Graphite Layer Planes Research Articles

Prediction of elastic properties of carbon fibers and CVI matrices

The mechanical properties of carbon materials are highly dependent upon nanostructure and orientation distribution of graphitic layer planes. A model of deformations based upon theory of elasticity for anisotropic solids is proposed. Then it is used for prediction of elastic modulus and Poisson coefficient from intrinsic elastic constants for particles and orientation distribution of graphitic planes. It was applied to carbon fibers and to carbon matrices produced via Chemical Vapor Deposition based techniques. The orientation distribution of graphitic planes was determined using the distribution of intensity of X-ray scattering I( ϕ). The predictions were compared to Young’s moduli measured on single fibers and matrices deposited on single fibers (microcomposites). The results underline the key role played by the modulus for shear between the graphitic layer planes. Influence of graphitic layer Poisson coefficient and Young’s modulus and nanostructure parameters is discussed.

A study of carbon black Corax N330 with small-angle scattering of neutrons and X-rays.

Carbon black Corax N330 (hereinafter called CB) is used as a filler in elastomers. The properties of the surface are important for the binding of the elastomer to the carbon black particles. Porod's law requires the intensity to satisfy I(q) approximately q(-alpha) with alpha = 4 for large q. Rieker et al. observed alpha = 3.7 +/- 0.1 for small-angle X-ray scattering (SAXS) data and concluded that the particle surface is fractally rough. Ruland critized this and suggested that the observed deviation is due to fluctuations of the spacing of the graphitic layer planes ("graphenes") which contribute a component I(q)fluc = 1Cflucq(-2) to the intensity component satisfying Porod's law. We studied CB by nitrogen adsorption, high-resolution transmission electron microscopy, synchroton SAXS, and small-angle neutron scattering (SANS). Our SAXS experiments with samples of high transmission (Tr = 0.96) confirmed the form of the scattering curves published by Rieker et al., but the correction for I(q)fluc restored Porod's law. SANS experiments were performed with a sample of low transmission in order to analyze the high q-range for scattering from voids and isolated graphenes. We found I(q) approximately q(-beta) with beta approximately 2 at q > 2.5 nm(-1) and will show that this intensity component requires graphenes consisting of about 12 benzene rings. The contrast matching technique revealed the presence of inaccessible voids. The SANS data for a sample with Tr = 0.363 satisfy Porods law, in contrast to the SAXS data for the high transmission samples. The latter discrepancy is likely due to the lower resolution of the SANS measurements because of wavelength smearing and multiple scattering. A SANS sample with Tr = 0.97 shows a minor deviation from Porod's law only (alpha = 3.9). The original SANS data and the SAXS data corrected for the fluctuation component indicate that the CB surface is essentially smooth.

Carbon Nanostructure Examined by Lattice Fringe Analysis of High-Resolution Transmission Electron Microscopy Images

The dimensions of graphitic layer planes directly affect the reactivity of soot towards oxidation and growth. Quantification of graphitic structure could be used to develop and test correlations between the soot nanostructure and its reactivity. Based upon transmission electron microscopy images, this paper provides a demonstration of the robustness of a fringe image analysis code for determining the level of graphitic structure within nanoscale carbon, i.e., soot. Results, in the form of histograms of graphitic layer plane lengths, are compared to their determination through Raman analysis.

Structure, Raman scattering, and transport properties of boron-doped graphite

Boron-doped highly oriented graphite films (B-HOGF's) with an atomic fraction of boron from 0.4 up to 2.2 at. % have been prepared from well-crystallized, highly oriented graphite. The effect of boron doping on crystal structure has been investigated in terms of texture observation with a field-emission gun-type scanning electron microscope and by measurements of the x-ray diffraction and Raman scattering. The results indicate that in B-HOGF's, boron atoms substituted in the graphite lattice and induced disorder, which caused the Raman bands related to the disorder in graphite layer planes to appear. For each of the B-HOGF's, the temperature dependence of the resistivity in a range 1.8--300 K has been measured. The Hall coefficient and transverse magnetoresistance have also been measured at 3.0 K in a magnetic field range up to 4 T. The Hall coefficient data indicate that each of the B-HOGF's is a mixed crystal of graphite grains with and without boron atoms. The temperature dependence of the resistivity and field dependence of the transverse magnetoresistance for B-HOGF's show a characteristic that is possibly explained by a three-dimensional weak localization theory proposed by Sugihara Hishiyama, and Kaburagi.

