 330.3 mAh g⁻¹ at 0.1 C, with an excellent rate capability of 183 mAh g⁻¹ at 1 C after 100 cycles, maintaining a retention rate of 68.2 %. The single-step K₂FeO₄-KOH impregnation-activation method effectively enhances the graphitization of EPOFB-derived carbon, offering potential applications in high-performance lithium battery anodes.

Development of graphitic and non-graphitic carbons using different grade biopitch sources

The growing demand for bio-renewable alternatives to fossil fuels in the production of sustainable carbon materials, aimed at reducing environmental impact, is crucial for advancing a greener future. This research explores an innovative approach for producing biopitches from bio-oils, which are subsequently utilized as a sustainable precursor for developing advanced graphitic carbons (GC) and non-graphitic carbons (NGC) through carbonization and graphitization processes. The study emphasizes the impact of the chemical composition of bio-oils and biopitches, including heteroatom structures, aromatic/aliphatic ratio, and oxygen content with oxygen-bearing functional groups, on the production of GC and NGC. The research also examines their structural parameters at various heating temperatures using characterization techniques such as X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. XRD analysis revealed that GC samples have lower interplanar spacing (d002) and larger crystallite size than NGC, while Raman shows more short-range order and defects in NGC. Furthermore, HRTEM images and fringe analysis demonstrated differences in lamellae structures, tortuosity, and fringe length. These observations, unveiling differences in crystallite size and degree of graphitization between GC and NGC, underscore the influence of temperature on structural order and defect annealing, which is crucial for optimizing material properties.

Comparative Analysis of Graphitization Characteristics in Bamboo and Oak Charcoals for Secondary Battery Anodes

When compared to natural graphite, artificial graphite has advantages such a longer cycle life, faster charging rates, and better performance. However, the process of producing it, which frequently uses coal, raises questions about the impact on the environment and the depletion of resources. Eco-friendly, wood-based graphite must be developed in order to solve these problems. This study assessed and investigated the characteristics of charcoals derived from bamboo and oak which were utilized to produce graphite. After heating to 1500 °C at 10 K/min, 86.87 wt% of oak charcoal and 88.33 wt% of bamboo charcoal remained, indicating a yield of more than 85% when charcoal was graphitized. Depending on the species of wood, different-sized pores showed different shapes as the graphitization process advanced, as revealed by SEM surface analyses. The carbon atoms seen in the XRD crystal development changed into graphite crystals when heated to 2400 °C, and the isotropic peaks vanished. Bamboo charcoal has a higher degree of crystallinity than other wood-based charcoals, such as oak charcoal, which is made up of turbostratic graphite, according to Raman spectroscopic research. Lithium-ion batteries employ bamboo charcoal as their anode material. At this point, the values for soft carbon were determined to be 196 mAh/g and for hard carbon to be 168 mAh/g at a current density of 0.02 A/g.

Tracing the graphitization of polymers: A novel approach for direct atomic-scale visualization

Due to its excellent physical, chemical, and electrochemical characteristics, pyrolytic carbon has become a promising material for a wide range of advanced technologies. Pyrolytic carbon can be obtained through the pyrolysis of a polymeric carbon precursor at high temperatures and in inert atmosphere. By tuning the pyrolysis conditions, the hybridization of carbon atoms and thus the physicochemical properties of the derived carbon can be tailored. Advancing its development requires a deeper understanding of the graphitization process. In this context, an in situ microstructural analysis of the pyrolysis process is needed. This work presents the microfabrication of suspended polymer thin film structures on transmission electron microscopy heating chips, by two-photon polymerization 3D printing. We visualized graphitization of these films during in situ transmission electron microscopy heating studies. The favorable identified conditions are a thin film with a thickness of around 700 nm pre-pyrolysis, a pyrolysis profile reaching a maximum temperature of 1300°C and a minimum of 2 h of dwell at this temperature. An increase in the number of stacked graphene layers was observed over dwell time. Overall, the developed method has the potential to enable the visualization of graphitization of different polymer precursors and thus help predict the microstructure and properties of pyrolytic carbon depending on its fabrication conditions.

Step-by-step silicon carbide graphitisation process study in terms of time and temperature parameters

This work investigates the temperature and time as key parameters for graphene formation on the silicon carbide surface during the high thermal decomposition process. Measurements were performed using various experimental techniques under ultra-high vacuum conditions. The graphitisation process was divided into various stages, after which the surface chemical composition and atomic structures were analysed in detail. It has been shown that despite the known theory of graphitisation mechanism and initial condition for occurrence of this process, the application of different temperatures and heating times affect the quality and quantity of formed graphene layers. Applying a temperature too low or annealing the sample for a too short time led to an inefficient silicon sublimation process. On the other hand, too high temperature during flashing modifies the visibility of surface structures, which may be crucial for other investigations and potential applications of such systems.

