Plasma Arc Method Research Articles

Co-Pt and Fe-Pt bimetallic nanoparticles in a carbon matrix are prepared by a plasma arc process

Nanoparticle ensembles in Co-Pt and Fe-Pt systems embedded in a carbon matrix are prepared by a plasma-arc method. Two-phase samples based on disordered FCC solid solutions are prepared in both systems. In the Co-Pt system, the solid solujtions are mixed within one ensemble; in the Fe-Pt system, they are spatially separated. A magnetization hysteresis curve from Co-Pt nanoparticles (3–12 nm) fully coincides with a magnetization curve from a single-phase disordered solid solution Co0.50Pt0.50 (7–9 nm) prepared at 325°C by thermolysis of the precursor double complex salt (DCS). Metal ratios, solid solution structures, and particle sizes being the same, the magnetic response is dictated exclusively by the amount of a magnetic phase of mixed and interacting particles and is independent of the distribution of the magnetic phase over the solid solution phases.

Mass-production of boron nitride double-wall nanotubes and nanococoons

Various techniques including plasma-arc, laser ablation, and chemical vapor-phase synthesis have been employed to produce bulk amounts of non-carbon (such as boron nitride, BN) nanotubes with some success, but in general the yields are low. We describe a new high-yield plasma-arc method that easily and reliably produces macroscopic amounts of pure BN nanotubes. Interestingly, the method produces almost exclusively double-walled nanotubes; these in turn self-assemble into BN nanotube bundles or ropes. Our synthesis method also produces BN-coated crystalline nanoparticles, whose cores can be preferentially etched leaving behind hollow BN `nanococoons'.

Effect of BeO on the Sintering and Properties of Boron-Doped High-Purity SiC Ceramics

In order to obtain pressureless-sintered SiC ceramics with high thermal conductivity, effect of BeO addition on sintering properties boron-doped β-SiC powder was investigated. The β-SiC powder was produced by the plasma arc method from SiH4, B2H6 and CH4 gases. Pressureless-sintered boron-doped β-SiC ceramics showed high thermal conductivity of 180 W·m-1·K-1 and electrical resistivity of 1100Ω·m (10mV). On the other hand, pressureless-sintered boron-doped β-SiC ceramics containing BeO showed varistor characteristics with electrical resistivity of 1011Ω·m at 10V, and thermal conductivity of 230 W·m-1·K-1. These ceramics consisted of net-like elongated β-SiC grains. Thus, addition of BeO increased the thermal conductivity and electrical resistivity.

Reaction Sintering Mechanism of Submicrometer Silicon Powder in Nitrogen

ABSTRACTKnowing the nitridation mechanism of Si is important to obtain near-net-shape high strength reaction bonded ceramics. In this report, comparison of nitridation mechanism of small spherical Si powder produced by plasma arc method and large faceted Si powder, is discussed on the basis of microstructural analyses by SEM and TEM. From the analyses, nitrogen diffuses through the oxide film of Si powder and forms Si3N4 under the oxide films during the initial stage of sintering. At higher temperature, the oxide film transform into fine Si3N4 grains when heated to the 1350°C. The Si3N4 has morphology of hollow shell and a size, which corresponds to that of the original Si particles.