Microstructure Of Graphite Research Articles

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.

Fabrication of Coconut Shell-Derived Graphitic Activated Carbon for Carbon-based Electrode Materials

This study aims to convert low-value plantation biomass waste into high-value materials. The process involves transforming coconut shell charcoal (CSC) into activated carbon and subsequently producing coconut shell graphitic-like activated carbon (CSGAC). Using a thermal graphitization method with a FeCl3 catalyst at 900°C for 1 hour in a nitrogen atmosphere, graphite microstructures (CSGAC) were formed on the coconut shell activated carbon (CSAC) framework. XRD, FTIR, SEM, and BET analyses confirmed the successful formation of CSGAC. The electrical conductivity of CSGAC, measured at 148 µS, highlights its potential as a cost-effective, renewable, and environmentally friendly raw material for carbon-based electrodes.

Microstructure of Gilsocarbon graphite revealed by a correlative study of optical texture and FIB-TEM

Transmission Electron Microscopy (TEM) alongside Polarized Optical Microscopy (POM), is used to investigate the microstructure of nuclear graphite, specifically Gilsocarbon coke, fillers, binders, and flour. Detailed analyses revealed domain structures, domain boundaries, sub-domains and two types of microcracks: intra-domain and inter-domain cracks. Analysis of TEM images, from samples prepared via Focused Ion Beam (FIB), showed domain sizes in coke filler and flour regions ranged from 1 to 3 μm, whereas binder regions had larger domains of up to tens of micrometers, with correspondingly longer Mrozowski cracks. Within these domains, sub-domain boundaries further constrained Mrozowski cracks, resulting in crack lengths significantly shorter than the domain size. Domain boundaries were classified into small-angle and large-angle boundaries based on orientation differences, with large-angle boundaries arising from multiple small-angle transformations facilitated by polygonal microcracks. This microstructural data obtained from virgin Gilsocarbon graphite provides essential inputs for an experimentally informed model predicting the deformation and fracture properties of this material at the micrometer length scale, which may offer improved insights to enhance our understanding of how these properties may evolve under reactor operating conditions.

The effect of active elements on the microstructure and properties of graphite and copper-brazed joints

The effect of active elements on the microstructure and properties of graphite and copper-brazed joints

Effect of Chemical Vapor Deposition Pressure on Preferred Orientation, Microstructure, and Oxidation Resistance of Pyrolytic Graphite

Effect of Chemical Vapor Deposition Pressure on Preferred Orientation, Microstructure, and Oxidation Resistance of Pyrolytic Graphite

An In Situ transmission electron microscopy study on the synergistic effects of Au-ion irradiation and high temperature on nuclear graphite microstructure

The combined effects of high-temperature and heavy-ion irradiation on Mrozowski cracks (MC) and nuclear graphite crystallographic dimensions have been studied using in situ heating and in situ ion-irradiation in the transmission electron microscope (TEM). Electron transparent lamella of nuclear graphite, IG-110, was irradiated using a 2.8 MeV Au beam at an ion flux of 3.991 ×1010 ion cm−2 s−1 for 70 min at 800 °C. Upon high-temperature irradiation, Mrozowski crack closure was studied quantitatively. The analysis showed linear, positive expansion of nuclear graphite which is significantly different from the dimensional changes previously reported for low-dose neutron irradiation of nuclear graphite in which the material undergoes negative to positive expansion via a turnaround radiation dose. The trend of the thermal expansion coefficient (CTE) of pristine IG-110 in this study is consistent with previous reports in the 100 °C–800 °C temperature region in which the dimensional change ranges from negative to positive values.

