Different Types Of Graphite Research Articles

A critical review and meta-analysis of xenon-on-carbon sputter yield data

A systematic review and meta-analysis of sputter yield data for xenon ions normally incident on graphite at energies below 2000 eV was undertaken to identify systematic errors, determine the best model parameter values to represent yield as a function of energy, quantify uncertainty, and determine if the data support differences in yields for different types of graphite. A critical examination of the 11 published data sets for high density graphite, pyrolytic graphite, and amorphous carbon showed that, in general, they were carefully controlled to minimize errors. The most significant quantifiable systematic errors were those caused by the neglect of doubly charged ions, chemical erosion, and the impact of secondary electron emission on ion flux measurements. The effects of gas uptake and outgassing on mass loss measurements and unrepresentative surface textures may have biased other experiments, but these effects could not be quantified. The semi-empirical Eckstein model for yield as a function of energy was fit to data for the three graphite types using a hierarchical Bayesian statistical model, producing recommended fit parameters and probability distributions representing uncertainty in yields. The results showed that differences in yield for high density graphite and pyrolytic graphite were not statistically significant. Apparent differences in yield for amorphous carbon disappeared when the single data set available for energies below 150 eV was corrected for reasonable values of double ion content. Recommended procedures to avoid systematic errors and additional experiments and modeling to fill in gaps in our understanding are included.

The Effect of Exposure Conditions on the Properties of Cementitious Composites with Reduced Electrical Resistivity

Cement composite materials with reduced resistivity are specialized building materials, which are constantly pushing their limits. Research into these composites requires a study of the influences of exposure conditions on resistivity. The mixes selected for the purpose of the research included the reference, pure cement mix, and mixes with proportions of graphite under and above the percolation threshold, with two different types of graphite. It was found that the resistivity of all the tested mixes decreases if moisture grows; the influence of moisture is more significant for mixes with graphite proportions below the percolation threshold. The resistivity of all the tested mixes decreases with increasing temperatures; the influence of a higher temperature (50 °C) is more significant for mixes with graphite proportions above the percolation threshold; however, these mixes are, at the same time, more resistant to permanent changes in resistivity caused by frost (−10 °C). It was found that the action of CO2 causes a reduction in resistivity. Mixes with proportions of graphite above the percolation threshold show higher stability when exposed to CO2. Mixes with proportions of graphite below the percolation threshold are extremely sensitive to horizontally oriented pressure loads. Increases in resistivity caused by vertical pressure loads were by 20–40%. The resistivity of the mixes with proportions of graphite above the percolation threshold was less sensitive to the pressure load.

Microfluidic-based ion-selective thermoplastic electrode array for point-of-care detection of potassium and sodium ions.

A microfluidic paper-based thermoplastic electrode (TPE) array has been developed for point-of-care detection of Na+ and K+ ions using a custom-made portable potentiometer. TPEs were fabricated using polystyrene as the binder and two different types of graphite to compare theelectrode performance. The newly designed TPE array embedded in a polymethyl methacrylate chip consists of two working electrodes modified with carbon black nanomaterial and an ion-selective membrane, and an all-solid-state reference electrode modified with Ag/AgCl ink and poly(butyl methacrylate-co-methyl methacrylate) membrane via drop-casting. Ion-selective membrane compositions and conditioning steps were optimized. Under optimized conditions, ion-selective TPEs demonstrated fast response time (4s) and good stability. The TPE array demonstrated a Nernstian behavior for K+ with a sensitivity of 59.2 ± 0.2mV decade-1 and near-Nernstian response for Na+ with a sensitivity of 54.0 ± 1.1mV decade-1 in the range 10-1 - 10-4M and 1 - 10-3M, respectively. The detection limits were 1 × 10-5M and 1 × 10-4M for K+ and Na+, respectively. In addition, a K+ and Na+ selective microfluidic paper-based analytical device (µPAD) was applied to artificial serum analysis and found in good agreement with average recoveries of 101.3% and 99.7%, respectively, suggesting that the developed ISE array is suitable for detection of sodium and potassium in complex matrix.

