Hidemasa Honda

Raman spectra of ground natural graphite

Abstract Structural changes in Ceylon natural graphite with grinding were studied by Raman spectroscopy along with X-ray diffraction. The natural graphite shows a single Raman band at 1580 cm−1, but the ground graphite samples exhibit two Raman bands at 1360 and 1620 cm−1 in addition to the 1580 cm−1 graphite band. The 1360 cm−1 band increases in intensity with increasing grinding time, and becomes much stronger than the 1580 cm−1 band after 200-hr grinding. Raman results are compared with structural parameters such as effective Debye parameter and C0 spacing obtained from X-ray diffraction measurements, and discussed in terms of structural defects introduced into the crystal lattice of natural graphite. A linear relationship was obtained for the ground graphite when the relative intensity of the 1360 cm−1 band is plotted as a function of effective Debye parameter. The slope of the linear plot is different for the ground graphite from that for the graphitized cokes, indicating a difference in the type of structural defects involved.

Characteristics of meso-carbon microbeads separated from pitch

Abstract Mesophase spherules separated by solvent fractionation from heat-treated coal-tar pitch and from heat-treated asphalt at 430°C are named “meso-carbon microbeads”. Characteristics of these mesophase microbeads were studied. The meso-carbon microbeads are classified into three types, type C, type M and type P, corresponding to the raw pitch materials. The chemical composition of type C and type M consists of high molecular weight aromatic hydrocarbons having short side chains of aliphatic hydrocarbons, and that of type P consists of small ring number aromatic hydrocarbons having long side chains of aliphatic hydrocarbons. The shapes of the meso-carbon microbeads are classified into lemon-like and spherical by their shape. The meso-carbon microbeads do not fuse or melt by heat-treatment. The graphitizability of heat-treated meso-carbon microbeads is not high. When the meso-carbon microbeads are heat-treated at 300–500°C in a medium of polynuclear aromatic hydrocarbons (anthracene, pyrene, chrysene and pitch) their behavior is similar to that of mesophase spherules in pitch. However, when the ratio of the meso-carbon microbeads to the polynuclear aromatic hydrocarbon was changed, the behavior of the microbeads was peculiar.

Optical mesophase texture and X-ray diffraction pattern of the early-stage carbonization of pitches

Abstract Low temperature carbonization of pitches was studied with polarized-light microscopic method, X-ray diffraction, solvent extraction and density measurements. The nucleation and growth of spherical bodies occur progressively with increase of residence time at a fixed temperature, until the spherical bodies eventually coalesce with each other. Fine irregular particles of insolubles in coal-tar pitch are observed in the region of boundary between spherules and matrix. They play an important role in the mesophase transformation. The typical changes of stacking height of lamellae, interlamellar spacing, weight loss, density and insolubility with residence time show nearly the same tendency at the various temperatures from 390° to 430°C. The time-temperature superposition has been successfully employed. In the master curve for coal-tar pitch reduced at 410°C, the reduced time scale extends from 10−2 to 102 hr. From the relation between the reducing factor of time translation and absolute temperature, the apparent activation energies can be estimated over the range of 35–45 kcal/mole. It seems probable that a model of the rearrangement of C—C bonding together with vaporization of low molecular substances is applicable for the growth of spherical bodies.

Changes of pleochroism and extinction contours in carbonaceous mesophase

Abstract Reflected polarized-light micrography using crossed polarizers with a gypsum plate has been employed to investigate the microstructure of carbonaceous mesophase formed at the early stage carbonization of pitches. It follows from the changes in pleochroism and in isogyres occurring with the stage rotation, that a simple mesophase spherule is optically a uniaxial positive liquid crystal belonging to the hexagonal system with a straight extinction. Observations of changes in pleochroism and in extinction contours for coalesced and for deformed mesophases, permit to distinguish crosses from nodes and by that to identify four types of linear defects in the stacking of the aromatic layer planes. It is explained schematically how the cross and nodal structures are formed in the coalescence of two simple spherules and in the deformation of such coalesced mesophase.

