Graphite Particle Size Research Articles

Effect of particle size of carbon catalyst on oxygen reduction activity for fuel cell applications

Graphite powders with particle sizes of 40, 100, 400, and 1000 nm were used as cathode catalysts. The influence of graphite particle size on the electrocatalytic behavior towards the oxygen reduction reaction (ORR) was investigated. The catalytic activity and kinetics of the ORR, and methanol tolerance were tested in alkaline solutions with saturated oxygen via cyclic voltammetry (CV), rotating disk electrode (RDE) and amperometric i-t curve techniques. Experimental results show that the ORR process of the graphite catalyst with a particle size of 40 nm was close to the four-electron pathway at -0.6 V, exhibiting the best ORR activity. This is ascribed to a greater number of edge defects as ORR active sites in the carbonmaterial. The number of sites can be characterized with X-ray diffraction (XRD) and Raman spectroscopy. Additionally, these graphite catalysts have been demonstrated a superior tolerance to methanol than the commercial 20 wt.% Pt/C electrode in alkaline solutions.

Effects of Graphite Particle Size on Microstructure and Properties of In-situ Ti-V Carbides Reinforced Fe-based Laser Cladding Layers

Effects of Graphite Particle Size on Microstructure and Properties of In-situ Ti-V Carbides Reinforced Fe-based Laser Cladding Layers

Preparation and application of ZrC-coated flake graphite for Al2O3-C refractories

In the study, ZrC-coated flake graphite was prepared by molten salt synthesis and added to the Al2O3-C refractory. The effects of the molar ratio of Zr/C and the graphite particle size on ZrC-coated flake graphite were investigated. Moreover, the oxidation resistance of the prepared ZrC-coated flake graphite was evaluated. Finally, the effect of ZrC-coated flake graphite on the properties of the Al2O3-C refractory was investigated. The results indicated that Zr and C reacted completely as the Zr/C molar ratio decreased. Furthermore, with a decrease in the graphite particle size, the reaction between Zr and C was more complete and the size of the peeling layer decreased. When compared with natural flake graphite, ZrC-coated flake graphite exhibited better oxidation resistance. The Al2O3-C refractory with 3 wt% ZrC-coated flake graphite exhibited optimal oxidation resistance and that with 1 wt% ZrC-coated flake graphite exhibited optimal slag corrosion resistance ability.

The effect of graphite particle size on the corrosion and wear behaviour of the PEO-EPD coating fabricated on commercially pure zirconium

The practical importance and intricacy in the application of zirconium and its alloys have triggered widespread attention towards the enhancement of its mechanical and corrosion resistance properties. Composite coatings were fabricated on zirconium metal by integrating Plasma electrolytic oxidation (PEO) and Electrophoretic deposition process (EPD). The effect of particle size on the PEO-EPD coating characteristics were studied by comparing the properties of the coatings produced in micro and nano sized graphite particle containing electrolytes. The surface morphology, topography was studied using scanning electron microscope (SEM) and optical profilometer, and the phase analysis was done using X-Ray diffraction (XRD). The diffraction peaks corresponding to graphite indicate the successful incorporation of graphite particles in the coating fabricated in the particles containing electrolyte. The electrochemical corrosion studies by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) reveals the superior corrosion resistance of nano graphite incorporated zirconia coating. The increase in wear resistance and scratch resistance was also observed for the nano graphite incorporated coating. Thus, incorporation of the nano graphite particle into the zirconia layer proved to be beneficial for improving wear, friction resistance, scratch resistance and electrochemical corrosion resistance.

Perspective Methods of Graphite Quality Improving

The influence of various methods of activation on the graphite particles average size and micro-relief of particles have been studied. It has been experimentally proved that the size of graphite particles decreases after the process of mechano-activation, however graphite particles don’t change significantly after being processed by chemical activation. It should be noted that in the course of chemical activation the state of particles surface varies on shearing cuts. Particles’ surface can be described as a poly stratified system, comprising separate complex-structured buildups of the “rosette” type, where the graphite petals are located around the reinforcing rod. Moreover, the graphite petals are placed at different angles to each other, and they are of different thickness. The empty space between these buildups is filled with graphite particles, their petals being orientated freely. The particles size decrease and the change in the particles surface state are followed by their porosity increase, which, in its turn, leads to the fact that graphite particles’ surface becomes “super-hydrophobic” and helps the capillary forces resist the filtration of the melt into the pores of graphite particles.

