Properties Of Graphite Research Articles

Glow-to-arc transition in graphite cathode with high-current magnetron discharge

The glow-to-arc transition is a critical phenomenon in plasma discharges, commonly leading to detrimental effects. The physical mechanisms triggering this transition remain poorly understood. The advent of a discharge called Hyper-Power Impulse Magnetron has opened possibilities. Hyper-Power Impulse Magnetron allows the glow mode to be maintained over long periods (1 ms) and at high-current densities (>5 A .cm−2), which has unveiled certain features in the glow-to-arc transition. This work focuses on a graphite target that transits easily in the arc regime. The high-speed video-camera analysis revealed specific properties of graphite in ExB discharges, and the statistical study of the arc transition revealed differences from other refractory target materials. The early stage of cathodic spot formation, observed as bright dots, will be presented and analyzed within the known “ecton” and “vaporization” models for spot formation. This experimental study highlights the role of luminous spot formation prior to arc transition, with possible optimization on the stability of magnetron discharges.

Enhanced thermal and mechanical properties of flame-retardant expandable graphite modified silk fibroin-based rigid polyurethane foam

At present, in order to reduce the environmental pollution caused by the use of petrochemical products, the preparation of flame-retardant polyurethane foam (PUF) using green raw materials is increasingly attracting widespread attention. A biomass protein-based green flame-retardant rigid PUF (RPUF) with expandable graphite (EG) and silk fibroin (SF) was prepared in a one-step process. Thermal stability, combustion characteristics and compression properties of modified RPUFs were investigated by thermogravimetric analysis, cone test, limiting oxygen index (LOI) test, UL-94 vertical burning test and mechanical compression test. The RPUF with 10 wt% EG (RPUF-SF/EG10) exhibited superior heat resistance, with the highest initial decomposition temperature (Ti), integral programmed decomposition temperatures (IPDT) and activation energy (E). And RPUF-SF/EG10 had the lowest peak heat release rate (PHRR) and total heat release (THR), and it also showed the highest LOI and had a flammability rating of V-0. In Addition, the apparent density and compressive strength of RPUF-SF/EG10 were the largest among the four EG-added materials. The results indicated that RPUF-SF/EG10 had excellent thermal stability, flame retardancy and compression resistance, which was attributed to the synergistic effect of SF and EG in the system. This provided a valuable reference for the development of new, environmentally friendly and high-performance RPUFs.

Synthesis and characterization of bacterial cellulose composite with graphite and TiO2-ZnO: structural and functional analysis

This research aims to synthesize and characterize a bacterial cellulose (BC)-based composite with graphite and TiO2-ZnO as reinforcement materials using ex-situ synthesis with CTAB as a surfactant. FTIR and SEM-EDS analysis revealed interactions between the matrix and the reinforcement materials, as well as irregular particle distribution in the BC/G-TiO2-ZnO composite. The addition of graphite to BC significantly increased the conductivity of the composite, while the addition of TiO2-ZnO had the opposite effect. The mechanical properties of the composite exhibited an inverse relationship with the conductivity parameter. Swelling tests indicated that pH and the addition of CTAB influenced the swelling behavior of the BC-based composite. The results of this study provide a strong foundation for the development of potential applications in the fields of electronics and pollutant filtration. The synthesis of this composite aims to harness the unique properties of BC, graphite, and TiO2-ZnO, creating a multifunctional material with potential uses in flexible electronics, sensors, biocompatible conductive materials, and advanced filtration systems.

Correlation study of graphitic shell encapsulated nickel: A multi-spectroscopic approach

