Graphite Composites Research Articles

Fabrication of a novelPNflame retardant and its synergistic flame retardancy with expandable graphite on rigid polyurethane foam

AbstractAn innovative phosphorus‐nitrogen flame retardant (ZrMP) is fabricated by reacting a‐zirconium phosphate (a‐ZrP), phenylphosphinic acid with melamine, and applied to improve the flame retardancy of rigid polyurethane foam/expandable graphite (RPUF/EG) composites. The synergistic effect of ZrMP and EG on the flame retardancy and thermal stability of RPUF was examined by the limiting oxygen index (LOI), UL‐94 vertical burning test, and thermogravimetric analyses. Benefiting from the P and N elements of ZrMP and the expanded char layer of EG, the synergistic effect of ZrMP and EG endows FPUF with excellent flame retardant and thermal properties. The RPUF composites containing 12.5% EG and 2.5% ZrMP can achieve a V‐0 level and its LOI value increases to 26.7%. RPUF/EG/ZrMP composites exhibit good thermal stability compared with pure RPUF. Accordingly, the flame‐retardant mechanism of RPUF composites is proposed by thermogravimetric analyses/infrared, scanning electron microscopy, and X‐ray photoelectron spectroscopy. The results indicate a combination of physical barriers in condensed‐phase and gaseous‐phase dilution activity during combustion. Therefore, this study provides a scalable and promising strategy for constructing flame‐retardant RPUF composites.

Low-Cost Tin Compounds as Seeds for the Growth of Silicon Nanowire–Graphite Composites Used in High-Performance Lithium-Ion Battery Anodes

Nanostructured silicon–graphite composites range among the best options for achieving next-generation high-energy anodes for high-performance lithium-ion batteries. Growing silicon nanowires on graphite give access to composites with high capacity and stability, as the silicon distributes homogeneously in the electrode, and the direct contact provides enhanced mechanical stability even in silicon-rich (>25 wt %) active materials. However, the cost-effective production of such composites remains a challenge. Here, we introduce low-cost catalysts, tin sulfide and tin oxide, enabling silicon nanowire growth at a lower temperature than with widely used gold catalysts, and investigate their impact on the composite nanostructure and composition. The small difference detected in the composition of the products obtained with both catalysts required the development of a reliable method to measure the low-level oxygen content and distribution within the composite. It revealed that oxygen from the SnO2 growth seeds is incorporated into the silicon nanowires, while no sulfur from the SnS catalyst could be detected. We show that SnS seeds result in an anode material of superior initial Coulombic efficiency of 81%, while capacity, stability in cycling, and rate capability are less affected by the choice of the catalyst. The composite anodes, optimized for a capacity of 1000 mAh g–1 at C/5 rate, deliver an areal capacity of up to 3.6 mAh cm–2 and 82% capacity retention over 200 cycles. Their rate capability of 780 mAh g–1 at 5C surpasses that of gold-seeded silicon–graphite composites. The insight obtained from this study provides guidance for the reliable low-cost synthesis and quality control of silicon-containing active materials for Li-ion battery anodes.

The interfacial properties and fracture behavior of the graphite (0001)/Cu (111) interface from a first–principles investigation

Interface considerably influences the properties of copper (Cu)–graphite composites. Therefore, considerable understanding of the interface is required to improve the mechanical and tribological properties of these composites. Because the graphite (0001) and Cu (111) interfaces are a good match, this study focuses on calculating the related properties of the interface structure using first–principles calculations. The parameter setting of this work is reasonable when comparing the theoretical and experimental results of the bulk Cu and graphite. Slabs of the nine-layer graphite (0001) and seven-layer Cu (111) surfaces have excellent convergence. The order of interfacial configuration stability is [Formula: see text] and HCP possesses the largest work of adhesion and smallest interface energy among the studied interface structures. Furthermore, the electron density and Mulliken population method are used to examine the interfacial bonds.

Vertical Array of Graphite Oxide Liquid Crystal by Microwire Shearing for Highly Thermally Conductive Composites.

