Graphite Matrix Research Articles

Effect of Graphite Addition on Mechanical and Tribological Properties of Sisal Glass FRP Composites

Composite materials are gaining more importance in present-day engineering design and development activities because of their attractive mechanical properties [1-2] and are composed of Fibers, Matrix and Fillers. In the present research work Glass and Sisal are used as fibers, Epoxy resin is used as a matrix and different volume fractions of graphite is used as a filler to develop FRP composites using hand layup and bag molding process to study the Mechanical and Tribological characteristics as per ASTM standards. It is evident from the results that Mechanical properties are improved marginally compared to unfilled composites. Further, it is noticed from POD and three-body abrasive tests that the addition of the Graphite enhances the coefficient of friction with the reduction in wear loss. Due to environmental consciousness, interest in the use natural fiber are enhanced in different applications. A comparative study was conducted between synthetic (Glass) and natural (Sisal) FRP composites filled with graphite for automotive brake material.

Integrated Three-Dimensional Carbon Nanopolyhedron/Metal Sulfides: An Efficient Electrocatalyst Toward Oxygen Reduction Reaction

Carbon-based materials hybridized with metal sulfides have gained growing attention as catalytic materials for oxygen reduction reaction (ORR) due to their synergistic effects in terms of richer structural features and higher electrochemical activities. Here, a series of Zn/Co/Fe-based metal-organic frameworks (MOFs) as the precursors, which can be adopted as efficient ORR catalysts, were synthesized through a sulfuration–calcination treatment. The effects of precursor composition, heteroatom doping, and pyrolysis temperature on the structure and electrochemical performance of the catalysts were discussed in detail. It is found that well-grown carbon nanotubes (CNTs) on the surface of graphitic carbon matrix are formed under the synergy effect of trimetallic-based species during pyrolysis. Benefiting from the three-dimensional unique structure with appropriate dopants and high porosity, the catalyst derived from the optimized Zn/Co/Fe-MOFs achieves a half-wave potential of 0.87 V in an alkaline medium for ORR, which is comparable with commercial electrocatalysts. In addition, an outstanding ORR durability of the proposed catalyst in alkaline media was also demonstrated. This work highlights the potential to rationally design and fabricate high-performance ORR catalysts for commercialization.

End‐of‐Life Photovoltaic Recycled Silicon: A Sustainable Circular Materials Source for Electronic Industries

One cannot claim solar panels to be recyclable, in a circular economy sense, until scientists find a way to harvest and repurpose their most valuable components, and silicon is one of them. The photovoltaic (PV) industry uses high‐quality silicon wafers for the fabrication of solar cells. PV recycled silicon, however, is not suitable for any application without further purification, as it contains various impurities. Herein, an advanced repurpose process of chemical etching combined ball milling is developed and optimized to produce high‐quality nanosilicon recovered from end‐of‐life PV panels and subsequent nanosilicon/graphite hybrid formation for the application in lithium‐ion batteries. The crucial feature of the hybrid's structure is that the obtained PV nanosilicon with various shapes and sizes is dispersed homogeneously and wrapped by graphitic matrix under ball milling, creating a superior electrode architecture. The PV nanosilicon/graphite anode consisting of 5 wt% nanosilicon exhibits promising electrochemical performance with a charge capacity of 426 mAh g−1 after 600 cycles, a capacity retention of 70%, a rate capability of 215 mAh g−1 at 5 C, and an average coulombic efficiency of ≈99.4%. By converting PV recycled silicon to exceptionally high‐value nanosilicon, the value of the recycled material is maximized.