A Comprehensive Experimental Study on Microstructure‐Graded Graphite Anodes for Enhancing Fast‐Charging Capability of Lithium‐Ion Batteries

Lithium‐ion batteries with high gravimetric capacity density and improved cycle life performance under fast‐charging conditions are crucial for widespread electric vehicle (EV) adoption. This study investigates how designing graphite anode microstructure, specifically porosity, and particle‐size gradients, improves lithium‐ion (Li+) transport during fast‐charging conditions. Three‐layered graphite anodes with varying porosity (24%, 36%, 46%) and particle size gradients (3, 5, 10 μm) were compared to a conventional single‐layered electrode in half‐cell configurations. At room temperature and high discharge rate (2C), both gradient structures showed significantly enhanced capacity retention (80% and 67% vs. 50%) compared to the conventional electrode, highlighting the effectiveness of microstructure engineering for fast charging. The study also investigated the temperature's impact on cycle life. After 200 cycles at 2°C and 45°C, all gradient structures demonstrated superior capacity retention (≈80%) compared to the conventional electrode (35%), suggesting the gradients mitigate degradation rate at high temperatures. Electrochemical impedance spectroscopy confirmed superior Li+ diffusion and lower resistivity in gradient electrodes. Simulations explored the influence of gradient profiles on reaction kinetics across the electrode thickness. Overall, this research demonstrates that the fast‐charging capability of graphite electrodes can be greatly enhanced by engineering the electrode microstructure, thereby making EV technology more accessible and appealing.

Laser Remelting of Ductile Cast Iron to Achieve a Graphite-Free Surface Layer for Enabling a Manual High-Gloss Finish

Laser remelting is being explored as a viable technique for obtaining a graphite-free, defect-free surface layer on cast iron EN GJS 400-15. The goal is to obtain a large remelted layer along with a low surface roughness to enable a subsequent manual high-gloss surface finish. The impact of the laser remelting process parameters is evaluated by using samples with three different cooling rates, resulting in different graphite microstructures. By utilizing four passes and a laser power of 300 W, the smallest roughness and largest remelting depth are achieved. The remelted layer is mostly devoid of graphite particles. Subsequent manual polishing is performed to evaluate the potential for achieving a high-gloss finish with a roughness of Sa < 0.05 µm. Laser remelting alone does not improve visual appearance or reduce roughness. However, after manual polishing, the roughness of the laser-remelted surfaces with Sa = 0.018 µm is one order of magnitude smaller than the manually polished initial state. Graphite removal during laser remelting therefore makes it possible to achieve a conventional and high-gloss polish, overcoming the previous limitations of GJS materials.

Examining the role of rare earth elements on grey iron’s microstructural and mechanical properties

ABSTRACT Grey cast iron, prized for its durability and thermal performance in applications like engine cylinder liners, sees widespread use in defence, engineering, and transportation. Investigating the impact of rare earth elements on its properties, a mix of lanthanum and cerium was introduced. These elements act as nucleating and graphitising agents, refining graphite microstructure and adjusting pearlite layer spacing. Results showed a notable improvement in Brinell hardness (453 HB, a 79% increase with 0.6 wt.% rare earth), compressive strength (2209 MPa), and tensile strength (501 MPa at 0.4 wt.% rare earth). However, excessive rare earth inclusion can have detrimental effects. The study underscores the potential to enhance greyggrey cast iron’s microstructure and mechanical properties through judicious rare earth additions.

Real-Time Observation of Nanoscale Kink Band Mediated Plasticity in Ion-Irradiated Graphite: An In Situ TEM Study.

Graphite IG-110 is a synthetic polycrystalline material used as a neutron moderator in reactors. Graphite is inherently brittle and is known to exhibit a further increase in brittleness due to radiation damage at room temperature. To understand the irradiation effects on pre-existing defects and their overall influence on external load, micropillar compression tests were performed using in situ nanoindentation in the Transmission Electron Microscopy (TEM) for both pristine and ion-irradiated samples. While pristine specimens showed brittle and subsequent catastrophic failure, the 2.8 MeV Au2+ ion (fluence of 4.378 × 1014 cm-2) irradiated specimens sustained extensive plasticity at room temperature without failure. In situ TEM characterization showed nucleation of nanoscale kink band structures at numerous sites, where the localized plasticity appeared to close the defects and cracks while allowing large average strain. We propose that compressive mechanical stress due to dimensional change during ion irradiation transforms buckled basal layers in graphite into kink bands. The externally applied load during the micropillar tests proliferates the nucleation and motion of kink bands to accommodate the large plastic strain. The inherent non-uniformity of graphite microstructure promotes such strain localization, making kink bands the predominant mechanism behind unprecedented toughness in an otherwise brittle material.

