Graphite Flake Size Research Articles

Innovative correlation relating the destruction of graphite flakes to the morphology characteristics of minerals

The morphology characteristics (sphericity, roundness, and surface roughness) affecting the destruction of gangue minerals on graphite flakes during the grinding process were systematically analyzed. Coupled with MS and SEM, sphericity analysis showed that graphite was flaky, which was similar to muscovite but different from granulous quartz and albite, and the roundness of the four minerals from high to low was graphite, quartz, albite, and muscovite. AFM analysis showed that the surface roughness of graphite and muscovite was very low compared to that of quartz and albite (higher than quartz). The size and crystal integrity of graphite flakes were both destroyed by gangues during the grinding process, and the destruction of quartz and albite was serious compared to that of muscovite. Sphericity dominantly affected the destruction: the larger the sphericity, the more serious the destruction, which was also negatively related to roundness but positively related to surface roughness.

Polyphenol modification of graphene-stabilized emulsions to form electrically conductive polymer spheres

HypothesisPolyphenols, specifically tannic acid, should increase the hydrophilicity of graphene when added during the interfacial exfoliation through π-π stacking. Following Bancroft’s rule, increasing the hydrophilicity of graphene will result in a phase inversion of water-in-oil emulsions stabilized by graphene. Polymerization of the oil phase will then lead to graphene-coated spheres rather than graphene-stabilized polyHIPEs. ExperimentsOptical particle sizing, microscopy, contact angle, and electrical conductivity measurements were performed to determine the mechanism of sphere formation in graphene-stabilized emulsions modified with tannic acid. Studies focused on the effect of graphite flake size, graphite concentration, tannic acid concentration, and oil phase composition. Particle sizing and scanning electron microscopy examined the spheres' size, shape, and surface morphology. Contact angle measurements gave insight into the change in graphene surface energy. Conductivity studies examined the graphene shell surrounding the spheres. FindingsAdding tannic acid to graphene-stabilized emulsions induced a phase change from water-in-oil to oil-in-water. Contact angle measurements confirmed greater hydrophilicity of graphene in the presence of tannic acid. However, very high tannic acid concentrations led to a decrease in the stability of the emulsion. Varying the graphite flake size and concentration resulted in morphology and conductivity changes. Dilution of the monomer phase produced hollow microcapsules.

Application of multispectral computed tomography for the characterisation of natural graphite

The established mineralogical and chemical analysis methods for graphite ores require complex sample preparation. Moreover, they do not produce 3D images of the polymineralic rock structure and texture. The lack of 3D information can lead to an erroneous assessment of the quality-determining properties of graphite ores, such as graphite flake size (grain size), graphite flake size distribution, and impurities. Therefore, there is a need to obtain 3D information from graphite ores and concentrates. Industrial computed tomography (CT or single-spectrum CT) is a unique technique that enables the examination of rocks in the 3D regime. The challenge in CT analysis of ores is the different absorption properties of mineral phases present. Low X-ray tube generator voltages lead to pronounced artefacts (volume defects) if highly absorbing gangue phases (e.g. iron sulfides) are present. Therefore, high X-ray tube voltages must be applied. However, graphite and associated gangue minerals, as well as contained cracks and voids in the ore, can exhibit similar absorption properties at higher generator energies (above 120 kV). Multispectral CT (MSP-CT) measurements offer a minimisation of CT artefacts and an increase in grey value contrasts. This work investigates the application of the MSP-CT measurements, significantly improving mineral differentiation.

Graphite Size Effect on Chemical Expansion and Graphene Oxide Properties.

Does larger graphite flake size always lead to larger and better graphene oxide (GO)? Is there an optimum size to balance between the large building blocks needed and the defects generated during oxidation? In this study, the effect of using four different graphite flake sources on the size, structure, and properties of GO and reduced graphene oxide (rGO) was investigated. GO was mainly prepared by the enhanced synthesis method except for the smallest graphite size, which could not be expanded before oxidation. The effect of the flakes’ lateral size and thickness on the expansion volume was also studied. Several characterization techniques were performed throughout this work, and their results provide evidence of how the graphite size changes not only the expansion volume of the chemically expanded graphite (CEG) as well as the final properties of GO or rGO but also the presence of organosulfate impurities, defects, wide size distribution, and the harsh oxidation reaction itself.

Dependence of Precursor Graphite Flake Size on Nitrogen Doping in Graphene Oxide and Its Effect on OER Catalytic Activity.

