Graphite Flakes Research Articles

EFFECT OF MAGNESIUM TREATMENT PROCESS ON THE PRODUCING COMPACTED GRAPHITECAST IRON WITH DIFFERENT CASTING THICKNESS

Strength, toughness, machinability and damping capacity are properties of compacted graphite iron that distinguish the properties between flake graphite cast iron and spheroidal cast iron. The formation of compacted graphite can be set to achieve the required specification. The formation of compacted graphite is started from spheroidal to compacted cast iron. The residual magnesium after magnesium treatment and the solidification ratehave a significant role in the formation of compacted graphite. The high content of residual magnesium can obstruct the graphite plane to grow during the transformation from spheroidal to compacted shape. In addition, the cooling rate of the casting can be controlled by varying the casting thickness. The compacted graphite in the cast iron are characterized according to shape, size ai`nd distribution. The optimum compacted graphite in the cast iron that can be produced has 30 mm of casting thickness with 0.017 % of residual magnesium.

Factors affecting the energy harvesting efficiency of graphite thermoelectric materials

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

Sustainable assembling of graphite flakes into graphite/carbon composite foams with thermal percolative interfaces for active heat dissipation

Current methods for producing open-pore graphite foams with heat dissipation potential involve costly graphitization processes, limiting their widespread use. This study presents a sustainable approach to fabricate high-performance graphite/carbon composite foams with porosities in the range of 49–82 %. The method involves the densification and carbonization of solid mixtures comprising natural graphite flakes, sucrose, and NaCl particles. The dissolution of NaCl creates coarse pores, while carbonized sucrose contributes fine porosity and serves as a binder to impart mechanical stability, ensuring the maintenance of thermally conductive percolative contacts between flakes. The composite foams exhibit thermal conductivities of up to 91 Wm−1K−1, permeability values in the range of 10−11–10−10 m2, and excellent mechanical properties. Experimental and computational findings demonstrate that the developed materials surpass the heat dissipation capabilities of conventional heat sinks based on graphite and aluminum foams by about 3 and 1.5 times, respectively, making them excellent candidates for thermal management applications.

Isotropic Structure and Polymer Interface Intensified Lithium-Ion Transmission in Spherical Graphite Tailings/Coke Composite Anode

Spherical graphite tailings (SGT) as the anode electrode for a lithium-ion battery not only improves the utilization value of SGT as solid waste, but also demonstrates the cleaner production of natural flake graphite (NG) compared with artificial graphite. However, SGT anodes present issues regarding rate performance and cycle stability due to the anisotropy structure and the instability of the solid electrolyte interface (SEI). In this work, a composite anode with isotropic structure was prepared by granulation of high-sulfur coal (HSC) and SGT, while an artificial SEI was prepared utilizing polyether amine/polyvinyl pyrrolidone (PEA/PVP) crosslinked polymer. Results showed that the coke from HSC pyrolysis enhanced the isotropy of the composite anode and improved its rate performance. Compared with SGT, the capacity retention rate of the sample (OSGT-50%OHSC) after oxidation - pyrolysis at a high current density of 5.0 A g−1 increased from 7.2% to 25.8%. Additionally, the PEA/PVP artificial SEI strengthened the cycle stability of the anode. After 1000 cycles, the capacity retention rate increased from 22.5% to 70.3%. The artificial SEI effectively avoided direct contact between the anode and the electrolyte, increasing the initial coulombic efficiency from 70.3% to 77.1%.

Continuously compressing crushing towards a dry processing method, a testing for graphite ore

In this study the comminution methods of graphite bearing ore were compared by using five different crushing methods, namely a jaw crusher, a roll crusher, uniaxial compression tests, and a new type of continuously compressing crushers. These new continuously compressing crushers were available in laboratory and pilot scales. The particles in the + 1700 µm size class produced by continuously compressing crushing were coarser and rougher in texture compared to the rounded particles produced traditionally by a jaw crusher. In the size class −100 µm, most of the graphite flakes were observed independently in the products of each of these crushing methods. The liberation of ultra-coarse-grained graphite flakes in size class + 300 µm was most observed after pilot-scale continuously compressing crusher. The shape and enrichment of the graphite flakes were very similar after both laboratory and pilot scale continuously compressing crushers. In contrast, the graphite flakes produced by jaw crusher appeared as broken particles in the form of accumulation of several layered and non-independent graphite flake structures. The results of this study demonstrate that the new innovative continuously compressing crushing method enables the enrichment of coarser and cleaner graphite, which has a much higher value and wider industrial applications compared to amorphous and fine-grained graphite.

