Graphite Fraction Research Articles

The Effect of Fractional Composition on the Graphite Matrices' Porosity.

Synthetic graphite of complex fractional composition was mixed with phenolic resin as a binder and pore-forming component. The mixtures were pressed and subsequently heat-treated to obtain porous matrices. The structural transformations of phenolic resin by heating up to 900 °C in oxygen and inert gas media were studied and the patterns of amorphization of fixed carbon formed on the walls of the pore system during carbonization were investigated. We found regularities in the changes in matrix volume density in the function of the open porosity and the average pore diameter. It is shown that, in order to obtain graphitized carbon matrices with a density of 1 g/cm3 and an open porosity of at least 50%, it is necessary to introduce no more than 20% of phenolic resin into the molding powder with an equal content of 60, 100 and 250 μm graphite fractions. This allows for high intensity and completeness of bulk silicon infiltration.

Enhancing wear resistance, mechanical properties of composite materials through sisal and glass fiber reinforcement with epoxy resin and graphite filler

This study investigates the mechanical and wears properties of sisal and glass fiber-reinforced epoxy composites with graphite as filler material. We assessed the mechanical properties of the hand-layup-fabricated composite materials, including hardness, tensile strength, flexural strength, and impact strength, by ASTM standards. We also performed wear evaluations using a pin-on-disc apparatus. The results showed that the weight fractions of sisal fiber, glass fiber, graphite, and epoxy resin significantly affected the mechanical properties of the composites. In contrast to composites reinforced with individual fibers, hybrid composites exhibited enhanced mechanical properties. The optimized compositions showed improvements in tensile, flexural, impact, and hardness properties. The wear analysis revealed that a variety of factors, including the weight percentage of reinforcement, sliding velocity, load, and sliding distance, had an impact on the composites' wear resistance. The SEM images provided significant insights into the composite material's micro structural characteristics and failure mechanisms. In general, this research showcases the potential of graphite filler-reinforced sisal and glass fiber epoxy composites for use in applications that demand exceptional abrasion resistance and mechanical strength. Further refinement of the composition and processing methodologies could lead to the development of composites tailored to specific application demands.

Carbon Xerogel as a Novel Minor Conductive Filler for Carbon‐Polymer Composite Bipolar Plates

The current research explores the potential of carbon xerogel as a conductive filler in bipolar plates. The composites comprise graphite as the primary conductive filler and polypropylene as the binder. Carbon xerogel is introduced as a minor conductive filler, and its performance is compared with commercial carbon black. Both nanocarbons exhibit resemblances in microstructure, texture, and surface carbon chemistry. Through‐plane conductivity measurements reveal enhanced electrical conductivity upon replacing a fraction of graphite with either nanofiller. Cross‐sectional analyses of the plates employing computed tomography based on X‐ray diffraction and phase contrasts indicate that the observed electrical conductivity difference stems from reduced trapped air during production and the distribution of the minor filler particles. Given the similarities between carbon xerogel and the reference nanofiller, this study introduces the innovative concept of employing carbon xerogel as a filler for conductive bipolar plates.

Co-deposition of TaC and SiC by chemical vapor deposition: A systematical thermodynamic exploration

A systematical thermodynamic analysis on the co-deposition of TaC and SiC via the chemical vapor deposition (CVD) is performed using the TaCl5-SiCl4-CH4-H2 system as the representative precursors system to guide experiments. The optimal deposition window for co-depositing TaC and SiC and tailoring their ratio is determined. The results show that temperature and pressure have limited influence on the content of TaC but mainly affect the mole fraction of SiC and graphite at equilibrium. CH4/(TaCl5 + SiCl4) ratios between 0.5 and 0.85 and H2/(TaCl5 + SiCl4) ratios of >5 favor the formation of the two-phase region of TaC + SiC. Medium temperatures (1000–1400 °C) are conducive to the co-deposition of TaC and SiC. Other condensed species will deposit at CH4/(TaCl5 + SiCl4) ratios below 0.6. By adjusting the ratios of CH4/(TaCl5 + SiCl4) and SiCl4/TaCl5, the mole fractions of TaC in the deposit can be regulated.

