Minoru Shiraishi

Amorphous diamond from C60 fullerene

Amorphous diamond was successfully quenched from shock‐compressed C60 fullerene by rapid cooling technique. This material is transparent and homogeneous glassy chips, and exists stably at ambient conditions. X‐ray diffractometry showed a halo, and electron diffractometry showed a diffuse pattern similar to those of common amorphous carbon materials. Electron energy loss spectroscopy represented evidently σ‐electron state in sp3 hybridization completely equivalent to that of a typical diamond. Therefore, this material is defined in long range order to be amorphous and in short range order to be diamond, namely it can be said as amorphous diamond.

New structural parameters for carbon: Comprehensive crystallization index and cavity index

Abstract New structural parameters designated ‘comprehensive crystallization index’ (CCI) and ‘cavity index’ have been mathematically derived from the density, lattice constant and crystallite size of carbon materials by assuming a model of crystallite. These indices calculated for several carbon materials were plotted as a function of the heat-treatment temperature (HTT). Thereby, it is demonstrated that CCI well represents the crystal growth with increasing HTT in the form of a logistic curve.

Carbonization and graphitization behavior of decacyclene

Decacyclene was carbonized in a glass tube or a molten salt at various temperatures and the products were analyzed by means of Raman spectroscopy, X-ray diffractometry, ESR and FT-IR spectroscopies in order to investigate the influence of contained pentagonal aromatic rings on the change of carbon structures with heat-treatment. It was found that the presence of the pentagonal rings disturbs the growth of planar aromatic layers at the early stage of carbonization and that the development of the layer stacking to c-axis with further heat-treatment is influenced predominantly by the phase during the carbonization stage rather than by the pentagonal rings.

EVALUATION OF ACCESSIBLE AND INACCESSIBLE MICROPOROSITIES OF MICROPOROUS CARBONS

A fine pore characterization method for less-crystalline porous solids has been applied to activated carbons. In the analysis, the microporosity of the solid was classified into effective micropores and inaccessible pores, depending upon the accessibility of the pore to an N2 molecule at 77 K. The volume fraction of each pore was determined via a N2 adsorption isotherm and two types of density measurements. The Debye–Bueche plot of the small-angle X-ray scattering (SAXS) was used to obtain the correlation length characteristic of the sample, followed by estimation of the average transversal length of the pore and the solid part. These dimensions were compared with the structural parameters given by the adsorption method and X-ray diffractometry in order to examine the geometric features of the system. The number and size of inaccessible pores were calculated for a sample with symmetrically shaped pores, considering the volume fraction of effective micropores and inaccessible pores, and specific surface areas due to these pores.

Transition process to diamond from C60 fullerene

Abstract A transition process of C 60 fullerene to diamond under shock compression was examined by exploring changes in the electron state and structure. A combined analysis using electronic energy loss spectroscopy and electron diffractometry was carried out on variously altered C 60 and transformed diamond at 16 to 25 GPa. A few transient states, (1)-(3), showing unique electron states and structures were found. (1) The fcc structure was almost unchanged, and the π plasmon was lost due to a decrease in the intercluster distance. (2) The basic structure was retained and intercluster bondings were generated. (3) The basic structure collapsed to become amorphous, while sp 3 bonding was locally produced. Finally, complete bonding and long-range order structure of diamond were reconstructed.

Structure of amorphous hydrogenated carbon film prepared from rf plasma deposition

