Synthesis of single and multi unit-wall MgB[sub 2] nanotubes by arc plasma in inert liquid via self-curling mechanism

Magnesium diboride (MgB2) is known as a promising superconductor due to its high transmission temperature. Similarly to single-wall carbon nanotube, unique characteristics would be seen if a nanotube structure of MgB2 having a unit-wall of Mg and B atomic bilayer is prepared. However, such MgB2 nanotubes have not ever been synthesized. In this article, formation mechanism of unit-wall MgB2 nanotube is elucidated by molecular mechanics calculation. From the viewpoint of energetic stability, the unit-wall will be curled up to form nanotube structure when MgB2 crystal is disassembled to an isolated unit-wall layer. An experiment using arc plasma in inert liquid was utilized to produce unit-wall MgB2 nanotubes. As a result, a single and multiunit-wall MgB2 nanotube was successfully synthesized. In this reaction field, the arc plasma may play a role to produce isolated MgB2 unit-wall fragment, and the cold cathode surface can contribute to preserve MgB2 nanotube structure

Orientation Relationship for Fine Grains Formed by Diffusion-Induced Recrystallization in the Ni(Cu) System

In order to examine the crystallography for diffusion-induced recrystallization (DIR) in the Ni(Cu) system, Cu/Ni/Cu diffusion couples were prepared by a diffusion bonding technique from a pure Cu single-crystal specimen and a pure Ni polycrystalline specimen, and then isothermally annealed at a temperature of 923 K for various times of 1-60 h. The Miller indices of the Cu specimen along the Cu/Ni interface are (111). The notation A (B) means that a solute B diffuses into a pure metal A or a binary A-B alloy with the A-rich single-phase microstructure. Due to DIR during annealing, a region with fine grains alloyed with Cu is produced into the Ni specimen from the Cu/Ni interface in the diffusion couple. The orientation relationship between the fine grain in the DIR region and the Cu or Ni specimen was analyzed by an electron backscattered diffraction technique as well as transmission electron microscopy. Orientation relationships close to but not identical to the cube/cube relationship exist between the Cu specimen and many fine grains in the DIR region. The chemical driving force for the formation of the DIR region, the boundary energy and the boundary diffusion coefficient were evaluated by mathematical models. According to the evaluation, it is likely that fine grains surrounded by small-angle boundaries are formed and grow moderately during DIR