Reaction Of Graphite Research Articles

Sovent-Free Synthesis of Lithium Intercalated Graphites Using Thermal or Mechanical Reactors

The intercalation of lithium into graphite is an important process for energy storage devices. The industrial route of intercalation is electrolysis in pre-assembled Li-ion batteries with excess Li loading in the cathode. This has a number of disadvantages: increased battery processing time, mass and volume (from needing excess Li loading), and parallel formation of a solid-electrolyte interphase (SEI). The later is difficult to control and is a major factor in the battery's overall performance and cost. An alternative is to prepare the anode with partially lithiated graphite prior to electrolyte contact. As far as we know this has not been demonstrated. Each step – lithiation of graphite followed by making slurry with binder – presents added complications with the reactive anode powder, but it offers compelling advantages such as, increase in "usable" Li, control of SEI formation, and decreased battery processing time. These advantages may also lead to battery performance and lifetime. Also, it would also allow for investigations into spontaneous formation of SEI, which may provide insight into producing an effective artificial SEI.As reported in the literature, LiC x has been chemically synthesized viacontact with lithium vapor and compression with lithium metal. Both of these has a flaw: graphite reaction with Li vapor is kinetically unfavored due to the low vapor pressure of Li and it is difficult to control the stoichiometry; the compression method has been shown to produce the important stages (I–IV) but it is slow, taking 24 h. Here we present two solvent-free and compression-free methods that can produce stage I or stage II lithiated graphites. The thermal method heats graphite and lithium powders to ca. 300 °C under ultrahigh vacuum (UHV) for 24 h. The mechanical method involves ball-milling the two powders together under ultra-high purity Ar(g) atmosphere for 1 h.Both processes work with different types of graphite sources and we compare the two synthetic methods using a battery-grade mesophase graphite. The products were characterized by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). We show that while the mechanical reactor seems to lithiate the graphite more quickly, it may affect the morphology. Hard carbon fibers were also lithiated using the mechanical reactor. We compare the stability of the LiC6made using mesophase graphite and carbon fiber.XRD and NMR are used to follow the delithiated of the products when in contact with a non-zero moisture environment. It was found that a surface passivation layer is formed that protects intercalated lithium. We also report open-circuit potential (OCP) and electrochemical impedance spectroscopy measurements of the products in contact with standard Li-ion battery electrolyte. These results are used to discuss the spontaneous formation SEI at the LiC6interface. Figure 1: SEM images of a) stabilized lithium metal powder; b) carbon fiber, Pyrograf I; c) MGPA; d) ball-milled lithiated-MGPA. e)X-ray diffractogram of mechanically synthesized lithiated MGPA. Inset is log-scaled expansions of regions in green boxes. (o) raw graphite; (*) LiC12; (†) LiC6.Research was supported by the Fluid Interface Reactions, Structures, and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (RLS, NJD). XPS analysis was done with support of the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division (GMV). The authors thank Applied Science, Inc. for samples of the Pyrograf I carbon fibers and Pred Materials International for the MGPA.

Gasification of Graphite and Coke in Carbon–Carbon Dioxide–Sodium or Potassium Carbonate Systems

The thermodynamics of possible reactions, including gasification and reduction reactions, in carbon–carbon dioxide–sodium or potassium carbonate systems was analyzed first. And then, the gasification reactions of graphite and coke with CO2 in this system were studied kinetically by temperature programmed thermogravimetry. The results showed that the carbon conversion curve shifted to a lower temperature zone after Na2CO3 or K2CO3 was added, and graphite was more susceptible than coke to be catalyzed by Na2CO3 or K2CO3. Ten kinetic equations were adopted to simulate the reaction process using the method of Coats–Redfern. The Avrami–Erofeev equation was found to be the most probable kinetic equation, with which the values of activation energy and frequency factor were calculated. The kinetic simulation indicated that the activation energy of coke carbon had been activated to the lowest level by its inner factors, thus it was difficult to be reduced by adding Na2CO3 or K2CO3. The kinetic compensation effect was confirmed to exist in both graphite gasification and coke gasification. X-ray diffraction and Raman spectra were used to characterize the inner difference between graphite and coke, which showed that coke carbon structure was greatly different from graphite structure because of its highly disordered and heterogeneous carbon structure.