Nanoscale brick and mortar strategy for mechanically strong multifunctional composites with extremely high filler-loading

To achieve the best physico-chemical properties of polymer composites, the concentration of fillers should be maximized in many cases. However, at extremely high concentrations of fillers, the discontinuity of the polymer matrix results in poor mechanical properties. To overcome this problem, we propose an efficient protocol to improve the mechanical strength significantly, even at an extremely high concentration of microscale fillers (graphite flakes, 95 wt%). Since the mechanical strength of the polymer composite strongly depends on both the homogeneous distribution of the polymer matrix around microscale fillers and the adhesion between them, we increased the mechanical strength of the composite by the preparation of a hybrid filler decorated with polymer nanoparticles. The decorated polymer nanoparticles eventually turned to the matrix during hot-pressing process like a mortar between bricks. Systematic studies on the mechanical strength as well as electrical and thermal conductivities of the composites revealed that both the precisely controlled size of the polymer nanoparticles and even distribution of them on the hybrid fillers were critical variables to enhance the material's properties above. The newly developed polymer composites with superior physical properties exhibited good electromagnetic interference shielding (EMI shielding effectiveness >80 dB in X-band, thickness ∼ 1.5 mm), making them suitable as electric heaters.

Analysis of the Microstructure and Hardness of Flake Graphite Cast Iron Using the Barkhausen Noise Method and Conventional Techniques

The new brake disc was evaluated for microstructure and hardness by the conventional destructive tests and non-destructive Barkhausen noise method (BNM). Ten non-destructive measurements were carried out in different areas of a brake disc, which were then cut out and made into metallographic test samples. Qualitative and quantitative analysis of graphite precipitates was performed to assess their volume in material matrix, anisotropy and size. Subsequently, graphs showing the relationships between selected stereological parameters of graphite precipitates and parameters determined from the RMS envelope of Barkhausen noise were elucidated. Similar relationships between hardness and parameters coming from non-destructive tests were carried out. Magnetic parameters that specified the size of a graphite precipitate was selected. In addition, repeatability studies using BNM were carried out in the areas of the material with the smallest and largest average size of graphite precipitates. A linear relationship between amplitude of BN and length of graphite flakes was found. The paper presents the possibilities of assessing the volume and size of graphite precipitates, as well as cast iron hardness using BNM.

S, N, and O tri-doped graphite nanosheets-based gas diffusion electrode boosts highly selective electrosynthesis of H2O2

Electrochemical synthesis of hydrogen peroxide (H2O2) via oxygen reduction reaction (ORR) is a promising environmentally friendly approach for on-site production of H2O2. The development of economically feasible cathodes with high activity and selectivity is of utmost importance to enable the large-scale application of the process of H2O2 electrosynthesis. Herein, a novel electrocatalyst of sulfur, nitrogen, and oxygen tri-doped graphite nanosheets (SNOGNSs) was developed, which exhibited the selectivity of up to 97.4 % for the electrosynthesis of H2O2, significantly higher than that of flake graphite (FG, 51.4 %), OGNSs (72.8 %) and NOGNSs (90.9 %). The gas diffusion electrode (GDE) was fabricated using SNOGNSs as catalysts, and the accumulation of H2O2 reached 732.8–1044.4 mg/Lh−1 at 0.3–0.5 A electrolytic current. The mechanism of the synergistic enhancement of two-electron ORR by S, N, and O tri-doping was revealed utilizing density functional theory (DFT) calculations. This work offers a suitable alternative for on-site clean production of H2O2 that can be applied in electrochemical advanced oxidation processes.