An X-ray diffraction study of phenol-formaldehyde resin carbons

Abstract An X-ray diffraction study of the carbons which were prepared from phenol-formaldehyde resin, 3-methylphenol-formaldehyde resin and 3.5-dimethylphenol-formaldehyde resin all heat treated in the temperature range from 900 to 3000°C was carried out in order to find the relation between the graphitizability of the carbon and the chemical structure of the starting material. It was found that the crystallite size L a (110) does not increase monotonously with the heat-treatment temperature (HTT). No considerable change in the size was observed for the carbons treated to temperatures from 1000 to 1400°C and from 2000 to 2400°C. The (002) diffraction pattern for both phenol-formaldehyde resin carbon and the 3-methyphenol-formaldehyde resin carbon treated to temperatures from 2800 to 3000°C, exhibits a composite line, but for the 3.5-dimethylphenol-formaldehyde resin carbon does not. The composite (002) pattern consists of three peaks for which the values of spacing d (002) and of the crystallite thickness L c (002) were obtained. The composite peak appears for the resin carbon with a lower graphitizability at a lower HTT. The overall result is that the phenol-formaldehyde resin produces a hard-type carbon, the 3.5-dimethylphenol-formaldehyde resin gives a soft-type carbon, and the 3-methylphenol-formaldehyde resin gives an intermediate-type carbon.

X-ray characteristics of non-graphitizing-type carbon

Abstract Changes in the structure of two graphitizable carbons and four non-graphitizable carbons were followed by measuring d(002), d(110), Lc(002), and La(110) as a function of HTT. It is observed that graphitizable carbons undergo rapid changes in the structure in the temperature range 2400–3000°C and become polycrystalline graphite. Non-graphitizable carbons change slowly and their (002) reflexions exhibit certain features. With heat treatment the (002) reflexions sharpen and their peak position shifts to higher angles. Two well-defined peaks, at 2θ = 26° and 26°, develop when Lc reaches a value 20–40 A. It appears that beyond that stage the profile may be resolved into a broad peak at 2θ = 26° and two sharp peaks at 26° and 26°, the sharp peaks indicating Lc values of several hundred A. With increased heat treatment to 3000°C, the peak at 26° gradually becomes more prominent at the expense of the other. A correlation is found to exist between d(002) and Lc or La.

Raman spectra, effective Debye parameter and magnetoresistance of graphitized cokes

Abstract The Raman intensity ratio R ( I 1360 I 1580 ), the effective Debye parameter Beff 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, Beff 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 Beff 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 Beff, ( Δρ ρ ) mx increases gradually but almost linearly with Beff and then rapidly. This behavior has been interpreted by an analysis based on a simple two band model.

Orientation behavior of carbonaceous mesophase spherules having a new molecular arrangement in a magnetic field

Abstract Carbonaceous mesophase spherules of a new-type have been found in the heat-treated products of quinoline-soluble portion of coal-tar pitch containing carbon black. Their spherules have molecular orientation different from that proposed by Brooks and Taylor. The effect of a magnetic field is discussed on the orientation of the spherules formed during carbonization processes using a polarization microscope.

Electronic properties of heat treated coals

Abstract Studies of the dependence of the electronic resistivity, Hall constant, diamagnetic susceptibility and electron spin resonance in dependence on heat-treatment temperature were carried out for coal solids molded at room temperature without binder. Akabira weakly-caking coal (d.a.f. C= 83·4 percent) and Itmann strongly-coking coal (d.a.f. C = 90·2 percent) were used. Electronic properties and X-ray diagrams indicate that the Akabira coal carbon is a hard carbon (non-graphitizing carbon) and the Itmann coal carbon is a soft carbon (graphitizing carbon) respectively. The change in sign of the Hall constant is closely related with presence of a fraction showing a narrow component in the (002) diffraction line. It is suggested that changes in the Hall constant depend on changes in concentration of defects; defects are created in heat-treatment when graphitic carbon is formed as a result of breaking the cross-links due to high internal stresses.

Formation of carbonaceous mesophase at lower temperature

Abstract The effects of heat-treatment at lower temperature on the formation of carbonaceous mesophase were studied. Heat-treatments of QS pitch below 340°C and of KF asphalt below 370°C lead to the formation of mesophase spherules having a different structure from those found previously. For QS pitch, the lowest temperature of mesophase formation was 290°C but more than one month was required for heat-treatment. The structure of the fourth-type spherule is proposed from the microscopic observations and its orientational behavior in a magnetic field. The structure of this type is very similar to that of the Brooks-Taylor-type one, and it is believed that the fourth-type spherule is a meta-stable phase of the Brooks-Taylor-type one.