Μm Graphite 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.

Differential effects of GAC and graphite on interspecies electron transfer during anaerobic digestion of waste activated sludge for methane production

This study investigated the effect of the particle size of granular activated carbon (GAC) and graphite on methane production efficiency. Additionally, differences in the mechanisms by which GAC and graphite-enhanced anaerobic digestion (AD) of waste activated sludge (WAS) were evaluated. The results showed that 150 μm GAC and 38 μm graphite had the best promoting effect, increasing cumulative biogas production by 14.6 % and 12.3 %, respectively, compared with blank control. GAC advanced the peak daily biogas production to day 8. Scanning electron microscopy revealed the formation of a dense bacterial biofilm on the GAC surface. Microorganisms on the graphite surface had more conductive pili than those on the GAC and blank surfaces. GAC enriched Methanobacterium (hydrogenotrophic methanotrophic archaea) while maintaining the relative abundance of existing acetate methanogenic bacteria. Conversely, graphite reduced the abundance of hydrogenotrophic methanogenic bacteria and enriched Methanosaeta, which participate in direct interspecies electron transfer. GAC increased the abundance of key enzymes in the hydrogenotrophic methanogenesis pathway and alleviated the inhibition of nitrate nitrogen and H2 in the methanogenesis reaction system. In contrast, graphite increased the abundance of pili genes and promoted electron exchange between symbiotic bacteria and methanogens, thereby accelerating substrate consumption and methane production.

Large-scale synthesis of dense Fe3C via ultra-high pressure method

In this work, a highly-dense cementite (Fe3C) was synthesized via ultra-high pressure method (UHPM). Different raw batches were prepared under identical synthetic conditions (1000 °C and 4.0 GPa for 10 min). Large amounts of Fe3C were produced from the raw material consisting of ∼ 6 µm iron powder with ∼ 1.5 µm graphite, illustrating that the particle size and carbon source are critical for synthesizing Fe3C via UHPM. The crystal size of the synthesized Fe3C was estimated to be approximately 19 nm by peak broadening of the X-ray diffraction pattern. Additionally, the synthesis of Fe3C was confirmed by electron probe microanalysis analyzer (EPMA) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) images showed clearly shaped grain boundaries. The excellent mechanical properties of the prepared Fe3C were confirmed based on an ultrasonic pulse reflecting method. According to the magnetic-hysteresis loop of the Fe3C, it displayed soft ferromagnetic properties.

Optimization of Pore Characteristics of Graphite-Based Anode for Li-Ion Batteries by Control of the Particle Size Distribution

We investigate the reassembly techniques for utilizing fine graphite particles, smaller than 5 µm, as high-efficiency, high-rate anode materials for lithium-ion batteries. Fine graphite particles of two sizes (0.4–1.2 µm and 5 µm) are utilized, and the mixing ratio of the two particles is varied to control the porosity of the assembled graphite. The packing characteristics of the assembled graphite change based on the mixing ratio of the two types of fine graphite particles, forming assembled graphite with varying porosities. The open porosity of the manufactured assembled graphite samples ranges from 0.94% to 3.55%, while the closed porosity ranges from 21.41% to 26.51%. All the assembled graphite shows improved electrochemical characteristics properties compared with anodes composed solely of fine graphite particles without granulation. The sample assembled by mixing 1.2 µm and 5 µm graphite at a 60:40 ratio exhibits the lowest total porosity (27.45%). Moreover, it exhibits a 92.3% initial Coulombic efficiency (a 4.7% improvement over fine graphite particles) and a capacity of 163.4 mAh/g at a 5C-rate (a 1.9-fold improvement over fine graphite particles).

