A comparison of the bromination dynamics of various carbon and graphite fibers

The electrical resistance of four grades of pitch-based graphite fibers (Amoco P-55, P-75, P-100 and P-120), and three experimental organic vapor-derived fibers (General Motors, GA Technologies and University of Nebraska) was recorded in situ during bromination and subsequent exposure to ambient laboratory air. The results of this study indicate that the least graphitic pitch-based fiber (P-55) does not brominate to any significant extent, and that bromination and debromination reactions proceed much slower for vapor-derived fibers than for pitch-based ones. While this decreased reaction rate may be due in part to the larger diameter of the vapor-derived, the majority of the effect can probably be attributed to the differences in graphene plane orientation between the fiber types. Although the reactions are slower in the vapor-derived than in the pitch-based fibers, the extent of reaction as measured by the change in electrical resistance is essentially the same, with comparable (or larger) decreases in resistivity. In both the vapor-derived and pitch-based fibers, bromination reaction proceeds with one or more plateaux in the resistance versus time curves, which suggests staging and strengthens the argument that these fibers produce true intercalation compounds.     

Some potential applications for intercalation compounds of graphite with high electrical conductivity

Intercalation compounds of graphite of the acceptor type have potential engineering applications because of their attractive electrical conductivity properties. Two kinds of applications are considered in this paper. The first concerns a composite, formed by enclosing an intercalation compound synthesized from high quality crystalline graphite in a matrix of copper. With this form of composite it is found that there are both intrinsic and extrinsic advantages pertaining to the use of a material that has a conductivity higher than and a density lower than that of copper. The second form is a composite compound of intercalated graphite fibers contained in a matrix of epoxy. Extraordinary advantages in this case result from the fact that while intercalation of the fibers produces an order of magnitude increase in their electrical conductivity, when these fibers are incorporated into an epoxy matrix, the composite conductivity is increased by two orders of magnitude over its pristine fiber counterpart. It is projected that these desirable electrical conductivity characteristics portend large scale uses for the acceptor compounds of graphite as substitutes for the present standard conductors, and as a way of upgrading the performance of carbon/graphite materials.     

Synergetic Effect of Discontinuous Carbon Fibers and Graphite Flakes on Thermo-Mechanical Properties of Aluminum Matrix Composites Fabricated by Solid–Liquid Phase Sintering

Metals and Materials International - Aluminum (Al) matrix composite materials reinforced with graphite flakes (GF) and pitch-based carbon fibers (CF) were fabricated by solid–liquid phase...     

Electrodic characteristics of various carbon materials for lithium rechargeable batteries

Electrodic characteristics of various carbon materials have been investigated to study the correlation between structures of carbon materials and performances of negative electrodes of lithium rechargeable batteries. In the case of highly graphitized carbon materials, the discharge capacity was determined mainly by their crystallinity with no dependence on textures and natural graphite; the highest graphitization at about 360 mAh/g was stage-1 lithium-intercalated graphite, C₆Li (theoretical maximum 372 mAh/g). The coulombic efficiency at the first cycle was strongly dependent on the textures of the carbon materials, and pitch-based carbon fiber of a radial structure showed an excellent coulombic efficiency over 96% by selecting appropriate electrolytes. The performances of the pitch-based carbon fiber were also excellent in the electrolytes consisting of mixed solvents containing propylene carbonate. On the other hand, the pitch coke heat-treated at 550 °C had an initial capacity over 550 mAh/g, which was beyond the theoretically maximum capacity of 372 mAh/g for C₆Li, although the capacity decreased rapidly to less than 250 mAh/g within ten cycles. Polyacrylonitrile (PAN)-based carbon fiber showed a stable capacity with cycling over 350 mAh/g in spite of low graphitization. The initial coulombic efficiency seemed to increase in accordance with decrease of hydrogen and oxygen in the pitch coke, and oxygen and nitrogen in the polyacrylonitrile (PAN) fibers. These phenomena seemed to suggest that carbon materials of disordered structure would have higher capacity than that of the graphitic carbon materials.     