Excellent through-plane thermally conductive composites are highly demanded for efficient heat dissipation. Giant sheets have large crystalline domain and significantly reduce interface phonon scattering, making them promising to build highly thermally conductive composites. However, realizing vertical orientation of giant sheets remains challenging due to their enormous mass and huge hydrodynamic drag force. Here, we achieve highly vertically ordered liquid crystals of giant graphite oxide (more than 100μm in lateral dimension) by microwire shearing, which endows the composite with a recorded through-plane thermal conductivity of 94W m-1 K-1 . Microscale shearing fields induced by vertical motion of microwires conquer huge hydrodynamic energy barrier and vertically reorient giant sheets. The resulting liquid crystals exhibit extremely retarded relaxation and impart large-scale vertical array with bidirectional ordering degree as high as 0.82. The graphite array-based composites demonstrate an ultrahigh thermal enhancement efficiency of over 35 times per unit volume. Furthermore, the composites improve cooling efficiency by 93% for thermal management tests compared to commercial thermal interface materials. Our work offers a novel methodology to precisely manipulate the orientation of giant particles and promote large-scale fabrication of vertical array with advanced functionalities. This article is protected by copyright. All rights reserved.

Biodegradable and Flexible Thermoplastic Composite Graphite Electrodes: A Promising Platform for Inexpensive and Sensitive Electrochemical Detection of Creatine Kinase at the Point-of-Care.

Acute myocardial infarction (AMI) is the main cause of death worldwide, and the time of diagnosis is decisive for the effectiveness of the treatment of patients with AMI. Creatine kinase-myocardial band (CK-MB) has a predominance and high affinity with myocardial tissue, making it considered one of the main biomarkers for the diagnosis of AMI. In this work, we report a novel biodegradable composite material based on a polymer blend of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Poly(butylene adipate-co-terephthalate) (PHBV:Ecoflex) and graphite microparticles for sensitive and selective electrochemical detection of CK-MB. The morphological and physicochemical characterizations of the thermoplastic composite material revealed a homogeneous and synergistic distribution of the graphite microparticles through the blend structure, providing low defects and high electrical conductivity with high electron transfer kinetics (k0 = 3.54 × 10-3 cm s-1) features with adequate flexibility for point-of-care applications. The portable and disposable devices were applied to detect CK-MB using the electrochemical impedance spectroscopy (EIS) technique in a relevant clinical concentration ranging from 5.0 ng mL-1 to 100.0 ng mL-1 and presented a limit of detection of 0.26 ng mL-1 CK-MB. The selectivity of the sensor was confirmed by testing the potential interference of major biomolecules found in biofluids and other relevant macromolecules. The accuracy and robustness were assessed by addition and recovery protocol in urine and saliva samples without sample pretreatment and demonstrated the potential of our method for rapid and decentralized tests of AMI. In addition, the study of the thermal, biological, and photodegradation of the devices after being used was also carried out, aiming at the disposal of the material more sustainably.

Si@Graphene composite anode with high capacity and energy density by fluidized chemical vapor deposition

The scalable fluidized chemical vapor deposition (FCVD) methodology is developed to prepare the Si nanoparticles (NPs) coated with graphene (Si@G), where the high heat and mass transfer efficiencies avoid uneven coating of present coating technologies. The fluidization behavior of Si NPs is investigated by the computational fluid dynamics simulation, and the result is consistent with the experiment, which verifies the appropriate design of reactor and optimization of operating conditions. Taking advantage of the good electrical conductivity and mechanical strength of graphene, thin and uniform carbon layers strike a balance between suppressing volume expansion of Si NPs and increasing Li+ diffusion rate, which makes Si@G deliver the extraordinary electrode properties of capacity and cyclability. The Si@G/graphite composite containing 15 wt% Si@G affords a high capacity and capacity retention. Moreover, LFP//Si@G/graphite full cell is fabricated and possesses an ultrahigh energy density of 302 Wh kg−1, indicating the practical commercial application of Si@G.