Evaluation of physical, mechanical and sliding wear properties of in-situ AB-TiC composite: a comparison with NAB alloy

The purpose of the present study is to evaluate the physical, mechanical and sliding wear properties/response of cast in-situ aluminium bronze (AB)-TiC [(Cu10Al3Fe)5TiC] composite and compare with cast nickel aluminium bronze (NAB) [Cu10Al5Ni5Fe] alloy. Sliding wear tests were conducted in dry and partially lubricant conditions using a pin-on-disc machine. A test material in the form of pin was evaluated against a rotating heat-treated EN-31 steel disc. Wear loss, frictional heating and friction coefficient properties were examined. The NAB alloy showed higher tensile strength (32.7%), compressive strength (7.68% at room temperature. and 4.18% at 500 °C), hardness (8.78%) and density (3.17%), whereas thermal conductivity of the AB-TiC composite was found 4.89% higher than NAB alloy. In dry sliding condition, composite outperformed NAB alloy in terms of wear resistance up to a critical applied load and/or sliding speed. Beyond this point, the wear behavior altered. Increasing sliding speed caused to reduce wear transition load. While friction coefficient showed mixed trend. Under lubricated wear test conditions, AB-TiC composite displayed considerably higher wear resistance (50.08%, 44.41% & 51.55%) and friction coefficient (26.37%, 40.75% & 14.96%) than the NAB alloy when tested in only oil, oil with 100 μm graphite and oil with 7–10 μm graphite respectively. Arrival of seizure in general caused significantly higher wear loss and temperature rise. In addition, it caused large adhesion of the specimen material to the disc surface. The reported wear behaviour of the samples has been validated using the features of wear surfaces and subsurface regions. The latter also permitted to comprehend the working wear processes. The analysis significantly shows good impacts of the oil lubrication (with and without solid particles) in terms of decreasing wear rate, frictional heating, and friction coefficient. Formation of steady lubricating film/layer was reported to be responsible for the better wear performance of the samples. Furthermore, irrespective of material composition and microstructure there exists a precise set of test parameters (e.g. load and speed) leading to optimal wear performance wherein the beneficial impacts of load bearing capability, thermal stability of various phases predominates.

A New Two-Step Method for Laser Cladding of Silicon Carbide in Wc-Co Substrates

WC-Co cutting tools are widely used by the metalworking industry. In order to improve the properties of these tools, research on the application of wear-resistant coatings, such as polycrystalline diamond, are of great importance to several applications. It is known that the occurrence of high-stress levels between the coating and the substrate can lead to adhesion failures. One strategy to minimize these failures is applying an intermediate layer of SiC. In this work, the deposition of a SiC layer was carried out by a novel two-step laser cladding approach. Instead of cladding directly the pre-synthesized SiC on the substrates, a 200 µm silicon powder layer was pre-deposited on the WC-Co substrates and then irradiated with a 30 W CO2 laser. To improve metallurgical bonding between the tungsten and the Si layer, all substrates were chemically attacked. This attack allows cobalt removal from the surface and increases surface roughness, improving the laser cladding process. After the SiC laser cladding, samples were coated with a 200 µm graphite powder layer and irradiated again by a CO2 laser. The samples were characterized by SEM, EDS, and XRD analysis. The results showed that in the first step, an irradiation energy of about 0.27 J was enough to fuse the silicon powder to the substrate and in the second step, 0.13 J was enough to promote the reaction between silicon, carbon and the WC substrate, resulting in the in-situ synthesis of SiC. Finally, a new method was proposed for the deposition of SiC on WC-Co based substrates and the observed results allowed the proposal of an empirical equation to describe the chemical reactions of the process.

Nano Porous Zinc Synthesis on Soft Polyurethane Foam Using Conductive Ink and Electroplating Method

High specific surface is a significant characteristic in zinc coatings that can be highly applicable in batteries and catalysts. Conventional methods to create foams are not cost-efficient, nor could they make a high specific surface. Electroplating has been developed that can produce a very high specific surface foam. On the other hand, conductive ink can create an affordable conductive surface with a high specific surface, so the study on using conductive ink, which has a cost-efficient nature, was necessary to create a conductive surface. This work has investigated the effect of crucial parameters, such as graphite size, coating time and bath composition, on the current efficiency and SEM microstructure. As a result, a 3 µm graphite size was found to be appropriate. Coated zinc escalates linearly with current efficiency for up to 5 h, and then it decreases. Although the zinc concentration increases up to 0.12 mol/L in the electrolyte, making a slight increase in loading, the current efficiency was almost unchanged. However, if it increases more, the loading and current efficiency significantly rise so that the loading grows up to 16 times and the current density increases up to 86%. Additionally, the morphology changes from dendritic to compact plates, sphere and semi-sphere, subsequently.