Synthesis and characterization of lithium-carbon compounds for hydrogen storage

Three carbon materials were prepared for the synthesis of Li-C compounds, such as Li intercalated graphite. The materials were as-received high purity polycrystalline graphite (G), graphite milled under a hydrogen atmosphere (HG), and graphite milled an argon atmosphere (AG). With respect to the difference for them, HG preserved a better crystalline structure than AG. Each material was milled with Li, where the products are denoted as Li-G, Li-HG, and Li-AG. In XRD patterns of Li-G and Li-HG, the peaks corresponding to LiC₆ and LiC₁₂ were revealed, while no peaks were observed in the case of Li-AG. However, the formation of lithium carbide Li₂C₂ was suggested for Li-AG by a thermal analysis under an inert gas. After the hydrogenation, LiH was formed for all the compounds, and graphite was recovered for Li-G and Li-HG. Each hydrogenated compound desorbed H₂ with different profile by heating up to 500 °C. As a reaction product, Li₂C₂ was formed for the hydrogenated Li-HG and Li-AG. In the case of the hydrogenated Li-G with better crystalline structure, Li intercalated graphite were formed after the dehydrogenation. Therefore, it is concluded that the hydrogen absorption and desorption process of Li intercalated graphite was different from those of Li₂C₂.     

A theoretical study of the electronic properties of intercalated graphite

We present the results of electronic structure calculations for first and second stages of lithium intercalated graphite (LiC₆ and LiC₁₂). The various stages of Li intercalated graphite all have hexagonal symmetry, where different carbon layers are stacked with C-atoms directly on top of each other (AIAI…), as opposed to natural graphite where the C-layers are staggered (ABAB…). All our calculations have been performed within the framework of the extended tight binding method with Gaussian type basis sets. From the orbital and total densities of states, we conclude that Li-2s electrons are transferred into carbon π-bands. This results in shifting the Fermi level into the region of high density of states (compared with pure graphite) and, hence, to observed metallic behavior. The calculated density of states for LiC₆ and LiC₁₂ is 0.25 and 0.12/(eV C-atom), respectively. Recall that for pure graphite the value is nearly zero and for copper it is 0.29. We also found it instructive to obtain the electronic structure of LiC₆ and LiC₁₂ based on a rigid band model.     

Synthesis of ternary intercalation compounds of carbon fiber

Ternary intercalation compounds of carbon fiber (ICCF) were successfully synthesized by soaking pitch-based carbon fibers in solvents such as 1,2-dimethoxyethane (DME) or tetrahydrofuran (THF) containing dissolved alkali metals (lithium, sodium, or potassium). ICCF with stage-1 and random stage was synthesized in alkali metal–DME and potassium–THF systems using different types of carbon fibers. However, ICCF with stage-1 could not be synthesized in lithium– or sodium–THF systems using carbon fibers with a low graphitization degree. Furthermore, the influence of the graphitization degree in the synthesis of ICCF was discussed. The graphitization degree of the host carbon fiber, in addition to the dimensions and steric structure of the intercalated complex affected the formation of TICCF.     

Comparisons between A.C impedance behaviour of graphite hydrogenosulfate and p-doped (CH)x

An electrocapillarity approach has been proposed in previous papers for electrochemical intercalation of H₂SO₄ into graphite, which explains the high capacitive values (170 F/g) deduced from equilibrium potential charge curves or from low frequency a.c. impedance measurements (extending the double layer capacitance to the intercalated electrolyte — graphite interface).We propose here a similar view for GaCl₄⁻ intercalated (CH)_x; “switching” between doped and undoped (CH)_x may correspond to the faradïc like stage transformation of Graphite Intercalation Compounds (GIC), while a charging process of (CH)_x chains with counter-ions recalls the capacitive “overcharging” of pure-stage GIC.     

Ferromagnetic resonance study of reduced NiCl2 graphite intercalation compound

A commercial reduction compound of graphite intercalated with NiCl₂ has been investigated by FMR. The X-band measurements for 573 ? T ? 3.5 K and Q-band for 293 ? T ? 150 K show the presence of metallic Ni and some unreduced NiCl₂. The Ni resonance signals have very large linewidths, δH_pp ～ 1800 ? 2000 Oe for 300 ? T ? 150 K. Analysis of the lineshape indicates that Ni remains intercalated in the graphite. The intercalated Ni exhibits a Curie temperature which is approximately 50 K lower than that of bulk Ni. The NiCl₂ X-band signals observed for 150 ? T 3.7 K show a maximum in intensity and linewidth at about 15 K, which is attributed to thermally induced magnetic excitations in the remaining finite NiCl₂ clusters. An in-plane exchange constant, J/k = 15 K, is estimated for NiCl₂ from the temperature dependence of the signal intensity.     

