Yousuke Murakami

Hydrogen storage capacity of commercially available carbon materials at room temperature

The hydrogen storage capacity of five types of commercially available carbon materials with different nanostructures was measured at up to 8 MPa at room temperature using an apparatus based on a volumetric method with an error of less than 0.04 wt %/gr. The highest storage capacity of 0.43 wt % was obtained for purified HiPco™ single-walled carbon nanotubes (SWNTs). In the SWNTs, the hydrogen density in pores with a diameter of less than 1 nm was estimated to be a 0.022 g/ml, which corresponds to 31% of the density of liquid hydrogen. Issues in the development of carbon-based hydrogen storage media are discussed.

High-quality single-walled carbon nanotubes from arc-produced soot

High-quality single-walled carbon nanotubes (SWNTs) were obtained from arc-produced soot using a three-step purification process consisting of soft oxidation, air oxidation, and a high-temperature vacuum treatment. Firstly an oxide layer was formed on the surface of the metal catalyst, which prevents the SWNTs from undergoing metal-assisted dissociation during the process. After the final step, about 20% of the weight of the initial raw soot remained and the final product contained less than 1% metal. Scanning electron microscopy, transmission electron microscopy and Raman spectroscopy were used to characterize the SWNTs obtained.

Repeatable hydrogen adsorption using nanostructured graphite at room temperature

Repeatable hydrogen adsorption and desorption by nanostructured graphite was confirmed using a high-accuracy volumetric measuring apparatus at room temperature. The nanostructured graphite was prepared from graphite powder using a mechanical milling process at a pressure of 2.0×10−4 Pa. The untreated graphite adsorbed 0.02 wt % of hydrogen, while 0.20–0.25 wt % of hydrogen can be repeatedly adsorbed by the nanostructured graphite. Measurements of the hydrogen adsorption rate at constant pressure and pore-size distribution suggest that the hydrogen molecules are adsorbed through a diffusion process into pores with a diameter less than 1 nm.

High-purity fibrous carbon deposit on the anode surface in hydrogen DC arc-discharge

Abstract A brittle porous deposit consisting of high-purity fibrous carbon products with a diameter of 25–100 nm was obtained on a heated anode surface in hydrogen DC arc-discharge. Hydrogen arc plasma was generated between a graphite cathode and a carbon/metal composite anode consisting of 1.0 at.% Fe, 0.6 at.% Co, 2.4 at.% Ni, and 0.4 at.% FeS. X-ray diffraction analysis revealed that the fibrous products had a turbostratic carbon structure, with an interlayer spacing of 0.346 nm. Elemental analysis showed that the fibrous products were composed of 98.4 mass% of carbon. Three types of nano-structured fibrous products were observed using transmission electron microscopy, (1) with a bamboo structure, (2) with a hollow core, and (3) without a hollow core. The formation of fibrous products was initiated by arc-generated metal particles with a diameter of 5–75 nm, then carbon for further growth was supplied by the decomposition of polycyclic aromatic hydrocarbons that were created by interactions between arc-generated carbon clusters and atomic hydrogen. The nano-structure of the fibrous products is thought to depend on the size and morphology of the catalytic metal particles. The synthesis conditions, microstructural characterization and the growth mechanism of the fibrous carbon products are reported.

Crystallographic and structural analyses of perpendicular magnetic Co‐Pt‐B‐O alloy films

CoPtBO reactive sputtered film is a new type of perpendicular recording media material with high perpendicular anisotropy fields and large perpendicular coercivities. To understand the origin of the magnetic properties, several materials parameters were explored. These included the effects of the introduced oxygen on the crystal structure, as well as the orientations and the microstructure of the CoPtBO films. With increasing the oxygen partial pressure, the crystallographic structure of CoPtBO alloy films were changed from face‐centered‐cubic (111) texture into hexagonal‐close‐packed (hcp) (001) texture. Pole figure analysis is a useful method to identify the crystalline structure of the oriented films. The strong hcp (001) texture and separation of the magnetic grains are the origin of the high Hk and large Hc of the films.