General Observation of Lithium Intercalation into Graphite in Ethylene-Carbonate-Free Superconcentrated Electrolytes

Lithium-ion batteries have exclusively employed an ethylene carbonate (EC)-based electrolyte to ensure the reversibility of the graphite negative electrode reaction. Because of the limitation of electrolyte compositions, there has been no remarkable progress in commercial lithium-ion batteries despite active research on positive electrode materials. Herein, we present a salt-superconcentrating strategy as a simple and effective method of universalizing a graphite negative electrode reaction in various organic solvents. A dilute electrolyte (e.g., 1 mol dm(-3)) of sulfoxide, ether, and sulfone results in solvent cointercalation and/or severe electrolyte decomposition at a graphite electrode, whereas their superconcentrated electrolyte (e.g., >3 mol dm(-3)) allows for highly reversible lithium intercalation into graphite. We have found a unique coordination structure in the superconcentrated solution and an anion-based inorganic SEI film on the cycled graphite electrode, which would be the origin of the reversible graphite negative electrode reaction without EC. Our salt-superconcentrating strategy, expanding the graphite negative electrode reaction in various organic solvents other than EC, will contribute to the development of advanced lithium-ion batteries with high-voltage and fast-charging characters based on new EC-free functional electrolytes.

A solvent-free Diels-Alder reaction of graphite into functionalized graphene nanosheets.

A solvent-free Diels-Alder reaction was carried out by heating a mixture of graphite and a typical dienophile, maleic anhydride (MA) or maleimide (MI), in a sealed glass ampoule of argon. The functionalization of graphite with dienophiles was confirmed by various characterization techniques, suggesting the efficient functionalization and delamination of graphite into a few layers of graphitic nanosheets.

Laser cladding in-situ NbC particle reinforced Fe-based composite coatings with rare earth oxide addition

Over the past decade, researchers have demonstrated much interest in laser cladded metal matrix composite coatings for its good wear resistance, corrosion resistance and high temperature properties. The effects of RE on the microstructure and properties of laser coatings have also got more and more attention. In this paper, in situ Fe-NbC composite coatings with different CeO2 addition were produced on die steel by laser cladding. The formation mechanism of NbC particles was analyzed. The effects of RE on microstructure and micro-hardness of coatings were investigated. It was revealed that larger NbC particles with hard edges formed around Nb particles, and smaller flocculent NbC particles formed by the chemical reaction of Nb and solid graphite in the molten pool. CeO2 plays important roles in reducing micro-porosities, refining grains, and improving the precipitation of NbC. Therefore, the average micro-hardness and its smoothness from the top to the bottom of the coating were improved after adding CeO2.

Expansion of tetrachloroaluminate-graphite intercalation compound by reaction with anhydrous hydrogen fluoride

Reaction of the stage-1 graphite tetrachloroaluminate intercalation compound prepared from highly oriented pyrolytic graphite with anhydrous HF yields expanded graphite. According to scanning electron microscopy, exfoliation of graphite layers occurs more intensely as the reaction temperature increases. X-ray diffraction shows the expanded graphite has low crystallinity and the layer structure of graphite is highly disordered. X-ray photoelectron spectroscopy confirms formation of AlF3 and absence of Cl and covalent C–F bonds. Infrared spectroscopy reveals the gaseous species released during the expansion are HCl and CF4. These observations suggest the following reaction is the source of the expansion: CxAlCl4s+4HFl→x-0.25Cs+AlF3s+4HClg+0.25CF4g.

ChemInform Abstract: Mechanochemistry of Fullerenes and Related Materials

AbstractReview: 369 refs.

C K‐edge NEXAFS study of fluorocarbon formation on carbon anodes in molten NaF–AlF3–CaF2

Operational instability from processes occurring at the anode during the production of aluminum in the commercial Hall‐Héroult process may lead to an increase in undesirable fluorocarbon emissions, higher energy use, and shorter plant life. One contribution to this instability may be the possible formation of a fluorocarbon film at the electrode interface. Here, the surface composition of graphite anodes after electrolysis in molten NaF–AlF3–CaF2 at 990 °C is investigated for evidence of fluorocarbon formation using C K‐edge near edge X‐ray absorption fine structure. Fluorocarbon is identified on an anode surface after prolonged anode effect (very high overpotential with increased cell resistance) and also on an anode surface after normal electrolysis without anode effect. This provides evidence that fluorocarbon formation may occur prior to anode effect lowering the surface tension of the anode and therefore resulting in dewetting to contribute to the onset of the anode effect. Confirmation that such compounds form furthers our understanding of electrochemical reactions of graphite with fluoride and of the fundamental processes that occur in an aluminum smelter cell. Copyright © 2013 John Wiley & Sons, Ltd.