Structure and electrical conductivity of graphite fibers prepared by pyrolysis of cyanoacetylene

Highly electroconductive graphite fibers are prepared by the pyrolysis (CVD) of cyanoacetylene on the surface of carbon fibers, followed by heat treatment. Many thin graphite strata, cylindrically layered and scrolled around an axial core of the original carbon fiber, are observed. The lattice constant C₀ of the graphite fiber obtained from cyanoacetylene and heat-treated at 3000 °C is 6.712° (002), which is smaller than that of a graphite fiber from benzene. The magnetoresistance of graphite fibers obtained from cyanoacetylene is as high as 800% (4.2K, 15 kG) (HTT 3300 °C), while that of graphite fibers obtained from benzene is around 150%. Measurements of Raman scattering and X-ray diffraction also show that cyanoacetylene forms more highly graphitized fiber than benzene. Cyanoacetylene is a good starting material for synthesizing graphite. The room temperature conductivity is as high as 1.8 × 10⁴ S/cm for fiber heat treated at 3250 °C. Treatment of the graphite fiber by fuming nitric acid increases the conductivity up to 1.3 sx 10⁵ S/cm in less than 10 min. Upon exposure of the nitrated fiber to air at ambient temperature, the conductivity decreases slightly. After this slight decrease, the conductivity is stable for at least 90 days.     

石墨烯纤维研究进展

石墨烯纤维是2011年才发展起来的一种以天然石墨为最初原料的新型碳质纤维,由石墨烯或者功能化石墨烯纳米片的液晶原液经湿法纺丝一维有序组装而成。石墨烯纤维具有良好的机械性能、电学性能和导热性能,可用于导电织物、散热、储能等领域。将其他物质引入石墨烯纤维中还可得到特定功能的石墨烯复合纤维,如将聚合物加入石墨烯纤维得到结构精巧、力学性能良好的石墨烯仿贝壳纤维;将磁性纳米粒子加入得到磁性的石墨烯复合纤维;加入Ag纳米线得到高导电的石墨烯复合纤维。石墨烯纤维良好的柔韧性使其在柔性器件如柔性超级电容器等领域得到应用。综述了石墨烯纤维的研究现状,对纯石墨烯纤维、石墨烯复合纤维的制备和应用进行了详细的阐述,并对石墨烯纤维的发展方向进行了展望。     

Orientation of nitric acid molecules in graphite nitrate

A new model for HNO₃ intercalation into graphite is proposed. It was supposed that nitric acid forms double parallel layers between the graphit ic network. The new model is characterized by X-ray methods on the 00l line intensity. It is shown that the nitrate molecules are intercalated perpendicular to the graphite planes. The crystallographic stoichiometry gives C_4.3nHNO₃ for the n^th stage.     

Intercalation of polypyrrole into graphite oxide

In this paper we report on the insertion of polypyrrole into layered graphite oxide. This was achieved by using the exfoliating and re-stacking properties of the host. The resulting intercalated product was characterized by powder X-ray diffraction, FT-IR spectroscopy, thermogravimetric analysis and scanning electron microscopy.     

X-ray photoelectron spectroscopy studies of SbF5 intercalated graphite

Two samples of graphite intercalated with SbF₅ have been studied by X-ray photoelectron spectroscopy (x.p.s.). In each case two fluorine (1s) peaks were observed, with binding energies 685.0 eV and 688.0 eV. The peak at 685.0 eV is attributed largely to volatile, quasi-liquid SbF₅ present in the interlayer. The peak at 688 eV is assigned to involatile SbF₆^? ions located at fixed sites in the interlayer, the fluorine atoms undergoing strong polarization interaction with the graphite lattice. Changes observed in carbon (1s) and antimony (3d_{$\text{5}\text{2}$}) spectra are consistent with these assignments.     