Short-Range promotion and long-range inhibition mechanism of sulfur release in high-sulfur petroleum coke for fast-charging graphite anodes

High-sulfur petroleum coke is considered a promising raw material for artificial graphite anode materials due to its low cost, abundant supply, and large overseas markets. However, the equipment corrosion caused by high-sulfur petroleum coke during graphitization and the unclear sulfur release mechanism limits its industrial application. Herein, the sulfur release characteristics and its effects on the microstructure and electrochemical properties of graphite were systematically investigated through heat treatment of petroleum coke with varying sulfur content at different temperatures. According to the rapid sulfur release characteristics of high-sulfur coke at 1400°C, an innovative pre-carbonization desulfurization process at about 1400 °C is proposed before the traditional graphitization process. Meanwhile, the impact of sulfur release on the microstructure and electrochemical properties of graphite during graphitization was systematically analyzed using XRD, TEM, cross-sectional SEM, and CV, a mechanism was proposed in which sulfur release promotes short-range while inhibiting long-range order in graphitization. Due to the abundance of micro-mesoporous structures, grain boundaries, and small-sized grains produced by sulfur release, high-sulfur petroleum coke-based graphite exhibits excellent fast-charging performance. Compared with the capacity at 0.2C, PC-7.24 %S-CG maintained 52.5 % of its capacity at 1C, which was much higher than that of PC-0.85 %S-CG (34.9 %). Moreover, a sulfur content threshold of 4 % was further established based on changes in compaction density. This work offers new insights into the application of high-sulfur coke for artificial graphite anodes.

Ultrasound-assisted freeze-drying graphitization process for the fabrication of two-dimensional carbon/Fe3O4 composite aerogels for microwave absorption

Magnetic Fe3O4 materials have received attention from researchers due to their significant wave absorption potential, but there are limitations to their efficient electromagnetic wave absorption and lightweight applications. Combining materials with dielectric properties to optimize the performance of Fe3O4 has become one of the research directions. In particular, carbon nanomaterials, such as graphene, show great application prospects in the field of microwave absorption due to their physical properties. To improve the impedance mismatch issue of graphene, researchers consider combining it with magnetic nanoparticles. Commercial applications require materials that are cost-effective, easy to produce, and environmentally sustainable, driving research on novel 2D carbon materials. In this study, 2D carbon materials were prepared by ultrasound-assisted freeze-drying/graphitization process using polymers as precursors, which simplifies the preparation process and avoids the use of expensive sacrificial templates and catalysts. The 2D carbon materials prepared by this method were used as the dielectric component in the wave-absorbing composites, and the nano effect was utilized to significantly improve the microwave absorption properties of the materials. The maximum reflection loss of the prepared graphite nano-aerogel reaches −84.16 dB and the EAB reaches 3.74 GHz. In addition, by adding Fe3O4 nanoparticles and applying an ultrasonic field for dispersion in the freeze-drying process, the nanoparticle agglomeration is effectively prevented, which provides a simple and efficient pathway for the preparation of nanocomposites.

Macroscopic perspective on phase transition behavior of natural single-crystal graphite under different pressure environments

Comprehensive understanding of the direct transformation pathway from graphite to diamond under high temperature and high pressure has long been one of the fundamental goals in materials science. Despite considerable experimental and theoretical progress, current experimental studies have mainly focused on the local microstructural characterizations of recovered samples, which has certain limitations for high-temperature and high-pressure products, which often exhibit diversity. Here, we report on the pressure-induced phase transition behavior of natural single-crystal graphite under three distinct pressure-transmitting media from a macroscopic perspective using in situ two-dimensional Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. The surface evolution process of graphite before and after the phase transition is captured, revealing that pressure-induced surface textures can impede the continuity of the phase transition process across the entire single crystal. Our results provide a fresh perspective for studying the phase transition behavior of graphite and greatly deepen our understanding of this behavior, which will be helpful in guiding further high-temperature and high-pressure syntheses of carbon allotropes.

Ablative property and mechanism of pitch-based carbon fiber modified C/C composites with high thermal conductivity

The novel C/C composites with thermal transport function were prepared using the mesophase-pitch carbon fibers (CFMP) as the thermal diffusion channels. The introduction of CFMP greatly improved the microstructure, thermal properties, and ablative resistance of the C/C composites. During the graphitization process, compared with PAN fibers (CFPAN), CFMP was more likely to be graphitized to form a highly ordered three-dimensional graphite structure. The highly organized microcrystalline structure of CFMP resulted in a tight interface with PyC that lessened the likelihood of flaws and cracks during graphitization. CFMP, which acted as a thermal conduction skeleton, significantly improved the thermal conductivity of C/C composites. After 3000 °C HTT, the thermal conductivity of C/C-3000-Z composites was increased to 51.70 and 225.02 W/(m K) in the XY and Z planes, respectively. During the ablation process, C/C-3000-Z specimen exhibited a lower temperature gradient and less thermal stress owing to the outstanding thermal properties and fewer defects. After 30 s ablation, the temperature difference of surface and backside was only 495.9 °C, and the mass and linear ablation rates were 0.3 μm/s and 0.9 mg/s, respectively.