Friction capabilities of graphite-based lubricants at room and over 1400 K temperatures

The present work investigates the lubricant capabilities at room and hot-forging temperatures (>1400 K) of three types of lubricants with two different graphite concentrations (8% and 12%). These lubricants are distinguished by measuring the percentage of chemical elements and average size of graphite particles. Later, two standardized methods, i.e., pin-on disc and ring test, are utilized to assess the main friction differences under laboratory and real industry conditions, respectively. The results exhibit that the friction values at room temperature are lower for lubricant B, no matter which type of graphite concentration is used, whereas at hot-forging temperatures, greater percentage of graphite enhances lower frictional values when higher deformations are assessed. Additionally, the ring tests performed at hot-forging temperatures show significant tribology differences when the degree of deformation reaches 50%. Particularly, the lubricant B shows the lowest values of friction coefficients of 0.22 and 0.21 for 8% and 12% of graphite concentration, respectively. Therefore, it can be concluded that the selection of a proper type of lubricant (regarding chemical composition and size of solid suspension) and the graphite concentration are sensitive parameters, when it comes to achieve different bulk deformations combined with extreme temperatures like in hot-forging process.

Investigation into thermal expansion coefficient, thermal conductivity and thermal stability of Al-graphite composite prepared by powder metallurgy

In this investigation, aluminum matrix composites with different graphite contents (6%, 12% and 18% volume fraction) are prepared using hot-press and powder metallurgy method. The distribution of graphite particles in the matrix is investigated by optical microscope. Density of the composite samples are examined and it is seen that increasing the graphite content decreases the densification due to graphite content and particle size. Results reveal that thermal conductivity of Al-18%G composite sample increased to 252 W/m.K. Similarly, results show that by compositing coefficient of thermal expansion (CTE) in 50–250 °C range decreased to 19.6 ppm/K. Finally, thermal stability of Al-18%G sample is evaluated by exposing to 1, 20, 50 and 100 thermal cycles. Due to difference between CTE of matrix and graphite, cracks propagate through the reinforcement/matrix interface and results in sample failure. Calculated CTE values are highly consistent with theoretical results of geometrical, Maxwell and Maxwell-Eiken models.

A route towards understanding the kinetic processes of bis(trifluoromethanesulfonyl) imide anion intercalation into graphite for dual-ion batteries

Even though lithium ion batteries are the state-of-the-art battery technology for numerous applications, there is extensive research on alternative battery technologies. Dual-ion batteries (DIBs) and in particular their all carbon/graphite versions, the dual-carbon (DCBs) and dual-graphite batteries (DGBs), have emerged as an upcoming and alternative approach for stationary energy storage systems. However, there are still fundamental electrochemical processes during charge and discharge operation of DIBs not fully understood so far. In this work, the kinetic processes during bis(trifluoromethanesulfonyl) imide (TFSI) anion intercalation into graphitic carbon, that proceeds by stage formation, are discussed in detail. The computational calculation of structural parameters of TFSI-graphite intercalation compounds (TFSI-GICs) indicates a possible maximum specific capacity of 140 mAh g−1 and a walking-like diffusion of the TFSI anion within the graphite lattice. Moreover, a particular focus is set on understanding the overpotential generation during the charge process and its correlation to different specific capacities for varying graphite particle sizes and operating temperatures. In this context, a mechanism, supported by electrochemical and computational experiments, is proposed explaining the overpotential evolution on the basis of (apparent) anion diffusion coefficients in graphite. Temporarily higher (apparent) diffusion activation energies close to filled stages seem to be responsible for temporarily lower (apparent) diffusion coefficients and, thus, for the evolution of additional overpotentials during intercalation.