Thermoluminescence dosimetry and microstructural characteristics of gamma-irradiated natural flake graphite

Thermoluminescence (TL) and microstructural analysis were conducted on natural flake graphite (NFG) to assess its suitability for radiotherapeutic x-ray dose measurements. The investigations encompassed the examination of TL glow curves, linearity, sensitivity, signal decay, and repeatability. NFG samples were exposed to 60Co gamma radiation doses ranging from 2 Gy to 20 Gy. The microstructure of the irradiated NFG was probed using a 532 nm laser Raman spectrometer. Promisingly, the NFG exhibited remarkable characteristics, including a moderately higher response to dose (R2 of about 96%), increased sensitivity at lower doses, and good repeatability (∼4%). Nevertheless, its fading rate reached about 80% after 14 days of irradiation. Additionally, the NFG intensity ratios of defect (D) to graphite (G), denoted as ID/IG, closely mirrored the oscillatory pattern observed in 50 μm thick graphite sheets and were approximately 1.6 times lower than those of similar graphite sheets with comparable carbon content (about 98% carbon). These findings suggest that NFG holds potential for the development of an affordable, non-hygroscopic, and tissue-equivalent TL dosimeter, with possible applications in the medical field.

Evaluating the effect of unidirectional loading on the piezoresistive characteristics of carbon nanoparticles

The piezoresistive effect of materials can be adopted for a plethora of sensing applications, including force sensors, structural health monitoring, motion detection in fabrics and wearable, etc. Although metals are the most widely adopted material for sensors due to their reliability and affordability, they are significantly affected by temperature. This work examines the piezoresistive performance of carbon nanoparticle (CNP) bulk powders and discusses their potential applications based on strain-induced changes in their resistance and displacement. The experimental results are correlated with the characteristics of the nanoparticles, namely, dimensionality and structure. This report comprehensively characterizes the piezoresistive behavior of carbon black (CB), onion-like carbon (OLC), carbon nanohorns (CNH), carbon nanotubes (CNT), dispersed carbon nanotubes (CNT-D), graphite flakes (GF), and graphene nanoplatelets (GNP). The characterization includes assessment of the ohmic range, load-dependent electrical resistance and displacement tracking, a modified gauge factor for bulk powders, and morphological evaluation of the CNP. Two-dimensional nanostructures exhibit promising results for low loads due to their constant compression-to-displacement relationship. Additionally, GF could also be used for high load applications. OLC’s compression-to-displacement relationship fluctuates, however, for high load it tends to stabilize. CNH could be applicable for both low and high loading conditions since its compression-to-displacement relationship fluctuates in the mid-load range. CB and CNT show the most promising results, as demonstrated by their linear load-resistance curves (logarithmic scale) and constant compression-to-displacement relationship. The dispersion process for CNT is unnecessary, as smaller agglomerates cause fluctuations in their compression-to-displacement relationship with negligible influence on its electrical performance.

Relationships Between Macrostructure and Microstructure in Lamellar Graphite Iron Castings

AbstractSpherical sheet steel molds filled with gray iron melts of varying chemical compositions and metallurgical conditions were air-cooled until solid, followed directly by austempering to preserve the austenite grain structure. The castings were studied using a combination of cooling curves and quantitative metallography, in order to clarify control of the austenite grain structure and its impact on the local microstructure. A novel method utilizing fast Fourier transform provided visual overview of macroscopic trends in the scale of the flake graphite structure. Castings inoculated with Sr-containing ferrosilicon featured finer eutectic cell structure but coarser equiaxed structure of austenite, emphasizing that melt treatments applied to control the graphite structure may have unintended effects on the austenite grain structure. In most non-inoculated castings, the microstructure was banded, with alternating layers of coarse and fine flake graphite with distance from the casting surface. The extent of the columnar zone of austenite grains showed no correlation with the graphite structure nor the volume fraction of dendrites. The volume-to-surface ratio of dendrites was more uniform in the columnar zone, but increased toward the center in the equiaxed zone. The casting with the highest carbon equivalent (4.34), featured zones containing finer dendrites and graphite. These zones appear to be gaps in the early solidification structure which filled later by secondary dendritic growth from surrounding austenite. This highlights that high carbon equivalent may lead to poor dendrite coherency which can make the microstructure less uniform and less predictable.