We report the synthesis of nitrogen-doped graphene oxide, with 5.7–7.0 wt % nitrogen doping, from different sizes of precursor graphite and study its effect on the oxygen evolution reaction (OER) activity of IrO2 in an acidic medium. The nitrogen-doped supports are expected to have pyridinic, pyrrolic, and graphitic functionalities at different ratios responsible for their improved performance. The N-doped supports and catalysts are synthesized via pyrolysis and the hydrothermal method using natural and synthetic graphite of three different flake sizes and evaluated for their structural and electrochemical characteristics. The average size of IrO2 nanoparticles deposited on the N-doped supports is independent of the flake size and doping amount of nitrogen. The catalysts show optimum current densities but improved stability with increasing flake sizes of 7, 20, and 125 μm. Our results demonstrate that the selection of the flake size of the doped support is necessary to achieve durable catalysts for the OER in an acidic medium.

Effect of microstructure on the hardness of ASTM A48 class 20 flaked graphite cast iron

ABSTRACT In foundries, it becomes necessary to minimise the machining allowance for economic reasons. It will save resources and costs by reducing the energy and expenses incurred on re-melting, machining and tooling. A deeper understanding of the complicated microstructures developed within about 3.5 mm of the mould-metal interface is necessary. The current research work uses a unique experimental design that involves performing surface and subsurface microscopy and spectroscopy at 0.5 mm intervals from the as-cast surface to a depth of up to 3.5 mm for three samples. The objective is on evaluating microstructure for determining graphite flake size, distribution, grouping, pearlite and ferrite percentage, and different elements. All three samples were subjected to a hardness test, which is a measure of machinability. The relationship between hardness as a single response to percentage presence of elements, graphite distribution and pearlite has been established using statistical analysis.

Structural and Morphological Studies of Bi2O3/MWCNTs Doped Reduced Graphene Oxide for Energy Storage Applications

Bismuth oxide (Bi2O3), multi-wall carbon nanotubes (MWCNTs), reduced graphene oxide (rGO) and its composite were synthesized by modified Hummers method followed by chemical and thermal reduction processes. During synthesis, graphene oxide (GO) was reduced to rGO and decorated evenly with Bi2O3 and CNTs. Average crystallite size of graphite flakes (GF), GO, rGO, rGO/Bi2O3, rGO/CNTs and rGO/Bi2O3/CNTs is calculated from XRD profiles using the Scherer equation are 77.75, 11.91, 1.79, 18.1, 21.05 and 18.05 nm, respectively. In XRD, deconvolution of rGO/Bi2O3/CNTs, C60 and C70 diffraction peaks were observed. The morphology of rGO/Bi2O3/CNTs have smoother surface similar to GO, rGO, rGO/Bi2O3 and rGO/CNTs except GF, was revealed in SEM images. HR-TEM analysis revealed carbon (002) in rGO with d-spacing of 0.34 nm, Bi (102) with d-spacing of 0.31 nm and MWCNTs on 2 nm scale. Bonding of Bi2O3 and CNTs with graphene layers led to the formation of novel functionalized nanocomposite which enhances electrical conductivity of rGO. Using AFM images of rGO/CNTs films thicknesses, arithmetic mean and RMS roughness were estimated as 6 nm at 14.91 nm and 19.27 nm, respectively. Results of rGO/Bi2O3/CNTs revealed that with the small crystallite size, functionalization and nanoscale roughness could be promising for energy storage applications.

Применение техники цифровой обработки изображений в анализе микроструктуры и исследовании обрабатываемости

Introduction. The world is at the stage of creating an interdisciplinary approach that will be implemented in metallurgical research. The paper formulates the technique of image analysis in the study of processing at different depths from the mold-metal interface. The purpose of the work. Processing of a cast-iron workpiece within the first 3.5 mm of thickness from the mold-metal interface is a serious problem of solid processing. The study of machinability at different depths is a key requirement of the industry for ease of processing. Machinability will determine a number of factors, including tool consumption, workpiece surface quality, energy consumption, etc. The method of investigation. Image analysis is performed to determine the percentage of graphite in etched and non-etched samples. K-means clustering allows to create a new image from a given one with a clear separation of white and black areas by converting a digital image into a binary image using a threshold value for segmentation. The volume fraction of perlite, the volume fraction of graphite and the average size of graphite flakes in microns are used as input variables for the machinability of cast iron. Results and discussion. The output, that is, the segmented image, will be the input function for calculating the workability index using formulas. Thus, microstructural analysis will help predict the workability index of grey cast iron ASTM A48 Class 20. Using this method and the program, based on the microstructure, it is possible to predict in advance the characteristics of the machining of the part, taking into account possible changes in the casting process itself.

