Graphite Particles Research Articles

Effects of Adding Graphite to Epoxy Resin on its Mechanical Properties and Mild-to-Severe Wear Performance at its Heat Distortion Temperature

In this study, epoxy/graphite composites were fabricated based on different weight fractions (0, 3, 6, and 9 wt.%) of graphite powder for bearing applications. The mechanical and tribological properties were assessed. Adhesive wear tests covered the severe regions, where the interface temperature (IFT) exceeded the heat distortion temperature (HDT) of the epoxy. Graphite additions improved elastic modulus and hardness but decreased fracture strain and toughness of the composites. The tribological behaviors in the mild wear region were improved as the graphite content increased. In the mild wear region, the increase in graphite additions showed a good improvement by reducing the specific wear rate (SWR) and coefficient of friction (COF). In the severe wear region, the neat epoxy and higher graphite concentrations exhibited a dramatic increase in SWR, whereas the lowest addition of 3 wt.% exhibited good wear performance. For epoxy, the reason was that IFT exceeded its HDT, while the aggregation of graphite particles was the main reason in the case of higher graphite concentrations. SEM examinations showed severe wear signs—high ploughing and fracture—when IFT exceeded the HDT. However, by reducing the IFT, graphite additions did not show such severe wear features due to the accelerated heat dissipation.

The aging pattern of lithium-ion batteries based on experiments at different temperatures

Abstract In this paper, we take an 18650-type LiFePO4 battery as the research object to investigate the aging mechanism of Li-ion batteries at different temperatures. The aging tests are conducted at 25°C, 35°C and 45°C. The results show that elevating the operating temperature can improve the cycle life of Li-ion batteries. The aging mechanism was analyzed by incremental capacity and electrochemical impedance spectrum analysis. The following conclusions were obtained: the aging mechanism of lithium-ion batteries mainly includes loss of lithium inventory, loss of active material, and conductivity loss, among which loss of lithium inventory and loss of active material are the main causes of Li-ion battery aging, and the contribution of conductivity loss is the smallest. Further analysis of the causes of battery aging by disassembling and testing the aging electrode sheet SEM and TEM shows that the aging of Li-ion battery is manifested by the rupture of graphite particles, the generation of SEI layer and lithium dendrite, and increasing the temperature can ease the rupture of graphite particles and the generation of lithium dendrite, thus improving the cycle life of the battery.

Mechanical mechanism of shear cavitating water jet dissociation of flake graphite

Abstract To obtain the mechanical mechanism of shear-type cavitation water jet dissociating flake graphite to improve the grinding technology of flake graphite, the motion state of flake graphite particles in shear-type cavitation water jet, the micro-jet impact process, the high-pressure elastic potential energy pressure release process, and the water wedge stretching process have been analyzed using the theory of hydraulic transport of liquid-solid two-phase, the theory of jets, the cavitation primordial principle, the principle of capacity conversion, and the water wedge action. The primary mechanical mechanism of shear cavitation water jet dissociation of flake graphite is collision friction effect, micro-jet impact, pressure release, and water wedge stretching effect, under these four kinds of loads individually or jointly, to achieve the purpose of removing the surface of flake graphite particles of the veinstone minerals to realize the dissociation of flake graphite. Moreover, the collision friction, pressure release, and water wedge stretching effects destroy the material under tensile stress to remove the veinstone minerals, and the micro-jet impact effect is the destruction of the material under compressive stress to remove the veinstone minerals.

A Macroscopic Interpretation of the Correlation between Electrical Percolation and Mechanical Properties of Poly-(Ethylene Vinyl Acetate)/Zn Composites.