Nanostructured Fe-N-C pyrolyzed catalyst for the H2O2 electrochemical sensing

Fe-N-C pyrolyzed materials have been proposed as substitutes of the noble-based catalyst for energy conversion reactions. However, their use as electrochemical sensors has not been deeply explored. In the present work, different Fe-N-C pyrolyzed catalysts were synthesized for the amperometric sensing of the H2O2 reduction in neutral media. The catalysts were characterized by BET, TEM, FESEM, XPS, Mössbauer spectroscopy, and cyclic voltammetry. The catalysts present an N-doped graphitic matrix with a macroporous structure and mesoporous contribution. Different amounts of N-pyridinic, N-pyrrolic, N-graphitic, N-oxides, and FeN4 sites have been detected on the catalysts. Among the different active sites present in the catalysts, the FeN4 structure is proposed as the most catalytic active site for the hydrogen peroxide reduction reaction (HPRR). Under optimal conditions (0.61 V vs. NHE, 0.00 V vs. Ag/AgCl), the materials show a lineal amperometric response in the range of 0.08 and 14 µM, with a sensitivity of 31.3 µA µM−1 cm−2, and a detection and quantification limits of 0.25 µM and 0.75 µM respectively. The amperometric results indicate that the best performance is reached when increasing the amount of FeN4 active sites, and the redox potential of the FeN4 species becomes more positive. The Fe-N-C catalyst stands out for the more positive working potential than other materials proposed in the literature.

Nonprecious Metal Bifunctional Catalysts for Oxygen Electrocatalysis Using a Metal‐Organic Framework

Green energy devices such as Zn‐air batteries require a highly active bifunctional oxygen electrocatalyst. In this study, heat‐treated (HT) FeNi‐alloy nanoparticles embedded on a porous carbon matrix (FeNi‐MOF‐HTs) are prepared by annealing Fe‐ and Ni‐based metal‐organic frameworks (MOFs). FeNi‐MOF‐HTs exhibit an improved oxygen catalytic performance when compared with that of the catalysts derived from Fe‐only MOFs. The enhanced activities of the FeNi‐MOF‐HTs are attributed to their nanoscale size and an electronic interaction between Fe and Ni in the FeNi alloy. An optimized annealing temperature of 800°C provides porosity and promotes graphitization of the carbon matrix in FeNi‐MOF‐HTs. This work describes an effective strategy for the design of highly active bifunctional electrocatalysts.

Monoclinic vanadium diphosphide as a high-performance lithium-ion battery anode

Vanadium diphosphide (VP2) and its graphite-modified composite (VP2@G) were fabricated using a fast and simple solid-state manner, and evaluated as Li-ion battery (LIB) anodes. The electrochemical Li-mechanism of VP2 was investigated using various ex situ tools. During Li-insertion, VP2 underwent a topotactic-reaction by the formation of LixVP2 (x ≤ 1.5), and then was converted to Li3P and V phases with a partially unconverted LixVP2 phase at the Li-inserted state of 0 V via a partial conversion reaction. Conversely, during Li-extraction, Li3P, V, and unconverted LixVP2 phases recombined fully into VP2. First, when VP2 was used the topotactic-reaction between LixVP2 and VP2 (potential region: 0.3–2.0 V), stable cycling performance with a high volumetric-capacity (595 mAh cm–3 after 100 cycles) and fast rate performance (~555 mAh cm–3 at 2 C and ~530 mAh cm–3 at 3 C) were attained. Additionally, the graphite-modified composite VP2@G (potential region: 0–2.0 V) also exhibited stable cycling performance with a high gravimetric-capacity (602 mAh g−1 after 100 cycles) and fast rate performance (~530 mAh g−1 at 1 C and ~470 mAh g−1 at 2 C), which was attributed to the well-dispersed nanocrystalline (~10–20 nm) VP2 in the Li-buffering graphite matrix. Therefore, the VP2 and VP2@G have high potential as a superior LIB anode.

Synthesis of core\u2013shell copper\u2013graphite submicronic particles and carbon nano-onions by spark discharges in liquid hydrocarbons

