Graphite Composites Research Articles

Effect of homemade PON compounded with expanded graphite ratio on flame retardancy of polystyrene resin

AbstractIn this paper, diphenyl phosphoryl chloride and anhydrous piperazine are used as raw materials to prepare a kind of homemade flame retardant (PON) with P‐N synergistic effect by nucleophilic substitution reaction. The properties of polystyrene/PON/ expandable graphite composites are analyzed by limiting oxygen index (LOI), thermogravimetric analysis (TGA), cone calorimetry (CONE) and scanning electron microscopy (SEM). The effects of different ratios of PON and expandable graphite (EG) on the flame retardant properties of polystyrene resin are investigated. The results show that when the total amount of flame retardant is 10 wt%, the ratio of PON and EG is 3:2 and 1:1, which is better than the other ratios. However, due to the small amount of flame retardant, the optimal synergistic effect of PON and EG is not obvious, and the flame retardant performance is similar. However, when the total amount of flame retardant increases to 20 wt%, it is obvious that the ratio of PON and EG 3:2 is better than 1:1.

Improving the tribological properties of ZrO2(Y2O3)-graphite composites at high temperature through three-dimensional continuous structure

ZrO2(Y2O3)-graphite composites with a three-dimensional (3D) continuous structure were prepared by using a core-shell design of graphite and ZrO2(Y2O3). The effect of structure on the friction-reducing and anti-wear mechanisms from room temperature to 700 °C was investigated. During high-temperature friction, abrasive wear and brittle fracture are the main wear mechanisms for ZrO2(Y2O3)-graphite composites with homogeneous composition. For the composites with 3D structure, the continuous ZrO2 matrix with high load-carrying capacity and the formation of a dense friction layer with self-lubricating and thermal oxidation resistance improve the tribological properties significantly, reducing the coefficient of friction by about 10% and the wear rate by nearly two orders of magnitude when coupled with GH4169 alloys at 600 °C.

B4C-SiC skeleton reinforced graphite composites with excellent mechanical properties

B4C-SiC skeleton reinforced graphite composites with excellent mechanical properties

A highly thermal conductive and compliant heterogeneous composite with strong interfacial strength controlled by the degree of vulcanization

Thermal interface materials with high thermal conductivity (TC) and mechanical compliance were essential for electronic devices. In this work, a highly thermal conductive and compliant composite with strong interfacial strength was fabricated by multilayer-stacking partially vulcanized silicone rubber (SR)/graphite (Gr) composites (Heter-SR/Gr) with high and low Gr contents, and then fully cured by further hot pressing. The multi-step vulcanization endowed great orientation of Gr and covalent bond between layers, thus heightened TC, maintained the mechanical compliance and enhanced the interfacial strength, respectively. The out-plane TC reached 25.45 W/(m·K) with an overall Gr content of 60.94 wt%, the TC value of the homogeneous structured composite was only 11.15 W/(m·K); these were consistent to the FEA simulation results. Moreover, the stress of Heter-SR/Gr reached 2.24 MPa at 25% compressive strain, which was 35.82% lower than that of homogeneous composite (3.49 MPa). This facile strategy is expected to be promoted in the further applications.

Effective upcycling of waste separator and boosting the electrochemical performance of recycled graphite anode for lithium-ion batteries

The forefront of current lithium-ion battery technology in various electronic applications concerns the enormous e-waste that gives rise to end-of-life batteries. Resource sustainability of battery-grade graphite, non-biodegradable polymeric separator, and ever-growing lithium-ion battery manufacturing cost extend a strong impetus for lithium-ion battery recycling. Herein, we report an effective strategy to upcycle the waste separator to valuable carbon. The recycle separator derive carbon is turbostratic with the simultaneous presence of an order-disorder phase. The carbon anode electrochemically delivers 695 mAh g−1 capacity at 100 mA g−1, which is double the capacity of the recover graphite anode (300 mAh g−1). Despite the significant electrochemistry, the poor conversion efficiency and low product yield after carbonization may impede large-scale implementations. However, the Li-ion storage capability of recycle separator derive carbon, in minimal quantity, enhances the capacity of the recycled graphite. The composite of recycle graphite and recycle separator derive carbon outperforms the capacity of recycled graphite with higher Li-ion diffusivity. It delivers a stable discharge capacity of 380 mAh g−1 at a 0.5C rate over 1200 cycles (285 mAh g−1 for recycled graphite). This study entails sustainable recycling of spent separators and boosts the efficiency of recycled graphite for high-performance lithium-ion batteries.