Synthesis and properties of graphene-like porous carbon from modified cellulose

The work is devoted to the synthesis of graphene-like magnetic nanocomposites by direct pyrolysis of hemp microcrystalline cellulose modified with citric acid containing nickel or cobalt salts. Their chemical structure and morphology were characterized by X-ray diffraction (XRD), electron microscopy (SEM), Raman spectroscopy, low-temperature N2 adsorption-desorption, and Fourier transform infrared spectroscopy (FT-IR). Thermogravimetry has established a possible mechanism of pyrolysis of a modified cellulose matrix containing Ni and Co metals. X-ray diffraction analysis and Raman spectroscopy have shown that an increase in the number of carboxyl groups accelerates the process of graphitization of the cellulose matrix with transition metals (Ni and Co), as well as increases the degree of structural order and the level of graphitization. The conducted studies have shown that nanoparticles of metals of the zero-valence state are enclosed in graphene-like shells having a mainly mesoporous structure.

Mechanistic Insights into the Evolution of Graphitic Carbon from Sulfur Containing Polar Aromatic Feedstock.

In the realm of carbon fiber research, a variety of structural configurations is noted, comprising crystalline, noncrystalline, and semicrystalline forms. Recent investigations into this domain have revealed an array of intriguing phases of carbon, among which amorphous graphite is the most notable for its unique mechanical, thermal, and electrical properties that arise from its inherent topological disorders. In this study, we utilized the ReaxFF molecular dynamics (MD) simulations to investigate the carbonization and graphitization processes involved in the production of amorphous graphite from benzothiophene, a sulfur-containing polar aromatic precursor. We developed C/H/S ReaxFF force field parameters to describe the high-temperature chemistry of benzothiophene. Our investigation reveals the reaction mechanisms, providing critical insights into the underlying chemical processes toward the formation of amorphous graphite and the structural characteristics of the end products. The formation of volatile gaseous molecules and their continuous elimination led to the development of noncontinuous layered graphite structures analogous to amorphous graphite consisting of pentagons, hexagons, and heptagons. These findings offer unprecedented insights into the carbonization and graphitization processes of sulfur-containing heavy-end aromatic feedstock. This knowledge lays the groundwork for advancing synthesis methods and developing amorphous graphite materials with specific properties.

Designing a model predictive controller for graphite baking process

Model predictive controller provides better control quality for graphite products baking process than PID and its variations. The drawback of MPC is its high sensitivity to object modelling errors. If all of object parameters are varied just by 3 % simultaneously then MPC provides satisfactory control no more. In the current paper we design an adaptive MPC for baking process control. In order to identify furnace section “under the fire” on-line, we utilize recursive least squares algorithm with forgetting factor equal to 0,98. We compare conventional and adaptive MPCs in the following cases: accurate model; undesirable deviations of object parameters from model parameters (object is time invariant); desirable deviations; time variant object with step-changing parameters. In each case adaptive MPC provides control that ensures temperature difference inside the hottest (the most “dangerous”) graphite bar to be small enough, and even gives some margin for it (0,8 % to 8 %). However, the cost for this is increased process duration (4,8 % to 142,1 %) and more fuel-consuming (1,2 % to 106,2 %) than in case of non-adaptive MPC, even if the latter provides satisfactory control as well. In general, it is reasonable to use an adaptive MPC instead of a conventional one. Margin of economical reasonability needs further research. Also, it is necessary to compare different identification methods in order to achieve faster transition process.

Investigation on spectroscopy characteristics of different metamorphic degrees of coal-based graphite

To gain insights into the spectroscopy characteristics from coal to graphite, we investigated different metamorphic degrees of coal-based graphite which were collected from Hunan Province China. In this paper, by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, graphite with different metamorphism degrees has been characterized to explore the evolution of macromolecular structure of organic matter during graphitization. The results show that with the increase of metamorphism degree, the 002-diffraction peak of the series of samples gradually shrinks and narrows, and the peak intensity becomes stronger, indicating that the microcrystalline structure gradually becomes regular and ordered. As the degree of graphitization increase, the uniformity of particle size in coal samples observed gradually increases, and the morphology becomes more regular, transitioning from disordered and irregular shapes to a structured large-scale flake pattern. The crystallinity improves, and the massive coal particles gradually coalesce into large plate crystals, with the inter-particle pores gradually closing. The graphite structure becomes increasingly evident. The FTIR spectra show that as the degree of graphitization increases, the peak at 1,581 cm−1 corresponding to C=C vibrations gradually intensifies. Some inert functional groups are retained throughout the graphitization process. The pores between coal particles gradually close, and the morphology of graphite particles becomes more regular and ordered. Additionally, during the graphitization process, structures similar to carbon nanotubes may develop. Throughout the structural transformation from coal macromolecules to graphite crystals, the size of the sp2 planar domains in single-layer graphene increases, and the lattice structure of carbon atoms gradually enlarges. These findings contribute to a comprehensive understanding of the properties and characteristics of coal-derived graphite, and can provide theoretical reference and basis for the metallogenic mechanism of coal-derived graphite and the efficient utilization of coal.