Enhancing microstructural and mechanical properties of magnesium AZ31 matrix composites through friction stir processing incorporating silicon carbide, titanium carbide, and graphite particles

The present study focuses on investigating the effect of reinforcement on the microstructure and mechanical properties of friction-stir-processed magnesium hybrid composites. The groove width (0, 0.7, 1.1, 1.7, and 2.3 mm) of the Magnesium AZ31 plates was varied by varying the volume fractions (0, 5, 10, 15, and 20 vol%) of Silicon Carbide (SiC), Titanium Carbide (TiC), and Graphite (Gr) particle reinforcements in the hybrid composite. Single-pass processing was suspended using a cylindrical tool shoulder with a rotational speed, transverse velocity, and axial pressure of 1000 rpm, 30 mm min−1, and 6 kN, respectively. The optical micrograph clearly shows that a non-cluster zone (reinforcement particles are uniformly distributed without agglomeration) was identified in the processed region of the least concentrated composites. The results revealed that a peak tensile strength of 293.546 ± 5.12 MPa was attained for the combination of 10 vol% composites, and a Vickers hardness number of 86.53 HV was achieved for the 20 vol.% composites. The fracture surface morphology was analyzed using a Scanning Electron Microscope (SEM). The mode of tensile fractography was ductile for the least composite and transformed into a brittle mode of failure with the addition of reinforcements.

The Effect of Graphite Flake Volume Fraction on the Thermophysical Proper Ties of Graphite Flake/Aluminum Composites

A vacuum hot‐press sintering process is utilized to manufacture graphite flake/aluminum composites, and the influence of graphite flake volume fraction on the microscopic structure, hardness, thermal conductivity (TC), and coefficient of thermal expansion (CTE) of the composites is investigated. The results indicate that the graphite flakes are neatly aligned along the in‐plane direction in the composites and exhibit a strong bond with the aluminum matrix interface. The in‐plane TC of the composite significantly increases with the addition of graphite flakes, whereas hardness, through‐plane TC, and CTE decrease. As the volume fraction of graphite flakes in the composites increases from 15% to 60%, in‐plane TC improves from 278.8 to 353.8 W m−1 K−1, through‐plane TC decreases from 164.4 to 33.2 W m−1 K−1, and the CTE decreases to 13.7 × 10−6 K−1, achieving high thermal conductivity and a low CTE.

Effect of regular thicknesses on the microstructural and quantitative analysis for a hypo-eutectic ductile iron alloyed with Ni and V

Ductile iron contains free graphite nodules within the metallic matrix, which generally consists of ferrite and pearlite in the as-cast condition. The casting thicknesses have a great influence on the size, shape, and quantity of the microconstituents of the metallic matrix and the graphite nodules and thus on the mechanical properties. In this study the cooling rate (caused by the casting thicknesses) on the metallic matrix and the nodular characteristics of a low alloyed ductile iron with 0.8 %Ni and 0.15 %V was investigated. The ductile iron was produced in a sandwich process with ladle inoculation. Six plates of different thicknesses, from 4.3 mm to 25.4 mm, were produced in a green sand mold. The microstructural characterization was performed by optical microscopy (OM), scanning electron microscopy (SEM), and the image J software using different quantification methods. The area method to determine the average nodule size and nodular structure provided more reliable results than the perimeter and total particle count methods. The hardness test on the Rockwell C scale was used for the mechanical characterization. The low content of vanadium added to the ductile cast iron had a negligible effect on the solidification pattern, which was mainly due to the graphitizing impact of the nickel and silicon addition. The results of the microstructural characteristics are therefore primarily due to the cooling rate, which is determined by the casting thickness. The thinnest casting section significantly improved the number of nodules (414 Nod/mm2), sphericity (0.96), and nodularity (96.21 %). In contrast, the thickest casting plate obtained the highest volume fraction of graphite (10.85 %) and the lowest volume fraction of unwanted particles (0.36 %). The high cooling rate in the thinnest casting plate resulted in the highest hardness of 31.56 HRC due to the higher volume fraction of the pearlite (33.7 %) and carbides (4.5 %).

Analysis of Paint Properties According to Expandable Graphite and Fire Simulation Research on Firewall Penetration Part.

