We review the observational evidence for the widespread existence of hydrogenated carbon dust in astronomical environments. Photoluminescence by such materials appears strongly enhanced in regions where additional hydrogenation becomes possible, e.g. through the photodissociation of abundant molecular hydrogen. Recent laboratory experiments have demonstrated that rehydrogenation of previously annealed hydrogenated amorphous carbon (HAC) does indeed restore the photoluminescence, and furthermore, hydrogenation of pure amorphous carbon leads to characteristic HAC photoluminescence, which can be further enhanced by UV irradiation. Present evidence suggests that hydrogenated amorphous carbon may represent a significant fraction of the interstellar dust mass in the Milky Way Galaxy.

Flat glassy polymeric carbon samples were prepared from phenolic resin by three techniques: spray coating, spin coating and molding. Cured at 110°C-180°C and pyrolyzed in argon at 600°C or at 1000°C, samples then were studied by RBS for trace impurities, by ESCA for surface oxidation and contamination and by Raman microprobe of the top surface and perpendicular to that for preferred orientation of aromatic ribbons. An increase of 13% to 24% in the relative area under the corresponding Raman peaks indicates increased orientation of the ribbon-like aromatic molecules in the sprayed and spin coated samples as compared with the molded sample.

Slow defluorination of graphite fluoride fibers during nitrogen heating produces both graphitized carbon fibers having high defect density and a yellow film which may contain fullerenerelated materials. The carbon fibers thus obtained can pick up some copper and form aluminum composite during direct molten metal exposure. Explosion of graphite fluoride fibers during quick nitrogen heating produced amorphous carbon containing very little fluorine. They cannot be wetted by copper, but pick up some aluminum during direct molten metal exposure. By either spreading the graphite fluoride fibers apart or adding a small amount of bromoform into the graphite fluoride fibers before the quick nitrogen heating, the possibility of explosion can be reduced.

Partially cured and cured PF-resin samples were prepared at 150°C, 170°C and at 200°C in an inert environment and then bombarded by MeV ion beams using protons, alphas and nitrogen. Using low ion beam current density, 100 to 500 pA/mm2 for the nitrogen ions, 10 to 20 nA/mm2 for the alpha ions, and 50 to 500 nA/mm2 for protons, we have produced buried carbon layers without breakdown i.e., crack formation. The thicknesses of the carbon layers produced were of the order of a few tens of nanometers at a depth of a few nanometers to several micrometers depending on the energy, the type of bombarding ions and the curing temperature of the precursor. The electrical resistivity of these layers was measured in situ and was reduced from 109 Ω-cm to 10 Ω-cm. The lowest resistivity, 10 Ω-cm, was measured in the alpha bombarded, 150°C heat-treated resin. The carbonized volumes were analyzed by Raman microprobe spectroscopy which showed that the strongest graphitic (G-line) and distorted (D-line) Raman signals observed were from the nitrogen and alpha irradiated samples.

Reactions between Ni and amorphous carbon (a-C) below 600°C have been investigated using differential scanning calorimetry (DSC) and in situ annealing in a transmission electron microscopy (TEM) of Ni/a-C layered films deposited by DC sputtering. DSC data show that there are two exothermic peaks in the temperature range around 200-600°C. One is a weak and broad peak below 500°C and the other is a strong and sharp peak at around 530°C. In situ heating in the TEM revealed that the low temperature peak corresponds to a series of reactions for nickel carbide (Ni3C) formation and decomposition into Ni and carbon, most likely in a glassy state. The higher temperature peak was found to correspond to graphitization of a-C by a solution-precipitation mechanism. Graphite formed in this process is strongly textured with the (0002) graphite basal planes parallel to the original Ni/a-C interface.

The present work reports on the properties of nitrogen rich carbon films produced by an intense gas discharge between carbon electrodes in a nitrogen atmosphere. The energy of the discharge, initial nitrogen pressure, number of discharges and geometry are varied to establish their effect on the nitrogen content and the mechanical, structural and morphological characteristics of the deposited carbon-nitride films. The structural diagnostics include optical and scanning electron microscopy, as well as Auger and Raman Spectroscopes and Rutherford Backscattering. The C-N films formed fell into two categories, differing in morphology and mechanical properties. Type I are C-N films, containing up to 35 at. % nitrogen, and which have an amorphous structure. These films are formed at relatively low plasma shock pressure and exhibit relatively low microhardness, ̴ 2 GPa. In a relatively narrow range of the plasma shock pressure and temperature the second type of C-N deposition is observed consisting of high density, closely-packed crystal-like grains growing perpendicular to the substrate surface and displaying a cauliflower-like morphology, The microhardness of these films reaches 15 GPa, as measured by the Vickers method.