Synthesis of Expanded Graphite: Effect of the graphite flake size on adsorption capacities to Methylene Blue

For the first time, the expansion grade of graphite was studied through the effect of the flake size. The result shown the larger flake size exhibits a higher expansion grade. In addition, the more expanded material, the higher specific surface area can be obtained. The synthesized expanded graphites were used for the adsorption of methylene blue. The expanded graphite with the highest expansion grade displayed the highest adsorption capacity due to its specific surface area.

Effects of graphite flake size on the properties of aligned graphene nanoplatelets covered graphite flakes/aluminum composites

Finding out the effects of graphite (Gr) flake size on the properties of Gr (Graphene Nanoplatelet (GNP))/Al composites will be helpful to design and develop various Gr(GNP)/Al composites which need to meet different application requirements. In this work, thermal conductivity (TC) and flexural strength of Gr/Al and Gr(GNP)/Al composites with different Gr flake size were investigated. Through-plane TC of Gr/Al composites is about 50% of the results predicted by EMA model. However, after introducing GNP to Gr flakes, through-plane TC of Gr(GNP)/Al composites reaches about 90% of the results predicted by EMA model. When Gr flake size are 150, 500, 850 μm, respectively, the in-plane TC of Gr/Al composites can be improved by 8.5%, 6.4%, 5.4% after introducing GNP, while the through-plane TC of Gr/Al composites can be improved by 62%, 75%, 83%. So the introduction of GNP to the Gr flake is more effective in improving through-plane TC than in-plane TC. GNP's improvement ratio on the through-plane TC of Gr/Al composites increases with the increase of Gr flake size. Furthermore, as Gr flake size increases, GNP's improvement ratio on the flexural strength of Gr/Al composites increases, which is attributed to the increase of strengthening effect of GNP on the interface region.

Prediction of the Fracture Location by Tensile Tests of Gray Cast Iron Based on the Dimensional Changes of Graphite Flakes

Abstract Gray cast iron has been used as a component in various mechanical parts, such as the blocks and heads of automobile and marine engines, cylinder liners for internal combustion engines, and machine tool bases. It is desirable because of its good castability and machinability, damping characteristics, and high performance-to-cost ratio. On the other hand, weak graphite flakes present in gray cast iron serve as stress concentrators and adversely affect the material strength. Therefore, it is crucial to examine the relationship between the distribution of graphite flakes and the strength or fracture of gray cast iron. In this study, tensile tests on gray cast iron were carried out using a plate specimen and observed by scanning electron microscopy, and the microscopic deformation was observed on the specimen surface. Particularly, the change in the size of graphite flakes during the tensile tests was examined, and the observed trend was discussed. The experimental results reveal that the dimensional changes in the graphite flakes vary in the observed area and that the final fracture occurs in an area where a large dimensional change is observed, suggesting that the fracture location or critical parts of gray cast iron can be predicted from the dimensional changes of the graphite flakes at an early stage of deformation.

Effect of silicon addition on microstructure and mechanical properties of grey cast Iron: An overview

Grey cast iron is used to make brake disc due to its high damping vibration resistance and low cost. In the present work, effect of silicon addition on microstructure and mechanical properties of grey cast iron is reviewed. Results of microstructure and mechanical properties are compiled, which are affected due to the addition of silicon in grey cast iron. From the review, it is found that the volume of soft graphite flakes increases i.e. grain size increases which reduces the hardness of grey cast iron, on increasing the silicon content. Similarly, tensile strength reduces as a function of silicon addition. Hardness and wear rate depends on the phase of microstructure and the size of graphite flakes. Maximum hardness was obtained at 3.33% of silicon content.

Effect of Cu-Ni and Cu-Ni-Mn on the Microstructural and Mechanical Behaviour of As-Cast Non-Inoculated Hypereutectic Grey Iron

The hypereutectic region of grey cast iron has received very little attention especially for designing cast products by researchers. Due to its high carbon equivalence, hypereutectic grey iron poses some challenges especially its tendency for grey to white transition (GWT) at this level of carbon content. However, hypereutectic grey iron possesses inherent properties that could be easily utilized for improved performance in automobile engines and brake pad system. Significantly, they could be modified for superior hardness, strength and toughness. This study presents the effect of microalloying on the mechanical behaviour of hypereutectic grey cast iron with carbon equivalence above 4.5. The first part of this work presented in this paper considers the addition of Cu-Ni and Cu-Ni-Mn to series of as-cast hypereutectic grey cast iron and their hardness and tensile strength were studied and compared. A total of 33 cast samples were obtained with the control sample. The examination of the micrographs revealed that graphite eutectics cells of Type A and A + D were obtained in the resulting microstructure. Results analyses showed that the ferrite forming tendency of silicon was suppressed due to the high carbon content of the as-cast hypereutectic grey iron coupled with the absence of inoculation which plays a great role in the graphite flake type, network, size and distribution. Cu-Ni microalloying was also confirmed to promote hardness with the hardening effect limit of nickel observed at 1.3% composition. For Cu-Mi-Mn addition, excess and free sulphur in the hyper- eutectic grey iron results in reverse effect of manganese on strength, hardness, reduced graphite flake size and shape.