In situ construction of oxygen deficient MoO3-x nanosheets/porous graphitic carbon nitride for enhanced photothermal-photocatalytic hydrogen evolution

In this work, the photocatalysts containing oxygen-deficient molybdenum oxide and macroscopic three-dimensional porous graphitic carbon nitride phase composite (MoO3-x/PCN) were prepared by in situ self-assembly method. The crystal phase and structure were characterized by XRD, XPS, FT-IR, SEM, and TEM measurements. Hydrogen production results showed that introducing of MoO3-x resulted in a higher hydrogen production rate of MoO3-x/PCN composite catalyst than that of PCN. Among them, the highest hydrogen production rate of 2336.15 μmol g−1 h−1 was achieved for MoO3-x-10/PCN, which was 2.23 times higher than PCN (1048.00 μmol g−1 h−1). When the reaction system temperature was 100 °C, the photothermal hydrogen production rate of MoO3-x-10/PCN was 8902.00 μmol g−1 h−1, which was 3.81 times higher than that at room temperature. PL spectra, UV–vis spectra and photoelectrochemical measurements showed that the localized surface plasmon resonance (LSPR) effect of MoO3-x effectively enhanced the photo response range and increased the temperature of the reaction system. ESR measurements showed that he composites should follow the Z-scheme charge transfer mechanism, the electrons in the CB of MoO3-x further migrate to the VB of PCN, which hinders the charge complexation in MoO3-x and PCN, improving the hydrogen production activity. This study provides a new idea for constructing a plasma-based photothermal synergistic catalytic hydrogen production strategy.

Photocatalytic hydrogen under visible light by nitrogen-doped rutile titania graphitic carbon nitride composites: an experimental and theoretical study

Photocatalytic hydrogen under visible light by nitrogen-doped rutile titania graphitic carbon nitride composites: an experimental and theoretical study

Structural Analysis of Phase Change Materials (PCMs)/Expanded Graphite (EG) Composites and Their Thermal Behavior under Hot and Humid Conditions.

Expanded graphite (EG) has been used to store phase change materials (PCM) to enhance thermal conductivity and avoid leakage. However, systematic investigation on physical structure of various embedded PCMs in EG is not reported. Besides, the effect of environment on thermal behavior of PCM/EG composites has not been investigated yet. In this work, three common PCMs (including myristic acid (MA), polyethylene glycol (PEG) and paraffin wax (PW)) were embedded in EG and three PCM/EG composites were obtained. As a result, capillary force between EG and PCMs supported encapsulation of PCMs in EG. PCM/EG composites had narrower phase change range while supercooling degree values were different when various PCMs were used. Besides, the hot and humid environment had a side effect on thermal energy storage of PCMs and PCM/EG composites. The inherent hydrophilicity of PCMs was essential for resistance against side effect of moisture on thermal energy storage.

Fabricating Well-Dispersed Poly(Vinylidene Fluoride)/Expanded Graphite Composites with High Thermal Conductivity by Melt Mixing with Maleic Anhydride Directly

Maleic anhydride (MA) is introduced to fabricate poly(vinylidene fluoride)/expanded graphite (PVDF/EG) composites via one-step melt mixing. SEM micrographs and WAXD results have demonstrated that the addition of MA helps to exfoliate and disperse the EG well in the PVDF matrix by promoting the mobility of PVDF molecular chains and enhancing the interfacial adhesion between the EG layers and the PVDF. Thus, much higher thermal conductivities are obtained for the PVDF/MA/EG composites compared to the PVDF/EG composites that are lacking MA. For instance, The PVDF/MA/EG composite prepared with a mass ratio of 93:14:7 exhibits a high thermal conductivity of up to 0.73 W/mK. It is 32.7% higher than the thermal conductivity of the PVDF/EG composite that is prepared with a mass ratio of 93:7. Moreover, the introduction of MA leads to an increased melting peak temperature and crystallinity due to an increased nucleation site provided by the uniformly dispersed EG in the PVDF matrix. This study provides an efficient preparation method for PVDF/EG composites with a high thermal conductivity.