Superlubricity of Materials: Progress, Potential, and Challenges.

This review paper provides a comprehensive overview of the phenomenon of superlubricity, its associated material characteristics, and its potential applications. Superlubricity, the state of near-zero friction between two surfaces, presents significant potential for enhancing the efficiency of mechanical systems, thus attracting significant attention in both academic and industrial realms. We explore the atomic/molecular structures that enable this characteristic and discuss notable superlubric materials, including graphite, diamond-like carbon, and advanced engineering composites. The review further elaborates on the methods of achieving superlubricity at both nanoscale and macroscale levels, highlighting the influence of environmental conditions. We also discuss superlubricity's applications, ranging from mechanical systems to energy conservation and biomedical applications. Despite the promising potential, the realization of superlubricity is laden with challenges. We address these technical difficulties, specifically those related to achieving and maintaining superlubricity, and the issues encountered in scaling up for industrial applications. The paper also underscores the sustainability concerns associated with superlubricity and proposes potential solutions. We conclude with a discussion of the possible future research directions and the impact of technological innovations in this field. This review thus provides a valuable resource for researchers and industry professionals engaged in the development and application of superlubric materials.

Influence of Graphite Particles on the Mechanical and Wear Characterization of Al6082 Alloy Composites.

In the current study, a two-stage stir cast process was used to produce Al6082 reinforced with sized graphite particulates, and the material's mechanical and tribological properties were analyzed. The graphite content in the Al6082 alloy was increased from 2 to 6% in steps of 2 wt %. The impact of graphite addition to Al6082 was evaluated using microstructural micrographs, hardness test, tensile test, and wear test outcomes. The matrix alloy's microstructure and particle distribution were analyzed using scanning electron microscopy and energy-dispersive spectroscopy. The microstructure of Al6082 shows that the reinforcement particles are evenly distributed throughout the matrix. Although the hardness of metal-matrix composites was slightly reduced when graphite was added at concentrations of up to 6 wt %, the material's tensile strength and wear resistance were significantly improved. Micrographs taken by a microscope were used to examine the fractured surfaces of tensile test specimens. Wear experiments were performed using a conventional pin-on-disc tribometer to examine the tribological properties of both unreinforced matrix and graphite composites. With the addition of 2, 4, and 6 wt % of graphite particles, the composites' wear resistance was significantly improved. Wear of alloys and their composites was analyzed to determine how load and sliding speed impacted wear loss.

Optimization of Filler Compositions of Electrically Conductive Polypropylene Composites for the Manufacturing of Bipolar Plates.

In this research, polypropylene (PP)-graphite composites were prepared using the melt mixing technique in a twin-screw extruder. Graphite, multi-walled carbon nanotubes (MWCNT), carbon black (CB), and expanded graphite (EG) were added to the PP in binary, ternary, and quaternary formations. The graphite was used as a primary filler, and MWCNT, CB, and EG were added to the PP-graphite composites as secondary fillers at different compositions. The secondary filler compositions were considered the control input factors of the optimization study. A full factorial design of the L-27 Orthogonal Array (OA) was used as a Design of Experiment (DOE). The through-plane electrical conductivity and flexural strength were considered the output responses. The experimental data were interpreted via Analysis of Variance (ANOVA) to evaluate the significance of each secondary filler. Furthermore, statistical modeling was performed using response surface methodology (RSM) to predict the properties of the composites as a function of filler composition. The empirical model for the filler formulation demonstrated an average accuracy of 83.9% and 93.4% for predicting the values of electrical conductivity and flexural strength, respectively. This comprehensive experimental study offers potential guidelines for producing electrically conductive thermoplastic composites for the manufacturing of bipolar fuel cell plates.

Enhanced power factor of expanded graphite phase change thermoelectric cement composites by metal oxides

Cement-based materials with thermoelectric effect can realize the conversion of waste heat in building environment, which is of great significance in energy conversion and utilization, and has become a research hotspot in recent years. In this study, three kinds of metal oxides were added into the phase change modified expanded graphite cement-based composites to investigate the impact of metal oxide content on the thermoelectric characteristics of cement composites. The findings shown that the thermoelectric properties of cement-based materials can be enhanced by the addition of metal oxides. The power factor increased to 3.15 μW·m−1·K−2, 3.60 μW·m−1·K−2, and 2.53 μW·m−1·K−2 after mixing ZnO, CuO, and TiO2. This is because the incorporation of metal oxides introduced a large number of interfaces into the cement, increased carrier scattering, strengthened the Seebeck coefficient of cement, and improved the power factor. This work presented a novel strategy to improving the thermoelectric properties of cement-based materials.