Graphite Nanocomposite Substrates for Improved Performance of Flexible, High-Power AlGaN/GaN Electronic Devices

High-power, flexible electronic devices require substrates that effectively dissipate heat while maintaining mechanical compliance. Nanocomposite substrates with ∼20 μm graphite nanoplatelets were ...

Change in Conductive-Radiative Heat Transfer Mechanism Forced by Graphite Microfiller in Expanded Polystyrene Thermal Insulation-Experimental and Simulated Investigations.

This article introduces an innovative approach to the investigation of the conductive–radiative heat transfer mechanism in expanded polystyrene (EPS) thermal insulation at negligible convection. Closed-cell EPS foam (bulk density 14–17 kg·m−3) in the form of panels (of thickness 0.02–0.18 m) was tested with 1–15 µm graphite microparticles (GMP) at two different industrial concentrations (up to 4.3% of the EPS mass). A heat flow meter (HFM) was found to be precise enough to observe all thermal effects under study: the dependence of the total thermal conductivity on thickness, density, and GMP content, as well as the thermal resistance relative gain. An alternative explanation of the total thermal conductivity “thickness effect” is proposed. The conductive–radiative components of the total thermal conductivity were separated, by comparing measured (with and without Al-foil) and simulated (i.e., calculated based on data reported in the literature) results. This helps to elucidate why a small addition of GMP (below 4.3%) forces such an evident drop in total thermal conductivity, down to 0.03 W·m−1·K−1. As proposed, a physical cause is related to the change in mechanism of the heat transfer by conduction and radiation. The main accomplishment is discovering that the change forced by GMP in the polymer matrix thermal conduction may dominate the radiation change. Hence, the matrix conduction component change is considered to be the major cause of the observed drop in total thermal conductivity of EPS insulation. At the microscopic level of the molecules or chains (e.g., in polymers), significant differences observed in the intensity of Raman spectra and in the glass transition temperature increase on differential scanning calorimetry(DSC) thermograms, when comparing EPS foam with and without GMP, complementarily support the above statement. An additional practical achievement is finding the maximum thickness at which one may reduce the “grey” EPS insulating layer, with respect to “dotted” EPS at a required level of thermal resistance. In the case of the thickest (0.30 m) panels for a passive building, above 18% of thickness reduction is found to be possible.

Properties of Carbon Pastes Prepared with Mixing Ratios of Nano Carbon and Graphite Flakes

To produce carbon electrodes for use in perovskite solar cells, electrode samples are prepared by mixing various weight ratios of 35 nm nano carbon(NC) and 1 μm graphite flakes(GF), GF/(NC+GF) = 0, 0.5, 0.7, and 1, in chlorobenzene(CB) solvent with a ZrO2 binder. The carbon electrodes are fabricated as glass/FTO/carbon electrode devices for microstructure characterization using transmission electron microscopy, optical microscopy, and a field emission scanning electron microscopy. The electrical characterization is performed with a four-point probe and a multi tester. The microstructure characterization shows that an electrode with excellent attachment to the substrate and no surface cracks at weight ratios above 0.5. The electrical characterization results show that the sheet resistance is < 70 Ω/sq and the interface resistance is < 70 Ω at weight ratios of 0.5 and 0.7. Therefore, a carbon paste electrode with microstructure and electrical properties similar to those of commercial carbon electrodes is proposed with an appropriate mixing ratio of NC and GF containing a CB solvent and ZrO2.