Influence of structural properties on (de-)intercalation of ClO4− anion in graphite from concentrated aqueous electrolyte

Graphite intercalation compounds (GICs) are widely known for their remarkable multifold physico-chemical properties and their numerous state-of-the-art applications, such as energy storage, sensors, lubrication, catalysis, magneto-optics, superconductivity, etc. However, the properties of GICs largely depend on the synthesis technique, structure, and morphology of the graphite; the size and properties of the intercalant species and its concentration in the host material. Accordingly, in the field of electrochemical energy storage, the appearance of novel ionic systems and detailed investigations of GICs are highly desired. In this study, two different types of graphite, natural graphite (NG) and kish graphite (KG), were used to gain insights into the intercalation of ClO4− anion in graphite from a concentrated Al(ClO4)3 aqueous electrolyte solution through extensive electrochemical studies and various in situ and ex situ spectroscopic characterization techniques. An analysis of cyclic voltammograms indicated the presence of surface-controlled charge storage along with diffusion-controlled ion intercalation into the interlayer spaces in NG and KG. Additionally, a comparative study on the electrochemical behavior of these two types of graphite showed differences that can be correlated with their structural properties. These findings open new perspectives for GIC formation in concentrated aqueous electrolytes and applications in electrochemical energy storage.

The effect of graphite type on the synthesis of SiC nanomaterials by microwave-assisted synthesis

SiC nanomaterial (SiCNM) is known for its excellent properties and has great potential for a wide range of applications. In this article, preparation of SiCNMs from different types of graphite was performed by microwave-assisted synthesis. Different types of graphite which are graphite flake (GF) and expanded graphite (EG) were used to react with silica for the synthesis of SiCNMs in laboratory microwave furnace at 1400 °C. It was found that SiC nanowhiskers (SiCNWs) were formed when EG was used, while irregular shaped SiC nanoparticles (SiCNPs) were formed when GF was used. β-SiC appeared as the only phase in the XRD patterns for both SiCNMs formed using GF and EG. SiCNWs and SiCNPs have interplanar spacing of around 0.25 nm which is the axial direction of [111]. The difference of formation mechanism is believed to be the origin of different morphology of SiCNMs synthesized from different types of graphite.

Structural and mechanical properties of different types of graphite used in nuclear applications

Graphite is known as a material with excellent thermo-mechanical, structural and neutron moderation properties. It is currently used as a core structural component for High Temperature Gas Cooled Reactor (HTGR). It is due to the fact that graphite has been extensively tested and proved to satisfy most of HTGR operating requirements. However, one question still remain unclear. Graphite, depending from the manufacture method, type and purity shows different mechanical and structural properties. In addition to that, literature data is poor in comparative studies of current and used in the past materials. For this reason, series of tests involving Scanning Electron Microscopy, Raman Spectroscopy, X-ray diffraction and nanoindentation have been performed on the virgin samples of two types of nuclear graphite’s: IG-110 and nuclear graphite used in decommissioned EWA reactor. Obtained results clearly shows differences in microstructural and mechanical properties of both types of graphite’s. Reported changes have been discusses and attributed to the density of the material and its origin.

Production of few-layer graphene by wet media milling using organic solvents and different types of graphite

One of the main challenges in the exploitation of nanomaterials is their production at low cost. Mechanical milling is an alternative for the production of nanomaterials, such as graphene. In this work we have studied the effect of different solvents (methanol, ethanol, acetone, hexane, toluene and xylene) on the production of graphene by attrition milling of graphite. Among the solvents tested, methanol showed to be able to produce graphene sheets more efficiently. Computer modeling suggests that although methanol and acetone have a weaker interaction with graphene (3.95 and 7.41 kcal/mol, respectively) compared to xylene (12.73 kcal/mol), they have a higher Gibbs free energy (6.46, 3.81 and 0.33 kcal/mol for methanol, acetone and xylene, respectively), suggesting a higher mobility on its surface, thus facilitating the exfoliation of graphene. The production of graphene was corroborated by Raman spectroscopy and transmission electron microscopy, showing to be a few layers graphene (<5 layers), approximately 1–6 μm in length, with a high degree of graphitization. Additionally, we also show that through this route is feasible to produce a few-layer graphene using synthetic and amorphous graphite as more economical alternatives.