Phase-field electrochemical simulations of reconstructed graphite electrodes

Graphite currently serves as the most predominant anode material in lithium-ion batteries due to its favorable balance of energy density, material cost, and relative safety in operations. While graphite anodes are manufactured mainly by randomly packing graphite particles, there is an avenue to improve the anode performance through optimized electrode microstructure. This is especially crucial for fast charging/discharging operations, where lithium plating is exaggerated and poses a critical safety concern. Therefore, the capability to investigate detailed electrochemical processes in electrode microstructures is essential for graphite anode designs. In this work, we incorporate the Cahn–Hilliard phase-field equation into a smoothed boundary method electrochemical simulation framework to account for phase transformations in graphite electrode complex microstructures upon lithiation/delithiation. These simulations quantitatively demonstrate that (i) modeling phase-separating graphite as a Li solid-solution material will overestimate graphite electrodes’ performance, (ii) particle size determines the electrode performance, (iii) pore tortuosity is important to enhance electrodes’ performance noticeably for thick electrodes, and (iv) introducing tunnels can spread insertion reaction more uniformly throughout the electrodes. Moreover, a substantial portion of this work focuses on simulating the behavior of thick electrodes. Thick electrode design holds a promising opportunity to increase overall energy density and our model enables computational predictions for such electrodes in an easy manner without conducting physical experiments. Thus, the presented simulation framework offers a fast and robust tool for designing electrode microstructures and operation protocols on digitally represented complex electrode microstructures. This approach has the potential to advance the electrode design of lithium-ion batteries.

Thermal Conductivity and Microstructure of Cu-Coated Graphite Flake/Ti Alloy Composites Fabricated by Spark Plasma Sintering

Thermal Conductivity and Microstructure of Cu-Coated Graphite Flake/Ti Alloy Composites Fabricated by Spark Plasma Sintering

Characterization and ion-irradiation studies of typical microstructures in nuclear graphite

Nuclear graphite is an important structural material for advanced gas cooled reactors and molten salt reactors. Graphite microstructures are always accompanied with typical pores or cracks which plays an important role in nuclear graphite behaviors. A new surface processing method involving ion milling and fast oxidation is used here to characterize typical microstructures from the large-size calcination cracks in fillers to very small quinoline insoluble particles in NBG-17 and NBG-18 graphites. By using this surface processing method and ion irradiation technique, an attempt is made to explore the microstructural basis of graphite irradiation behaviors. Heating-induced relaxation of graphite microstructures is observed, indicating the presence of residual stresses in nuclear graphite. Creased graphite sheets are identified on ion-milled surface and are believed to accommodate a-axis shrinkage of graphite crystallites at the beginning of irradiation, which is consistent with the initial plateau of slow dimensional shrinking. Compared to NBG-17 graphite, NBG-18 is found to have much more calcination cracks which contract during irradiation, resulting in a deeper volume shrinkage of NBG-18. The quinoline insoluble particles containing chaotic structures are shown to severely contract and separate from surrounding structures, leading to voids in between. Both NBG-18 and NBG-17 have abundant quinoline insoluble particles, which might make a contribution to their smaller volume shrinkage than other medium-grain graphite.

Kinetic Limits of Graphite Anode for Fast-Charging Lithium-Ion Batteries

HighlightsThe microstructure of graphite upon rapid Li+ intercalation is a mixture of differently staging structures in the macroscopic and microscopic scales due to the incomplete and inhomogeneous intercalation reactions hindered by the sluggish reaction kinetics.The Li+ interface diffusion dominates the reaction kinetics at high rates in thin graphite electrode, while Li+ diffusion through the electrode cannot to be neglected for thick graphite electrode.