Achieving extraordinary thermal stability of salt hydrate eutectic composites by amending crystallization behaviour with thickener

Commercial thermal energy storage (TES) systems necessitate reliable thermal performance throughout their operational lifetime. Repeated volume changes of the phase change materials (PCMs) during thermal cycling disengages thermal contacts between the conductive fillers like expanded graphite (EG) in TES composites, causing unstable thermal conductivity (k) that fades with cycling. Our in-operando crystallization studies on eutectic PCM made of zinc nitrate hexahydrate (ZNH) and KNO3 revealed that the thermal stability of PCM composites can be considerably degraded by the formation of large and sharp-cornered PCM crystals during the freezing cycle. While the crystals can push EG particles, disengaging thermal contacts between them, we have newly discovered that carboxymethyl cellulose (CMC) can be used to retain the thermal contacts by forming networks of smaller PCM crystals. Furthermore, the scalable synthesis methodology of EG/ZNH eutectic composites was introduced. Here EG particles were strongly connected into a matrix via a stable, corrosion resistant polydimethylsiloxane (PDMS) binder, stabilizing thermal networks and thereby maintaining k up to 1000 melt/freeze cycles. The thermal conductivity of our 25 vol% EG sample (13.3 W m−1 K−1) is more than 48% higher than other salt hydrate eutectic composites reported in the literature. We expect this study to provide insights on cooperative interaction between different components of TES systems (PCM, filler, thickener, binder) for exceptionally robust thermal properties.

Magnetic Carbon Nanocomposites: Preparation from Cellulose via Chemical Activation with FeCl3 and Characterization

We have studied the preparation of magnetic graphitic carbon composites, which combine the adsorption properties of activated carbon with magnetic properties and properties intrinsic to graphite. The preparation method is efficient; it comprises modifying flax shive cellulose with citric acid to enhance the chelating ability of the flax shive cellulose matrix, impregnating the modified cellulose with iron chloride, and pyrolysis in an inert atmosphere to control the composition, morphology, specific surface, and porosity of hybrid carbon materials. The scenario of cellulose matrix pyrolysis was suggested using thermogravimetry. X-ray structural analysis was used to characterize the graphitic composites. The citric acid modification of cellulose helps to prepare a high-graphite (74%) carbon composite where the graphitization level of the graphite structure approaches the graphitization level of commercially available graphite at 700°С. Low-temperature N2 adsorption–desorption and ζ-potential measurements helped to suggest the adsorption mechanism for environmentally hazardous dyes. The greatest equilibrium adsorption of Methylene Blue (MB) and Methyl Orange (MO) dyes was 127.4 and 23.7 mg/g, respectively. The prepared composites can be used as adsorbents and fillers in polymer composite materials.

Composite Graphite Bipolar Plates Under Different Working Conditions

This study uses the molding method to prepare composite graphite bipolar plates to improve the corrosion resistance and electrical conductivity of fuel cell bipolar plates, improve the conversion efficiency and service life, and test their environmental adaptability under different working conditions. In this experiment, the fuel cell test system (850e) is used to test the voltage change curve and power density change curve of the proton exchange membrane fuel cell (PEMFC). Under 200 KPa, the voltage of the fuel cell at a current density of 1000 mA/cm2 is 0.719 V. The power density reaches the maximum at 1540 mA/cm2 current density, which is 911 mW/cm 2. The radii of the three curves from 0.1 A/cm2 to 0.5 A/cm2 decrease with the increase of current density. This indicates that at the beginning, the greater the current density is, the smaller the mass transfer resistance inside the fuel cell is, and the smaller the electron transfer resistance during the electrochemical reaction is. However, when the current density increases to 1 A/cm2, the power density of the fuel cell increases slowly. In the 12-hour constant current density test, it is found that the fuel cell voltage dropped from 0.641 V to 0.611 V, and the rate of decline was 2.5 mV/h, proving that the overall performance of the fuel cell is relatively stable. The graphite bipolar plate prepared by the molding method has good adaptability under different working conditions, and the comprehensive performance is stable under long-term testing.