Effect of polarity and various contact pairing combinations of electrographite, polymer-bonded graphite and copper on the performance of sliding electrical contacts

This study focuses on the wear, friction and electrical characteristics of the newly developed, disc-disc contact design for sliding electrical contacts. Different types of graphite and copper, as the material combinations, different contact operating variables and, in particular, different directions of the electrical current, i.e., the disc polarity, were investigated under real contact conditions in a dedicated tribological test rig. The electrographite and polymer-bonded graphite were running in a self-mated contact, against copper and against each other. The polymer-bonded-graphite/polymer-bonded-graphite pair performed the best for almost all the studied parameters, while the mixed, dissimilar, polymer-bonded-graphite/electrographite combination had the worst performance. Moreover, all the pairs containing electrographite material exhibited unstable contact behaviour, and generally gave a worse overall performance. The wear of the self-mated graphite pairs was less than that of the graphite/copper pairs. The effect of the polarity on the graphite/graphite material combinations was negligible, while in the graphite/copper combinations the direction of the electrical current was found to significantly affect the wear of the discs. The wear of the positive graphite disc was up to 30% lower than the negative graphite disc, while the wear of the positive copper disc was up to 8 times more than that of the negative copper disc. Differences in the boundary contact film were observed in the graphite/copper contacts depending on the surface polarity, meaning that sliding contacts with the current flowing from the graphite disc to the copper disc saw less wear than the contacts where the current flows from the copper disc to the graphite disc.

Preparation and Experimental Study of Graphite Material for Water Lubricated Thrust Bearing of Nuclear Main Pump

Based on technical difficulties of graphite water-lubricated thrust bearing such as preparation and properties detection, this paper investigated graphite bearing systematically from preparation and property testing, three different types of graphite (#1, #2 and #3) were carried out. The result indicated the tribological properties are poor if the graphitization of graphite is too high or low. The pads of water-lubricated thrust bearing are manufactured by the three kinds of graphite, and the start-stop test were carried out on a test platform for half-size bearing of nuclear primary pump. The result of start-stop test were indicated the graphitization have a visible influence on the wear loss mass of graphite pad.

Effects of Different Graphite Types on the Thermal Fatigue Behavior of Bionic Laser-Processed Gray Cast Iron

In order to study the thermal fatigue behavior of bionic gray cast iron with different types of graphite (from A to E), first, the effects of A to E types of graphite on the thermal fatigue properties were studied. At the same time, the crack initiation and propagation modes of different gray cast iron types were analyzed. In addition, for improving the thermal fatigue properties of gray cast iron, the anti-fatigue mechanism of the coupled bionic structure on gray cast iron was investigated. In this case, the thermal fatigue properties were measured by the number, length, and width of cracks. The results revealed that the gray cast iron with A-type graphite had the best fatigue resistance compared to others. However, C-, D-, and E-type graphite exhibited the greatest effect on the number, length, and width of crack. Interestingly, the bionic gray cast iron sample with D-type graphite exhibited improved fatigue resistance most obviously compared to the non-bionic sample.

Genetic significance of the 867 cm− 1 out-of-plane Raman mode in graphite associated with V-bearing green grossular

