Petroleum-based needle coke will be losing its dominance for the production of graphite electrodes, due to the growing production capacities in the field of coal tar pitch (CTP)-based needle coke types. Up to now, CTP needle coke does not harmonize with the conditions prevailing in modern lengthwise graphitization furnaces. The reason is the volumetric expansion during graphitization—the so called puffing—caused by the removal of gaseous nitrogen. Earlier research activity has failed to depress (or even prevent) the nitrogen puffing of CTP needle coke to a similar level as found with petroleum needle coke standards. This paper gives a brief review of the research carried out in the past. It evaluates several measures to depress nitrogen puffing and reports recently obtained results. It is expected that a chemical inhibition of nitrogen puffing is not possible on an industrial scale. However, solutions are seen in physical measures—like thermal reduction of the nitrogen content and in tailoring the coke morphology by the thermal processes involved in its production.

View full abstract

Carbon-based materials containing heteroatoms, such as boron and nitrogen, are called heteroatom-substituted carbon alloys. Preparation and applications of heteroatom-substituted carbon alloys, particularly materials composed of boron, carbon and nitrogen (B/C/N materials), and carbon and nitrogen (C/N materials) are summarized in this review. Examples of potential applications of the materials to energy conversion and storage systems, such as secondary batteries, capacitors and photocatalysts are described. B/C/N materials can be intercalated with sodium (Na) to form a first stage intercalation compound, which can be used as the anode of Na ion batteries. C/N materials used as the electrode of capacitors have higher volumetric capacities than commercially-used activated carbon, and show photocatalytic behavior as an electrode for the production of hydrogen by the electrolysis of water. Important roles of boron and nitrogen in B/C/N and C/N materials are also discussed.

View full abstract

Carbon catalysts for the oxygen reduction reaction (ORR) were prepared from mixtures of humic acid and cobalt compounds. To examine the effects of cobalt and nitrogen on the ORR, cobalt phthalocyanine (CoPc), cobalt chloride (CoCl₂) and phthalocyanine (H₂Pc) were mixed with the humic acid and carbonized at 800 °C. The carbons were washed with hydrochloric acid to remove metals on the surface of the carbons. The carbon prepared by mixing HA, CoCl₂ and H₂Pc (HA-CoCl₂-H₂Pc) had the highest ORR activity, while the carbons, HA-CoPc and HA-H₂Pc, had lower ORR activities. HA-CoCl₂ had moderate activity. The results imply that both of cobalt and nitrogen are important to obtain ORR catalysts with higher activities. A uniform distribution of Co atoms in the precursor is also important to obtain carbon alloy catalysts with higher ORR activities.

View full abstract

It has been found that activated carbon oxidized with a solution prepared by dissolving (NH₄)₂S₂O₈ in 1.0 M sulfuric acid has a very large number of functional groups and increases the adsorption of metal ions. However, the oxidation simultaneously produces a decrease in surface area and causes the activated carbon to have a fragile structure. This study examined the effects of nitric acid, sodium sulfate and sulfuric acid as (NH₄)₂S₂O₈ solvents used for the oxidation of activated carbons on Ni(II) adsorption, oxygen content, functional groups and surface area. The results showed that 1.0 M solvents introduce more carboxy groups than 0.1 M solvents and a 1.0 M sodium sulfate solution produces a high adsorption capacity without decreasing the surface area drastically.

View full abstract

Screwed-stacked cone carbon (SSCC) is produced by the pyrolysis of certain organic compounds and appears to be columnar or whisker-like in shape and formed of continuous helical hexagonal carbon layers. The rotation angle between adjacent layers is commonly 21.7° or 27.8°. It has been found that SSCCs show birefringence and vertical orientation in a magnetic field. Although they are a kind of ordered turbostratic carbon, they intercalate sulfuric acid and can be subsequently expanded like graphite by heating. Further studies will elucidate their mechanical and electric properties and how they depend on the continuous non-planar graphitic features.

View full abstract

The structural parameters of coke and mesocarbon microbeads were measured using three diffractometers with different angular resolutions based on the standard X-ray diffraction measurement procedure for carbon (Gakushin method). There was no observable difference in the values of the lattice constants, a₀ and c₀, obtained using the three instruments. However, because the half width of the profile is affected by the angular resolution there were differences in the measured crystallite size.

View full abstract

The scope of this thesis is to examine the emergence and the chemical modification of the edge state in a single sheet of graphene. Firstly, it has been verified by Raman spectroscopy and low-temperature magneto-conductivity measurements that the carrier scattering sources in artificially nanostructured graphene and graphene having randomly distributed atomic vacancies are inevitably-involved charged impurities and edges of vacancies, respectively. Next, the emergence of the edge state over a macroscopic area of a sample upon the creation of atomic vacancies has been revealed by using near-edge X-ray absorption fine structure. Finally, in order to establish a way of tuning the electronic properties of the edge state by an artificial control of functional groups at vacancies, hydrogenation of vacancies has been investigated by exposing graphene with atomic vacancies to hydrogen flows. The spontaneous dissociative adsorption of H₂ at vacancies is suggested to occur because of high reactivity of edge carbon atoms. The author expects that this thesis contributes to the fundamental understanding of electronic properties of the edge state upon chemical decoration with arbitrary functional group.

View full abstract