Atomically Resolved Structure of the Directly Bonded Aluminum–Carbon Interface in Aluminum–Graphite Composites by Solid-State Friction Stir Processing: Im plications for a High-Performance Aluminum Conductor

Atomically Resolved Structure of the Directly Bonded Aluminum–Carbon Interface in Aluminum–Graphite Composites by Solid-State Friction Stir Processing: Im plications for a High-Performance Aluminum Conductor

Preparation and investigation of wear and corrosion behaviour of Al 7475/ CSA/Graphite hybrid metal matrix composites

ABSTRACT The Aluminium Metal Matrix Composites are preferred in automotive and aerospace industries for higher strength to weight ratio, good corrosion resistance, and also for better tribological properties. Aluminium improves its qualities by adding reinforcements like fly ash, silicon carbide, tungsten carbide, boron carbide, and ceramic fired bricks. Stir casting is the most common and cost-effective method for processing and creating metal matrix composites, and it is dependent on the processing parameters, reinforcement, and matrix choices. In this investigation stir casting method was used to prepare composites by using Al7475 alloy with preheated reinforced particles of CSA and Graphite. The successful distribution of reinforcements in the Al7475 matrix was confirmed by SEM images of AMMCs and the improved wear and corrosion resistance of AMMC was revealed by the corresponding test results. At 3% Gr and 30N load, the wear rate reduction is 38.4% at 600 rpm, 50.6% at 800 rpm, and 69.4% at 1000 rpm. The highest corrosion rate reduction is possible with 9 % of graphite in CSA composite is 58 %.

Effect of Mo content on the properties of graphite–MoC composites sintered by spark plasma sintering

Graphite–molybdenum–titanium powders prepared by colloidal processing technique were sintered by Spark Plasma Sintering (SPS). This material is proposed in this manuscript due to its potential interest as heat sink. The influence of the molybdenum content (2.5, 5.0 and 10.0vol.%) on the thermal, electrical, and mechanical properties of the composite are studied to define the composite with the best properties. Thermal, electrical, and mechanical properties of the composite graphite–10vol.% Mo–1vol.% Ti (that are composites of graphite with molybdenum and titanium carbides after sintering) are significantly better than those of the composites with lower molybdenum contents (2.5vol.% and 5vol.%). This way, flexural strength, electrical conductivity, and thermal conductivity are 1.5, 7.8 and 18 times greater, respectively, than in the composite graphite–2.5vol.% Mo–1vol.% Ti. In the case of comparing with the composite graphite–5vol.% Mo–1vol.% Ti, flexural strength, electrical conductivity, and thermal conductivity are 1.2, 5.1 and 3.2 greater in the composite graphite–10vol.% Mo–1vol.% Ti, respectively.

Glutaric acid/expanded graphite composites as highly efficient shape-stabilized phase change materials at medium-temperature

Interest in phase change materials (PCMs) in the medium-temperature range has recently gained significant attention due to their economic benefits and environmental sustainability. This study focuses on investigating the thermal properties of glutaric acid/expanded graphite shape-stabilized phase change materials (GA/EG SSPCMs) prepared by varying GA contents. The morphology, porosity, crystal structure, and chemical and thermal reliability of the prepared SSPCMs were characterized using a range of instrumental analyses. Given a high porosity, EG porous network can confine and stabilize up to 85 wt% GA without leakage, while maintaining the excellent crystallinity of the PCM, due to the capillary and surface tension forces. The SSPCMs exhibited high latent heat storage capacities of up to 167 J/g and crystallization fraction of up to 96.8 %. Interestingly, the SSPCMs effectively suppressed the supercooling degree of GA to below 5 °C, making them ideal for practical applications due to the shifts in both the melting and solidification temperatures. The SSPCMs also showed a significant enhancement in thermal conductivity and heat charge/discharge rates compared to the pure GA. Finally, the thermal reliability and stability of the 85 wt% GA/EG SSPCM were confirmed after 300 accelerated thermal cycle tests, making them a promising candidate for long-term applications in medium-temperature thermal energy storage.