Elastic composites were prepared using a procedure involving hot plates and zinc powder that was directly dispersed into an EVA matrix. The correlation between the zinc content and the conductive properties of the material was studied via impedance spectroscopy, the thermal properties of the material were studied via differential calorimetry and the mechanical properties of the composites were studied via tensile strength curves, representing an important advancement in the characterization of this type of composite material. The composites' tensile strength and elongation at break decrease with the addition of filler since zinc particles act as stress-concentrating centres, while the composites' hardness and Young's modulus increase because of an increase in the stiffness of the material. The AC perturbation across the EVA/Zn composites was characterized using an RC parallel equivalent circuit that allowed us to easily measure their resistivity (ρp) and permittivity (εp). The dependence of these electrical magnitudes on the zinc content is correlated with their mechanical properties across the characteristic time constant τp = ρp·εp of this equivalent circuit. The dependence of the mechanical and electrical magnitudes on the zinc content is consistent with the formation of percolation clusters. The addition of graphite particles increases their potential performance. Three possible mechanisms for the electrical transport of the ac-perturbation across the EVA/Zn composites have been identified. Chemical corrosion in acid media causes the loss of zinc surface particles, but their bulk physical properties practically remain constant.

Tribological investigation into nickel-coated graphite polytetrafluoroethylene composites

The friction and wear resistance of polytetrafluoroethylene (PTFE) composites can be enhanced by incorporating nickel-coated graphite. An electroless coating method employing Gin plates (418A, 418B) is utilized to produce nickel-coated graphite. X-ray diffractometer analysis reveals the presence of nickel and graphite peaks in the coated graphite powders at 44° and 26.4°, respectively. Scanning electron microscopy images confirm the presence of nickel coating on graphite particles. Tribological tests using a pin-on-disc tribometer (L9) demonstrate that composites filled with 20 wt.% Nickel-coated graphite exhibits the lowest wear rate of 220 µm, compared to 1166 µm for pure PTFE specimens. The notable improvement in wear resistance is attributed to enhanced bonding strength between the filler and matrix material. Pure PTFE exhibits varying coefficient of friction (CoF) at different parameters, with the highest and lowest CoF observed at 200 rpm, 20N and 180 rpm, 10 N, respectively. Optimal parameters for minimizing wear rate and CoF, determined through analysis of means, include a 20 wt.% filler concentration, disc speed of 180 rpm, and 10N load. Analysis of variance identifies composition and speed as primary factors affecting wear and CoF.

Relationship between particle shape and fast-charging capability of a dry-processed graphite electrode in lithium-ion batteries

Improving lithium-ion transport in electrodes by controlling electrode microstructure is a promising option for enhancing the fast-charging capability of graphite anodes in lithium-ion batteries. Dry processing of electrodes based on a polytetrafluoroethylene binder has attracted considerable attention as an alternative to solvent-based wet processing. The morphology of graphite particles has a significant impact on electrode microstructure, but few reports have been published on dry-processed graphite anodes. In this work, we found that the morphology of graphite particles is a key factor to determine the fast-charging capability of the dry-processed graphite electrode as well as the microstructure of the dry-processed graphite electrode. X-ray microscopy combined with mercury porosimetry and symmetrical cell electrochemical impedance spectroscopy reveal that the difference in porosity between the top and bottom layers of a dry electrode with spherical graphite particles is greater than that of flake-shaped graphite particles, resulting in enhanced lithium-ion transport in the electrode and improved fast-charging capability at a high charging rate of 5C (17.5 mA cm−2). These findings supply insights into the effective design of dry-processed graphite anodes with an emphasis on fast-charging capability as well as the development of graphite anode materials for dry-processing based lithium-ion batteries.

Leaching kinetics of ash impurities from aphanitic graphite by combining dual-ultrasound and hydrochloric acid–potassium hydrogen fluoride