Graphite-encapsulated metal nanoparticles hold great potential across various applications due to their unique combination of metal and graphitic properties. While Raman spectroscopy is widely used to assess the graphitic shells, metrics derived from prominent Raman bands often prove unreliable when analyzing such structures with a large number of heterogeneous flakes and are mostly applicable to few-layer graphene. However, researchers continue to face challenges in identifying reliable metrics that accurately reflect two key properties of graphitic shells: thickness and degree of graphitization. In this study, graphitic shells were synthesized via plasma-enhanced chemical vapor deposition (PECVD) at low temperatures (500 °C), seeded by nickel nano-islands. A full-factorial experiment was designed to explore a diverse sample space by varying two key input factors: the initial thickness of the nickel seeding film and the duration of carbon deposition. Using resource-intensive surface characterization techniques (SEM, EDS, XPS, and AFM), we verified encapsulation efficiency and morphology, identifying strong correlations between the input factors and properties of the shells. To gain insights into structural characteristics, we employed conventional spectroscopy techniques (Raman, UV–Vis-nIR transmission, and Transient Absorption Spectroscopy), introducing 107 metrics derived from spectral data. Principal Component Analysis (PCA) aligned the input factors, and their corresponding shell properties, with the first two principal components. Accordingly, we identified the most relevant metrics including new candidates derived from less prominent Raman bands. Additionally, inter-metric correlations enable interchangeable use of spectroscopy techniques. This study marks the first multi-spectroscopic correlation analysis of graphitic shells and provides a novel framework for evaluating their properties.

Nanoscale friction and wear of graphite surface in ambient and underwater conditions

The tribological properties of graphite are extremely sensitive to surrounding environment, which affects its longevity and friction reduction performance. This study aims to develop a comprehensive understanding of the effects of a liquid environment on interactions at the sliding interface, thereby influencing the nanoscale tribological properties of graphite surfaces. By combining atomic force microscopy experiments and molecular dynamics simulations, we conducted a comparative analysis of friction and wear behavior of graphite under two different environmental conditions: ambient (air) and underwater condition. Our investigations explored both the step edge and interior (step-free) graphite surfaces. The experimental results revealed a notable contrast in the frictional and wear behavior of graphite at nanoscale in these two environments. The interior surface exhibited a friction coefficient (COF) of approximately 0.003 and 0.006 against a diamond-coated surface in ambient and underwater conditions, respectively. Interestingly, the underwater environment not only increased friction but also significantly compromised the wear resistance of graphene layers near the graphite surface compared to the ambient environment, as evidenced in both step edge and interior step-free regions. The interior region sustained up to ∼7400 nN load in ambient condition but failed at ∼1500 nN under water. Similarly, the step edge failed at ∼375 and ∼187.5 nN in ambient and underwater conditions, respectively. Our simulations revealed that the increased friction in underwater condition is due to resistance of surrounding water molecules during tip sliding. The presence of water at tip-graphite contact interface generated substantial localized stress, leading to the initiation of wear and revealing the pronounced effect of water on the wear characteristics of graphite in underwater condition.

Effects of ultraviolet sterilization exposure on the structural and surface properties of graphite-/polymer-like carbon films

Existing research on the biological responses of amorphous carbon films has not adequately explored the influences of exposure to ultraviolet (UV) sterilization at 253.7 nm before cell culture. Thus, in this study, two types of amorphous carbon films, namely hydrogen-rich graphite-like carbon (GLC) and hydrogen-free polymer-like carbon (PLC) films, were deposited on Si substrates. The influences of different doses of UV sterilization exposure (at 253.7 nm) on the structures and surface properties of the amorphous carbon films were investigated. Spectroscopic ellipsometry and Raman analysis showed that there is no significant change in the optical constants and Raman spectra of GLC and PLC films. The surface properties of the amorphous carbon films, characterized by water contact angle measurements and X-ray photoelectron spectroscopy analysis, indicated that both types of films exhibited hydrophilicity and surface oxidation in response to UV sterilization. However, the effects of UV sterilization on PLC were more notable than those on GLC. Our findings highlight the need for standardization and optimization of UV sterilization conditions for specific films to promote the application of amorphous carbon film coatings in the medical domain.