Preparation of high density graphite materials from coal tar pitch was investigated. The effect of β-resin content on the mechanical properties of graphite solid prepared from semi-coke, which was prepared by wet milling method, was examined. β-Resin content was effective for fabrication of green bodies without lamination and for improving the mechanical properties of graphite materials.

Chemically pure carbon fibers with small fiber diameters and high growth rates were obtained by laser assisted chemical vapor deposition (LCVD) using high reactor pressures and a unique rate control mechanism. Depending upon growth conditions and gases, these fibers were either flexible (elastic), brittle (thickened) or graphitic (strong). The elastic carbon fibers were uniform and appear to represent a novel form of carbon. The reactants were acetylene, ethylene or methane, and the reaction pressures ranged from 1.9 to 7.5 bar. The highest fiber growth rate was 0.33 mrn/s, and the lowest fiber diameter was 10 μm.

In order to produce a three-dimensional interconected graphitic network, foams were produced from carbon fiber precursor pitch and processed similarly to high modulus carbon fibers. Uniform size distributions of open spherical cell graphitic carbon foams were produced by microcellular foam blowing of anisotropic pitch using homogeneous and heterogeneous nucleation. The widths of cell walls and ligaments were in the range of the diameters of pitch-based carbon fibers (7-10 μm) and possessed significant alignment of anisotropic pitch crystallites.

Graphitic foams offer exciting potential for mass savings in structures. A hypothetical family of graphitic foams having ligament mechanical properties identical to those of P120 graphite fiber is considered; the mechanical properties of the hypothetical foams are viewed as realistic upper bounds on the performance of this class of materials. Various commercially available materials are compared to the hypothetical foams for application to tension bars, beams in bending and buckling, and plates in bending and buckling.

Activated carbon fibers are a kind of microporous carbon. Using dangling bond spins attached to the peripheries of the micropores, we investigated the microporous structures in relation to the heat-treatment and gas adsorption effects. Functional groups weakly bonded to the graphitic backbone are removed by the heat-treatment at moderate temperatures 200-400°C, resulting in the generation of a variety of dangling bond spins. The heattreatment above 500°C brings about homogenization of the dangling bond spins. For gas adsorption, the introduction of helium gas strongly enhances the spin-lattice relaxation rate for the dangling bond spins. In addition to a remarkably large condensation of helium gas in the microporous region, the enhancement proves the presence of ultra-micropores which can accommodate only the smallest diameter helium atoms.

The chemistry and physics of small clusters of atoms (1-100 nm) has received considerable attention in recent years because these assemblies often have properties between the molecular and bulk solid-state limits. The different properties can be explained in terms of the large fraction of atoms that are at the surface of a cluster as compared to the interior. Although the synthesis and properties of metal and semiconductor clusters, metallocarbohedrenes, fullerenes, and nanotubes are the subject of extensive investigations, little attention has been paid to cluster-assembled porous materials. This oversight is of particular interest to us since we believe that aerogels are one of the few monolithic materials presently available where the benefits of cluster assembly can be demonstrated. In particular, the unique optical, thermal, acoustic, mechanical, and electrical properties of aerogels are directly related to their nanostructure, which is composed of interconnected particles (3-30 nrm) with small interstitial pores (< 50 nm). This structure leads to extremely high surface areas (400-1100 m2/g) with a large fraction of the atoms covering the surface of the interconnected particles. As a result of these structural features, carbon aerogels are finding applications as electrodes in supercapacitors with high energy and power densities.

Aerogels are highly porous solids prepared by sol-gel processing and supercritical evacuation. Because of their high surface area, aerogels can be used as an effective catalyst for the thermal decomposition of many gaseous compounds. A variety of hydrocarbon gases have been chosen to deposit carbon in the aerogel matrix, with the deposition temperature varying from 500° to 850°C depending on the hydrocarbon used. The amount of carbon that can be deposited in the aerogel is surprisingly large, reaching up to 10 times the original weight after extensive deposition using acetylene. Overall, the aerogel composites prepared have a uniform microstructure with the average particle size in the nanometer range. In addition, we have observed some interesting graphitic structures including carbon nanotubes and rings of various shapes. Carbon deposited in the aerogel can reduce infrared transmission of the material as well as volume shrinkage at elevated temperatures, thereby improving its thermal performance.

An analytical method was developed to calculate efficiency of densifying carbon/carbon (C/C) composite with pitch for each cycle. Three factors were defined in the densificationprocess: an impregnation efficiency, w, a retention efficiency, x, and an overall densification efficiency, E. The relationships developed were applied to the results for three cycles of densification of C/C composite to evaluate the factors which depend on the route of impregnation and carbonization. The impregnation efficiency increases as the process is repeated due to a decrease of porosity, and the retention efficiency shows a tendency to be in a reverse proportion to the impregnation efficiency. The overall densification efficiency depends on the carbonization yield of pitch impregnant. The carbonization route P+A+G is the most effective method in densifying C/C composites, in which pressure carbonization(P) increases the carbonization yield and the retention efficiency of pitch, and graphitization(G) increases the impregnation efficiency.