Synthesis, characterization, and optimization of a quaternary nanocomposite for efficient electromagnetic absorption coating in the X-band

Abstract In this study, a quaternary composite of graphite, polyaniline, cobalt ferrite, and thermoplastic polyurethane as a shielding material was prepared. The composite materials were analyzed with X-ray diffraction, field emission scanning electron microscopy, vibrating-sample magnetometer and thermogravimetric analysis. The electromagnetic characterization of the samples was achieved using a Vector Network Analyzer in the X-band. The composites’ conductivity was analyzed by using the four-point probe method. For the investigation of water absorption, the ASTM D570-98 Standard Method was used. Design-Expert software applied design optimization for broadband electromagnetic shielding of the composite film. Ultimately, we introduced a composite film as an efficient microwave absorbent that had a weight percentage of cobalt ferrite 6.95 %, polyaniline 20.04 %, graphite 12.13 %, and thermoplastic polyurethane 60.88 % in a thickness of 1.26 mm, which had shielding effectiveness higher than 30 dB, which was suitable for commercial purposes. The results showed that graphite played an essential role in increasing the composite’s electrical conductivity and thermal stability but was unsuitable for water absorption resistance.

Characterization and piezo-resistivity studies on graphite-enabled self-sensing cementitious composites with high stress and strain sensitivity

Carbon-based conductive fillers have recently been incorporated into a cement matrix to develop an intrinsic self-sensing concrete for data monitoring without the need for embedded, attached, or remote sensors while maintaining or improving its mechanical properties and durability. This paper studies cementitious composites filled with graphite as a novel self-sensing construction material. Experiments were systematically conducted to investigate the dispersion, chemical, mechanical, electroconductivity and piezo-resistivity properties of the composites. Experimental results showed an effective mixing with uniform dispersion of the graphite which acted as an inert filler in the mix and did not alter the microstructure of cement hydration products. Isothermal calorimetry, TGA and rheology tests showed good hydration and adequate workability of the composites with low graphite concentration (≤ 10%), while the effect of adding graphite on the compressive strength is insignificant for graphite concentrations of up to 10%. Monotonic and cyclic compressive test results indicated a repeatable piezo-resistivity performance for low graphite concentration cementitious composites whose stress sensitivity values vary from 0.75 to 7.25%/MPa, and strain sensitivity/gauge factor (GF) 150–1250 with some hysteresis. These combinations showed a stable and reliable piezo-resistivity and the ability to detect damage upon failure.

Enhanced thermal properties of HDPE/EG nanocomposites via synergy of multi‐source pulsating flow and phase transition

AbstractA new melt mixing and in‐situ exfoliation method based on the synergy of multi‐source pulsating flow and phase transition (MSPFPT) was reported. The corresponding device was also developed, and the structure and mixing process of the mixer were introduced in detail. High‐density polyethylene (HDPE)/expanded graphite (EG) composites were prepared via this new mixer, and microstructure and thermal properties of the composites were comprehensively investigated. Morphological analyses demonstrate that MSPFPT method promotes the efficient exfoliation and uniform dispersion of EG. The well‐exfoliated EG layers form more thermal conductive paths in the composites prepared by MSPFPT, increasing thermal conductivity from 0.47 of pure HDPE to 1.16 W/(m·K) with 9 wt.% EG. The crystallinity degree of HDPE is increased by 11.1%. The increment of crystallinity reduces phonon scattering, which further confirms that MSPFPT method can significantly improve the thermal performance. The research provides a practical strategy for fabricating high‐performance composites filled with layered fillers.

Effect of combination methods for nanosilicon and graphite composites on the anode performance of lithium batteries

Effect of combination methods for nanosilicon and graphite composites on the anode performance of lithium batteries

Three-Dimensional Flower-like MoS2 Nanosheets Grown on Graphite as High-Performance Anode Materials for Fast-Charging Lithium-Ion Batteries.