Coarse-grained molecular dynamic model and wettability simulation of graphite materials

Although progress has been made in high-performance computing, there are still limitations on temporal and spatial scales of molecular dynamic calculations. A major issue in molecular dynamic (MD) simulations is the computational cost, and coarse-grained methods can save computational costs and accelerate calculations by reducing the degrees of freedom in the system. This method takes a selected group of representative atoms in the atomic microstructure as a bead and uses the proportional relationship of atomic scale atomic potentials in MD simulation to define the interaction between beads and solve the motion equation of beads. This article proposed a coarse-grained potential for graphite based on the modification of Airebo potential, with an n3: 1 mapping, and established a corresponding n3: 1 coarse-grained model, where one bead represents the number of n3 atoms. The results indicated that the coarse-grained model well reflected the basic thermal and mechanical properties of graphite. In addition, this article also proposed a coarsening method for the Lennard–Jones (L–J) potential function parameters and established a coarse-grained wetting model with n = 2. The results indicate that the coarse-grained wetting model can effectively predict the wetting performance of copper droplets on graphite in only 60% of the time using the all-atom model. The coarsening potential function and model proposed in this article are also applicable to graphite with rough surfaces. It can be anticipated that coarse-grained molecular dynamics methods will have more applications in the future, as they can handle large-scale calculations more quickly.

A Novel Structured Si‐Based Composite with 2D Structured Graphite for High‐Performance Lithium‐Ion Batteries

AbstractSilicon is a promising alternative to graphite anodes for achieving high‐energy‐density in lithium‐ion batteries (LIBs) because of its high theoretical capacity (3579 mAh g−1). However, silicon anode must be developed to address its disadvantages, such as volume expansion and low electronic conductivity. Therefore, the use of silicon as composed with graphite and carbon anode materials is investigated, which requires properties such as a spherical morphology for high density and encapsulation of silicon particles in the composite. Herein, a graphite@silicon@carbon (Gr@Si@C) micro‐sized spherical anode composite is synthesized by mechanofusion process. This composite comprises an outer surface, middle layer, and core pore, which are formed by the capillary force arising from 2D structured graphite and pitch properties. This structure effectively addresses the intrinsic issues associated with Si. Gr@Si@C exhibits a high capacity of 1622 mAh g−1 and capacity retention of 72.2% after 100 cycles, with a high areal capacity 4.2 mAh cm−2. When Gr@Si@C is blended with commercial graphite, the composite exhibits high capacity retention and average Coulombic efficiency after cycling. The Gr@Si@C blended electrode exhibits a high energy density of 820 Wh L−1 with ≈16% metallic Si in the electrode (40 wt.% composite), enabling the realization of practical commercial LIBs.

Sustainable Fabrication of Graphene Oxide Cathodes from Graphite of Failed Commercial Li-Ion Batteries for High-Performance Aqueous Zn-Ion Batteries.

The need for revamping spent graphite (SG) from battery waste of commercial lithium-ion batteries and employing it as a source for the synthesis of graphene oxide (GO) is focused. Thus, this work emphasizes the study of GO sheets, synthesized via modified Hummer's method from spent graphite (SG-GO) as cathodes for an aqueous zinc ion battery (AZIB) system, for the first time in literature. For comparison, graphene oxide is also synthesized using commercial graphite powder, its structural and morphological properties are analyzed with SG-GO. The coin cell AZIB device is fabricated for both the GOs and the electrochemical performances revealed that SG-GO portrayed an enhanced charge capacity of 270 mAh g-1 at 0.1 A g-1 in 3m ZnSO4 in comparison to GO which delivered ≈198 mAh g-1 at the same current density of 0.1 A g-1. The long-run cycling analysis of SG-GO elucidated the capacity retention of 77.3% at 1 A g-1 even after 1000 cycles. Moreover, the performance of SG-GO is inspected in different electrolyte systems and the suitable electrolyte underwent concentration variation studies to figure out the capability of the system in storing Zn2+ ions which is found to be more in 3M ZnSO4 electrolyte.