CVR-SiC coating of graphite pebbles for fusion blanket application

Abstract The Helium Cooled Ceramic Reflector (HCCR) Test Blanket Module (TBM), recently planned for installation and testing in the nuclear fusion energy project of International Thermonuclear Experimental Reactor (ITER), uses graphite in the form of pebbles as a neutron reflector, opening the possibility of avoiding the use of a beryllium neutron multiplier. A silicon carbide (SiC) coating should be formed on the graphite pebbles to prohibit the reaction of graphite with steam and/or air and to reinforce the surface strength. In this work, a dense β-SiC coating was formed over the surface of the graphite pebbles by a chemical vapor reaction (CVR) process of the solid–solid (SS) and vapor–solid (VS) reaction of the SiO2(s)–C(s)–SiO(v)–CO(v) system. The microstructural features, XRD patterns, pore size distribution, porosity and oxidation behavior of the SiC-coated graphite pebbles were investigated. A SiC coating with a thickness of approximately 30 μm remarkably improved the oxidation resistance and the density of the graphite pebbles. In an isothermal oxidation test conducted at 700 °C, the SiC-coated graphite pebbles showed strong oxidation resistance and a weight loss of approximately 2 wt% over the course of 2 h. This paper describes the major results obtained from our experiments on the CVR-SiC coating of nuclear graphite pebbles, recently conducted in the Korean HCCR TBM team of the ITER project.

ChemInform Abstract: Synthesis and Crystal Structure of the Highly Reduced Metalate Ba3[Ir(CN)3

AbstractThe title compound is synthesized by solid state reaction of Ba2N, Ir, NaCN, and graphite (pressed pellets, Ta ampules, argon, 1020 K, 24 h).

Mechanochemistry of fullerenes and related materials

The low or lack of solubility of fullerenes, carbon nanotubes and graphene/graphite in organic solvents and water severely hampers the study of their chemical functionalizations and practical applications. Covalent and noncovalent functionalizations of fullerenes and related materials via mechanochemistry seem appealing to tackle these problems. In this review article, we provide a comprehensive coverage on the mechanochemical reactions of fullerenes, carbon nanotubes and graphite, including dimerizations and trimerizations, nucleophilic additions, 1,3-dipolar cycloadditions, Diels-Alder reactions, [2 + 1] cycloadditions of carbenes and nitrenes, radical additions, oxidations, etc. It is intriguing to find that some reactions of fullerenes can only proceed under solvent-free conditions or undergo different reaction pathways from those of the liquid-phase counterparts to generate completely different products. We also present the application of the mechanical milling technique to complex formation, nanocomposite formation and enhanced hydrogen storage of carbon-related materials.

Reduction of Magnetite in the Presence of Activated Carbon Using Mechanical Alloying

The reduction behaviour of magnetite using graphite under ball‐milling conditions (using a planetary mono mill, Fritsch Pulverisette 6) has been investigated. The reaction of magnetite and graphite at different milling conditions leads to the formation of Fe2+ and Fe3+ species, the former increasing at the expense of Fe3O4. Fe3O4 completely disappeared after a ball to powder ratio of 50 : 1 and beyond. The Fe2+ species were confirmed to be due to FeO using Mössbauer Spectroscopy and X‐ray diffraction techniques. Scanning electron microscopy and transmission electron microscopy analyses confirm the reduction of magnetite to wüstite.

Mechanochemically driven solid-state Diels–Alder reaction of graphite into graphene nanoplatelets

A mechanochemically driven solid-state Diels–Alder reaction is demonstrated via dry ball-milling graphite as the diene in the presence of maleic anhydride or maleimide as the dienophile. On the basis of various characterizations, the Diels–Alder adducts are edge-selectively functionalized and subsequently delaminated into graphene nanoplatelets.

Reaction-composite brazing of carbon fiber reinforced SiC composite and TC4 alloy using Ag–Cu–Ti–(Ti+C) mixed powder

Carbon fiber reinforced SiC (Cf/SiC) was successfully joined to TC4 alloy with Ag–Cu–Ti–(Ti+C) mixed powder by proper parameters. The interfacial microstructure was investigated by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The mechanical properties of the brazed joints were measured by a mechanical testing machine. The results show that the Ti element in the interlayer can react with the brazed composite, the brazed joints mainly consist of TiC, Ti3SiC2, Ti5Si3, Ag, residual graphite, TiCu, Ti3Cu4 and Ti2Cu reaction products, and the performed joints have dense bonding layers reinforced by residual graphite and in situ synthesized TiC from reaction between C and Ti in the filler materials. The TiC particulates obviously relax the thermal stress in the heterogeneous joint resulting in an increase in shear strengths of the brazed joint. The maximum shear strengths of the brazed joints at room temperature, 500°C and 800°C are 145MPa, 70MPa and 39MPa, respectively. The shear strengths of the joints are remarkably higher than the optimal of the joints brazed with Ag–Cu–Ti.