In this research, we attempted to develop paints that can be applied to various fields such as high-rise building structures and electric vehicle batteries. To minimize damage to life and property in the event of a fire, we attempted to manufacture a highly elastic paint material that can block flames and control smoke spread, and that has additional sound insulation and waterproofing functions. A high-elasticity paint was manufactured by mixing a flame-retardant polyurethane dispersion (PUD) with an acrylic emulsion binder and adding different mass fractions of expandable graphite (EG). The thermal, physical, and morphological properties of the prepared mixed paint were analyzed. The thermal properties of the mixed paint were analyzed and intended to be used as input data (heat transfer coefficient, specific heat capacity) for fire simulation. Output data were used to predict how much the temperature would change depending on the time of fire occurrence. The reason for conducting simulations on the fire stability of paint materials is that the fire stability of paints can be predicted without conducting fire tests. Two hours after the fire broke out, the thermal temperature distribution was analyzed. The temperature distribution was compared with and without mixed paint. Two hours after a fire broke out in a virtual space, it was found that when the mixed paint was applied, the surrounding temperature of the penetration area was lower than when the mixed paint was not applied. Development costs for developing excellent paints can be reduced. Since fire safety can be predicted without actually conducting tests, the time required for product development can be reduced. We are confident that this is a very groundbreaking technology because it allows fire safety simulations for developed products to be conducted in a virtual space by creating an environment similar to actual fire test standards.

Electrical conductivity of geopolymer-graphite composites: Percolation, mesostructure and analytical modeling

The incorporation of carbon fillers into geopolymers enhances conductivity, forming intricate networks for integrated energy conversion in construction materials. This study employs a novel computational modeling approach to investigate the electrical conductivity of geopolymer-graphite composites. Utilizing a particle-based Monte Carlo method, percolation thresholds in virtual composite mesostructures are simulated, and Bruggeman's effective medium model is applied to predict conductivity. The research explores how mesostructural characteristics, including pore and particle size distribution, influence percolation and conductivity in multi-phase mixtures. The findings indicate that graphite polydispersity increases the percolation threshold from 10 vol% to 24.4 vol%, while the introduction of two additional (segregated) phases, metakaolin and pores, decreases the percolation threshold to 11.9 vol%. The concept of effective volume fraction is introduced to assess the influence of metakaolin and porosity on the percolation threshold. This enabled to establish a linear relationship between the electrical conductivity and effective volume fraction of graphite with a slope of 2 S/m/vol%. In a three-phase mixture, the percolation threshold is 12.18 vol%, with a 2.35% increase due to capillary water drying, enhancing graphite particle aggregation in the dried pores. Finally, Bruggeman's analytical effective medium model is used to simulate conductivity variation with increasing graphite content, aligning well with conductivity measurements. These findings provide valuable insights into percolation behavior and offer a relatively simple quantitative modeling approach to understand the factors influencing the effective conductivity of geopolymer-graphite composites.

Effect of Varying the Volume Fractions of Ledeburitic Cementite and Graphite on the Tribological Properties of Commercially Used Cast Irons

The types and volume fractions of the carbonaceous phases present in the microstructures of cast irons strongly influence their properties. In the case of materials used commercially for tools, an important parameter with regard to their use is the resistance to abrasion wear. Cementite is the main reinforcing phase in cast irons and is present in significant quantities. In addition, cast irons contain graphite precipitates, which also affect wear by interacting with the matrix of the alloys. In this study, abrasive wear tests were carried out on a group of cast irons with different chemical compositions and, consequently, different microstructural morphologies. Due to the wide scatter of the results and the commercial rather than laboratory nature of the alloys studied, it was decided to use analysis of variance (ANOVA) to determine whether there was a statistically significant difference between the volume fractions of the carbonaceous phases. The volume fractions of graphite and ledeburite were then related to the results of the tribological tests. Statistical analysis confirmed significant differences in the results obtained for the alloys tested. A continuous increase in the volume fractions of both graphite and ledeburitic cementite is unfavourable in terms of the wear resistance and friction coefficient values. Optimum results can be obtained by balancing the volume fractions of the two phases observed. In addition, the phase composition of the material matrix plays an important role in wear, as the differences in the matrix of the tested alloys modify the nature of the influence of cementite and graphite on the wear.