High temperature annealing of irradiated nuclear grade graphite

Previous work has shown that the material properties of nuclear grade graphite are substantially affected by the atomic and microstructural changes that occur during neutron-irradiation. The parameters that play a role in these changes are irradiation dose, temperature, graphite composition and the initial microstructure of the graphite. Understanding the details of how these material changes occur and exactly what the changes consists of will enable the prediction of the material property changes as a function of these variables. Other work has shown these atomic level and microstructural changes can be healed or annealed out by raising the irradiated graphite above its irradiation temperature. In this work, experiments were carried out to investigate how the properties of irradiated graphite recover when heated. By showing property recovery as a function of annealing temperature or energy, insight is provided into the type of damage that occurred during neutron-irradiation. The data presented here shows recovery of thermal diffusivity, coefficient of thermal expansion, Young's modulus and electrical resistivity between annealing temperatures of 500 °C and 2380 °C. Graphite grades NBG-18, IG-110 and PCEA are considered that were both stressed and unstressed during irradiation.

Characterisation of microstructure, microhardness and tribological properties of Al matrix hybrid nanocomposites reinforced with B4C and in-situ GNSs

With the increasing demands of automobile and aerospace industries, it is necessary to develop novel wear-resistant Al matrix composites (AMCs). Graphene is commonly used as an additive in self-lubricating AMCs due to its high strengthening efficiency and 2D structure. Considering the high cost of graphene and reinforcing the Al matrix by multiple reinforcements, novel Al matrix hybrid nanocomposites reinforced with B4C and in-situ GNSs were developed in this study. Al-10 vol% (x1 B4C-x2 graphite) composites (x1: x2 = 10:0, 9:1, 7:3, 5:5) were prepared by powder metallurgy. Vickers hardness tests and ball-on-disc wear tests were used to assess the mechanical and tribological properties of the composites. It is found that in-situ GNSs can be formed in Al-9 vol% B4C-1 vol% graphite (Al–9B-1G) and Al-7 vol% B4C-3 vol% graphite (Al–7B-3G) composites, thereby significantly increasing the Vickers hardness. Benefiting from the strengthening effects of B4C and in-situ GNSs, as well as the lubricating effect of the GNSs, the wear resistance of Al–9B-1G and Al–7B-3G is improved remarkably. Al–7B-3G has the best wear resistance with the least wear rate of 1.41 × 10−3 mm3/Nm, which is 87.4% and 76.7% lower than that of Al and Al–10B, respectively.

Selection of optimal hyperparameter for detecting multiple contacts from large-area tactile sensors based on electrical impedance tomography

Large-area tactile sensors based on the technique of electrical impedance tomography (EIT) has drawn considerable interest in human-robot interactions. However, due to the ill-posed condition, it is challenging to differentiate between the real contacts and the artifacts from the reconstructed image. To address this issue, a new method to select an optimal hyperparameter that tunes the amount of regularization is developed in the context of tactile sensing. The optimal hyperparameter is determined to be the minimum value to obtain a stabilized number of sub-regions in the reconstructed image. The proposed method not only guarantees a correct detection on the number of multiple contacts at the minimum amount of regularization, but also provides a proper range of hyperparameters. The optimal hyperparameter is found in a chair-shape relation with the boundary signal-to-noise ratio (SNR), by varying the noise level of the hardware in simulation. The optimal hyperparameter decreases significantly when the boundary SNR increases between 5 ∼ 10 dB and 25 ∼ 35 dB, and keeps almost unchanged when SNR is between 10 ∼ 25 dB. The chair-shape relation also holds for contact conditions with varied intensities and sizes. Experimental validations on the proposed method are conducted on a compliant piezoresistive tactile sensor made of exfoliated graphite polymer composites. By varying the number of contacts in experiments, the relation between the optimal hyperparameter and the boundary SNR is consistent with the chair-shape curve. The investigation made in this work helps improve the performance of identifying multiple contacts from tactile sensors based on electrical impedance tomography.