Quantitative Measurement of Lithium Ion Concentration in an Operating Lib Using Low Energy X-Ray

The lithium ion secondary battery (LIB) is essential device for electric vehicle (EV). However, the fundamental mechanisms of ion transport phenomena in LiB during operation, which determine battery performance, are yet to be elucidated. In this study, inside the operating LIB was visualized by using low energy X-ray microscopy technique. As a result, ion concentration distribution in the negative electrode and the separator were measured quantitatively. Figure 1 shows schematic image of experimental apparatus. Using a low energy X-ray is quite effective to measure the slight difference of ion concentration because the amount of X-ray absorption is greater than that of conventional X-ray. In order to observe the ion concentration distribution in a micro-scale thin layer of the battery, present study achieved high magnification (1 mm/pixel resolution) by irradiating the cone-shaped soft X-ray beam. Cells for visualization, positive electrode, negative electrode, and separator, were cut with the dimension of 6 mm x 20 mm by a cutting machine. Those were sandwiched by aluminum and copper current collector in a plastic frame. After injection of the electrolyte, cell was sealed by covering with the stainless plates that have X-ray transparent windows. All of assembling process was performed in Ar filled glove box. In this study, graphite was employed for negative electrode. Graphite electrode was prepared by mixing graphite (particle size 20 μm), conductive assistant, and binder (polyvinylidene fluoride). Active material for positive electrode was LiMn2O4. Separator was polypropylene microporous membrane. The electrolyte was 1 M LiPF6 / EC:DEC(3:7). Figure 2 shows X-ray transparent image of the graphite negative electrode and the separator. Since Mn significantly absorbs low energy X-rays in the positive electrode, it could not be visualized. The intensity of X-ray transmission indicates density and concentration of the materials that obeys Beer-Lambert law. Thus, by calculating the ratio of X-ray intensity between initial condition and charge/discharge experiments, ion concentration change that is caused by ion transport phenomena can be observed qualitatively. Based on the calibration experiment, quantitative ion concentration distributions were derived from the X-ray intensity ratio distribution. Figure 3 shows quantitative ion concentration distribution in an operating LIB. Constant current discharge was performed (1C, 2C, and 3C). As the discharge rate increases, the ion concentration gradient in the negative electrode becomes steep. Under the discharge condition of 3 C, the maximum ion concentration in the negative electrode reached about 2.5 M. These results suggest that the ion transport resistance increased at higher discharge rate condition because the diffusivity decreases in the higher concentration electrolyte. As mentioned above, using the low energy X-ray microscopy technique, we have succeeded in quantitative measurement of the ion concentration distribution in an operating LIB. In order to improve battery performance, it is important to design an optimum structure (electrode thickness, porosity, etc.) and increases ion transport efficiency in the deep portion of the electrode. Figure 1

Dependence of Structure of Multilayer Graphene Oxide on Degree of Graphitization of Initial Graphite

It was shown that the structure of multilayer graphene oxide (GrO) synthesized by Tour method depends substantially on the degree of graphitization (g) and on the particle size of initial graphite. The obtained GrO was characterized by Raman and infrared spectroscopy, X-ray diffraction, and elemental analysis. The GrO contains carbonyl, carboxyl, and hydroxyl groups as well as C–O–C fragments. The dependence of the O/C molar ratio of GrO on the degree of graphitization of the parent graphite is nonmonotonic with a maximum at g ≈ 90%.

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).

The complete oxidation of nuclear graphite waste via thermal treatment: An alternative to geological disposal

This paper introduces a novel approach, developed through an academic and industrial collaboration, to the thermal treatment of nuclear graphite waste arising as a result of reactor decommissioning and oxide fuel assembly dismantling. A crucial part of the process is the thermal oxidation of the graphite via a plasma furnace. Laboratory scale treatment of the graphite found the oxidation rate to increase with temperature, with a significant increase in the CO/CO2 production ratio at T > 1000 °C. There was also a linear increase of oxidation rate with air flow rate, up to 100 ml/min, after which, the process became less efficient due to oxygen wastage. Effects of graphite particle size, over the range 0.5–10.0 mm, was found to be relatively small and importantly the effect of the graphite provenance on the oxidation rate was also found to be minimal. Treatment of virgin and irradiated graphite analogues, under the same conditions, showed little difference in oxidation behaviour, providing confidence that this process could be scaled up and used effectively in the disposal of reactor cores.Scale-up of this work was carried out on a “nuclear-ready” full-scale industrial facility, demonstrating graphite feeding, furnace operation and graphite destruction successfully. Experiments showed that comparable conditions between lab scale and pilot-scale showed similar oxidation behaviour, with 71.6 kg (equating to 90%) of graphite gasified in 6 h, giving an oxidation rate of ∼12 kg/h.Engagement with UK regulators has indicated that it is likely to be desirable to further investigate the possibility that isolation and confinement of graphite-derived 14C (t1/2 = 5730 yrs) in a carbon sequestration scheme may be an improvement on the baseline strategy, which is to store it in its solid form as untreated graphite in a geological repository.