Electrochemical intercalation of bromine into graphite in an aqueous electrolyte solution

By electrochemical oxidation of a graphite sheet in an aqueous solution of potassium bromide, the intercalation of bromine was observed. It was confirmed by the measurements of weight increase of about 10%, decrease in relative electrical resistivity down to 0.69, and enlargement of average interlayer spacing. On the graphite sheet pre-electrolyzed in KBr solution, the chronopotentiogram in K₂SO₄ aqueous solution showed some plateaux corresponding to the reduction of graphite intercalation compounds with bromine. The longest time on a plateau was observed on the graphite sheet pre-electrolyzed in a potential region of bromine gas evolution, where the most pronounced decrease in electrical resistivity of graphite sheet was detected.     

Formation Process of FeCl<Subscript>3</Subscript>-NiCl<Subscript>2</Subscript>-Graphite Intercalation Compounds

The intercalation reaction of NiCl₂ from the mixture of FeCl₃ and NiCl₂ has been studied by using natural graphite at a wide range of residence times from 1 to 24 h. The microstructure changes of reaction products were investigated by XRD, SEM, and EDS, and the formation of ternary FeCl₃-NiCl₂-GICs was confirmed. In the process FeCl₃ was found to be intercalated preferentially at the initial stage of the intercalation, and set up the framework of the stage domain of GICs. Then NiCl₂ intercalated along the channels cut by FeCl₃. The diffusion rate and distribution uniformity of NiCl₂ controlled the rate of the intercalation reaction and the ternary grade of the FeCl₃-NiCl₂-GICs.     

Are ferric chloride intercalated graphite compounds air stable?

Mössbauer spectroscopy has been used as a tool to analyze the effect of long term exposure to air on ferric chloride intercalated graphite samples. After periods of about a year three phenomena occur in sequence: there is a migration of some FeCl₃ from the sample, some of the FeCl₃ is converted into (FeCl₄)^? and finally the sample becomes unstaged.     

Influence of adding carbon nanotubes and graphite to Ag-MoS2 composites on the electrical sliding wear properties

Silver matrix composite brushes were fabricated by means of powder metallurgy, which included pressing at 300 MPa and then sintering for 1 h in pure H₂ protective atmosphere at 700 ℃ and repressing at 500 MPa. Four kinds composites with different compositions were produced, and the mechanical properties and electrical wear performance were investigated. The results showed that the composite added with carbon nanotubes had a higher hardness and strength, a lower contact voltage drop and an excellent anti-wear property in electrical sliding wear, because of the reinforcement ability of carbon nanotubes. Adding graphite to the composite also decreased the wear loss and contact voltage drop, because graphite had an electrical current conducting ability which not only made the current pass the lubricating films easily but also eliminated and reduced the arc and spark effectively.     

MoCl5 intercalation into carbon fibers

The host effect on the intercalation of MoCl₅ was studied using vapor-grown (VGCFs), mesophase-pitch-based (MPCFs) and PAN-based carbon fibers (PANCFs) heat-treated to different temperatures. MoCl₅ successfully intercalated into VGCFs, but MPCFs and PANCFs showed no intercalation. MoCl₅ intercalated into 2000°C- and 2200°C-treated VGCFs having larger interlayer spacing than 2900°C-treated MPCFs where no intercalation was observed. The use of MoO₃ or MoOCl₃ with MoCl₅ found to affect the stage structure in VGCFs but was not able to perform intercalation in MPCFs and PANCFs. In VGCFs, the intercalation of MoCl₅ depends on the heat treatment temperature. Stage-1 structure in single phase was formed from 3000°C-treated VGCF with MoCl₅ and MoO₃ in the molar ratio of 1:1:0.37. SEM studies of stage-1 VGCF 3000°C-treated fiber showed the peeling of thin layers from the fiber surface and cleavage along the fiber axis of the fiber. Apparent diameter of fibers increased to roughly 3 times after intercalation.     

Synthesis and characterization of poly acrylic acid/graphite oxide nanocomposite

1　INTRODUCTIONOrganic intercalatedlayeredsolidshavebeenstudiedbyscientistsindifferentfieldsformanyyearsbecauseoftheirnew physicalandchemicalpropertiessuchaselectricalproperties[1] ,mechanicalproper ties ,thermalbehavior[2 ] ,surfaceandinterfacialproperties[3] .Graphiteoxide (GO)hasbeenstudiedformany years ,itsstructuralmodel[4 6 ] ,formationprocessandkinetics[7,8] havebeenstudiedindetail.IthasbeenreportedthatGOpossessesC OHande poxidefunctionalgroups[9] whichmakegraphiteox ideeasilyabs…