SE Kenya is the world’s largest producer of green vanadium grossular gemstones (tsavorite). Samples from one of the mines near Mwatate, and of occurrences in Tanzania yielded remarkable new insights into the genesis of tsavorite. Graphite is intimately associated with V-grossular and is one of the keys to understanding its origin. In the course of this study we found five different types of graphite. Surprisingly, in one graphite type the “Raman-forbidden” and IR-active 867 cm− 1 band was observed. In this communication, we attempt to find an explanation for this unusual phenomenon. Additionally, our observations also address some of the issues pertaining to the origin of the green grossular-dominated rocks (grossularites), as well as the gem quality tsavorite crystals, since we propose that the anomalous spectroscopic behavior of the graphite is related to the unusual conditions during crystallization of both the grossular and graphite from a near-supercritical volatile- and sulfur-rich silicate melt. The massive green vanadium grossular contains abundant unequivocal crystallized melt inclusions, while the transparent gem quality grossular (tsavorite) displays only fluid inclusions. On the basis of inclusion studies we suggest that anatectic melts originated in the peculiar evaporitic host lithology of the tsavorite deposits. Near peak metamorphic temperatures (~ 700 °C) these liquids occurred as a supercritical volatile-rich “fluid/melt phase” characterized by complete miscibility between H2O and silicate liquid. Relatively dry liquid batches precipitated non-transparent green grossular, whereas wet batches segregated fluids that formed transparent tsavorite.

Structural Studies of Hydrographenes.

As a result of the unique physical and electrical properties, graphene continues to attract the interest of a large segment of the scientific community. Since graphene does not occur naturally, the ability to exfoliate and isolate individual layers of graphene from graphite is an important and challenging process. The interlayer cohesive energy of graphite that results from van der Waals attractions has been determined experimentally to be 61 meV per carbon atom (61 meV/C atom). This requires the development of a method to overcome the strong attractive forces associated with graphite. The exfoliation process that we, and others, have investigated involves electron transfer into bulk graphite from intercalated lithium to yield lithium graphenide. The resulting graphenide can be reacted with various reagents to yield functionalized graphene. As a part of our interest in the functionalization of graphene, we have explored the Birch reduction as a route to hydrographenes. The addition of hydrogen transforms graphene into an insulator, leading to the prediction that important applications will emerge. This Account focuses mainly on the characterization of the hydrographenes that are obtained from different types of graphite including synthetic graphite powder, natural flake graphite, and annealed graphite powder. Analysis by solid state 13C NMR spectroscopy proved to be important since it was shown that the hydrographenes are composed of interior, isolated aromatic (predominantly fully substituted benzene) rings surrounded by saturated rings. The expected clusters of benzene rings were not found. NMR spectroscopy also offers strong evidence for the presence of tert-butyl alcohol and ethanol (workup solvent) that could not be removed in vacuo from the samples. These compounds could be observed to move freely within the layers of the hydrographene. High-resolution transmission electron microscopy images revealed a remarkable change in morphology that results when hydrogen is added to the graphenide. The appearance of edge and circular dislocations and increased distances between graphitic layers are most visible in the case of the hydrographenes that are formed from annealed graphite. The repetitive hydrogenation of synthetic graphite powder leads to an increase in the distances between the graphitic layers in the (002) direction from 3.4 Å for the initial graphite to 4.11 Å after the first reduction and to 4.29 Å after a third reduction of the same material. Defect-free graphite is formed when the hydrographenes are heated. The distance between carbon layers decreases from 4.11 to 3.44 Å after heating the samples to 1200 °C. This trend toward the spacing of graphite confirms the reversibility of the functionalization process. The C-H bonds have been broken yielding hydrogen, and the exposed carbon orbitals are in close enough proximity to have reverted to graphite. This Account introduces only a narrow area of materials chemistry, and many applications of graphene and its derivatives can be expected as researchers exploit this burgeoning field.

Dilatometric Study of the Electrochemical Intercalation of Bis(trifluoromethanesulfonyl) Imide and Hexafluorophosphate Anions into Carbon-Based Positive Electrodes