Tribological and Mechanical Properties of Al 6061/SiC/ GO Hybrid Composites Produced with Stir Casting

A constant prerequisite for technological advancement is the improvement of composite materials’ mechanical properties. In this study, stir casting was used to create hybrid Aluminium Matrix Composites (AMC). To enhance the mechanical properties, silicon carbide and graphite were used as reinforcement. AMC are made by adding different volume fractions of SiC (3%, 6%, 9% and 12%), whereas composites use a fixed volume fraction of graphite (5%). Mechanical Properties like Hardness, Tensile and wear characteristics of the manufactured AMC samples were evaluated. Under various loads 10N-40N and sliding velocities 0.6m/s-2.0 m/s the wear rate was calculated. The mechanical characteristics of manufactured AMCs are compared with Al 6061 alloy. From the experimental results, the addition of silicon carbide and graphite particles improve the mechanical characteristics. The wear rate increases with increase in applied load. However, sliding velocity surges up to 1.8 m/s before sharply declining.

Development of Graphitic 2024 Al Alloy by Mechanical Alloying

In this study, the 2024 Al powder with different weight fractions of graphite is mechanically milled using a high-energy ball mill for 3 hours each in the nitrogen environment. The milled powder is compacted at an elevated temperature. X-ray diffraction is used to phase analysis of milled powder as well as compacted specimens. Optical microscopy is used for microstructural analysis and hardness measurements are done for the evaluation of mechanical properties. The hot compacted specimens are also tested for their wear properties. Results show that there is no new phase formed during mechanical milling. But, after hot compaction of the milled powder, Al2Cu formed due to precipitation. No reaction is observed between the aluminum and the carbon (graphite) after milling as well as hot compaction. Microstructures of all hot compacted specimens are not showing pores, which, signifies full density after compaction. The formation of Al4C3 is not observed at any stage of processing. Therefore, graphite is uniformly distributed in all specimens, and the same is observed at grain boundaries of α-Al grains in the microstructures. Hardness increases with the addition of 1 wt.% graphite but it decreases with a further increase in graphite. The wear resistance of 2024 Al with 1 wt% graphite is the highest among all the compositions. The high hardness and wear resistance of 2024Al with 1 wt% graphite is the consequence of precipitation of Al2Cu during hot compaction and the presence of graphite which creates hindrances in the metal matrix. The presence of free graphite in the vicinity of grain boundaries acts as a solid lubricant which improves wear resistance of 2024 Al.

Investigation of Impact Energy Absorption of AA6061 and Composites: Role of Post-Aging Cooling Methods

Al6061 and its composites are widely employed in applications requiring high strength and impact resistance. Heat treatment, particularly ageing, is a well-established method for enhancing the mechanical properties of these composites. However, the influence of post-ageing cooling methods on the impact energy absorption capacity of Al6061 and its composites remains inadequately understood. This investigation aims to examine the impact energy absorption of Al6061 and its composites after ageing at 460°C for 2 hours, employing different cooling methods, including furnace cooling, air cooling, and water cooling. The composites were produced using the stir casting technique with varying weight fractions of graphite and SiC particles based on Taguchi's design of experiments. Charpy impact tests were conducted using a specialised testing machine. The results reveal that the impact energy absorption capacity of the composites is influenced by the cooling method employed after the ageing treatment. Furnace cooling demonstrated the highest impact energy absorption capacity compared to the other cooling methods, exhibiting a 28% increase compared to the monolithic aluminium alloy. Furthermore, it was observed that the impact energy absorption capacity of the composites did not improve with an increase in the weight fraction of SiC particles, while the addition of graphite negatively impacted the absorption capacity.