Surface alteration of aluminium alloy by an exfoliated graphitic tribolayer during friction surfacing using a consumable graphite rich tool

In present study, a strategy for mechanical exfoliation of graphite to a few layered graphene (FLG) coupled with its mechanical infusion onto aluminium (Al6061) substrate through a solid-state friction surfacing (FS) methodology is developed and documented. Here, a graphite-rich and expendable FS tool fabricated through conventional powder metallurgy is used as a source of graphite. Later on, this expendable tool is utilized for impregnating graphite on the aluminium alloy surface through FS. The high frictional shear stress during FS results in the exfoliation of graphite to FLG which is confirmed by the characteristic wrinkled morphology through FE-SEM studies. Experimental results revealed successful impregnation of FLG flakes up to ∼165 μm depth on the surface of aluminium matrix. The effect of graphite flake size (60 mesh (max. 250 μm) and 325 mesh (max. 44 μm)) on specific wear rate and its ability to mechanically exfoliate into a FLG structure is also analysed. Dynamic recrystallization due to plastic deformation during FS results in ∼ 90% grain size reduction relative to the as-received aluminium alloy (reference Al). Excellent interfacial bonding with mechanical intercalation between graphite flake and aluminium matrix is also observed through TEM studies. Intermetallic phase such as Al4C3 is observed at the Al/graphite interface with larger flake size. The tribological properties are significantly improved with the graphite reinforcement leading to the decrease in coefficient of friction by ∼12.5 and 26.7% with graphite of 250 (FS250) and 44 μm (FS44) flake size respectively as compared to the reference Al. The least specific wear rate is observed for FS44 which is about ∼53.4 % and ∼ 28.57 % less than the wear rate of reference Al and FS250, respectively. The microhardness, nano-hardness and XRD studies further corroborate the results.

Yakutites from the Popigai meteorite crater

For the first time, 60 large diamond aggregates were found inside the Popigai meteorite crater during washing of alluvial deposits along the Dogoi river crossing the crater. These aggregates are similar in appearance to yakutites from the placers of Northern Yakutia (YPY), and we regard them as yakutites from the Popigai crater (YPC). The structure and optical properties of Popigai impact diamonds from the impact melt rocks (tagamites) in the crater (PIDT) and yakutites YPC/YPY were compared in detail. In all these cases, a polycrystalline structure consisting of nanoscale grains of cubic and twinned cubic diamond (lonsdaleite) was found. This is the result of a solid-phase graphite-diamond transition due to an impact event 35 million years ago. The diamond aggregates show the following features: a red shift of the short-wave edge of the transmission, broadening of the diamond Raman peaks, signals from other diamond polytypes and numerous inclusions of other minerals in the Raman spectra, and a dominant broadband photoluminescence (PL). PL in the N3 system associated with N3V centers in PIDT diamonds indicates a high-temperature annealing of these aggregates with resulting aggregation of impurities during the prolonged cooling of large impact melt pockets and pools. It is assumed that some of the impact diamonds were ejected from the crater during the impact event and experienced rapid cooling. Some of these diamonds fell back into the crater (YPC yakutites), others have been deposited outside the crater and displaced during erosion (YPY yakutites). Difference in size and shape between the PIDTs and yakutites YPC/YPY is due to the difference in size of original graphite flakes or aggregates and/or due to the fundamentally different technologies of diamond extraction.

Effect of graphite flakes particle sizes on the microstructure and properties of graphite flakes/copper composites

Copper matrix composites were successfully prepared from the mixtures composed of modified copper-coated graphite flakes and copper powder via vacuum hot pressing process. Under the condition with same volume fraction of graphite flakes, the particle size of graphite flakes had a great effect on the properties of graphite flakes/copper composites. The phase compositions and microstructure of the composites were analyzed by XRD and SEM, respectively. Thermophysical and mechanical properties performance of composite materials were analyzed with different particle sizes of graphite flakes. The results showed that with the increasing of particle size, the thermal conductivity of composites in X-Y direction (basal plane of graphite flake) increased and coefficient of thermal expansion of composites in X-Y direction initially decreased and then increased. As the particle size of graphite flakes decreased, the bending and compressive strength increased. When the equivalent particle size of graphite flakes was 292 μm, the composites had superior thermal conductivity (612 W m−1 k−1), ideal flexural strength (42.5 MPa), suitable electrical conductivity (14.7% international annealed copper standard) and apposite coefficient of thermal expansion (6.6 ppm k−1).