The Mechanism of Transformation of Graphite Electrode Materials in Lithium-ion Batteries After Cycling

To reveal how graphite electrodes change with cycling in lithium-ion batteries, electrochemical experiments involving charge-discharge cycling at different current density conditions are performed on commercial pouch cells and the graphite electrodes after cycling. This research shows that the polyvinylidene fluoride (PVDF) binder does not degrade, confirmed by the stable molecular weight after different cycling conditions. Particle size analysis results indicate that the diameter of graphite particles after cycling is ~10% larger than that of the graphite before cycling, which results in a ~30% volume expansion after cycling. For the cells cycled at the same current density, the graphite particle size increases with cycle time. For the cells with the same cycle numbers, the graphite particle size is larger in the cells cycled at lower current density. X-ray diffraction characterization shows that the d-spacings of the graphite particles in all the cells at different cycling conditions are identical. These results suggest that the graphite particle size increase associated with cycling may arise specifically when primary particles inflate the secondary particle size, leading to dramatic volume expansion of graphite secondary particles.

Influence of expandable graphite particle size on the synergy flame retardant property between expandable graphite and ammonium polyphosphate in semi-rigid polyurethane foam

Effect of the difference of expandable graphite (EG) particle size on the synergistic flame retardant effect between expandable graphite (EG) and ammonium polyphosphate (APP) in the semi-rigid polyurethane foam (SPUF) was studied for the first time. Three large-span particle sizes of EG were added into SPUF with different mass ratios of EG/APP. The synergistic effect between EG and APP on the flame retardant property of composites was investigated using the limiting oxygen index test, horizontal–vertical burning test, thermogravimetric analysis (TGA), scanning electron microscope (SEM), etc. Flammability performance tests indicated that the larger particle size the EG possessed, the more obvious will be the synergistic effect exhibited between EG and APP. SEM images and TGA results provided positive evidence for the combustion tests. Synergistic effect was strongly influenced by the compactness of united protective layer. The maximal rate of the degradation of the SPUF composite system further confirmed the relationship between the rate of the composites’ degradation and the compactness of united protective layer. Speculative reactions which were related to the changes of EG in the presence of APP under high temperature were discussed.

Development of graphite-based conductive textile coatings

Conductive yarns and coatings are necessary for a broad variety of smart textile applications, such as sensors, data transmission lines, or heated fabrics. The main problems of such conductive textile elements are abrasion and washing resistance. Since different findings with respect to these properties are reported in the literature for similar coatings, the required optimization is impeded. In a recent study, the washing resistance of different graphite–polyurethane coatings with graphite contents between 25% and 33% on cotton, linen, viscose, and polyester woven fabrics was compared, using two different graphite particle sizes on diverse textile substrates. It was found that not only the graphite particle dimensions and graphite concentration strongly influence the longevity of the coatings, but also the textile substrates which were coated with the conductive mass. This means that conductive coatings cannot be optimized without knowledge of the planned application.

Перспективные способы повышения качества графита

The influence of various methods of activation on the graphite particles average size and microrelief of particles has been studied. It has been experimentally proved that the size of graphite particles decreases after the process of mechanoactivation, however graphite particles don’t change significantly after being processed by chemical activation. It should be noted that in the course of chemical activation the state of particles surface varies on shearing cuts. Particles surface can be described as a poly stratified system, comprising separate complex-structured buildups of the “rosette” type where the graphite petals are located around the reinforcing rod. Moreover, the graphite petals are placed at different angles to each other, and they are of different thickness. The empty space between these buildups is filled with graphite particles, their petals being orientated freely. The particles size decrease and the change in the particles surface state are followed by their porosity increase which in its turn leads to the fact that graphite particles surface becomes “superhydrophobic” and helps the capillary forces resist the filtration of the melt into the pores of graphite particles

Predicting High-Temperature Decomposition of Lithiated Graphite: Part I. Review of Phenomena and a Comprehensive Model