The demand for fast-charging lithium-ion batteries (LIBs) with long cycle life is growing rapidly due to the increasing use of electric vehicles (EVs) and energy storage systems (ESSs). Meeting this demand requires the development of advanced anode materials with improved rate capabilities and cycling stability. Graphite is a widely used anode material for LIBs due to its stable cycling performance and high reversibility. However, the sluggish kinetics and lithium plating on the graphite anode during high-rate charging conditions hinder the development of fast-charging LIBs. In this work, we report on a facile hydrothermal method to achieve three-dimensional (3D) flower-like MoS2 nanosheets grown on the surface of graphite as anode materials with high capacity and high power for LIBs. The composite of artificial graphite decorated with varying amounts of MoS2 nanosheets, denoted as MoS2@AG composites, deliver excellent rate performance and cycling stability. The 20-MoS2@AG composite exhibits high reversible cycle stability (~463 mAh g-1 at 200 mA g-1 after 100 cycles), excellent rate capability, and a stable cycle life at the high current density of 1200 mA g-1 over 300 cycles. We demonstrate that the MoS2-nanosheets-decorated graphite composites synthesized via a simple method have significant potential for the development of fast-charging LIBs with improved rate capabilities and interfacial kinetics.

High-performance polybenzoxazine based composites PEMFC bipolar plates with a multi-layer structure for surface enrichment of conductive phase

In this study, a multilayer high-performance polybenzoxazine/expanded graphite composite bipolar plate with a ‘graphite-composites-graphite’ structure was prepared by compressing molding. The surface graphite layer and the conductive network were constructed by hot compressing of graphite paper and the polybenzoxazine/expanded graphite composites. The results show that the multilayer synergy makes composite BP reach an in-plane conductivity of 278.85 S cm−1, an area specific resistance of 9.70 mΩ cm2 and a flexural strength of 75.75 MPa. The ‘graphite-composites-graphite’ structure can make the power density of a single cell assembled by the multilayer composite BP increase by 111.02% and 113.80%. In conclusion, the multilayer bipolar plate with a ‘graphite-composites-graphite’ structure is a promising polymer composite bipolar plate for the proton exchange membrane fuel cell (PEMFC).

Fabrication and Thermal Analysis of Hybrid A356 Aluminium Metal Matrix Composites Prepared by Stir Casting Process

Background: Electronic packaging makes use of hybrid A356 aluminium alloy MMCs (matrix metal composites). Enhanced endurance limit, increased production and energy, low maintenance cost, and benefits to the environment, such as reduced noise and airborne pollutants, are among the features that are recommended to be evaluated. Objective: This study aimed to analyze the thermal properties of A356 aluminium alloy with graphite (Gr) and boron carbide (B4C) hybrid metal matrix composites. For this purpose, the A356 hybrid composite was primed by the stir casting process with the addition of 5 wt % and 10 wt % of Gr and B4C reinforcements. In general, A356 hybrid composite material thermal analysis is crucial for electrical equipment. Methods: The liquid-in-filtration method was used to create the hybrid composites, which were then tested thermally for parameters, like melting point, thermal diffusivity, and thermal coefficient of expansion. The thermocouple sensor of a calorimeter was used to examine the disparity in the composites. A thermal analysis tool called TGA was used to visually represent the relationship between a material's weight and temperature. Results: The temperature was found to be 300oC at the 0.411 W/g maximum heat flow rate. Thermal conductivity is the ratio of the temperature difference divided by the area of the heat transfer from one substance to another. The thermal coefficient of expansion illustrates how a material's dimensions and weight change as temperature increases. Conclusion: The proportion of the weight of the hybrid composites was found to fall with a rise in the temperature. The melting point curve of the composites demonstrated a little increase in temperature to be accompanied by a sharp increase in heat flow.

Improved Rate Capability in Composite Solid-State Battery Electrodes Using 3-D Architectures

The limited rate capability observed at faster charging rates is a critical challenge for composite electrodes in solid-state batteries (SSBs). This becomes further amplified with increasing electrode thickness and higher ratios of active material to solid electrode, which result in trade-offs between energy and power density. To overcome these trade-offs, it is necessary to understand the factors responsible for poor rate capability by exploring new approaches to boost power density without compromising energy density. Herein, we fabricated 3-D patterned composite graphite (Gr/Li6PS5Cl) electrodes with low-tortuosity electrolyte channels using a templating approach. Graphite was chosen as a model system to study inhomogeneous lithiation in composite SSB electrode architectures because of the visible color changes that occur as a function of local state-of-charge. At faster cycling rates (1C), the 3-D patterned electrodes enabled considerably higher accessible capacity (38% increase) compared to the unpatterned control electrodes. These enhancements were visualized using operando video microscopy, where 3-D electrode architectures showed improved homogeneity in the local state-of-charge throughout the electrode thickness. The insights presented here will enable new strategies based on 3-D electrode architectures to overcome power/energy trade-offs in SSBs.