Intercalation of Graphite Fibers

Abstract

With 45 FiguresIntercalated carbon fibers are of interest for both applications and basic science. The availability of intercalation compounds in fibrous form opens up a number of scientific opportunities, many of which exploit the favorable geometry of fibrous samples. For example, the large aspect ratio (length/diameter) greatly improves the sensitivity of transport measurements such as resistivity, magnetoresistance, thermopower, and thermal conductivity, thereby allowing systematic investigations of these properties to be made in graphite intercalation compounds (GICs). For this reason, there is a strong connection between the study of transport properties in GICs (Chap. 6) and the present review of intercalated carbon fibers. For example, with fibrous intercalation compounds it has been possible to separate the lattice and electronic contributions to the thermal conductivity of GICs by measuring the thermal and electrical conductivities on the same fiber sample and invoking the Wiedemann-Franz law [8.1]. The small fiber diameters are of particular utility for structural studies using transmission electron microscopy, where observations can be made directly without thinning of the specimens. The small fiber diameters also allow preparation of compounds not readily synthesized in bulk form, such as stage-1 NiCl2 GICs.Among the examples of new science that has been explored through the availability of fibrous host materials are precision measurements of the unusual functional form of the temperature dependence of the resistivity of GICs in the low-temperature limit, exploiting the favorable geometry of fibers for highresolution studies. Closely related are the weak localization studies of transport properties of GICs, exploiting the two-dimensionality of fibrous acceptor compounds, and the ability to control the degree of disorder in the sample by control of the heat treatment temperature and the general fiber microstructure. Studies of the "metal-insulator" transition in ammoniated alkali-metal GICs have also exploited the favorable fiber geometry for transport measurements [8.1].From an applications standpoint, many of the applications of intercalated carbon fibers exploit the high specific conductivity of GICs, which can be expressed as a figure of merit in terms of the conductivity (J divided by the mass density {}m' which for a good conductor like copper is ,..., 6 X 10-2 cm 2 /g¢l. Composite wires based on graphite intercalation compounds can be formed by packing GIC powder into a Cu or Ag tube, which is cold-worked down to a thin thread of suitable diameter [8.2]. However, then the light weight performance is severely reduced by using the metal cladding. The high conductivity of individual small flakes of crystalline graphite is not reflected in the final conductivity

Microscopic Analysis of the Different Perchlorate Anions Intercalation Stages of Graphite

“…Blisters are known to evolve due to the development of CO, CO 2 , and O 2 − produced during the oxidation of the graphite. In panels a–d, a blister is clearly visible and it remains stable in the same position for ∼45 min.…”

“…Chlorate anions, surrounded by water molecules (solvated anions), percolate within the graphite crystal through defects on the surface and inside the stratified crystal. At relative high electrochemical (EC) potentials, oxidation occurs and is accompanied by the formation of gas (namely, CO, CO 2 , O 2 ), which swells the uppermost graphite layers and produces blisters on the electrode surface. − The presence of solvated anions in the graphite interlayer spaces screens the layer–layer interaction favoring crystal delamination; the latter usually occurs after a gentle sonication, which results in an electrolyte containing small graphene flakes (lateral size of the order of several micrometers) . Currently, this electrochemical protocol represents one of the cheapest ways to produce large amounts of graphene sheets.…”

CVD Graphene/Ni Interface Evolution in Sulfuric Electrolyte

“…The HOPG electrode properties, when immersed in diluted sulfuric acid, have been widely investigated. − In Figure , we report a traditional CV from cathodic to anodic EC regions where the Faradaic current, flowing through the HOPG electrode, is measured as a function of the applied EC potential referred to the standard hydrogen electrode (SHE).…”

Electrokinetics of Carbon Fibers Produced by a Direct Oxyfluorination

“…Carbon fibers are widely used as reinforcements in composites, especially in composites with epoxide matrices and of potential importance due to their real applications. They combine a high stress factor and strength with a low density, which has led to their increasing use in high-performance construction materials. , …”