High-speed visualization of metal oxide precursor in multiphase AC arc during nanoparticle formation

The purpose of the present work is to elucidate the formation mechanism of metal oxide nanoparticles in a multiphase AC arc, which is one of the most attractive thermal plasma sources. Lanthanum oxide nanoparticles were focused on, on the basis of spectroscopic diagnostics and thermodynamic considerations. The dynamic behavior of lanthanum vapor and lanthanum monoxide in a multiphase AC arc was visualized by a high-speed camera through band-pass filter optics. Furthermore, the two-dimensional temperature field of the multiphase AC arc was successfully estimated by the same camera system based on the relative intensity method, which included the emissions from the lanthanum atom and lanthanum ion. The obtained temperature profile and intensity profile of lanthanum and lanthanum monoxide suggest that the oxidation from lanthanum to lanthanum monoxide occurred following thermodynamic equilibrium. Understanding these fundamental phenomena in the thermal plasma nanofabrication process enables one to expand the capability of thermal plasma for innovative material processing.