Spark discharge in hydrocarbon liquids is considered a promising method for the synthesis of various nanomaterials, including nanocomposites. In this study, copper–carbon particles were synthesized by generating spark discharges between two Cu electrodes immersed in heptane, cyclohexane, or toluene. The synthesized particles were characterized using scanning electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. Overall, two families of particles were observed: Cu particles (diameter < 10 nm) embedded in a carbon matrix and submicrometric Cu particles encapsulated in a carbon shell. The obtained results indicate that the size distribution of the Cu nanoparticles and the degree of graphitization of the carbon matrix depend on the liquid. Indeed, discharges in heptane lead to Cu particles with diameters of 2–6 nm embedded in a carbon matrix of low graphitization degree, while discharges in toluene result in particles with diameters of 2–14 nm embedded in carbon matrix of high graphitization degree. Based on the obtained experimental results, it is proposed that the Cu nanoparticles are produced in the plasma core where Cu (evaporated from the electrode surface) and carbonaceous species (decomposition of the liquid) are present. When the plasma hits the electrode surface, hot (thousands of Kelvin) Cu particles are ejected from the electrode, and they propagate in the liquid. The propagation of the hot particles in the liquid results in the local evaporation of this liquid, which leads to the formation of a C-shell around each Cu particle. In few cases where the shape of the Cu particle is not spherical, carbon nanoonions are detected between the C-shell and the Cu core. These nanoonions are supposedly formed under the effect of the fluid vortices generated close to the particle surfaces when these latter are ejected into the liquid.

Single Atomic Iron Site Catalysts via Benign Aqueous Synthesis for Durability Improvement in Proton Exchange Membrane Fuel Cells

Atomically-dispersed iron-nitrogen-carbon (Fe–N–C) catalysts have arisen as promising candidates for replacing the costly precious metal catalysts in fuel cells but still face some grand challenges, such as insufficient site density and durability. Herein, we report a self-assembly method in an aqueous solution to develop an atomically-dispersed iron catalyst with high oxygen reduction reaction (ORR) activity and stability in acidic electrolytes. As determined by high-resolution transmission electron microscopy (HR-TEM), X-ray absorption spectroscopy (XAS), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), this benign aqueous synthesis strategy facilitates the formation of homogeneous atomic nitrogen-coordinated iron sites embedded in a popcorn-like porous graphitic carbon matrix. These catalyst properties contribute to the improved ORR kinetic current density and mass transport. By controlling synthesis chemistry, the correlation between structure and property is systematically investigated. The iron content is the most critical material property and can regulate site density and graphitic carbon structures in the catalyst, impacting catalytic activity and stability. The enhanced performance and durability were examined in both acidic aqueous electrolytes and membrane electrode assemblies.

Neutron Depth Profiling Study on 6Lithium and 10Boron Contents of Nuclear Graphite

ABSTRACT 6Li and 10B contents in the nuclear graphite need to be calculated and evaluated for 4He and the gaseous nuclear radioactive waste 3H, which should be eliminated to an acceptable low level. Furthermore, it will help analyze the diffusion and adsorption behavior as precursors of 3H and 4He. Based on reactions of 6Li(n,α)3H and 10B(n,α)7Li, we employ Neutron Depth Profiling (NDP) as a non-invasive and versatile technique, providing 6Li and 10B content of three different kinds of nuclear graphite, including fuel element matrix graphite, reflector graphite, and boron-containing carbon bricks in High-temperature Gas Reactor (HTGR). The 6Li depth distributions and total amounts calculated from 4He and 3H are compared with high precision for evaluating gaseous radionuclides release. The calculated 10B content of boron-containing carbon bricks is needed for analyzing the impurity and neutron absorption capacity. We offer a new method to measure the trace content of isotopes along the depth of various nuclear materials, which is important for studying the reactor activation products and supporting the service and safety of reactors.

Synthesis of Air-Stable Cu Nanoparticles Using Laser Reduction in Liquid

We report the synthesis of air-stable Cu nanoparticles (NPs) using the bottom-up laser reduction in liquid method. Precursor solutions of copper acetlyacetonate in a mixture of methanol and isopropyl alcohol were irradiated with femtosecond laser pulses to produce Cu NPs. The Cu NPs were left at ambient conditions and analyzed at different ages up to seven days. TEM analysis indicates a broad size distribution of spherical NPs surrounded by a carbon matrix, with the majority of the NPs less than 10 nm and small numbers of large particles up to ∼100 nm in diameter. XRD collected over seven days confirmed the presence of fcc-Cu NPs, with some amorphous Cu2O, indicating the stability of the zero-valent Cu phase. Raman, FTIR, and XPS data for oxygen and carbon regions put together indicated the presence of a graphite oxide-like carbon matrix with oxygen functional groups that developed within the first 24 h after synthesis. The Cu NPs were highly active towards the model catalytic reaction of para-nitrophenol reduction in the presence of NaBH4.