Optocapacitance-Mediated Responses of Excitable Cells: New Developments

Optocapacitance is a technique whereby flash illumination quickly changes membrane capacitance to elicit action potentials (APs) in unmodified (not genetically engineered) excitable cells. Spherical 20-nm gold nanoparticles (AuNPs) interfaced with the plasma membrane serve as light absorbers to induce AP generation in response to 1-ms, 100 μJ, 532-nm laser pulses. Light absorption by the AuNP produces localized heating that changes local temperature by <2⁰C. This increases membrane capacitance, and a resulting depolarizing membrane current (VdC/dt; proportional to the rate of temperature change; Nat. Commun., 2012;3:736) induces opening of voltage-gated sodium channels and thus AP initiation in neurons (Neuron, 2015;86:207-17). Here we present new findings obtained from dorsal root ganglion (DRG) cells, by varying the flash wavelength, light-absorbing particle, and flash duration. Using cylindrical AuNPs (nanorods; 25x94 nm; plasmon absorbance peak at ∼780 nm), a 1-ms, 20 μJ, 785-nm laser pulse was sufficient to elicit APs. A single 1-2 μm graphite particle placed on the DRG cell induced AP generation upon delivery of a 532-nm laser flash of 4 ns duration and 47 nJ energy, representing 130-fold less energy than the 6.2 μJ needed with a 0.5-ms laser pulse. With AuNPs, reduction in flash duration similarly decreased the flash energy required for AP generation. Our data demonstrate the use of near-infrared flashes that penetrate deeper into tissue than green light to elicit APs with light. They also indicate that, in addition to gold and mesoporous silicon (Nat. Mater., 2016;15:1023-30), graphite can enable optocapacitive AP generation. The data furthermore show that, with ∼nanosecond flash durations, APs can be elicited by flashes of ∼nano-Joule energy, i.e., in the range of those used in optogenetic approaches. Support: NIH grants R21-EY023430, R01-GM030376, and the Beckman Initiative for Macular Research.

Effect of graphite powder as a forming filler on the mechanical properties of SiCp/Al composites by pressure infiltration

(38vol% SiCp + 2vol% Al2O3f)/2024 Al composites were fabricated by pressure infiltration. Graphite powder was introduced as a forming filler in preform preparation, and the effects of the powder size on the microstructures and mechanical properties of the final composites were investigated. The results showed that the composite with 15 μm graphite powder as a forming filler had the maximum tensile strength of 506 MPa, maximum yield strength of 489 MPa, and maximum elongation of 1.2%, which decreased to 490 MPa, 430 MPa, and 0.4%, respectively, on increasing the graphite powder size from 15 to 60 μm. The composite with 60 μm graphite powder showed the highest elastic modulus, and the value decreased from 129 to 113 GPa on decreasing the graphite powder size from 60 to 15 μm. The differences between these properties are related to the different microstructures of the corresponding composites, which determine their failure modes.

Evaluation of pulmonary and systemic toxicity following lung exposure to graphite nanoplates: a member of the graphene-based nanomaterial family

BackgroundGraphene, a monolayer of carbon, is an engineered nanomaterial (ENM) with physical and chemical properties that may offer application advantages over other carbonaceous ENMs, such as carbon nanotubes (CNT). The goal of this study was to comparatively assess pulmonary and systemic toxicity of graphite nanoplates, a member of the graphene-based nanomaterial family, with respect to nanoplate size.MethodsThree sizes of graphite nanoplates [20 μm lateral (Gr20), 5 μm lateral (Gr5), and <2 μm lateral (Gr1)] ranging from 8–25 nm in thickness were characterized for difference in surface area, structure,, zeta potential, and agglomeration in dispersion medium, the vehicle for in vivo studies. Mice were exposed by pharyngeal aspiration to these 3 sizes of graphite nanoplates at doses of 4 or 40 μg/mouse, or to carbon black (CB) as a carbonaceous control material. At 4 h, 1 day, 7 days, 1 month, and 2 months post-exposure, bronchoalveolar lavage was performed to collect fluid and cells for analysis of lung injury and inflammation. Particle clearance, histopathology and gene expression in lung tissue were evaluated. In addition, protein levels and gene expression were measured in blood, heart, aorta and liver to assess systemic responses.ResultsAll Gr samples were found to be similarly composed of two graphite structures and agglomerated to varying degrees in DM in proportion to the lateral dimension. Surface area for Gr1 was approximately 7-fold greater than Gr5 and Gr20, but was less reactive reactive per m2. At the low dose, none of the Gr materials induced toxicity. At the high dose, Gr20 and Gr5 exposure increased indices of lung inflammation and injury in lavage fluid and tissue gene expression to a greater degree and duration than Gr1 and CB. Gr5 and Gr20 showed no or minimal lung epithelial hypertrophy and hyperplasia, and no development of fibrosis by 2 months post-exposure. In addition, the aorta and liver inflammatory and acute phase genes were transiently elevated in Gr5 and Gr20, relative to Gr1.ConclusionsPulmonary and systemic toxicity of graphite nanoplates may be dependent on lateral size and/or surface reactivity, with the graphite nanoplates > 5 μm laterally inducing greater toxicity which peaked at the early time points post-exposure relative to the 1–2 μm graphite nanoplate.Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-016-0145-5) contains supplementary material, which is available to authorized users.

