Takeshi Hamada

Transverse structure of pitch fiber from coal tar mesophase pitch

Abstract The transverse structure of pitch fiber has been successfully controlled by changing the pitch flow conditions at the upper portion of the capillary in spinning. The mean size of mesophase domains in the transverse section of pitch rod extruded from the capillary was found to decrease monotonously with decreasing rod diameter and with increasing pitch viscosity. Also, the stirring of molten pitch located just above the capillary gave rise to a decrease of the mesophase domain size. It has been revealed that the graphitizability of the pitch fiber depends mainly on the mean domain size in the transverse section, as long as the degree of preferred orientation is the same.

Coke powder heat-treated with boron oxide using an Acheson furnace for lithium battery anodes

Abstract Coal tar pitch-based coke power was heat-treated with B 2 O 3 using an Acheson furnace. The heat-treated coke powder contained nitrogen and oxygen probably derived from BN and B 2 O 3 , respectively, and exhibited a large irreversible capacity in the first charge–discharge (lithium dope–undope) cycle. The large irreversible capacity was decreased not by the decomposition of BN or B 2 O 3 but drastically by the increase of dissolved boron concentration. The discharge capacity also correlated well with the concentration of dissolved boron.

Structure of coke powder heat-treated with boron

Abstract Coal tar pitch-based coke powder with a fine mosaic texture was heat-treated with various concentrations of boron powder at 2900°C. Increasing the boron amount led to smaller d 002 and larger d 110 , and made the original fine texture coarser. Some small particles showed specific structures of polyhedrons, of which surfaces are 002 planes of graphite lattice, after heat treatment with boron. The size of the polyhedron increased with boron content. Boron concentration was lower at the surface than at the inner portions of particles for a powder heat-treated with a higher amount of boron, while it depended less on the depth for that heat-treated with a lower amount of boron. The formation mechanism of the polyhedron particle is discussed.

Coaltar pitch based carbon fiber having high Young's modulus

This invention relates to a coaltar pitch based carbon fiber having a high Youngs modulus produced by using coaltar pitch as a starting material, which has a microstructure with a preferred orientation parameter (HWHM) of 10° or less, a crystallite size (Lc(002)) of not more than 25 nm and not less than 18 nm and an interlayer spacing (d002) of not more than 0.345 nm and not less than 0.338 nm as determined by X-ray diffraction, and has a magnetoresistance of less than -0.40% and not less than -2.00% as measured by applying a magnetic field of 10 KG perpendicular to the fiber axis at liquid nitrogen temperature, and a Youngs modulus of 55 ton·mm-2 or more, preferably 75 ton·mm-2 or more. The carbon fiber of this invention has a high Youngs modulus, is flexible, and does not split in the fiber axis direction, and therefore it is easy to handle, is good in workability, and contributed also to improvement of the production efficiency. Further, when the carbon fiber of this invention is used in composite material, the resulting composite material can be expected to have an improved impact strength and hence can be used for various purposes.

Irreversible and Discharge Capacities Depending on Dissolved Boron Concentration of Coke Powder

Well-graphitized coke powder was further heat-treated at 2200°C with various amounts of boron in Ar to prepare coke powders containing different amounts of dissolved boron. The particle size distribution, specific surface area, crystallite size, and the texture observed with transmission electron microscopy were less dependent on the concentration of residue boron, [B] res , after the heat-treatment. The dissolved boron concentration, [B] sol , was quantitatively estimated from the potential curve of the first lithium doping. [B] sol was equal to [B] res when [B] res ≤1.0 wt % and slightly decreases with the increase of [B] res when [B] res ≥ 1.0 wt %. The irreversible capacity of the first lithium dope-undope cycle monotonously decreased, became minimum at about 0.4-0.5 wt % [B] sol , and again slightly increased with the increase of [B] sol . The discharge capacity of the first cycle was monotonously raised with the increase of [B] sol . The mechanisms of irreversible capacity and discharge capacity depending on [B] sol are discussed.