Role of ammonium ionic liquid and Pd nanoparticles in cavitation-based graphite decontamination and recycling process

Sonochemical recovery of radioactive contaminants from nuclear graphite has been demonstrated to be quite invaluable in recent studies. However, graphite is a soft material and is prone to erosion and wear. This restricts the recycle of graphite cleaned using ultrasound beyond a few decontamination cycles. Hence, it is an imperative to prevent the surface erosion of graphite in the sonic field. The current work studies the efficacy of ultrasound in decontaminating ceria contaminated graphite coupons using a cocktail of acids (0.25 M HNO3 − 1 M HCOOH − 0.2 M [N2H5][NO3]). Based on the superlative effects of ionic liquids in lubrication and erosion prevention, the effect of adding ionic liquid stabilized Pd nanoparticles to the leachate was also studied. It was observed that the Trioctylmethyl ammonium chloride (TOMAC) ionic liquid prevented the generation of the carbon residue due to a protective viscous layer formation reducing the mechanical effects of cavitation on graphite surface. It also helped in maintaining the porosity change in graphite microstructure around 5% after 15 cycles of decontamination. TOMAC also proved to offer better surface protection on graphite compared to imidazolium-based ILs, based on the change in compressive strength and porosity in different ionic liquids. The palladium nanoparticles, on the other hand, helped in reductive dissolution of ceria layer by acting as a reducing agent due to its lower reduction potential compared to cerium. With the surge in demand of graphite worldwide, a non-destructive decontamination process for graphite with no secondary waste generation is the need of the hour. This study is an attempt in that direction.

Insertion of AlCl3 in graphite as both cation and anion insertion host for dual-ion battery

Dual-ion batteries (DIBs) are emerging energy storage devices with the unique energy storage mechanism in which both anions and cations are involved during charge-discharge processes. Graphite is usually used as both cathode and anode in DIBs, however, the limited layer spacing and the elongated diffusion channels make the ion migration resistance larger. To break the bottleneck, a strategy is proposed by incorporating AlCl3 into the layer of graphite, which increases the layer spacing while acting as a pillar to stabilize the structure. In addition, a significant fraction of defects is inducted at the edges of the folds of graphite. This engineering accelerates the electron/ion transport on the stable graphite stacking microstructure. As a result, it could be used as both cation and anion insertion host in DIBs. Electrochemical tests showed that AlCl3-GICs-5 materials could deliver a Li+ storage capacity of 169.1 mAh g−1 at 2A g−1 when cycles consistently for over 500 cycles which is much higher than graphite (60.7 mAh g−1). Furthermore, when used as a PF6− insertion cathode in a DIB, it showed a high specific capacity of 100.8 mAh g−1at 100 mA g−1. This research is anticipated to provide inspiration to design new materials for DIBs.

Fabrication and Enhanced Supercapacitive Performance of Fe2N@Cotton-based Porous Carbon fibers as Electrode Material

With the emergence of supercapacitors (SCs), the creation of bio-based electrode materials has grown in significance for the advancement of energy storage. However, it is particularly difficult for cathode materials to meet the demands of practical uses due to their low energy density. Herein, MIL-88 was fabricated in situ on the surface of cotton fibers used in cosmetics, followed by creating Fe2N@porous carbon fiber composite (Fe2N@PCF) through heat treatment at various temperatures. Fe2N@PCF-800 demonstrates excellent specific capacitance performance (552 F g−1 at 1 A g−1). Meanwhile, The AC//Fe2N@PCF-800 device exhibits the largest energy density of 38 Wh kg−1 at 800 W kg−1 and a long cycling stability (83.3% capacity retention after 6000 cycles). Our elaborately designed Fe2N@PCF demonstrate multiple advantages: i) the Fe2N@PCF-800 shows abundant mesopores, providing abundant ion-diffusion pathways for mass transport and rich graphite microstructures, improving electrical conductivity for electron transferowning; ii) the rich nitrogen dopants and Fe2N structure within all carbon components increase the capacitance through their pseudocapacitive contribution. These findings highlight the importance of biomass derived carbon materials for SCs applications.