Enhanced mechanical, tribological and corrosion properties of graphite and carbon nanotube-reinforced copper-based hybrid composites

Copper (Cu)-based hybrid composites were fabricated by powder metallurgy, incorporating Graphite (Gr) and Carbon nanotube (CNT) reinforcements at various fractions. The composites were formed using a cold pressing technique and subsequently sintered at various temperatures. The structural properties of the hybrid composites were evaluated using Scanning Electron Microscopy (SEM), Energy Dispersion Spectrum (EDX) and X-ray diffraction (XRD). Hardness, compression, wear and corrosion tests were performed to show the effect of the reinforcements. It was shown that the hardness of Gr and CNT reinforcements have significantly improved the properties of pure Cu. The Cu-Gr-2CNT hybrid composite, which was subjected to sintering at a temperature of 850°C, exhibited the highest level of hardness, showing a significant increase of 51.4% in comparison to the pure Cu sample. While the compressive stresses increased in the Cu matrix with the addition of Cu-Gr, it increased to 350 MPa with the addition of 2 wt% CNT. The hardness value exhibited a similar increase and was measured to be 122 HV in Cu-Gr-2CNT. During the wear tests, the coefficient of friction values fell by 9.2% for Cu-2CNT, by 3.88% for Cu-CNT, by 3.92% for Cu-Gr-2CNT, and by 5.27% for Cu-Gr-CNT, as compared to pure Cu. The comprehensive findings demonstrated that the tests and analyses yielded consistent results, and the utilization of various combinations of Gr and CNT reinforcements enhanced the mechanical, tribological, and corrosion resistance properties of the fabricated hybrid composites. Nevertheless, the combination of Cu-Gr-2CNT yielded the most advantageous outcomes.

Unveiling the Interplay Between Silicon and Graphite in Composite Anodes for Lithium-Ion Batteries.

Si provides an effective approach to achieving high-energy batteries owing to its high energy density and abundance. However, the poor stability of Si requires buffering with graphite particles when used as anodes. Currently, commercial lithium-ion batteries with Si/graphite composite anodes can provide a high energy density and are expected to replace traditional graphite-based batteries. The different lithium storage properties of Si and graphite lead to different degrees of lithiation and chemical environments for this composite anode, which significantly affects the performance of batteries. Herein, the interplay between Si and graphite in mechanically mixed Si/graphite composite anodes is emphasized, which alters the lithiation sequence of the active materials and thus the cycling performance of the battery. Furthermore, performance optimization can be achieved by changing the intrinsic properties of the active materials and external operating conditions, which are summarized and explained in detail. The investigation of the interplay based on Si/graphite composite anodes lays the foundation for developing long-life and high-energy batteries. The abovementioned experimental methods provide logical guidance for future research on composite electrodes with multiple active materials.

Adsorption Performance of Modified Graphite from Synthetic Dyes Solutions.

Due to the severe harmful impacts of industrial dyeing wastewater on ecosystems and human health, proper treatment is crucial. Herein, the use of modified graphite as an adsorbent for dyeing wastewater treatment was investigated in this study. The graphite was oxidized and intercalated using a phosphoric acid-nitric acid-potassium permanganate system and then thermally treated at high temperatures to optimize its structure. By adjusting the thermal treatment temperature, the graphite adsorbent with varying porosity was obtained. The optimized graphite demonstrated significant improvement in adsorption performance for dyes and organic compounds, achieving a removal rate of over 85% for methylene blue (MB) dye. The optimal adsorption performance is achieved with a 1.6 mg modified graphite adsorbent at 60 °C under alkaline conditions for adsorbing 10 ppm MB. Adsorption kinetics and isotherm models were applied to elucidate the adsorption mechanisms. The results fit the Langmuir model, suggesting that monolayer homogeneous adsorption is favorable. Importantly, the results demonstrate that high-temperature treatment can significantly enhance the adsorption properties of coal-based graphite, supporting its application in dyeing wastewater treatment.

3D analysis of crack propagation in nuclear graphite using DVC coupled with finite element analysis