Thermal energy storage performance of PCM/graphite matrix composite in a tube-in-shell geometry

Melting heat transfer performance and measuring energy storage efficiency via total melting time of PCM/graphite matrix in a tube-in-shell for solar thermal energy storage and recovering waste heat applications is studied experimentally. The phase change material (PCM)-organic/paraffin (P56-58), is impregnated into the graphite matrix, with the bulk density of 50 g/L. The effect of inlet temperature (Tinlet = 75 °C and 85 °C) of heat transfer fluid (HTF) on total melting time is obtained. The time-history of temperature measurements, thermal camera imaging, and liquid fraction are obtained to reveal the thermal performance of PCM/graphite matrix in a tube-in-shell latent heat thermal energy storage (LHTES) system in detail. The results show that the PCM/graphite matrix has a remarkable effect on the phase change heat transfer and total melting time. The thermal performance of the PCM/graphite matrix is presented comparatively with the conventional tube-in-shell storage unit. Effective thermal conductivity which enhances the heat transfer rate is shown to increase 35 times compared to that of pure paraffin. The total melting time decreases by about 92% compared to the conventional tube-in-shell unit. Uniform melting behaviour is observed based on highly conductive abundant thermal paths for PCM/graphite matrix. Heat transfer takes place by dominant conduction for the PCM/graphite matrix. Leakage issue is prevented using graphite matrix encapsulation. Total melting time is decreased by about 31% with the increase in HTF inlet temperature for the PCM/graphite matrix.

Tuning dual three-dimensional porous copper/graphite composite to achieve diversified utilization of copper current collector for lithium storage

Graphite anode materials are widely used in commercial lithium-ion batteries; however, the long electron/ion transportation path restricted its high energy storage. In this experiment, we designed a copper/graphite composite with a dual three-dimensional (3D) continuous porous structure combining used nonsolvent-induced phase separation and heat treatment, in which a large amount of graphite is embedded in the 3D porous copper/carbon architecture. In the novel structure, not only the electron and Li+ transmission performances are improved, but also the space of current collector is fully utilized. Meanwhile, carbonized polyacrylonitrile network stabilizes the interface between graphite and copper matrix. The obtained copper/graphite composite anode has an initial discharge capacity of 524.6 mAh·g−1, a holding capacity of 350 mAh·g−1 and excellent cycle stability (299.3 mAh·g−1 after 180 cycles at 0.1C rate), exhibiting good electrochemical performance. The experimental results show that the mass loading of the copper/graphite composite electrode material is about 4.39 mg·cm−2. We also envisage replacing graphite with other high-capacity active materials to fill the current collector, which can provide a reference for the future development of next-generation advanced electrodes.

Determination of boron in in-house graphite reference material by instrumental charged particle activation analysis

Due to high thermal neutron absorption cross-section, boron (B) content is a binding specification for nuclear grade graphite. Reliable analytical methods are essential to determine boron at trace to ultra-trace levels. Analytical Chemistry Division, Bhabha Atomic Research Centre, India has prepared an in-house graphite reference material (GRM). A Charged particle activation analysis methodology has been developed for quantification of B in graphite matrix. Detection limit for boron using this methodology is 1.4 mg kg−1. This in-house GRM can be used for quantification of B in unknown graphite samples, validating existing analytical methods and for the development of new analytical methods.

