Graphite Interlayer Research Articles

Intercalation reactions in CuCl2-FeCl3 system

The intercalation reactions in CuCl2-FeCl3 system were studied by gravimetric analysis, X-ray powder diffractometry and energy dispersive X-ray spectroscopy (EDS). The reactions between graphite and a mixture of CuCl2 and FeCl3, between CuCl2-GIC's and FeCl3, and also between FeCl3-GIC's and CuCl2 were examined at 300 and 550°C.At 300°C, where the de-intercalation of CuCl2 or FeCl3 from their GIC's in a sealed tube was negligibly small, it was found that FeCl3 is intercalated into vacant graphite galleries and also exchanged with CuCl2 existing in graphite interlayer spaces, while CuCl2 can be merely exchanged with FeCl3 in graphite interlayer spaces. At 550°C, however, the de-intercalation of the intercalates, the intercalation of CuCl2 or FeCl3 into the vacant graphite galleries and the exchange reaction between FeCl3 and CuCl2 proceeded simultaneously. The formation of a molten salt in the CuCl2-FeCl3 system was observed, which seemed to lower the reactivities of CuCl2 and FeCl3 to graphite. The results of the line analysis by EDS showed that CuCl2 and FeCl3 intercalated seemed to coexist in separated domains. From the present results, the following four processes seemed to affect the formation of the ternary GIC's (Fig. 2); (1) exchange reaction between intercalates and reagents, (2) intercalation of reagents into vacant graphite galleries, (3) de-intercalation reaction from the starting GIC's and (4) formation of molten salt which seemed to lower the reactivities of metal chlorides.

ChemInform Abstract: Electrochemical Synthesis of Graphite Intercalation Compounds with Nickel and Hydroxides.

Abstract Graphite intercalation compounds (GIGs) with nickel and iron hydroxides were synthesized from the corresponding GICs with metal chlorides by galvanostatic oxidation and also by repeated charge-discharge cycles in an alkaline secondary battery with KOH aqueous solution. The stage-one structure in the original chloride-GICs was found to disappear after the first charge-discharge process and the compounds kept the stage-two structure. A gradual increase in the capacity of the battery with charge-discharge repetition suggests a slow replacement of chloride ions by hydroxide ones in the graphite interlayer space.

Electrochemical synthesis of graphite intercalation compounds with nickel and hydroxides

Graphite intercalation compounds (GIGs) with nickel and iron hydroxides were synthesized from the corresponding GICs with metal chlorides by galvanostatic oxidation and also by repeated charge-discharge cycles in an alkaline secondary battery with KOH aqueous solution. The stage-one structure in the original chloride-GICs was found to disappear after the first charge-discharge process and the compounds kept the stage-two structure. A gradual increase in the capacity of the battery with charge-discharge repetition suggests a slow replacement of chloride ions by hydroxide ones in the graphite interlayer space.

Angle resolved photoemission spectroscopy of CsC 8: Evidence for a charge density wave localized at the surface

Detailed ARPES of single crystal CsC 8 at low temperature reveals several features whose k ∥ dispersion and intensity variation are inconsistent with the bulk structure. We propose that these are signatures of a new kind of charge density wave parallel to the cleavage plane, in which Fermi surface nesting is correlated to a change in local Cs density within the outermost graphite interlayer spaces.

Raman scattering study of the high-frequency graphitic intralayer modes in Li-graphite and the stage dependence of the mode frequency in donor graphite intercalation compounds.