Effect of Cross-Sectional Textures on Transverse Compressive Properties of Pitch-Based Carbon Fibers

The effect of the orientation texture of cross-sectional graphitic layer planes on transverse compressive properties was studied in pitch-based carbon fibers. The finite element analysis indicated that radially oriented fiber could be expected to display higher transverse modulus and lower transverse compressive strength than randomly oriented fiber. The transverse compressive test was carried out by means of direct pressing of single filaments in which each filament's strength and modulus were measured. The cross-sectional orientation texture was identified not only by observation under scanning electron microscope (SEM) but also by torsional modulus measurement. The transverse modules and transverse compressive strength were found to decrease with increasing crystallite size. It was however not possible to find out clear differences between radially and randomly oriented fiber. These transverse properties cannot therefore be attributed to differences in cross-sectional texture. Bonding between crystallites appears to be the dominant factor in determining the transverse modulus, while the strength in the central area of the cross section is expected to determine the transverse compressive strength of the filament.

Millennial Special Leading Papers on Ceramics in the 20<sup>th</sup> Century: the Best of JCerSJ Some Properties of PAN-Based Carbon Fiber

In the late 19th century, T. A. Edison, a great inventor, applied a carbon filament made from bamboo fibers grown in Kyoto to an incandescent lamp, which was one of the earliest technical applications of carbon fiber. The need for carbon fiber for use in military aircraft originated shortly after World War II in the U.S.A. as carbon fiber reinforced structural materials. Since the early 1950s, many varieties of reinforcing fibers have been developed and the UCC demonstrated high-performance carbon fiber made from rayon. However, its tensile strength and elastic modulus were not particularly high. A technical and commercial breakthrough for high-performance carbon fibers occurred in the mid 1960s-the production of carbon fibers from polyacrylonitrile (PAN) precursor fibers. This process proved to be more economical due to the lower cost of the PAN precursor fiber and the simpler process required to convert PAN fiber to carbon fiber. Shindo first reported the use of PAN as a precursor for carbon fibers. At that time almost no military application of engineering materials was considered in Japan. The history of these carbon fibers can be found in “Carbon Reinforcements and Carbon/Carbon Composites, ” by E. Fitzer and L. M. Manocha, Springer-Verlag (1998).Shindo's invention appeared as Japanese Patent No. 304892 (1963, applied for in 1959). His claim was a method of manufacturing carbon or graphite materials, which comprises heating PAN polymer up to 350°C in an oxygen-rich atmosphere followed by heating to a temperature above 800°C. The heating PAN fiber at lower temperatures in an oxidizing atmosphere does not cause melting or deformation of the fiber during subsequent heating. This heat treatment was referred to as a stabilization process and became a fundamental process for conversion of organic precursors to inorganic fibers.Shindo's paper describes, (1) the growth of crystallites in two kinds of PAN-based carbon fibers, (2) changes in the mechanical properties and (3) changes in the electrical resistance by heat treatment in the temperature range, 1000 to 3000°C. From the viewpoint of the remarkable development of carbon fiber applications subsequently, the available data on mechanical and crystallite growth must be significant. High grade of preferred orientation of graphite layer planes parallel to the fiber axis, which is shown in X-ray diffraction photos and electron diffraction pattern, could be due to the high-strength and high-modulus of the fiber. Furthermore, after heat treatment at a temperature as low as 1000°C, the fiber assumed significantly higher preferred orientation. This shows that a high-modulus carbon fiber can be more easily manufactured from PAN fiber than rayon-based fiber.The density of the carbon fibers vs. heat treatment temperature curve (Fig. 8) shows a fairly large increase above 2000°C. The electrical resistivity vs. heat treatment temperature curve (Fig. 9) shows three regions: a steep decrease below 1000°C, a slight decrease from 1000 to 2300°C and a very small decrease above 2300°C. Figure 10 shows that the tensile strength of the fibers decreases steadily from 5000-10000 to 2000-5000kgf/cm2 with raising heat treatment temperature from 1000 to more than 2500°C. The elongation at the breaking point decreases from 1 to 0.3% with raising heat treatment temperature, as shown in Fig. 12. Young's modulus, as determined from these curves, increases from about 11000kgf/mm2 at a heat treatment temperature of 1000°C to 15000kgf/mm2 at 3000°C with a maximum at 2000°C, as shown in Fig. 13. The content of the Shindo's paper appeared in Govt. Res. Inst., Osaka, Report No. 317 (1961) in English, which has been widely cited in many articles concerning carbon.