Heat release that leads to thermal runaway of lithium-ion batteries begins with decomposition reactions associated with lithiated graphite. We broadly review the observed phenomena related to lithiated graphite electrodes and develop a comprehensive model that predicts with a single parameter set and with reasonable accuracy measurements over the available temperature range with a range of graphite particle sizes. The model developed in this work uses a standardized total heat release and takes advantage of a revised dependence of reaction rates and the tunneling barrier on specific surface area. The reaction extent is limited by inadequate electrolyte or lithium. Calorimetry measurements show that heat release from the reaction between lithiated graphite and electrolyte accelerates above ∼200°C, and the model addresses this without introducing additional chemical reactions. This method assumes that the electron-tunneling barrier through the solid electrolyte interphase (SEI) grows initially and then becomes constant at some critical magnitude, which allows the reaction to accelerate as the temperature rises by means of its activation energy. Phenomena that could result in the upper limit on the tunneling barrier are discussed. The model predictions with two candidate activation energies are evaluated through comparisons to calorimetry data, and recommendations are made for optimal parameters.

Electrical Resistivity of Natural Graphite-Fluorine Resin Composite for Bipolar Plates of Phosphoric Acid Fuel Cell(PAFC) Depending on Graphite Particle Size

A composite material was prepared for the bipolar plates of phosphoric acid fuel cells(PAFC) by hot pressing a flake type natural graphite powder as a filler material and a fluorine resin as a binder. Average particle sizes of the powders were 610.3, 401.6, 99.5, and 37.7 μm. The density of the composite increased from 2.25 to 2.72 g/cm3 as the graphite size increased from 37.7 to 610.3 μm. The anisotropy ratio of the composite increased from 1.8 to 490.9 as the graphite size increased. The flexural strength of the composite decreased from 15.60 to 8.94MPa as the graphite size increased. The porosity and the resistivity of the composite showed the same tendencies, and decreased as the graphite size increased. The lowest resistivity and porosity of the composite were 1.99 × 10−3 Ωcm and 2.02 %, respectively, when the graphite size was 401.6 μm. The flexural strength of the composite was 10.3MPa when the graphite size was 401.6 μm. The lowest resistance to electron mobility was well correlated with the composite with lowest porosity. It was possible the flaky large graphite particles survive after the hot pressing process.

Lithium dual uptake anode materials: crystalline Fe3O4 nanoparticles supported over graphite for lithium-ion batteries

Graphite, the usual anode material for current technology of lithium ion batteries (LIB), has great advantages and its processing is widely known and industrially feasible. For improving the anode’s capacity, recent research has focused in using nano-carbons as an overcoming strategy rather than including cheap, conversion-type oxide metals. Here, we present the application of in-situ synthesized hybrid LIB active anode materials composed of magnetite nanoparticles (Fe3O4 NPs) and graphite of different sizes. The results show that the graphite’s flake size plays an important role in the Fe3O4 NPs deposition and loading, and therefore in the morphology of the resulting laminate film. The electrochemical performance (evaluated by cyclic voltammetry, galvanostatic charge/discharge cycles and impedance spectroscopy) is determined not only by the edge density of graphite flakes and Fe3O4 loading but also by the porosity of the anode films. The hybrid material electrode with smallest graphite particle size shows the highest reversible capacity of 845mAhg−1, good rate capability and great cycling performance. This remarkable improvement in graphite’s capacity is reached by only adding 16wt% of magnetite to the carbon material.

Effects of initial graphite particle size and shape on oxidation time in graphene oxide prepared by Hummers' method

Abstract The effects of initial graphite particle size and shape on oxidation time of graphite prepared by Hummers' method have been investigated. The oxidation was performed on three series of graphite particles, clod powder with two different sizes of 18 and 6 μm, and flake shaped powder with an average particle size of 25 μm. The samples were characterized by means of particle size analyzer, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ratio of XRD graphite oxide peak intensity to graphite peak intensity was considered as an indicator of the oxidation degree. It was observed that the oxidation time has a critical dependence on the initial graphite particle size and shape. While the oxidation of the clod samples was completed in several days, the oxidation of flake powder was completed just in 2 h. These findings help researchers to save time by choosing the particle size and shape of initial graphite powders.