Aramid nanofiber assisted preparation of 3D-oriented graphite/silicone composite slices with high through-plane thermal conductivity and efficient electromagnetic interference shielding

High-performance electromagnetic interference (EMI) shielding materials with outstanding thermal transfer ability are urgently needed for modern electronics. Here, efficient 3D-oriented graphite/silicone EMI shielding composite slices with high through-plane thermal conductivity were prepared through the construction of 3D-oriented graphite skeletons followed by incorporation of silicone and cutting. The flaky graphite was utilized as functional fillers, and an ultra-low addition of aramid nanofibers (ANFs) was conducted to construct the supporting frameworks to maintain the structure of 3D-oriented graphite skeletons. The strategy of constructing of 3D-oriented graphite skeletons before incorporating of silicone facilitated the forming of efficient electrically conductive network and thermal transfer pathway in the prepared composite slices. The differences in thermal, electrical and EMI shielding properties that originated from the orientation of interconnected flaky graphite were systematically studied. As a result, the composite slices show significant enhancements of EMI SE of 65.28 dB in X-band, 76.62 dB in Ka-band and through-plane thermal conductivity of 10.53 W m−1 K−1 at the graphite fraction of 32.68 vol%. Additionally, the composite slices exhibit a good near-field (NF) shielding performance at the frequency range of 1–9 GHz. The composite slices reveal substantial potential for advanced EMI shielding and thermal management applications.

Thermal characteristics of expandable graphite as a burning rate enhancer in hybrid propulsion

AbstractHybrid propulsion, consisting of solid fuel and liquid oxidizer, exhibits major advantage regarding safety, development costs, energetic performance, and controllability. Hence, it has been considered for space and other propulsion programs. One of the characteristic features of hybrid motors, that may be of major disadvantage, is their relatively low thrust due to the characteristic low regression rate of the typical polymeric solid fuels. This research group had revealed that a small fraction of an expandable graphite (EG) additive could double the burning rate and thrust of hybrid motors. EG is an intercalated form of graphite, elongating and swelling, getting a worm‐like string shape at elevated temperatures. In an earlier work it was hypothesized that enhanced heat transfer via conduction through the EG strings protruding from the hot surface, is a significant parameter increasing the burning rate. In the present investigation, thermal analysis revealed that the ignition temperature of polyester fuel containing 5 wt% of EG, is substantially lower than that of the pure polymer, which may promote higher burning rate as well. High‐speed photography of the surface of EG‐containing solid fuels as well as that of individual EG particles during controlled heating, demonstrated the dynamic behavior resulting in the formation of EG strings longer by an order of magnitude compared to the original particles. The different phenomena were related to the observation of enhanced burning rate.

High-Temperature Hardness in Hypereutectoid Steels with Various Microstructures Measured by Using Small Ball Rebound Hardness Test

The temperature dependence of hardness in hypereutectoid steels with various microstructures was measured by using the small ball rebound hardness test, and the effect of carbon state on the high-temperature hardness was discussed. As-received and spheroidized cementite steels consisted of spheroidized cementite, graphite and ferrite matrix, and the volume fraction of graphite in the spheroidized cementite steel was larger than that in the as-received steel. Pearlite steel had ferrite and cementite lamellar structure without graphite. The characteristic hardening was detected above 700 K in all steels, suggesting that the solid solute carbon enhances the hardness even in hypereutectoid steels with high strength. The pearlite steel exhibited the highest hardness owing to the ferrite and cementite lamellar structure and no graphite. While the spheroidized cementite steel exhibited the lowest hardness, although the size of cementite was finer than that in the as-received steel. It was quantitatively demonstrated that the large volume fraction of graphite caused the low hardness in the spheroidized cementite steel.

Increasing Burning Rate and Motor Thrust by Expandable Graphite Additives

Controlling rocket thrust may be done via propellant burning rate catalysts and enhancers. This paper presents an experimental investigation on increasing the thrust of hybrid and solid motors by adding a small fraction of expandable graphite (EG) within the binder matrix to enhance burning rate. EG is a form of intercalated graphite flakes that upon heating change their appearance to elongated fibers/strings of substantially larger length and volume. The elongated EG strings at the burning surface are hypothesized to conduct heat from the hot surroundings to the bulk, thereby increasing the burning rate. High-speed photography of the surface phenomena of fuel slabs containing EG additive subjected to flame supports the greater effect on burning rate enhancement (up to twofold) for polyester versus hydroxyl-terminated polybutadiene or paraffin wax fuels in hybrid motors. Similar investigation on the burning of ammonium perchlorate–polymer solid propellant strands revealed different surface phenomena and substantial burning rate increase (60% and more) for hydroxyl-terminated polybutadiene versus polyester binder with 5% EG additive. It can be concluded that EG can serve as a novel burning rate and thrust enhancer without deterioration of the mechanical properties of the polymeric fuel/binder for hybrid (including solid fuel ramjet) and solid propellant motors.