Abstract An amorphous hydrogenated carbon (a-C : H) film was prepared from rf plasma deposition, and the structure was investigated by means of FT-IR, TEM and electron energy-loss spectrometry (EELS). The proportions among aromatic, aliphatic sp2- and sp3-coordinated carbons were determined to be 1 : 4 : 10 by curve-separation technique of FT-IR absorption peaks. The diameters of the hexagonal planes and the cluster of sp3-coordinated carbons were made to be about 7 A with the electron diffraction pattern of the a-C : H. The low energy-loss region of the EELS spectrum for the a-C : H was analyzed by the use of the energy-loss function and separated into one π plasmon peak and two plasmon peaks, each of which was associated with sp2- and sp3-coordinated carbons, respectively. The ratio of electrons contributing to the peaks was calculated using the theory of the effective number of electrons. The σ electrons associated with the peak by sp2-coordinated carbons (σg) were distinguished from those with sp3-coordinated carbons (σd). Considering the π electrons (Π), the relative numbers of electrons were estimated to be π : σg: σd = 1 : 6 : 4. One of the possible structures for the a-C : H used was exemplified on the basis of these quantitative data.

Carbon film from polyphenylene prepared by electrochemical polymerization

A carbon film was produced from polyphenylene (PP) film prepared by electrochemical polymerization of benzene to obtain a uniform and thin film. The PP film (∼10μm thick) was transformed into the carbon or graphite film without drastic changes of shape or size. The electrical conductivity of the film was remarkably enhanced by heat-treatment between 600 and 800° C, but further increase in the conductivity was not observed by treating at higher temperatures. This behaviour is considered to correlate with a poor degree of graphitization of the PP film. The carbonization and graphitization mechanisms of the film are discussed in connection with the structure of polyphenylene in the film.

Effect of Enhanced Contact Between Finely Pulverized Coal and Catalyst on Liquefaction

Publisher Summary This chapter discusses the effect of the finely pulverized coal particle on the product distribution of Taiheiyo coal liquefaction that is experimentally compared with that of conventional particle-size coal. To examine the effective dispersion among components in the slurry for liquefaction, the effect of surfactant addition, which was developed and used now for preparing stable slurry, on the yield of liquid product and the conversion from liquefaction is examined. Result of the product yield and the hydrogen consumption using some of the nonionic and the cationic urfactant is shown. Comparisons of various catalyst precursors impregnated by the aqueous solutions of inorganic salts and of solvent-soluble organic complex catalysts are discussed in connection with coal swelling. The detailed mechanisms of hydrogen transfer by catalyst are not completely clarified. The conventional ground coals are used, which causes some limitation on the surface dispersion with fine catalyst particles and on contact between the coal and solvent, due to the relatively large coal particle size.

Microstructure of carbonaceous mesophase spherule

Carbonaceous spherules of mesophase were examined by transmission electron microscopy (TEM) and X-ray diffraction to precisely clarify its structure. A series of thin sections were cut from a single spherule with a microtome, and the three-dimensional lamellar structure of the spherule investigated. From 002 dark-field images and selected area electron diffractions (SAD), it was observed that the spherule was of the Brooks-Taylor type, with the lamellae being parallel even at the poles of the spherule. Structural changes within the spherule was studied following carbonization and graphitization. The structure of the resultant coke was essentially that of spherule of mesophase. Size of the lamellae increased as well as. The number of stacking lamellae also increased, but a rapid increase was not seen. The spherules of mesophase show a high degree of homogeneity and an excellent degree of graphitization.

Carbonization and Graphitization of Anthracene Polymers

Carbonization and graphitization behaviors of anthracene polymers were investigated to characterize the carbon products obtained. The polymers consisting of 3-4 anthracene units (Poly (9, 10-anthracene diylidene)) were synthesized by use of dehydration and polycondensation of polyphosphoric acids. The weight loss of the polymers occurs predominantly between 350-500°C and the yield of the products treated at 1000°C reaches 72-79%. It was found from the analyses of the evoluved gases and the FT-IR spectra that dehydrogenation at the terminal CH2 groups of the polymer and elimination of CO from quinone groups at the anthracene terminal take place at these temperature ranges. The carbonized product from anthrone polymer showed a fine mozaic texture although it melted at 290-300°C. This may be because the anthracene units are twisted with each other. Also, d002 spacing and La values obtained from X-ray diffraction profilesof the heat-treated polymer suggest that the graphitizability of the polymer is less enhanced even at high temperatures.