Tribo-pair dependence of friction and wear moisture sensitivity for a-C:Si:Al carbon-based coating

Providing a low, predictable and stable friction as well as low wear for mechanical components across a wide range from dry to wet atmosphere is of great importance in many engineering applications, the urgent challenge is to control tribological moisture sensitivity of their protective coatings. In this paper, the a-C:Si:Al carbon-based coating was fabricated successfully using multifunctional magnetron sputtering system. The microstructure and mechanical properties of as-fabricated coating were investigated; especially the friction and wear of coating sliding against Si3N4, SiO2, GCr15, brass and aluminum counterparts were evaluated under different relative humidity atmospheres. Results showed that the as-fabricated a-C:Si:Al carbon-based coating presented typical amorphous microstructure and good combined mechanical properties. Under low relative humidity conditions, the graphitized carbon tribo-layers on the contact surfaces were responsible for low friction; under high relative humidity conditions, the low shear strength colloidal silica on the contact surfaces induced by tribo-chemical reaction were mainly responsible for low friction. In particular, the lowest tribological moisture sensitivity can be achieved by the a-C:Si:Al/SiO2 pair, which was mainly attributed to the formation of tribo-layers on the contact surfaces induced by the graphitization and tribo-chemical reaction under different relative humidity conditions. These indicate that the a-C:Si:Al carbon-based coating might be a good candidate as low tribological moisture sensitivity material in engineering applications.

ZnO nanowire co-growth on SiO2 and C by carbothermal reduction and vapour advection

Vertically aligned ZnO nanowires (NWs) were grown on Au-nanocluster-seeded amorphous SiO2 films by the advective transport and deposition of Zn vapours obtained from the carbothermal reaction of graphite and ZnO powders. Both the NW volume and visible-to-UV photoluminescence ratio were found to be strong functions of, and hence could be tailored by, the (ZnO+C) source–SiO2 substrate distance. We observe C flakes on the ZnO NWs/SiO2 substrates which exhibit short NWs that developed on both sides. The SiO2 and C substrates/NW interfaces were studied in detail to determine growth mechanisms. NWs on Au-seeded SiO2 were promoted by a rough ZnO seed layer whose formation was catalysed by the Au clusters. In contrast, NWs grew without any seed on C. A correlation comprising three orders of magnitude between the visible-to-UV photoluminescence intensity ratio and the NW volume is found, which results from a characteristic Zn partial pressure profile that fixes both O deficiency defect concentration and growth rate.

Thermal degradation mechanism, carbon precursor structure, and graphitization reaction of PMDA-ODA type polyimide

Thermal degradation mechanism, carbon precursor structure, and graphitization reaction of PMDA-ODA type polyimide

PREPARATION OF HIGH DILATABILITY EXPANDABLE GRAPHITE AND ITS FLAME RETARDANCY FOR LLDPE

To prepare expandable graphite (EG) with high anti-flame property for Linear low density polyethylene (LLDPE), dosages of oxidant KMnO4, intercalation reagent H2SO4 and ancillary intercalation reagent Na4P2O7 were optimized during oxidation intercalation reaction of natural graphite. EG with an initiation expansion temperature of 148 ± 2 °C and expansion volume of 550 mL/g can be prepared according to the mass ratio of C:KMnO4:H2SO4(98%):Na4P2O7 = 1.0:0.4:5.0:0.6 (H2SO4 should be diluted to the mass concentration of 80% before intercalation reaction), the reaction time is 40 min at constant 40 °C. Addition of 30% of the prepared EG to LLDPE can improve its limiting oxygen index LOI from 17.5% to 29.4%, and the synergistic anti-flame LOI of 20% EG with 10 polyphosphate (APP II) can reach to 31.2%. TG and DTA analysis were completed to discuss the anti-flame mechanism. 70%LLDPE/10%APP(II)/20%EG synergistic anti-flame system can cause higher residual carbon and lower material surface temperature.

PMDA-ODA型芳香族ポリイミドの熱分解機構，炭素前駆体構造とグラファイト化反応

PMDA-ODA型芳香族ポリイミドの熱分解機構，炭素前駆体構造とグラファイト化反応

Combination of mechanochemical activation and self-propagating behavior for the synthesis of nanocomposite Al 2O 3/B 4C powder

In this research, Al 2O 3/B 4C nanocomposite was successfully synthesized by combining of mechanically induced self-propagating reaction of aluminum, graphite and boric acid powders mixture. For this purpose the starting materials were activated in a planetary ball mill under Argon atmosphere. The structural evaluation of powder particles was investigated by X-ray diffraction, FTIR spectrometer and scanning electron microscopy (SEM). The effect of activation time on the combustion temperature and the reaction products was discussed based on STA experiments. The results indicated that the reaction between Al and B 2O 3 (aluminothermic reaction) is highly exothermic and should be in combustion mode. According to XRD analyses, the Al 2O 3/B 4C nanocomposite was fabricated after 4 h of high energy ball milling. Simultaneous thermogravimetric analyzer (STA) results showed that increasing the activation time to 3 h can decrease the temperature of combustion reaction to590 °C. SEM observations confirmed that the range of particle size was within 100 nm.