Promotion effect of ultraviolet light on graphene oxide aggregation in the presence of different climatic zone's humic and fulvic acid

Aggregation of graphene oxide (GO) is significantly affected by dissolved organic matter (DOM) in natural waters, while DOM's climate zone and light irradiation is seldom considered. This study investigated the effect of humic/fulvic acid (HA/FA) from various climate zones of China on aggregation of small (200 nm) and large (500 nm) GO under 120-h UV irradiation. GO aggregation was promoted by HA/FA because UV irradiation decreased hydrophilicity of GO and steric forces among particles. GO generated electron and hole pair under UV irradiation, which reduce GO with more hydrophilic oxygen-containing functional group (C-O) to rGO with high hydrophobicity and oxidize DOM into organic matter with smaller molecular weight. Most severe GO aggregation was observed with Makou HA from Subtropical Monsoon climate zone and Maqin FA from Plateau and Mountain climate zone, which was primarily because HA/FA's high molecular weight and aromaticity dispersed GO initially that facilitated UV penetration. GO aggregation ratio was positively correlated with graphitic fraction content (R2 = 0.82-0.99) and negatively correlated with C-O group content (R2 = 0.61-0.98) in the presence of DOM under UV irradiation. This work highlights different dispersity of GO during photochemical reactions in various climate zones, providing new insight into the environmental implications of nanomaterial release.

Effect on the Thermal Performance of a Bio-based Phase Change Material with the Addition of Graphite with Surfactants

This work presents an experimental investigation into how adding graphite with different surfactants to a bio-based phase change material (PCM) affects its cooling performance. Graphite-based phase change materials (GraPCMs) are prepared by stirring and sonicating graphite with different surfactants, including Sodium Stearoyl Lactylate, Sodium Dodecylbenzene Sulfonate (SDBS), and Sodium Dodecyl Sulfate (SDS), in a liquid bio-based PCM. Based on the experiments, the thermal conductivity of the bio-based PCM is increased by 240% to 0.748 W/m⋅K and 218% to 0.70 W/m⋅K when mixed with graphite-SDBS and graphite-SDS, respectively, at a 5% mass fraction of graphite. The ratio of 1:3 graphite to surfactant at a 5% mass fraction of graphite results in the longest amount of time for GraPCM-SDBS and GraPCM-SDS to reach the reference temperature of 43 °C, with delays of 185 and 175 s, respectively. It is observed that increasing the concentration of surfactant leads to further delay in reaching the reference temperature in the case of GraPCM-SDS. The results agree with the literature, as the surfactants and graphite enhanced the thermal conductivity of the PCM.

Thermal Management of Lithium-Ion Batteries Based on Honeycomb-Structured Liquid Cooling and Phase Change Materials

Batteries with high energy density are packed into compact groups to solve the range anxiety of new-energy vehicles, which brings greater workload and insecurity, risking thermal runaway in harsh conditions. To improve the battery thermal performance under high ambient temperature and discharge rate, a battery thermal management system (BTMS) based on honeycomb-structured liquid cooling and phase change materials (PCM) is innovatively proposed. In this paper, the thermal characteristics of INR18650/25P battery are studied theoretically and experimentally. Moreover, the influence of structure, material and operating parameters are studied based on verifying the simplified BTMS model. The results show that the counterflow, honeycomb structure of six cooling tubes and fins, 12% expanded graphite mass fraction and 25 mm battery spacing give a better battery thermal performance with high group efficiency. The maximum temperature and temperature difference in the battery in the optimal BTMS are 45.71 °C and 4.4 °C at the 40 °C environment/coolant, as against 30.4 °C and 4.97 °C at the 23.6 °C environment/coolant, respectively. Precooling the coolant can further reduce the maximum battery temperature in high temperature environments, and the precooling temperature difference within 5 °C could meet the uniformity requirements. Furthermore, this study can provide guidance for the design and optimization of BTMS under harsh conditions.