Densification of A3-3 matrix graphite to inhibit the infiltration of liquid FLiBe salt in molten salt reactors

In this study, a novel graphite was prepared by adding MCMBs (mesocarbon microbeads) to densify matrix graphite A3−3, a typical fuel element and moderator material in high-temperature gas-cooled reactors. The densified graphite was evaluated as a potential fuel element material for molten salt reactors (MSRs). In particular, the effects of MCMB loading on physical properties and the corresponding effects on the infiltration of liquid fluoride salt in MSRs were studied, as molten salt infiltration can impact safe reactor operation. MCMBs with a mean particle size of approximately 3 μm were added to matrix graphite A3−3 at loading levels of 1 wt%, 5 wt%, 10 wt%, and 15 wt%, and samples were prepared by a quasi-isostatic pressing process at 250 MPa. Mercury porosimetry data showed that MCMB-densified graphite (MDGs) had lower porosity (approximately 15 vol%) and median pore diameters (ranging from 105 to 306 nm) compared to A3−3 itself (22.9 vol% porosity and 573 nm median pore diameter). Importantly, the MDGs exhibited greatly reduced infiltration by FLiBe molten salt compared to unmodified A3−3. For instance, A3−3 modified with 1 wt% MCMB exhibited a 2.1 % weight increase after treatment at 1 MPa for 20 h, while unmodified A3−3 exhibited a weight increase of 11.6 %. This study revealed that MDGs could be promising candidate materials for the graphite matrix of fuel elements as well as a neutron moderator and reflector in MSRs.

Microstructure and wear behavior of laser-cladded Ni-based coatings decorated by graphite particles

Abstract In order to improve the anti-friction and wear-resistance properties of 42CrMo steel, Ni-coated graphite composite powder and Ni45 alloy powder were designed to fabricate Ni-based self-lubricating wear-resistant coating with simple process and low cost on 42CrMo steel substrate by laser cladding. The effect of scanning speed on pore defects, graphite particle distribution, microstructure and wear behavior of the coatings were investigated, respectively. Through the synergy between adjusting scanning speed and Ni-coated graphite composite powder, the contradiction among the coating density, the interface bonding strength between graphite and Ni matrix and the excessive loss of graphite caused by ablation and in-situ reaction during laser cladding were resolved. Results showed that Ni-coated layer could effectively prevent the graphite from ablation and delay the reaction between carbon and other components. Ni-based self-lubricating coating with low porosity, uniform microstructure, moderate hardness, low friction coefficient and low wear rate can be prepared at an appropriate scanning speed of 300 mm/s. Its average friction coefficient and wear volume were approximately 0.480 and 6.824 × 10−6 mm3/N·m, respectively. The main wear mechanism is slight abrasive wear and adhesive wear. These results obtained are not only applicable to Ni-based alloy coatings, but also to Ni-based composite coatings reinforced by ceramic particle, and even to other material systems. Particularly, when the reinforcing phase is carbide ceramics, the addition of graphite can also inhibit the dissolution of carbide during laser cladding.

FABRICATION OF PROTECTIVE SiC/TiO2/SiO2 COATING FOR GRAPHITE ELECTRODES

Today, there is a rapid growing demand for graphite electrodes used at steel making factories. Graphite electrodes are expensive materials that are used at steel making factories. Increasing the working longevity of these materials can significantly improve the benefit of steel melting process. Therefore, the increase in the stability of graphite at high elevated temperatures in electric arc furnaces is necessary. The mixture of SiC/TiO2/SiO2 coating can desirably reduce the oxidation of the graphite matrix at high temperatures. Evidently, the SiC/TiO2/SiO2 coating can specially decrease the mass loss rate of the graphite at high elevated temperatures and improve its working longevity in these conditions. Moreover, this coating can effectively improve the stability and thermal shock properties of graphite at the temperatures up to 1000∘C.

Graphite-Embedded Lithium Iron Phosphate for High-Power-Energy Cathodes.

Lithium iron phosphate (LiFePO4) is broadly used as a low-cost cathode material for lithium-ion batteries, but its low ionic and electronic conductivity limit the rate performance. We report herein the synthesis of LiFePO4/graphite composites in which LiFePO4 nanoparticles were grown within a graphite matrix. The graphite matrix is porous, highly conductive, and mechanically robust, giving electrodes outstanding cycle performance and high rate capability. High-mass-loading electrodes with high reversible capacity (160 mA h g-1 under 0.2 C), ultrahigh rate capability (107 mA h g-1 under 60 C), and outstanding cycle performance (>95% reversible capacity retention over 2000 cycles) were achieved, providing a new strategy toward low-cost, long-life, and high-power batteries. Adoption of such material leads to electrodes with volumetric energy density as high as 427 W h L-1 under 60 C, which is of great interest for electric vehicles and other applications.