Vergleichende Untersuchungen zur Mikrostruktur von auf PAN-Precursoren basierenden Kohlenstoffasern: Ramanspektroskopie, TEM-Untersuchungen, Röntgendiffraktometrie / Examination of Microstructures of Pan-Precursor Based Carbon Fibres: Raman Spectroscopy, TEM-Investigations, X-Ray Diffractometry

The microstructure of T800 H and HMS-4 carbon fibres is investigated using Raman spectroscopy, TEM and X-ray diffractometry. The T800 H fibres were found to contain a high proportion of amorphous carbon, to have a mean crystallite size of 1.5 nm and to contain pores within the edge regions of the fibres. The HMS-4 fibres were found to consist of crystallites with a mean dimension of 7 nm. In the HMS-4 fibres, the graphite layer planes are arranged in loops or S-shaped fibrals and were not found to contain pores. Between aluminium and T 800 H fibres, aluminium reaction products are formed parallel to the fibre surface in the form of Al 3 C 4 - needles. Between aluminium and HMS-4 fibres, this phase is formed at an angle of ca, 45° to the fibre surface.

Tensile deformation of carbon fibers and the relationship with the modulus for shear between the basal planes

The tensile deformation of well-oriented carbon fibers has been investigated. It is shown that the relation between stress and strain can be described by the uniform stress model. Three parameters determine the modulus and the tensile curve: the in-plane modulus of the graphite plane e 1, the modulus for shear between the graphitic layer planes g, and the orientation distribution of these planes. Non-graphitized PAN-based fibers have a considerably higher shear modulus g than the pitch-based fibers. Results of structural studies indicate that this difference may be caused by covalent crosslinking. It is proposed that these crosslinks determine to a large extent the compressive strength of carbon fibers.

Discharge performance on the electrode of ternary intercalation compounds of graphite with metal hydroxides

The graphite intercalation compounds with metal hydroxides (metal hydroxide—GICs) were used as the cathode materials of an alkaline secondary battery. The performance of charge and discharge reactions on the electrode was characterized by activation energies for both reactions. The activation energy for the discharge reaction on the GIC electrode was lower than that on the conventional nickel hydroxide electrode. for a battery with a hydroxide—GIC electrode, it was shown tha the discharge curve had a well-defined plateau and also the overvoltage was small even in the discharge under a large current. The lowering of activation energy would strongly be related with the structure of the GIC, in which nickel hydroxide was held in between conductive graphite layer planes and charges transfer occured easily between intercalate and host graphite.

Studies on X-ray diffraction and Raman spectra of B-doped natural graphite

The structure of B-doped natural graphite has been investigated using X-ray diffraction and Raman scattering methods. The B-doped graphite has crystal lattice parameters different from those of pristine graphite. The a-axis is elongated and the c-axis contracted by B doping. Furthermore, B doping induces both an increase in intensity of the 1360 cm −1 Raman band and the appearance of a new Raman band at 1620 cm −1, accompanied by a gradual shift of the 1580 cm −1 Raman band to a higher frequency. It appeared that boron doping introduces a local distortion around substitutional B atoms within the graphite layer planes.