Upgrading anode graphite from retired lithium ion batteries via solid-phase exfoliation by mechanochemical strategy

Vast quantities of anode graphite from waste lithium ion batteries (LIBs), as a type of underrated urban mine, has enormous potential to be exploited for resource recovery. Herein, we propose a benign process integrating low-temperature pyrolysis and mechanochemical techniques to upcycle spent graphite (SG) from end-of-life LIBs. Pyrolysis at 500 °C leads to about 82.2 % PVDF dissociation in thermal treated graphite (TG). Solid-phase exfoliation via ball milling assisted by urea successfully produces abundant graphite flakes and a small amount of monolayer graphene nanosheet at the edge of mechanochemically processed graphite (MG). Subsequent rinsing removes the residual LiF salts. High purity and unique edge structural features of the as-prepared MG offer more active sites and storage reservoir for intercalation and de-intercalation of lithium ions, resulting in enhanced lithium-ion diffusion kinetics, excellent reversible specific capacity and desirable rate capability. Inspiringly, MG exhibits a remarkably enhanced initial specific charge capacity of 521.3 mAh g−1 during the first charge–discharge, and only declines from 569.9 mAh g−1 to 538 mAh g−1 with slight attenuation after 50 consecutive cycles at 0.1 A/g, indicating satisfactory cycle stability. Additionally, the purification and reconstruction mechanism for MG have been illustrated in detail. This study offers a green strategy to reconstruct and upgrade anode graphite from LIBs, which can realize sustainable waste management.

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

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

γ-Fe2O3 modified exfoliated graphite flexible paper based non-enzymatic glucose sensor

We report the γ-Fe2O3 modified exfoliated graphite (γ-Fe2O3@ExGCP) flexible paper electrode as a non-enzymatic glucose sensor. The γ-Fe2O3 was physically mixed with exfoliated graphite flakes, and mechanically pressed to get a thin sheet. The amperommetric analysis of γ-Fe2O3@ExGCP electrode shows that the sensor current increases with increasing glucose concentration. The impedance analysis of γ-Fe2O3@ExGCP substantiates the reduction in charge transfer resistance with increasing glucose concentration. The observed values of sensitivity for Ex-GCP and γ-Fe2O3@ExGCP electrodes are 3.51 µA mM-1cm−2 and 7.1 µA mM-1cm−2, respectively. The calculated LOD is 512 μM for γ-Fe2O3@ExGCP. Thus, γ-Fe2O3@ExGCP flexible electrode may be used for non-enzymatic glucose sensor with enhanced sensitivity.

High temperature mechanical properties of novel MgO–Al3BC3 refractories for electric arc furnace lining

In this study, novel MgO–Al3BC3 refractories were developed by gradually replacing flake graphite with Al3BC3 in unfired low–carbon MgO–C refractories. The high temperature mechanical properties of these novel refractories were investigated for the first time. The results demonstrated significant enhancements in cold crushing strength, thermal shock resistance, and hot modulus of rupture when compared with low–carbon MgO–C refractories. These enhancements can be attributed to the formation of an appropriate amount of boron–containing liquid phases within the novel MgO–Al3BC3 refractories at elevated temperatures. These liquid phases serve multiple functions, including acting as a mineralizer for MgAl2O4, facilitating self–healing by filling cracks and pores, and strengthening the bonding between the aggregate and matrix interface. Furthermore, the thermal stability of Al3BC3 enables it to maintain its functionality consistently, even at high temperatures.

Development of a magnetite nanocomposite based on expanded graphite/chitosan for efficient removal of brilliant green dye from aqueous solutions

ABSTRACT In this research, to develop an efficient and magnetic graphite-based nanocomposite (Fe3O4/EG-chitosan), the natural flake graphite was first expanded to improve its active surface area. The expanded graphite (EG) was then functionalized and magnetized with chitosan and Fe3O4 nanoparticles to increase its adsorption performance. Structure of EG/chitosan and nanocomposite Fe3O4/EG-chitosan were determined and confirmed by FT-IR, XRD, EDX, FESEM, VSM, zeta potential measurement and BET surface area measurements. The surface area of EG was improved from 10.13 to 83.08 m2/g after the functionalization of it using chitosan. Fe3O4/EG-chitosan exhibited a lower magnetization saturation value (30.9 emu/g) in compared with pure Fe3O4 NPs (60.2 emu/g). The fabricated nanocomposite was then applied to adsorb BG dye from aqueous media. The optimal removal of 98% BG dye was achieved at pH 8.0, adsorbent dosage 0.04 g, initial concentration 50 ppm, and temperature 293 K. The adsorption of BG is described well with the pseudo-second order kinetic model and the Freundlich isotherm model. The results also showed that the maximum adsorption capacity of BG dye was 21.8 mg/g using the Langmuir isotherm model. In addition, after 6 adsorption-desorption cycles, the adsorption capacity of the developed Fe3O4/EXG-chitosan toward BG remains high (90%).