The initiation and propagation of cracks within nuclear graphite components compromise the lifespan of advanced gas-cooled reactors and even lead to safety incidents. A thorough understanding of fracture properties in nuclear graphite is crucial for the effective management and design of graphite structural components. In this work, an in-situ test of a double cleavage drilled compression (DCDC) specimen was conducted using X-ray tomographic imaging to fully analyze the 3D crack propagation behavior in IG-11 nuclear graphite. “Subvolume Splitting” digital volume correlation (SS-DVC) was employed to accurately quantify the displacement fields surrounding the crack. The entire 3D crack propagation and crack surface around the crack front were precisely captured through 3D imaging processing of the gray level residual (GLR) field. Additionally, crack opening displacements (CODs) and stress intensity factors (SIFs) were determined using finite element (FE) analysis with extended finite element method (XFEM). Experimental results indicate that although mode I crack remains predominant throughout the whole process, complex crack propagation exists around the crack front. The utilization of irregular crack surfaces in FE analysis helps to obtain refined displacement fields and accurate SIFs of the crack front. This work provides comprehensive insights into crack propagation and reveals the influence of complex crack morphology on SIF calculations, facilitating accurate prediction of structural integrity and rational design of graphite components.

Evaluation of wear and friction properties of graphite modified Lubri polylactic acid with various infill fabricated by additive manufacturing techniques

AbstractThree‐dimension (3D) printing technology, also known as additive manufacturing, is a manufacturing technology that creates three‐dimensional objects by depositing material layer by layer, as opposed to subtractive manufacturing methods. However, the newness of the technology brings with it many unknowns. In particular, the raw materials used are constantly increasing. For this reason, testing each raw material used in many aspects and to determine the optimum production conditions is important for the wide use of 3D printing technology. These optimal conditions may be the parameters used to produce a material, and sometimes they can appear as a new material. In addition, the production of new materials with varying production parameters is fundamental research topic that requires comprehensive study. For all these purposes, in this study, a new material type known as Lubri PLA (LPLA) was selected and produced in different filling types and subjected to a series of friction and wear tests. Thus, it is aimed to determine the tribological properties of the material. Additionally, samples were produced in ten different infill types (grid, lines, triangels, hexagon, cubic, octal, zigzag, diagonal, diagonal 3D and gyroid) to show the effect of filler type on friction and wear behavior. These filler types were used for both PLA and Lubri PLA materials and a total of twenty samples were produced. Thereby, it is aimed to conduct a comprehensive study showing the effect of both material difference and filling type on friction‐wear behavior. Diameter deviations, hardness deviations, friction coefficient, temperature, specific wear rates (SWr), and vibration were selected as output parameters. According to the analysis of the test results, the best result in terms of material structure was given by Lubri PLA, while the best result in terms of filling type was obtained with Diagonal 3D filling type. In addition, the lowest vibration level was obtained in the LP‐Diagonal 3D sample with 0.041 mm/s2, while the highest vibration level was obtained in the P‐Grid sample with 1.756 mm/s2.Highlights LPLA closed to nominal value in diameter and hardness deviations Addition of graphite nanoparticle increased the dimensional accuracy Diagonal 3D infill type Lubri PLA composites showed the superior performance Graphite modified Lubri PLA composites demonstrated superior performance

Elucidating the impact of non-spherical morphology on kinetic behavior of graphite using single-particle microelectrode

The precise assessment of the kinetic properties of graphite is crucial for the design of the material and the development of electrochemical models for lithium-ion batteries. However, conventional evaluation methods using composite electrodes fall short in excluding the influence of its porous structure and evaluating the influence of particle shape on kinetic behavior. In this work, we elucidate the impact of non-spherical morphology on kinetic behavior of single artificial graphite particle, employing the single-particle microelectrode technique. Three single artificial graphite particles with different sizes are pre-cycled and exhibit outstanding rate capability, maintaining a maximum capacity retention of 78.1 % at 200 C. Further, exchange current density and diffusion coefficients are determined through Tafel plots and the potentiostatic intermittent titration technique (PITT), respectively. It is found that the particle with a higher exposure of edge planes present elevated exchange current density and diffusion coefficients. Considering that the graphite particles typically feature an ellipsoidal rather than spherical shape, we propose an approach based on an ellipsoidal diffusion model for extracting diffusion coefficients. This model takes into account the non-spherical morphology of graphite, addressing the limitations inherent in the geometric assumptions of previous methods. The average relative error between the diffusion coefficients derived from the ellipsoidal diffusion model and the previous method using spherical assumptions is 215 %, indicating that accurately depicting the shape of ellipsoidal graphite particles in the model is crucial for obtaining correct estimates of kinetic parameters. This study offers direct experimental evidence of superior kinetic behavior of edge planes over basal planes. To leverage this characteristic, it is recommended to employ an out-of-plane aligned architecture for composite electrodes using novel techniques, e.g., 3D printing or magnetic alignment techniques.