Comparison of Cold-Sprayed Coatings of Copper-Based Composite Deposited on AZ31B Magnesium Alloy and 6061 T6 Aluminum Alloy Substrates.

Copper-coated graphite and copper mixture powders were deposited on AZ31B magnesium alloy and 6061 T6 aluminum alloy substrates under different process parameters by a solid-state cold spray technique. The microstructure of the copper-coated graphite and copper composite coatings was visually examined using photographs taken with an optical microscope and a scanning electron microscope. The surface roughness of the coatings was investigated with a 3D profilometer. The thickness of the coatings was determined through the analysis of the microstructure images, while the adhesion of the coatings was characterized using the scratch test method. The results indicate that the surface roughness of the coatings sprayed on the two different substrates gradually decreases as gas temperature and gas pressure increase. Additionally, the thickness and adhesion of the coatings deposited on the two different substrates both increase with an increase in gas temperature and gas pressure. Comparing the surface roughness, thickness, and adhesion of the coatings deposited on the two different substrates, the surface roughness and adhesion of the coatings on the soft substrate are greater than those of the coatings on the hard substrate, while the thickness of the coatings is not obviously affected by the hardness of the substrate. Furthermore, it is noteworthy that the surface roughness, thickness, and adhesion of the copper-coated graphite and copper composite coatings sprayed on the two different substrates exhibit a distinct linear relationship with particle velocity.

Ion-beam-milled graphite nanoribbons as mesoscopic carbon-based polarizers

We demonstrate optical reflectivity and Raman responses of graphite microstructures as a function of light polarization when the incident light is applied perpendicular to the material's stacking direction (c-axis). For this, we employed novel graphite nanoribbons with edges polished through ion-beam etching. In this unique configuration, a strong polarization dependence of the D, G, and 2D Raman modes is observed. At the same time, polarized reflectivity measurements demonstrate the potential of such a device as a carbon-based, on-chip polarizer. We discuss the advantages of the proposed fabrication method as opposed to the mechanical polishing of bulk crystals.

Catalytic graphitization of coke and electrochemical performances of coke-based graphite

The effect of minerals on the high-temperature graphitization process of coke was thoroughly investigated using by X-ray diffraction (XRD), Raman spectroscopy (Raman), scanning electron microscope (SEM), physical adsorption instrument, etc. The structure-activity relationship between the microstructure of coke-based graphite and lithium storage performances was identified. The findings demonstrate that the microstructure of coke-based graphite is related to the mineral content and the final graphitization temperature affects the Si or Fe catalytic graphitization of coke. The appropriate amount of minerals as the catalyst can reduce the interlayer spacing, improve the graphitization degree and increase the crystallite size of the coke graphitization sample. The catalytic graphitization of coke involves the carbide transition, which is further confirmed by XRD and SEM-EDS analysis. By proper adding the mineral to the coke during the graphitization process, it is clear that the electrochemical performances of the synthetic graphite as anode for lithium-ion batteries can be improved obviously. Coke-based graphite DCG-20Si-2800 and DCG-30Fe-2800 as anode material show good comprehensive electrochemical performances. And the reversible specific capacities of both at 0.1 C are as high as 353.9 mAh/g and 361.9 mAh/g, respectively, which are quite close to the theoretical capacity of graphite (1 C = 372 mAh/g). Thus, the study successfully reveals the law of mineral catalysis in the graphitization process of coke and demonstrates the feasibility of coke-based graphite products as anode material. It can be expected that coke can be useful sources of artificial graphite if the graphitization process is adequately improved.