The hydrochloric acid-fluoride salt is useful for purifying graphite. Ultrasonic-assisted technique can significantly reduce the leaching time and improve the leaching efficiency. Compared with single-frequency, dual-frequency ultrasound has the advantages of high energy efficiency and wide cavitation area. In this study, the combination of a dual-frequency ultrasound-assisted technique and hydrochloric acid–potassium hydrogen fluoride leaching agent was proposed for the leaching of aphanitic graphite to remove impurity minerals. First, the effects of probe-type ultrasonic power, tank-type ultrasonic power, temperature, HCl concentration, ultrasonication time, and KHF2 concentration on the purification efficiency of impurities from aphanitic graphite with the assistance of dual-frequency ultrasound were investigated. It was found that the combination of dual-frequency ultrasound and hydrochloric acid–potassium hydrogen fluoride can reduce the ash content of aphanitic graphite from 13.02 % to 1.02 % with an ash removal rate of 94.17 %. Second, volumetric reaction models and unreacted shrinkage nucleation models were used to fit the kinetics of impurities from aphanitic graphite with dual-frequency ultrasound-assisted HCl-KHF2 leaching. Kinetic analysis shows that the volumetric reaction model with chemical control was better to fit the leaching process. This is consistent with the calculation results of the activation energy of the reaction (Ea = 58.13 kJ/mol). Finally, laser particle size analyzer, X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) were used to analyze the fugacity of impurity minerals during the process of dual-frequency ultrasound-assisted HCl-KHF2 leaching. It was revealed that combining ultrasonic cavitation fragmentation with chloric acid–potassium fluoride generated SiF4 with high solubility, thereby removing silica-bearing impurities more efficiently. The challenges in further reducing ash content from 1.02 % in the leached concentrate of aphanitic graphite could be attributed to the existence of titanium-bearing mineral impurities on the surface of graphite particles and the presence of silica-bearing minerals between graphite carbon layers.

Promoting CH4 Hydrate Formation Kinetics by Utilizing Synergistic Promotion Effects of Graphite Particles with Sodium Dodecyl Sulfate

Promoting CH₄ Hydrate Formation Kinetics by Utilizing Synergistic Promotion Effects of Graphite Particles with Sodium Dodecyl Sulfate

A facile treatment of graphite as a reinforcement for Al‐based nanostructured composite

Aluminum‐graphite composites find extensive applications in diverse industries, including automotive and aerospace sectors. However, the fabrication of these composites faces a significant challenge due to poor wettability and weak interfacial bonding between graphite and aluminum. This work aims to modify the graphite particles to improve the characteristics of aluminum. In this study, treated graphite (TG) was synthesized using a facile method for the first time. Graphite (G) was mixed with acetone and stirred with a mechanical stirrer at 2000 rpm for 1 h, followed by drying in an electric oven at 80°C for 1 h. Mechanical milling and subsequent hot pressing were employed to manufacture composites with 1, 3, and 5 wt.% of G and TG. The results demonstrated that the addition of G and TG up to 5 wt.% substantially improved the wear rate and coefficient of friction (COF). However, it also resulted in a deterioration of the mechanical properties of aluminum. The TG‐reinforced composites exhibited enhanced mechanical and tribological properties owing to the stronger bonds formed between carbon and aluminum atoms. Notably, the composite with 5‐wt.% G and TG exhibited an 80% and 58% lower COF compared with unreinforced aluminum. Composites containing 1‐wt.% G and TG showed an 11% and 1% reduction in yield strength, respectively. Consequently, the investigated graphite treatment proves to be an effective method for modifying the interfacial bonding and enhancing the comprehensive properties of aluminum. This treatment offers a simple and cost‐effective approach to improve the tribological and mechanical characteristics of aluminum matrix composites.

Studies of Fractal Microstructure in Nanocarbon Polymer Composites.

The in situ study of fractal microstructure in nanocarbon polymers is an actual task for their application and for the improvement in their functional properties. This article presents a visualization of the bulk structural features of the composites using pulsed acoustic microscopy and synchrotron X-ray microtomography. This article presents details of fractal structure formation using carbon particles of different sizes and shapes-exfoliated graphite, carbon platelets and nanotubes. Individual structural elements of the composite, i.e., conglomerations of the particles in the air capsule as well as their distribution in the composite volume, were observed at the micro- and nanoscale. We have considered the influence of particle architecture on the fractal formation and elastic properties of the composite. Acoustic and X-ray imaging results were compared to validate the carbon agglomeration.