Relationship between residual resistivity ratio ρRT/ρ4.2K and transverse magnetoresistance in highly oriented graphite

Relationship between residual resistivity ratio ρRT/ρ4.2K and maximum transverse magnetoresistance (Δρ/ρ) max at 77 K and fields up to 1 T was investigated in a wide range of ρRT/ρ4.2K values for a large number of highly oriented graphite samples, i. e. kish graphite (KG) and highly oriented pyrolytic graphite (HOPG) samples. Relationship between ρRT/ρ4.2K and anisotropy factors γT and γTL, which represent the degeree of deviation from single crystal ordering of graphite layer planes, was also studied. For KG samples values of γT and γTL are very small (<0.02), and there is no correlation between ρRT/ρ4.2K and γT and γTL for KG samples, while for HOPG samples γT and γTL increase with decreasing ρRT/ρ4.2K. Plots of (Δρ/ρ) max at 77 K and 1 T against ρRT/ρ4.2K show some scatter, but the correlation is clearly good, and (Δρ/ρ) max shows a trend of saturation at large values of ρ4.2K . It can be experimentally shown that this trend is due to the limitation to the mean relaxation time of the carriers by carrier-phonon scatteringin highly oriented graphite even at 77 K.

Electrochemical Formation of Graphite‐Sulfuric Acid Intercalation Compounds on Carbon Fibers

The cyclic voltammograms in 98% were measured on the mesophase‐pitch‐based carbon fibers heat‐treated at various temperatures. They showed a marked dependence on the heat‐treatment temperature of the carbon fibers. The electrochemical formation of graphite‐sulfuric acid intercalation compounds was confirmed by x‐ray diffraction. The change of graphite layer planes in the carbon fibers due to electrolysis was examined by Raman spectra.

Adsorption on packed bed electrodes

The potential-dependent sorption which occurs on a graphite surface is quite different from that on metals and permits a wide range of materials from molecules to bacteria to be sorbed. The active sites for this process are the edges of the graphite layer planes where the pK of the surface functional groups is modified by the applied potential to control the sorption in a manner analogous to that on an ion exchange resin.

Syntheses of transition metal-graphite-organic molecule ternary compounds

Ternary graphite intercalation compounds of transition metal and organic molecule were synthesized by the reaction between KC8 and transition metal chloride in an organic solvent. The first-stage graphite intercalation compounds of either Co or Fe and tetrahydro- furan (THF) had the identity period lc of 8.9 A. The second-stage compound with lc = 12.6 A was also obtained. The compound of Co-graphite-dimethoxyethane (DME) with lc = 12.2 A was synthesized in DME solution. All of these compounds were attracted by a magnet through the glass wall of flask. The magnetic residue compound which was stable in air was prepared from the ternary intercalation compounds by washing repeatedly with water and then heating to 100 °C under evacuation. From the experimental results — large content of Co up to 33 wt % and no aggregation of Co under XMA, magnetic properties (saturation magnetization of about 6.6 emu/g and attracted by making their basal plane parallel to the magnetic field) and exfoliated above 200 °C — it was concluted to be a ternary residue compound which contains an effective amount of cobalt and THF between the graphite layer planes.

Graphite filaments and their alkali-metal intercalation compounds

A new type of carbon filaments, each about 20 cm long and 7 μm in diameter, have been grown from purified graphitic material in argon plasma. The filaments heat-treated at 3000°C and at 3400°C were found to consist of the concentric stacking of graphitic layer planes, all the individual c-axes being perpendicular to the filament axis. The heat-treated filament forms intercalation compounds of K, Rb and Cs: the first-stage compounds of brilliant golden luster and the second-stage compounds of dark blue luster. The electrical resistivities were found to be 1300, 610–660, 23–25 and 28–30 μω cm at 300 K for the original filament, the heat-treated filament, the first-stage compounds, and the second-stage compounds, respectively.