C60 and C70 polycrystalline thin films, prepared by sublimation of powders onto carbon holey film substrates held at temperatures Ts of 40 and 200 °C, were investigated at room temperature using conventional and high resolution TEM. A strong dependence of grain size on Ts is observed. We obtain a mean grain size ˜25 nm for both C60 and C70 films when using Ts = 40 °C, but this size is ˜250 nm for C60 and ˜130 nm for C70 when using Ts = 200 °C. In all cases, however, an fc.c. structure with a high density of planar defecTs, twins and stacking faulTs, is observed. When a C60 film grown at Ts = 40 °C was annealed for several hours at only about 250 °C in vacuum, recrystallization took place, with grains as large as 250 nm now being present in the film. A condition to observe this recrystallization seems to be that the powder used to grow the film must be dried for long enough periods of time to minimize the amount of solvent residues.

C60 Cl6 can be phenylated and arylated to give derivatives of the type C60Ar5Cl, which may be readily converted to C60Ar5. The compounds C60Ar5 and various other phenylated derivatives have been isolated from the product of reaction of [60]fullerene with bromine/ferric chloride/benzene, and partially characterised.

C60 is sultonated in fuming sulfuric acid and chlorinated in chlorosulfonic acid. Both reactions involve initial oxidation of C60 followed by in situ trapping of electrophilic C60 cation.

Dodecylated C60 {(Do)nC60(H)n} and butylated C60 {(Bu)nC60(H)n} were synthesized. Spectroscopic and thermal methods, mass spectrometry, XPD, have been employed to characterize the products. X-ray Powder Diffraction (XPD) results reveal that the facecentered- cubic (fcc) structure of C60 expands to a primitive hexagonal structure upon butylation and to a layered structure upon dodecylation. Butylated C60 diffraction pattern has been indexed as a primitive hexagonal structure with ao = 11.5 angstroms and axial ratio = 1.169. The dodecylated C60 also shows sidechain melting behavior with a transition temperature of around 25°C. The paraffinic crystals are produced by the interdigitation of the sidechains. Butylated C60 does not show any sidechain melting.

The ionization potentials (IP) and electron affinities (EA) for a number of hydrogenated and fluorinated derivatives of C60 and C70 have been determined using the charge exchange “bracketing” technique. Samples of C60Hx and C70Hy were prepared by direct solid phase hydrogenation (x=2-18, y=2-30) or platinum oxide catalytic hydrogen reduction (x=36, y=36). The IP's for C60H2-18 are between 6.75 and 7.53 eV for even x<10 and lower than 6.75 for odd x<10. The EAs for C60F44,46,48, and C70F52,54 were “bracketed” to be 4.0 ± 0.25 eV. The highly fluorinated chiral C3h molecule C60F48 was observed to directly attach two electrons in the gas phase to produce C60F482- and C60F462− + F2−. Studies of the metastable decompositions and collision-induced dissociation of C60F482− showed fluorine atom and F2 loss, but no loss of an electron. In addition, the C60F48,46,442− dianions do not charge exchange with molecules possessing high electron affinities, including the neutral parent compound, C60F482− (EA = 4.06 eV). The remarkable stability of C60F482− to the removal of an excess electron is attributed to a long-range Coulomb barrier which is built from the bound state for the two electrons near the molecule and the electron-electron Coulomb repulsion between the two at large distance.

Hydroboration of C70 in toluene yields a 2:1 mixture of 1,9-C70H2 and 7,8-C70H2. Equilibration of these two isomers in the presence of a Pt catalyst reveals a free energy difference of 1.4 ± 0.2 kcal/mol. Whereas semiempirical calculations have been found to predict the energy ordering of many fullerene derivatives incorrectly, ab initio Hartree-Fock (HF) calculations have been found to yield quantitative predictions of experiment. The HF/6-31G* level energy separation of l,9-C70H2 and 7,8-C70H2 of 1.3 kcal/mol is in excellent agreement with experiment. Relative stabilities of isomers of bis(methano)fullerenes were found to parallel those of analogous C60H4 isomers. Density functional theory (DFT) methods have been tested and are equivalent in accuracy to HF methods if similar basis sets are used. C60H2 and C60H4 can be efficiently produced on larger (≥ 50 mg) scales with diimide generated from potassium azodicarboxylate and acetic acid in o-dichlorobenzene.