Multi‐response optimization of characteristics for graphite reinforced biodegradable PVA‐fumaric acid cross‐linked composite: A gray‐fuzzy logic‐based hybrid approach

AbstractIn the current investigation, enhancement in the mechanical properties, thermal stability, and decrement in the moisture absorption capabilities of polyvinyl alcohol was observed by cross‐linking it with different weight percentages (wt. %) of fumaric acid and reinforcing them along with sulfuric acid‐modified graphite particles. The effects of altering the cross‐linking duration and fumaric acid wt. % were investigated in the resulting composite using the Taguchi L16 experimental design method. As in this contemporary era of rapid industrial expansion and fierce competition, the primary goals of manufacturers revolve around the production of high‐quality goods at optimal costs within a specified timeframe. Therefore, to save both cost and time, the authors have utilized a technique known as “gray‐fuzzy optimization” to balance competing goals between mechanical (toughness, elongation and strength) and physical (water intake capacity) attributes. The present approach aimed to reduce the experimentation expenses and increase the effectiveness of composite manufacturing by considerably reducing the intricacy of practical multi‐response optimization issues. Response graphs and analysis of variance tests were also utilized to calculate the percentage contribution of the input variables and provide model significance.Highlights Polyvinyl alcohol is cross‐linked with different weight percentages (wt. %) of fumaric acid, and reinforced them with sulfuric acid‐modified graphite particles. Enhancement in mechanical properties, thermal stability, and decrease in moisture absorption capabilities were perceived for the fabricated composite. Effects of altering the cross‐linking duration and fumaric acid wt. % were investigated in the resulting composite using the Taguchi L16 experimental design. Gray‐fuzzy optimization technique was utilized to balance competing goals between water intake and mechanical attributes like toughness, elongation and strength. Response graphs and analysis of variance (ANOVA) tests were also utilized to evaluate the percentage contribution of input variables and provide model significance.

Factors affecting the energy harvesting efficiency of graphite thermoelectric materials

Thermoelectric materials have attracted significant attention for their ability to utilize waste heat for power generation whereas natural flake graphite holds great potential as a thermoelectric material. In this work, a pressure-assisted molding process was employed to fabricate graphite bulks using natural flake graphite with different purities and particle sizes. The effect of structure on the properties of the samples was analyzed. It was found that increasing the purity of graphite is beneficial for its electrical and thermal conductivity. Notably, the thermoelectric performance of graphite initially improves and then decreases with increasing purity. The decrease of flake graphite particle size is advantageous for enhancing the Seebeck coefficient of the samples but detrimental to their electrical and thermal conductivity. It is verified that changing the forming pressure can alter the arrangement orientation of flake graphite in the sample. However, the ordered arrangement of flake graphite is not conducive to the thermoelectric properties of the sample. Ultimately, an optimized process for preparing thermoelectric materials containing graphite was obtained, namely minimizing the orientation of flake graphite in the sample, and selecting graphite with a purity of about 99 % and a particle size of nearly 50 μm.

Sublimation and oxidation measurements of graphite and carbon black at high temperatures in a shock tube using absorption imaging and thermal emission

Surface mass loss rates due to sublimation and oxidation at temperatures of 3000–7000 K have been measured in a shock tube for graphite and carbon black (CB) particles. Diagnostics are presented for measuring surface mass loss rates by diffuse backlit illumination extinction imaging and thermal emission. The surface mass loss rate is found by regression fitting extinction and emission signals with an independent spherical primary particle assumption. Measured graphite sublimation and oxidation rates are reported to be an order of magnitude greater than CB sublimation and oxidation rates. It is speculated that the difference between CB and graphite surface mass loss rates is largely due to the primary particle assumption of the presented technique which misrepresents the effective surface area of an aggregate particle where primary particles overlap and shield inner particles. Measured sublimation rates are compared to sublimation models in the literature, and it is seen graphite shows fair agreement with the models while CB underestimates, likely a result of the particle shielding affect not being considered in the sublimation model.