Morphology Matters: Surface Properties Inform ALD Deposition and Subsequent Electrochemical Performance in Graphite Substrates

The physical properties of graphite, such as pore volume, shape, and crystallinity; are critical factors in determining the performance of a li-ion cell. These properties are determined by the graphite manufacturing process, which often terminates with a surface treatment process to optimize the morphology. Currently most surface treatments are done using a carbon pitch coating, which involves a high temperature, multi-step process. Coatings using atomic layer deposition (ALD) are, by comparison, less energy intensive and a more customizable approach to target specific physical properties leading to increased cycle life, higher coulombic efficiency, and better rate performance. In this work we will show how ALD coatings are optimized based on the graphite production process and resulting particle morphology. We will demonstrate that these optimized coatings will serve to reduce surface area, prevent graphite exfoliation, and improve li-ion diffusion pathways.

Ultrathin Graphite‐Based Full‐Color Electrochromic Devices

AbstractUltrathin graphite‐based materials have revolutionized optoelectronics through their multispectral and energy‐efficient tunability. However, their narrow color range poses a challenge in applications requiring a broad spectrum of colors for effective information delivery or aesthetic enhancement. Here, full‐color tunability is achieved in ultrathin graphite‐based electrochromic devices using Fabry‐Perot (F‐P) nanocavities. By adjusting the optical properties (n, k) of ultrathin graphite through lithium‐ion intercalation/de‐intercalation and the thickness of the dielectronic SiO2 layer, managed to control the optical reflectivity in the visible spectrum. Moreover, this prototype device consumes only 1.59 mW cm−2, just one‐tenth of the commercial organic light‐emitting displays’ energy usage. Furthermore, the pixel size in the Fabry‐Perot nanocavity‐type electrodes can be reduced to 2 µm, under half that of contemporary displays like Micro‐LED. These results pave the way for full‐color displays with minimal energy consumption and inspire extensive research in low‐power photonics.

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

Comparative study on fretting friction and wear characteristics of different impregnated graphite for sealing application

Impregnated graphite has attracted considerable attention and has been widely used as an ideal sealing material in many fields. However, the service environment often contains vibrations, which can easily lead to severe fretting wear and leakage. In this study, the fretting friction and wear properties of resin-impregnated graphite and antimony-impregnated graphite were investigated. The results revealed that only gross slipping regime (GSR) occurred for two impregnated graphite. For resin-impregnated graphite, both abrasive and adhesive wear were discovered. Yet slight fatigue wear occurred on the worn surface of antimony-impregnated graphite at higher cyclic contact stress. The significant properties of the impregnated graphite can be attributed to a transfer film, which uniformly and stably adsorbs on the contact interfaces. This study provides an important basis for matching the industrial applicability of graphite-based modified sealing materials.

Multi-pulse femtosecond laser ablation of SiC/SiC composites: Morphological evolution, oxidation mechanisms and component characterization

SiC fiber reinforced SiC matrix (SiosC/SiC) composites processed by femtosecond laser play a pivotal role in thermal protection systems. This paper reveals the ablation characteristics of multi-pulse femtosecond laser ablation of SiC/SiC composites, including morphological evolution, oxidation mechanisms and component characterization by heat accumulation simulation and advanced experimental analysis. The results show that the ablation depth induced by the heat accumulation effect is an exponential function of laser parameters. Morphological analysis and component characterization indicate that two types of ablation regions are formed, normal ablation region is an oxidized zone induced by passive oxidation mechanism, and central ablation region is a non-oxidized zone induced by active oxidation mechanism. The increase of single pulse energy and decrease of scanning speed enhance the driving force of chemical reactions, thus dramatically affecting the gas hole and graphite properties in the normal ablation region. Furthermore, the propagation path of thermal stress-induced cracks is determined which emerges from the center ablation region, extending through gas holes to the normal ablation region.