Effect of high-temperature neutron irradiation on the crystallites of graphite materials

Changes in crystal lattice parameter, c-axis lattice strain and apparent crystallite height induced by neutron irradiation at 720–1350°C were investigated by means of X-ray diffraction for fourteen specimens which included five bands of nuclear graphite and two kinds of pyrolytic graphite. All irradiated materials show a marked increase in c-axis lattice strain, while changes in the lattice parameters are very small. The relation between lattice strain and layer spacing was analyzed for pre- and post-irradiated graphites, and it is inferred that, whereas the predominant constituent of strain in the unirradiated graphite is the statistical fluctuation in distribution of layer spacings, for the irradiated material it is the distortion of layer planes. On the basis of the relation between c-axis lattice strain and apparent crystallite height, the stacking height of graphite layer planes is estimated to be about 70 Å for pre-irradiated graphite.

Interpretation for the micropore diffusivities of gases in molecular-sieving carbon

Physical interpretations were tried for the experimental data on micropore diffusivity of gases in molecular-sieving carbon (MSC) reported by the authors elsewhere. Micropore diffusion is so-called activated diffusion in the space between graphite layer planes and diffusion coefficient is expressed as D = D 0 exp( −E/RT). The experimentally determined D 0 for Ar, Kr, Xe, N 2, and CH 4 agreed with D 0 estimated theoretically from the activation energy, E, and structural parameters of MSC by using the absolute rate theory. The isosteric heats of adsorption, q st , and E are compared with those calculated on the basis of Lennard-Jones potential with London expressions for the space between two graphitized carbon surfaces. The values of q st and E for Ar, Kr, and Xe suggested that the distance of the two graphite layers was 4.4 ± 0.1 Å.

Magneto-optical studies of graphite intercalation compounds

High field magnetoreflection measurements are reported on the first observation of interband Landau level transitions in residue and lamellar compounds of graphite intercalated with the halogens Br 2, IBr and ICl. These magnetoreflection spectra are interpreted to yield a model for the magnetic energy level structure of these intercalation compounds in the dilute limit corresponding to stage ≳5. In this dilute limit, the insensitivity of the magnetoreflection resonances to intercalate concentration shows that near the Fermi level for pure graphite the electronic structure of the intercalation compounds is essentially independent of intercalate concentration. This conclusion results from analysis of both infrared and far-infrared magnetoreflection spectra for Landau level transitions within ±0.1 eV of the graphite Fermi level. The model for the electronic structure deduced from the magnetoreflection spectra is supported by Raman scattering results presented for the in-plane lattice modes of carbon atoms in the graphitic layer planes.

Raman spectra, effective Debye parameter and magnetoresistance of graphitized cokes

The Raman intensity ratio R ( I 1360 I 1580 ), the effective Debye parameter B eff and the maximum transverse magnetoresistance ( Δρ ρ ) mx at liquid nitrogen temperature and 10 kG were measured on various cokes heat-treated at high temperatures. The observed values of R, B eff and ( Δρ ρ ) mx are closely related with each other and are discussed in relation to the lattice defects in the graphite layer planes. The plot of R against B eff shows a linear relation, suggesting that both parameters are related to projections along a- and c-axes respectively of the same carbon atom displacement due to lattice defects. With decreasing B eff , ( Δρ ρ ) mx increases gradually but almost linearly with B eff and then rapidly. This behavior has been interpreted by an analysis based on a simple two band model.

High‐resolution electron microscopy of high‐modulus carbon fibres*

SummaryHigh‐resolution electron‐microscope images of high‐modulus carbon‐fibre fragments have been recorded under conditions which allow resolution of the individual 0.34 nm graphite layer planes. Extinction bands previously observed at low resolution are now seen to originate from several different structural features. Single bands are caused by lattice distortion due to non‐basal edge dislocations and low‐angle boundaries of tilt or twist character; periodic bands are the result of Moiré effects from overlapping or interlinked crystallites. Accurately controlled tilting experiments give further insight into the complex interlinked nature of the crystallites and the results are summarized in terms of a model which is also capable of explaining the partial recrystallization observed with boron doping.