Experimental study on the internal short circuit and failure mechanism of lithium-ion batteries under mechanical abuse conditions

The safety issues of lithium-ion batteries under mechanical abuse conditions have attracted widespread attention due to their high uncertainty and risk. This research takes cylindrical lithium-ion batteries as the research object and conducts three-point bending tests on cylindrical lithium-ion batteries with different states of charge (SOC), electrode thicknesses and electrode materials. The mechanical response, voltage changes, temperature changes during the loading process of the battery, and the microstructural changes of the battery's electrodes and separator after the bending test were examined. The results show that the maximum load-bearing capacity of the battery and the displacement corresponding to the short circuit decreases with the SOC of battery; the higher the battery SOC means a faster average temperature rise rate of the battery. When the SOC is higher than 60 %, the battery will experience violent thermal runaway phenomena such as explosions and spouting fire after bending tests. The mass loss rate of the battery is also greatly affected by the battery SOC and the electrode thickness, however, electrode material have almost no effect on the mass loss rate of the battery. According to the SEM images of the electrodes, it is found that short circuits cause graphite particles to break, separators to close and electrolytes oxidize on the surface of positive electrode particles. After triggering the internal short circuit, more broken particles are observed in the positive electrode material of the battery with thicker electrodes and the surface roughness of the broken particles is higher. By comparing the electrode changes of LFP and NCM, it is found that the intensity of the internal electrochemical reactions in NCM is far greater than that in LFP. The research results provide theoretical insights for understanding the electrothermal characteristics and mechanical integrity of lithium-ion batteries under mechanical abuse, which can shed light on the design and optimization of high-performance and safe lithium-ion batteries.

EXPERIMENTAL STUDIES OF ELECTRIC CONDUCTIVITY DISTRIBUTION ALONG THE HEIGHT OF THE FLUIDIZED BED

This work is focused on the experimental research into the electrical conductivity of a fluidized bed with graphite particles. The aim of the study is to determine the change in electrical conductivity along the height of the fluidized bed. The study was carried out on a chamber-type unit with a working space diameter 110 mm at a fluidization index 2-3. As a result of the experimental research, during heating in electrothermal fluidized bed, the uneven distribution of electrical resistance along the bed height was confirmed for the first time. The resistivity value increases 3-5 times with the depth of immersion into the bed from its surface. The unevenness of the resistivity along the height of the bed decreases with increasing temperature. The difference in power distribution due to uneven electrical resistance along the bed height can lead to a temperature difference of several tens of degrees.

Head-Mounted coating on graphite host enabling highly reversible Li Plating/Stripping in Lithium-ion/Lithium metal hybrid anode

Commercial graphite hosting excessive Li is a promising hybrid Li-ion/Li metal anode for high energy battery. Nevertheless, the issue of Li plating on the top surface of the graphite anode (Gra) is not well tackled, resulting in the uncontrollable growth of Li dendrites and accumulation of “dead Li”, as well as the deactivation of graphite particles. In this work, an insulating ethylene vinyl alcohol copolymer (EVOH) layer is head-mounted covered on the graphite anode surface (Gra-OH) via a simple spray coating method. Due to the electron retarding ability of EVOH film, the top surface of the graphite host is passivated and the excessive Li can be well accommodated inside the porous structure of graphite host. Meanwhile, the lithiophilic –OH group of EVOH can regulate the Li+ flux and render the uniform Li plating behavior. Featuring these, the Gra-OH anodes with a Li storage capacity of 600 mAh/g show high Coulombic efficiencies (CEs) in both coin-cell and pouch cell even under carbonate electrolyte condition. When operating in Li-ion working mode, higher capacity retentions are readily achieved in the half-cell, full-cell and 5 Ah NCM811 pouch-cell, further demonstrating the application compatibility of this surface passivated Gra-OH anode.