Correlating topographical characteristics of relaxed layer to tribology in Cu-Gr-TiC composite system

The copper graphite composites are often being applied as bearing materials in various industries. In present investigation, the correlation between the topographical characteristics of relaxed layer to tribology in Cu-Gr-TiC composite system has been investigated. For this purpose, the flake powder metallurgy approach was used to fabricate Cu-Gr-TiC composites and the tribology of these composites was studied under lubricating (synthetic SAE 20W40 motor oil) condition. Variable loads of 10 N–70 N, sliding velocities of 0.75 m s−1–3 m s−1, and sliding distances of 2000 m–8000 m were the test parameters for sliding wear of composites under lubricating conditions. The worn surfaces were examined using SEM and EDS while topographical parameters were studied by AFM. The other properties like mechanical and physical properties were also studied for the sintered samples to better correlate the overall results of surface topography and tribology. The tests depict the successful fabrication of the composites. The composite having 4.5 wt% TiC particles exhibit maximum hardness and least wear and CoF under lubricating environment. The results of sliding wear test conducted under lubrications revealed that rise in the concentration of nano TiC particles in the matrix improves the composite’s tribological performance. The mechanism of wear for pure copper sample is abrasion whereas for TiC particle reinforced composite is smooth ploughing and delamination. The surface topographical parameters that are average surface roughness, area peak to valley height and skewness depicted less roughness values and better load bearing capacity for 4.5 wt% TiC reinforced Cu-Gr sample. The fabricated TiC reinforced copper graphite composites could be utilized as bearing materials in automotive industries.

Unveiling the role of electrode-level heterogeneity alleviated in a silicon-graphite electrode under operando microscopy

Reaction heterogeneity is a crucial factor that influences the design of composite electrodes. Silicon–graphite composites exhibit practical use as anodes, but the complex mechanisms in blended electrodes have not been investigated. Considering mechanisms at an electrode level, intra-/interparticle heterogeneity depending on state-of-charge (SOC) becomes problematic due to their complex kinetic properties. We investigate the complex dynamics of a silicon–graphite blended electrode using side-view operando optical microscopy, highlighting the proper mechanisms of SOC heterogeneity. Graphite and silicon simultaneously lithiated during lithiation by competition between redox potentials and interparticle diffusion. During delithiation, the driving force of electrochemical potentials increases, resulting in sequential reactions from graphite to silicon. Different kinetics induces interplay during the competitive reaction, affecting depth heterogeneity. Silicon mitigates the depth heterogeneity of graphite during lithiation due to its rapid surface diffusion and kinetic-derived overpotential. These findings pave new avenues for a more sophisticated design of high-energy Si-graphite anodes.

Dependence of current conductivity of polyethylene-graphite compositions on the method of their manufacture

The paper presents the results of the study of the dependence of the properties of polymer composites of the linear high-pressure polyethylene (LHPPET) system – graphite fillers of various types: natural GAK-2, thermally expanded (TEG) and with ultrasonic treatment. The test samples contained a filler in a wide concentration range (5–35 wt. %). Samples were manufactured using rolling, pressing and powder technology methods. Electrical resistance was measured by the four-probe potentiometric method at constant current. It is shown that the electrical resistance decreases sharply in a narrow concentration interval of 5–15 wt. % from 6.77·1010 to 4.9·102 Ω·m (for compositions obtained by rolling), from 2.96·1010 to 1.2 Ω·m (for pressed samples), from 2.87·109 to 0.14 Ω·m (for compositions obtained by powder technology). For samples of the LHPPET – GAK-2 system, a rapid decrease in electrical resistance is observed at filler concentrations of 5–30 wt. % from 1.36·1012 Ω·m to 2.79·102 Ω·m. Using thermally expanded graphite with and without ultrasonic treatment (and to a lesser extent GAK-2) it is possible to obtain polymer composite materials (PCM) with volume resistivity ranging from 6.77 to 1.9·10-3 Ω·m. It has been experimentally confirmed that electrical conductivity largely depends on the PCM manufacturing technology. The established dependences of the current conductivity of composites, depending on the manufacturing method, are associated with the corresponding structural differences. These structural differences are manifested in an increase in the number and area of contacts of filler particles – graphite and in a change in the thickness of the layers of the polymer matrix. Dry powder technology is the most effective method of obtaining LHPPET – graphite compositions. The optimal composition of the composition is 25 wt. % TEG and 75 wt. % LHPPET. Directions of practical use of the obtained results can be effectively used in industry and housing and communal economy.