“Dual-ion cells” are electrochemical energy storage devices that employ graphitic carbons as positive electrode material. The electrolyte in this cell system does not only behave as a charge carrier but also as active material.[1] The negative electrode in the dual-ion system can be built up by typical anode materials for lithium ion cells such as lithium metal, lithium titanate (Li4Ti5O12, LTO) or graphite.[2] During charging, the anions of the electrolyte are intercalated into the layered structure of the graphite positive electrode, while the lithium ions of the electrolyte deposit on the surface of the metallic lithium negative electrode. The gallery height expansion for graphite positive electrodes by bis(trifluoromethanesulfonyl) imide (TFSI-) intercalation is around 140%[3] and 130% if hexafluorophosphate (PF6-) is intercalated.[4] On discharge, both ions are stripped/de-intercalated and solvated again in the electrolyte. Furthermore several carbon materials like graphite, carbon black or carbon nanofibers are applied as conductive additives in high voltage cathodes. At potentials above 4.5 V vs. Li/Li+, major problems are related to electrolyte degradation and to anion and solvent co-intercalation. Co-intercalation can lead to the destruction of the carbon structure (exfoliation) and therefore to continuous electrolyte degradation.[5,6] The method of electrochemical dilatometry has been used since the 1970s to investigate the height change of layered host compounds when a guest molecule or ion is inserted.[7] The Li+ intercalation into different types of graphite or the BF4-intercalation into carbons are two examples that were already investigated using the electrochemical dilatometer (ECD-1), which was developed by Hahn et al.[8,9] The complete electrode height change or the electrode height change per cycle can be calculated. An illustration of the ECD-1 cell core is presented in Figure 1. In this work, we report the intercalation of TFSI- and PF6 - anions into graphitic and carbon black-based positive electrodes from an ionic liquid-based and organic solvent-based electrolyte using LiTFSI and LiPF6 as the conductive salts. Furthermore, we investigated the influence of two electrode binders, namely sodium-carboxymethyl cellulose (CMC) and poly(vinylidene diflouride) (PVdF) on the electrochemical intercalation/de-intercalation behavior of the electrode. Especially, the influence of the electrode binder on the electrode expansion behavior and the electrode material stability are discussed. Additionally, the influence of a constant voltage step at the upper cut-off potential and the influence of a higher operation temperature of 60 °C on the electrode expansion are discussed. Figure 1: Illustration of the in-situelectrochemical dilatometer cell (ECD-1 (EL-Cell GmbH)). 1: Metal membrane; 2: Working electrode (WE); 3: Glass T-frit; 4: Metallic lithium (CE); 5: CE plunger; 6: Sensor tip; 7: Spacer disc; 8: RE with metallic lithium on top.

Graphite Behavior During a gas Phase Method for Aluminum Nitride Preparation

Purity of AlN, synthesized by means of gas-phase technology, depends to a considerable extent on charge component and intermediate compound reactions with structural materials. Chemical aspects are considered for transformations and the nature of reaction of aluminium fluoride and nitride with different types of graphite, the effect of fluorides on final synthesis product is revealed, and chemical aspects of their reaction with graphite during AlN synthesis are explained. The possibility is established of creating a protective coating on graphite made of chemically deposited AlN. Calculated and experimental data are obtained for developing a modernized industrial test unit for preparing high purity fine AlN.

Development of a Zirconia-Graphite Refractory for a SEN Application

Zirconia-graphite refractories are generally used in the slag-like zone of the subentry nozzle in continuous casting. A zirconia-graphite refractory has superior thermal shock resistance and corrosion resistance compared to MgO-C and Al2O3-C refractories. The effect of graphite on the zirconia-graphite refractory is not well documented. Therefore, in the present work an attempt has been made to evaluate the effect of graphite on the properties of the zirconia refractory. Graphite can be classified in terms of fixed carbon content and in this work three different types of graphite with varying fixed carbon content were used (99, 94, and 80%). The amount of zirconia was maintained at 82% and that of the graphite at 18%. Other processing parameters and ingredient concentrations were constant throughout the work. Refractory samples were fabricated using the cold isostatic method and refractory samples were coked at 1000°C in a reducing atmosphere. The effect of fixed carbon percentage on apparent porosity, bulk density, spalling resistance, and oxidation resistance were evaluated.