Impact of Screw Geometry and Solids Content on the Properties of Continuously Produced Si Anodes

Within the realm of lithium‐ion batteries, there is a growing emphasis on achieving high energy density and environmentally friendly production at a low cost. To address these demands, the battery slurries in this study incorporate the high‐energy anode material silicon. They are systematically produced through continuous extrusion, aiming to realize cost reductions by significantly reducing the overall process time. In this study, it is demonstrated that the choice of screw configuration and solids content during kneading influences the specific energy input and the stress intensity during processing significantly. The stress intensity, represented here by the specific torque, has a great influence on the slurry properties as well as the electrochemical performance of the battery. An increased stress intensity leads to an increase in adhesive strength and ionic resistance. In the results, it is indicated that carbon black decomposition increases significantly, but when a critical specific stress intensity in form of the specific torque is reached, delamination and fracture of the graphite particles occur, leading to a loss of lithium‐ion storage capacity, favoring lithium plating and severely degrading both capacity by up to 40% at 1C and long‐term performance by up to 10% after 50 cycles.

Structural and Tribological Analysis of Brake Disc–Pad Pair Material for Cars

The study of the tribological behavior of the braking system in auto vehicles requires knowing the characteristics of the material in contact and, in the work process, the friction pair brake disc pads. Material structural analysis is necessary because the wear process depends both on the friction-pair chemical composition (brake disc pads) and on the work process parameters (pressing force, rotational speed, traffic conditions, etc.). The material of the brake discs is generally the same, gray cast iron, and the brake pads can be semimetallic (particles of steel, copper, brass, and graphite, all united with a special resin), organic materials (particles of rubber, glass, and Kevlar, all joined with the help of a resin), composite materials that contain different constituents, and ceramic materials (rarely have small copper particles). Therefore, the purpose of this paper is to analyze the crystalline structure, tribological behavior (at friction and wear), and the mechanical properties of the materials of the brake disc–pad friction pair specific to the field through study and analysis.

Influence of copper salts on the physical and mechanical properties of copper–graphite composite materials

We investigated composite materials based on electrolytic copper powder containing 1 and 5 wt. % powder of colloidal graphite the addition of trace amounts of copper sulfate and acetate. The materials were obtained through double cold pressing in a mold at a pressure of 600 MPa, intermediate sintering (annealing) in hydrogen at a temperature of 870 °C, and final sintering in vacuum at the copper premelting temperature. To analyze the influence of copper salts on the density, porosity, electrical resistivity, and strength of copper–graphite composite materials, we employed X-ray phase analysis, scanning electron microscopy, conducted strength tests in three-point bending, and determined electrical resistivity. We established that higher graphite content results in increased porosity and electrical resistivity of composite materials, along with decreased strength. In the materials containing copper sulfate, copper is reduced from the salt in the form of nanodispersed particles on the surfaces and inside graphite flakes, leading to a decrease in electrical resistivity compared to copper–graphite composites without salt additives. When copper acetate was added to the composite material, copper is reduced from the salt mainly on the surfaces of graphite particles in the form of microdispersed particles and their aggregations, as the copper acetate solution does not wet the graphite. In this case, the electrical resistivity was somewhat higher than that of the composite with sulfate but lower than that of the material without salts. The bending strength of the studied materials decreased as salts were introduced due to increased porosity and emerging defects in the crystal structure of graphite during its intercalation with copper.

Tribological analysis of titanium alloy (Ti-6Al-4V) hybrid metal matrix composite through the use of Taguchi’s method and machine learning classifiers

The preparation and tribological behavior of the titanium metal matrix (Ti-6Al-4V) composite reinforced with tungsten carbide (WCp) and graphite (Grp) particles were investigated in this study. The stir casting procedure was used to fabricate the titanium metal matrix composites (TMMCs), which had 8 weight percent of WCp and Grp. The tribological studies were designed using Taguchi’s L27 orthogonal array technique and were carried out as wear tests using a pin-on-disc device. According to Taguchi’s analysis and ANOVA, the most significant factors that affect wear rate are load and distance, followed by velocity. The wear process was ascertained by scanning electron microscopy investigation of the worn surfaces of the composite specimens. Pearson’s heatmap and Feature importance (F-test) were plotted for data analysis to study the significance of input parameters on wear. Machine learning classification algorithms such as k-nearest neighbors, support vector machine, and XGBoost algorithms accurately classified the wear rate data, giving an accuracy value of 71.25%, 65%, and 56.25%, respectively.