Experimental study of flake graphite large-area explosion electron emission cathode performance based on particle size discrepancy

Graphite is the most commonly used large-area cathode material in the high-power vacuum electron device for its long life and good repetitive-frequency performance, but its particle size selection scheme has not been elucidated. Therefore, in the present work, the explosive electron emission properties of flake graphite large area explosive electron emission cathodes with varied particle sizes are studied. The 320 mesh flake graphite has a current delay reduction of 0.2–0.9 ns compared to other samples at the same peak voltage. According to the Murphy–Good equation, the emission performance of each sample during the priming stage was calculated, and the threshold characteristics of 320 mesh flake graphite were significantly better than the other samples. After the space charge limited current is formed, the plasma expansion rate of all samples is 1.2±0.2cm/μs with a difference not exceeding 4% between samples. Our research provides a strong basis for the selection of raw materials for graphite based large area explosive electron emission cathodes and contributes to the development of cross-field high-power vacuum devices.

Positive-Negative Tunable Coefficients of Friction in Superlubric Contacts.

In conventional systems, the coefficient of friction (COF) is typically positive, signifying a direct relationship between frictional and normal forces. Contrary to this, we observe that the load dependence of friction exhibits a unique bell-shaped curve when studying the frictional properties between graphite and α-Al_{2}O_{3} surfaces. As the applied normal force increases, the friction initially rises and then decreases. Finite element simulations reveal this behavior is due to edge detachment at the graphite/α-Al_{2}O_{3} interface as the normal force approaches a critical value. Because friction in superlubric contacts predominantly arises from edges, their detachment leads to a decrease in overall friction. We empirically validate these findings by varying the radii of curvature of the tips and the thicknesses of graphite flakes. This unprecedented observation offers a new paradigm for tuning COF in superlubric applications, enabling transitions from positive to negative values.

The effects of ultrasound modified kerosene on the flotation of flake graphite

ABSTRACT In the mineral processing engineering, ultrasound is usually used to modify reagents to improve the flotation. The study analyses the effects of the modified kerosene on the flotation of flake graphite. The outcomes demonstrate that the modified kerosene can substantially improve flake graphite’s floatation efficiency. In comparison to unmodified kerosene, the dosage of modified kerosene can be reduced while the recovery of graphite remains the same. Furthermore, the effect of modified kerosene was evaluated using various detection techniques including particle size distribution measurement, contact angle tests, turbidity tests, and cryo-scanning electron microscopy (Cryo-SEM) . The findings indicate that ultrasound modification significantly reduces the size of kerosene to 1–2 μm droplets and improves their dispersion in the aqueous solution. The enhanced dispersion and reduced droplets size of modified kerosene led to a better interaction between kerosene and the surface of flake graphite minerals. As a result, the consumption of kerosene was reduced, but the graphite flotation efficiency was improved.

Robust natural graphite-based bulk graphites with nanodiamond-containing fibrous nanofiller as reinforcement by electrohydrodynamic processing

One-dimensional (1D) structures, such as carbon nanotubes and carbon fibers, used as reinforcements in advanced carbon materials, have been greatly appreciated but facing with some significant challenges of dispersion and interfacial bonding. We utilized electrospinning technology to create a new 1D nanofiller. This material is a superfine fiber composed of polyacrylonitrile (PAN) with a high nanodiamond (ND) content of 75 %, which is referred to as PDNF. During the preparation process, these nanofillers were blended with natural flake graphite (NFG) through electro-spraying. The as-prepared mixture served as the precursor powder sintered into NFG-based high-strength bulk graphite (HPG). During spark plasma sintering at 1800 °C, fibrous PDNF undergoes a phase transformation of diamond to graphite, with onion carbon pinning into and markedly reducing cleavage along the (002) plane of NFG, foundational to the high strength of NFG-based HPG. The PDNF's fiber-like structure and NFG's flake structure greatly increase the interfacial area between the matrix and reinforcement. Furthermore, the PDNF excels at blunting and deflecting cracks, thus bolstering the NFG-based HPG's overall resistance to crack propagation. The density, Young's modulus, and flexural strength of the as-prepared NFG-based HPG achieve 1.65 g/cm3, 17.4 GPa, and 145 MPa, respectively. Most importantly, this process can be a general approach for other high-performance composite materials.