Morphologies of Some Graphites in Ductile Cast Irons

The internal structure of different types of graphite commonly found in the ductile cast iron were investigated by TEM technique for TEM samples prepared by FIB method to understand their nucleation and growth. Spheroidal and vermicular graphite were observed in the ductile cast iron with spheroidizing treatment. Flake graphite was observed in the same cast iron without the spheroidizing treatment. The spheroidal graphite had a three-fold internal structure, with an amorphous-like central region, annual rings of a layered intermediate region, and an outer region made up of large polygonal crystalline platelets in a mosaic-like structure. The vermicular and flake graphite had a similar to that of the outer region of the spheroidal graphite, in that it consisted of similar crystalline platelets. [doi:10.2320/matertrans.M2014167]

In Situ Detection of Lithium Plating on Graphite Electrodes by Electrochemical Calorimetry

The measured heat flow of graphite/NMC lithium ion cells under charging conditions show a characteristic and easily identifiable signal at the onset of lithium plating on the graphite electrode. A marked decrease in heat flow signals the full lithiation of the graphite host. The origin of this signal is shown to arise from the combined effects of entropy and cell over potentials. This signal allows for an accurate measure of the maximum amount of lithium intercalation possible in the host. Metallic lithium deposition begins within 5–7 mAh/g after the heat flow begins to decrease. Two different types of graphite were examined; G25 and MCMB. The onset of lithium plating was detected at 336 mAh/g for the G25 graphite and 297 mAh/g for the MCMB graphite, yielding empirical formulas of Li0.888C6 and Li0.804C6, respectively. The effect of plated lithium on the electrode/electrolyte reactivity was also examined by precise measurement of the coulombic efficiency, parasitic thermal energy and cell capacity fade. These measurements then allowed for the calculation of the efficiency of lithium plating on the graphite surface: 0.98 and 0.97 for G25 and MCMB graphites, respectively.

Thermodynamic Analysis of Cast Irons Solidification With Various Types of Graphite

Abstract The contribution summarises the results of oxygen activity determinations, which were measured and registered continuously in castings from cast irons with various types of graphite. The results were used to find the relationship between two variables: natural logarithm of oxygen activities and reverse value of thermodynamic temperature 1 /T. Obtained regression lines were used to calculate oxygen activity at different temperatures, to calculate Gibbs free energy ΔG at the different temperatures and to calculate the single ΔG value for significant temperature of the graphite solidification. The results were processed by a statistical analysis of data files for the different types of graphite with flake, vermicular and spheroidal graphite. Each material has its proper typical oxygen activities range and individual temperature function of Gibbs free energy for analysing and governing casting quality.

Development and Characterization of Amorphous Thermoplastic Matrix Graphene Nanocomposites

The aim of the present work is the development of amorphous thermoplastic matrix nanocomposites based on graphite nanoparticles. Different types of graphite were used, including unmodified graphite, graphene nanoplatelets and graphite intercalation compounds. Graphite intercalation compounds were subjected to thermal treatment to attain exfoliation of the nanofiller. The exfoliation process was studied by means of thermal analysis. The nanofillers and nanocomposites were characterized by means of X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) analysis. The nanocomposites were further characterized by means of mechanical and dielectric analysis. The flammability of the nanocomposites was also analyzed. Results obtained indicate that addition of the nanofiller allows improving the proprieties of the amorphous thermoplastic matrix. The effect of the degree of dispersion of the nanofiller is particularly relevant for the dielectric properties of the nanocomposites, whereas no direct correlation between degree of dispersion and mechanical properties can be observed.

Impaction of Graphite Type on Performance of Polycrystalline Diamond Powder

Taking different types of graphite as raw materials ， polycrystalline diamond powder is prepared by shock wave synthesis through copper to absorb and transfer the heat in the article. Yield and abrasion resistance performance are tested, and impaction of graphite crystallite structure on the yield and abrasion resistance performance is researched. As the result, diamond yield and abrasion resistance synthesized from scale graphite is not as good as from earthy graphite. It is easy for polycrystalline diamond powder synthesized from artificial graphite which crystallite has parallel coke-base to graphitize and difficult to get diamond. Yield of artificial graphite which crystallite has disorderly carbon black base is higher than that of earthy graphite, there are more pores for the first baked artificial graphite of carbon black base, the abrasion resistance performance of synthesized diamond is worse than earthy graphite, and the abrasion resistance performance of the second baked polycrystalline diamond powder is better than earthy graphite.