Lithium metal oxide nanoparticles were synthesized by induction thermal plasma. Four different systems—Li–Mn, Li–Cr, Li–Co, and Li–Ni—were compared to understand formation mechanism of Li–Me oxide nanoparticles in thermal plasma process. Analyses of X-ray diffractometry and electron microscopy showed that Li–Me oxide nanoparticles were successfully synthesized in Li–Mn, Li–Cr, and Li–Co systems. Spinel structured LiMn₂O₄ with truncated octahedral shape was formed. Layer structured LiCrO₂ or LiCoO₂ nanoparticles with polyhedral shapes were also synthesized in Li–Cr or Li–Co systems. By contrast, Li–Ni oxide nanoparticles were not synthesized in the Li–Ni system. Nucleation temperatures of each metal in the considered system were evaluated. The relationship between the nucleation temperature and melting and boiling points suggests that the melting points of metal oxides have a strong influence on the formation of lithium metal oxide nanoparticles. A lower melting temperature leads to a longer reaction time, resulting in a higher fraction of the lithium metal oxide nanoparticles in the prepared nanoparticles.

Nickel nanoparticles were prepared by the arc discharge method. Argon and argon/hydrogen mixtures were used as plasma gas; the evaporation of anode material chiefly resulted in the formation of different arc-anode attachments at different hydrogen concentrations. The concentration of hydrogen was fixed at 0, 30, and 50 vol% in argon arc, corresponding to diffuse, multiple, and constricted arc-anode attachments, respectively, which were observed by using a high-speed camera. The images of the cathode and anode jets were observed with a suitable band-pass filter. The relationship between the area change of the cathode/anode jet and the synchronous voltage/current waveform was studied. By investigating diverse arc-anode attachments, the effect of hydrogen concentration on the features of nickel nanoparticles were investigated, finding that 50 vol% H₂ concentration has high productivity, fine crystallinity, and appropriate size distribution. The synthesized nickel nanoparticles were then used as catalysts in a hybrid sodium–air battery. Compared with commercial a silver nanoparticle catalyst and carbon black, nickel nanoparticles have better electrocatalytic performance. The promising electrocatalytic activity of nickel nanoparticles can be ascribed to their good crystallinity, effective activation sites, and Ni/NiO composite structures. Nickel nanoparticles prepared by the direct current (DC) arc discharge method have the potential to be applied as catalysts on a large scale.

We describe magnetohydrodynamic power generation experiments with seed-free high-temperature inert gas plasma using a linear-shaped Faraday-type generator driven by a shock-tunnel facility. The influence of inlet total temperature between 6500 and 9000 K on the plasma characteristics and its influence on generator performance are shown. By increasing the inlet total temperature, streaky and unstable plasma, characterized by large fluctuations in power output, is transformed into homogeneous and stable plasma, providing stabilized and improved power output. A quasi-1-D numerical simulation suggests that the plasma in the generator undergoes recombination when the inlet total temperature is high, which might be a factor in plasma stabilization. At the optimum load resistance, the enthalpy extraction ratio is improved to 12.9%; the optimum load resistance decreases as inlet total temperature is increased by the increase in electrical conductivity.

Effects of the driving frequency on temperature in a multiphase ac arc were successfully clarified. A multiphase ac arc is one of the thermal plasmas, which is suitable for producing functional materials such as nanoparticles, in-flight glass melting, and waste treatment in terms of its large plasma volume, high-energy efficiency, and low flow velocity. The temperature and arc behavior in various driving frequencies were investigated by the observation system consisting of a high-speed video camera and bandpass filters for plasma spectroscopy. The temperature measurement was conducted on the basis of the Boltzmann plot method. The obtained results indicated that the arc behavior and its temperature field were strongly influenced by the driving frequency. An increase of the frequency led to concentrated arc region, higher arc temperature at the center of electrode region and lower arc fluctuation. The temperature and its distribution can be controlled depending on the material properties to be treated and the purpose of the process.

In order to investigate effects of metal vapor on the plasma state in welding process, electron temperature in helium Gas Tungsten Arc(GTA) plasma during welding was measured by using the laser scattering method. Furthermore, density distributions of metal ions were also measured by using the spectroscopic analysis. Our results showed that plasma during welding consisted of two plasma regions, namely, pure helium plasma region and quasi-metal plasma region.