Development of the inorganic composite phase change materials for passive thermal management of Li-ion batteries: Application

In this study, two inorganic phase change materials (PCM) were tested to be used for thermal control of lithium-ion batteries. Paraffin wax was used as a reference material. To increase thermal conductivity, the PCMs were impregnated into the expanded graphite matrix, forming composite PCM (CPCM). Four types of Li-ion battery packs were manufactured to show the difference in performance between the packs with various CPCMs and No-CPCM.Electrical cycling studies at ambient temperature showed that at C/2 discharge the No-CPCM pack surpasses 35 °C, while all CPCM packs remain around 30 °C, demonstrating similar behavior. At 1C discharge, No-CPCM pack reaches 49 °C, whereas the CPCM packs do not exceed 40 °C. At 2C discharge, the No-CPCM pack overpassed the safety limit of 65 °C and was stopped before completing the first discharge. The CPCM packs successfully completed the cycling. Studies performed at 45 °C demonstrate a similar trend, but with higher peak temperatures. Nail penetration testing proved that the inorganic CPCMс inhibited the pack from self-accelerated degradation, successfully prevented thermal runaway propagation and potential explosion. Low cost and incombustibility make inorganic PCMs а viable alternative to the organic PCMs, with a positive impact on environmental and economic issues.

SnO2-ZnO nanoparticles wrapped in graphite nanosheets as a large-capacity, high-rate and long-lifetime anode for lithium-ion batteries

SnO2-ZnO nanoparticles were wrapped in the ultrathin graphite network to synthesize SnO2-ZnO-C nanocomposite by the hydrothermal and ball milling methods. The SnO2-ZnO hybrid was uniformly dispersed in the graphite matrix. The ultrathin graphite in the composite alleviated the volume expansion during cycling, improved conductivity and shortened the transmission path of electrons and Li+. Therefore, the SnO2-ZnO-C composite shows intense invertible capacity of 1192.2 mAhg−1 after 300 cycles at 0.2 Ag−1 with high initial coulomb efficiency of 78.5% and stabilizes above 99.0% after four cycles, high-rate capacity of 723.6 mAhg−1 at 5.0 Ag−1, and long-term capacity of 596.3 mAhg−1 at 5.0 Ag−1 after 1000 cycles. Thanks to its outstanding properties, the SnO2-ZnO-C nanocomposite is a prospective anode material for next-generation lithium-ion batteries.

Study on the microwave absorbing properties of Fe nanoparticles prepared by the HEIBE method in expanded graphite matrix composites

Recent findings reveal that expanded graphite (EG) composite with metal nanoparticles has an excellent performance in the field of absorbing materials. The N-dope broken EG/FeNPs (NBEG/Fe) composites with sandwich structure and low graphitization degree were prepared through hydrothermal reaction. The doping N element further enhances the electrical conductivity of EG, the purpose is to be consistent with the high permeability of the core-shell Fe/Fe3O4 nanoparticles (FeNPs), which can effectively improve the matching impedance. The experimental results in the 2–18 GHz range prove that NBEG/Fe has better absorption performance than pure EG and BEG/Fe, and by changing the content of FeNPs, the purpose of effectively absorbing electromagnetic microwaves in different frequency bands can be achieved. With only 10% addition of NBEG/Fe, when the matching frequency is 15.67 and 4.51 GHz, and the matching thickness is 1.42 and 5.40 mm, the reflection loss (RL) of NBEG/Fe reaches −56.75 and −43.3 dB, the RL value of NBEG/Fe has also reached an effective absorption bandwidth of 3.92 GHz (RL ≤ 20.0 dB) in the interval 4.06–10.64 GHz. In particular, the RL value of NBEG/Fe in the S-band (at 3.74 GHz) reaches −40.3 dB at a thickness of 6.5 mm. Moreover, under the matching frequency and matching thickness good absorption performance (RL<−20.0 dB) from 2.00 GHz to 18.00 GHz is obtained.