Effect of graphite structures on the productivity and quality of few-layer graphene in liquid-phase exfoliation

Liquid-phase exfoliation (LPE) is a promising technique for commercializing graphene production because of its simplicity and cost-effectiveness. However, the low yield of graphene in laboratory-scale production, less than 10 g/h, necessitates modifications to the process for it to be feasible for commercial applications. Natural graphite has various size distribution, crystallite sizes, and interlayer space, making the choice of initial graphite very important. Five types of natural graphite with different structures were prepared for the experiment. The structural parameters of graphite such as crystallite size and d-spacing were precisely determined based on a standard procedure of X-ray diffraction measurements for carbon materials. The effects of graphite flake size and crystallite size on the productivity and quality of few-layer graphene (FLG) were investigated. The results showed that small graphite was easier to fragment and exfoliate. FLG productivity improvement up to 1500% was attained when graphite with smaller flakes was used instead of graphite with large flakes. The crystallite size of graphite was manipulated by plenary ball milling, and the effect of crystallite on FLG productivity in LPE process was also discussed.

Correlation between Solidification Time and Cooling Rate, Microstructure and Tensile Strength of a Low Alloyed Grey Cast Iron

Despite more than hundred years of research the quantitative relation between microstructure and tensile strength of pearlitic grey irons is not fully understood. Relations found in literature mainly consist of formulas based on regression analysis of chemical composition and wall thickness. Microstructural features like size and shape of the graphite as well as pearlite fineness are seldom included in these equations. In this paper is presented an experimental correlation between microstructure and tensile strength for a low alloyed grey iron including the influence of course of solidification, pearlite hardness and graphite size and shape. The experimental material consists of two six-cylinder engine blocks which were gravity cast in horizontally parted green sand moulds. The alloy is similar to EN-GJL-200 but with addition of Cr. Measured values of hardness and tensile strength have been correlated to simulated values of solidification time and cooling rate at pearlite transformation with excellent agreement. It was also possible to confirm these findings by observation of the tensile test bar fracture surfaces. The main conclusions are: - Tensile strength is mainly dependent on solidification time and the related graphite flake size. - Hardness is mainly dependent on pearlite transformation rate and the related pearlite fineness.

Effect of Pressure on Graphite Morphology and Mechanical Properties of Squeeze Cast Hyper-Eutectic Grey Cast Iron

Squeeze casting is a process in which a high external pressure is applied and maintained on the molten metal during the whole solidification process resulting in the lower porosity, higher solidification rate and improved mechanical properties. In this research, the effects of applied pressure on the morphology of graphite flakes in a squeeze cast hyper-eutectic grey cast iron were investigated. The molten grey cast irons were solidified under atmospheric pressure as well as 25, 50 and 75 MPa externally applied pressures. The results indicated that the pressure increase during solidification decreased the amount of free graphite flakes, reduced the size of pro-eutectic Kish graphite flakes and increased the density of the castings. D-type graphite enclosing austenite dendrites, resembling that expected in hypo-eutectic grey cast iron, was observed near the surfaces of the castings solidified under externally applied pressures. Moreover, some compacted and spheroidal graphite particles were observed in the castings solidified under 50 and 75 MPa pressures. Furthermore, by increasing the squeeze casting pressure from atmospheric pressure to 75 MPa, the hardness, ultimate tensile strength and elongation increased by about 13, 68 and 128%, respectively. The results have been discussed in terms of increased cooling rate, expected change in the phase diagram of the alloy, different atomic structure of the interfaces of graphite and austenite as well as some proposed theories for formation of eutectic cells and spheroidal graphite.

X-ray spectroscopy study of lithiated graphite obtained by thermal deposition of lithium

X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy are used for in situ studies of the electronic structure of lithiated natural graphite produced by thermal deposition of lithium upon graphite in a vacuum. By XPS and NEXAFS spectroscopy it is found that lithium vapor thermal deposition results in the formation of a lithiated graphite surface layer and a change in its electronic structure. Based on the quantum chemical simulation of the experimental СKα XES spectrum of lithiated graphite, it is found that lithium atoms are located mostly on the edges of graphite crystallites. Atomic force microscopy reveals that the size of natural graphite flakes varies from 50 nm to 200 nm.