Effect of Graphite as Forming Additive on Wear Properties of (SiCp + Al2O3f)/Al Composites Prepared by Pressure Infiltration

The 2024Al matrix composites reinforced by 30 vol% SiCp and 10 vol% Al2O3f as wear-resistant materials are prepared by pressure infiltration. The graphite powders are added during the preparation of the preform to support shaping. In this article, the effect of the size of the graphite powder on the friction and wear properties of the composites is researched. The results showed that at a given conditions, namely, the size of the SiCp is 14 µm and the diameter of the Al2O3 fiber is 4–5 µm, the composites made from 5 ∼ 30 µm have a more stable friction coefficience and lower wear rate than those from 30 ∼ 50 µm and 50 ∼ 70 µm graphite because the diameter of the generated pores in the corresponding preforms is smaller and more concentrated, resulting in a uniform distribution of the reinforcements in the matrix. The detailed effect mechanisms of different graphite sizes on wear and friction properties of the composites as well as the porosity of the corresponding preforms are also discussed.

Microstructure and Cell Performance of NiO-YSZ Composite Anode-Supported Solid Oxide Fuel Cells Using Graphite as Anode Pore-Former: Effects of Graphite Particle Size and HNO3Treatment

The influences of graphite particle size and HNO3 treatment on microstructure and cell performance of the NiO–YSZ anode-supported solid oxide fuel cells were investigated. The peak power density for the cells using 1, 3, and 6 μm graphite was 679, 603, and 549 mW/cm2, respectively. HNO3 treatment was an efficient approach to improve the wettability of graphite in water, to modify the microstructure and to enhance the cell performance. The peak power density for the cell using HNO3-treated graphite (1 μm) was 766 mW/cm2, approximately 13% higher than that of the cell using pristine graphite.

Oxidation Resistance of Graphite-SiAlON Bonded SiC Composite

Based mainly on SiC aggregate and fine powder, silicon powder, flake graphite (300 μm, 45 μm), α-Al2O3 micro-powder and AlN powder, Graphite-SiAlON bonded SiC composite were prepared. The influence of graphite addition, which varied from 0 to 9.7%, and its grain size on the oxidation resistance was investigated at 1 150 °C under air atmosphere. The results show that: 1) mass change rate reduces with the increase of graphite addition, the mass change rate of sample with 45 μm graphite is higher than that of sample with 300 μm graphite; 2) the cold modulus of rupture of sample with 45 μm graphite after oxidation is higher than that of sample with 300 μm graphite; 3)the oxidation resistance declines along with the increase of graphite addition, additionally, the oxidation resistance of sample with 45 μm graphite is superior to that of sample with 300 μm graphite; 4) 7.5% graphite is recommended as the proper addition.