Raman spectra of the high-frequency (\ensuremath{\sim}1600 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) graphite interlayer modes have been studied in several Li-graphite intercalation compounds (GIC's) ${\mathrm{LiC}}_{\mathrm{p}}$=6,12,17,18. In stage-2 ${\mathrm{LiC}}_{17}$ we have also used these modes to study the T=250 K reversible structural phase transition from high-T disordered to low-T ordered Li intercalate layers and found that a Raman singlet at room temperature evolves into an unresolved Raman doublet (or triplet) below the phase transition temperature. A careful line-shape study of the low-T spectrum could not clearly distinguish between these two possibilities. A triplet is consistent, however, with previous x-ray diffraction studies of the phase transition in the bulk. Raman spectra of ${\mathrm{LiC}}_{6}$ were obtained and found to be in good agreement with previous studies. Spectra of pure stage-2 ${\mathrm{LiC}}_{12}$ were recorded for the first time. The high-frequency graphitic intralayer mode frequencies obtained in this work, together with other previously published data, indicate that a ``universal'' linear relation between mode frequency and reciprocal stage index does not exist in donor-type GIC's. That is, well outside of experimental error, the Li results show clearly that several factors (i.e., intercalate layer order, charge transfer, etc.) all make significant contributions to the small fractional change (\ensuremath{\sim}0.5%) observed in the graphitic mode frequencies. The net effect of all factors in the graphitic intralayer mode frequency is not well parametrized by the stage index alone.

Interlayer states in graphite and in alkali-metal-graphite intercalation compounds

The character of the first unoccupied band in the graphite intercalation compound ${\mathrm{LiC}}_{6}$ is examined. Based on a framework of interacting nonorthogonal states, an analysis of previous band-structure results shows that this band can be interpreted as a hybrid of Li $2s$ and graphite interlayer states.

Structural and electrical properties of intercalated and ion-implanted highly ordered graphite fibers

Because of their high degree of structural order, high mechanical strength, and small diameter (\ensuremath{\sim}1 \ensuremath{\mu}m), benzene-derived graphite fibers provide an excellent host material for a structural analysis of both the intercalation and ion-implantation processes in graphite. Using the $c$-axis lattice imaging technique, with a high-resolution electron microscope, we observe well-staged intercalated regions in this fiber matrix. With regard to ion implantation, we find a distribution in the density of lattice defects with depth from the fiber surface. Ion implantation is also found to increase the graphite interlayer spacing. This information is correlated with electrical properties of these fibers.

カリウム‐黒鉛‐テトラヒドロフラン三元層間化合物の生成反応

The reaction of the first-stage potassium-graphite intercalation compound, KC8, with aromatic hydrocarbon molecules of benzene, phenanthrene, anthracene and benzophenone in tetra. hydrofuran (THF) and formation of ternary intercalation compound of potassium-graphiteTHF were examined. Starting material, KC8, was prepared from the powder of Ceylon natural graphite. The formation reaction is divided into three steps, as shown in Table 1 in the case of phenanthrene. The first step is electron transfer from KC8 to phenanthrene and closely related with the electron affinity of aromatic hydrocarbon used. The second step is the formation of stable ion pair by the coordination of THF. The third step is the penetration of THF molecules into graphite interlayers to result in ternary compound such as KC24(THF)2.

An Appraisal of the Effect of Graphite Interlayers on the Tolerance of Water Reactor Fuel Rods to Power Ramp Defects

As a result of a post-irradiation metallographic study of power-ramped Canadian natural uranium, heavy-water-moderated and -cooled power (CANDU) reactor fuel rods, it was recently concluded that the observed beneficial effects of graphite CANLUB coating on CANDU fuel’s tolerance to power-ramp defects stem primarily from the interaction of the coating with fission products, rather than by lubrication of the fuel-cladding interface. These arguments are based on a consideration of fuel cracking patterns and the assumption that stress corrosion crack growth within the cladding is the controlling event in the failure process. While these arguments are examined in detail, the present reappraisal leads to the same view of the primary origin of the beneficial effects of graphite coatings on CANDU fuel rod performance.

Sorption of Molecular Hydrogen by Potassium Graphite

WE report here the new type of sorption of hydrogen by graphite-potassium intercalation compounds. The sorption of hydrogen by C8K and C24K, previously reported by Herold1, takes place at room temperature and above and may be regarded as either chemisorption (C24K) or hydride formation (C8K). We observed another type of sorption, of a physical nature, at lower temperatures 90 K and below. Volumetric measurements on C8K and C24K show that this physical sorption may be due to the intercalation of molecular hydrogen into the graphite interlayers.