Thermo-mechanical analyses of beryllium compound refractive lens for NSLS-II beamline

In this paper we discuss the finite-element analysis (FEA) of a one-dimensional beryllium compound refractive lens (Be-CRL) that was undertaken to study the feasibility of installing the CRL in the Inelastic X-ray Scattering (IXS) beamline of National Synchrotron Light Source-II (NSLS-II) (a new state-of-the-art medium-energy third-generation storage ring). The current insertion device for this beamline is an IVU22-6m in-vacuum planar undulator delivering a total power of ~9 kW with a peak power density of ~90 kW/mrad2. Through analysis, based on calculation of spectral angular distribution of undulator radiation from IVU22, we determined that it is essential to install a 30 µm graphite filter upstream of the CRL in order to restrict the temperature rise in the CRL to 65°C for acceptable thermal strain.

Microstructure and Properties of Graphite Embedded SiC Composite by Coating Method

Gp/SiC composite was prepared with electrode graphite particle and SiC powders as the raw materials, using coating process and hot-pressing sintering technology. The microstructure and phase constitution was measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron energy spectrum (EDS). It was found that the graphite cores are embedded in the SiC matrix as the islands. The apparent porosity increased, density decreased, with graphite particle content increasing, the bending strength decreased, however, fracture toughness increased with the graphite particle content increasing. Increasing hot-pressing sintering temperature imparted Gp/SiC composite characteristic behaviors of better mechanical strength. The apparent porosity, bulk density, bending strength, fracture toughness were 4.0%, 2.58 g•cm-3, 50 MPa, 6.3 MPa•m1/2, respectively, with the size 200 μm graphite core at 2050 °C, while the volume rate of SiC and graphite was 6:4.

Fluorinated Graphites as Energetic Cathodes for Nonaqueous Al Batteries

Conventional cathodes utilized in nonaqueous lithium anode batteries, including manganese and vanadium oxides, and molybdenum or titanium sulfides, are incompatible with nonaqueous aluminum anode electrochemical storage processes. Alternative cathodes systems were explored to develop high charge capacity nonaqueous aluminum cells. A series of high storage capacity Al cells, utilizing cathodes composed of CF x fluorinated polymer graphite compounds are demonstrated. Significant CF x cathodic capacities are obtained in aluminum anode cells utilizing a 0.3 M tetraethylammonium chloride, 10 mM Hg(CH 3 COO) 2 acetonitrile electrolyte. The addition of hydroxide to the CF x cathode mixture increases discharge potential, while the addition of nonfluorinated 1 μm graphite increases measured cathodic capacity. The CF x cathode capacity increases with the degree of fluorination from 27 to 35% fluorine, is approximately constant from 35 to 58% fluorine, increases in capacity for 61% fluorine, and increases again with 63% fluorine (the highest available level of 63% fluorine available in the CF x ). Measured cathode capacities exceed 250 mAh g - 1 . For example, in excess of 300 mAh g - 1 , total cathode mass is measured for a 50:50 wt % cathode composite containing 55% fluorinated CF x and half 1 μm nonfluorinated graphite.

Electrochemical characteristics and structures of surface-fluorinated graphites with different particle sizes for lithium ion secondary batteries

Electrochemical characteristics of surface-fluorinated graphite samples with average particle diameters of 25 and 40 μm (NG-25 and NG-40) have been investigated in 1 mol dm −3 LiClO 4–ethylene carbonate (EC)/diethyl carbonate (DEC) at 25 °C. The fluorine contents obtained by elemental analysis are 0.2–0.4 at.% and the surface fluorine concentrations obtained by X-ray photoelectron spectroscopy (XPS) are 4–12 at.% for the samples fluorinated between 150 and 300 °C. Raman spectra and transmission electron micrographs indicate the increase in the surface disordering of graphite. The surface areas of graphite samples are increased by 64–77% and the mesopores with diameter of 2–3 nm are also increased by surface fluorination. The charge capacities of surface-fluorinated samples are larger than those of original graphites and even the theoretical capacity of graphite, 372 mAh g −1. The increments of the capacities are ∼10 and ∼13% for 25 and 40 μm graphite samples, respectively. Nevertheless, the first Coulombic efficiencies are the same as those of original graphites for the samples fluorinated between 150 and 300 °C. The increase in the capacities was discussed on the basis of surface compositions and structures of fluorinated graphite samples.