Numerical Investigation for Growth Mechanisms of Ti-Based Intermetallic Nanoparticles in RF Thermal Plasmas

Summary form only given. Nanoparticle synthesis with RF thermal plasmas has been proposed as an attractive material process since RF thermal plasmas have several advantages such as high enthalpy, high chemical reactivity, variable properties, large plasma volume and long residence/reaction time due to the comparatively low velocity. Furthermore, they are inherently clean since they can be generated without internal electrodes. RF thermal plasmas are intensively useful to synthesize intermetallic nanoparticles of borides and silicides providing high electrical conductivity, heat/wear resistance and hardness. However, the synthesis includes difficult processes with vapor pressure differences. Only a few studies about the synthesis of boride and silicide nanoparticles in RF thermal plasmas have been conducted up to the present. The growth mechanisms of Ti-based intermetallic nanoparticles of borides and silicides in RF thermal plasmas are still poorly understood. Therefore, numerical investigation was conducted for the synthesis of Ti-based intermetallic nanoparticles in an RF thermal plasma to clarify the growth mechanism for Ti-B system and Ti-Si system. In Ti-B system, nuclei of boron are produced and grow in the upstream position, and titanium vapor subsequently condenses on the boron nanoparticles. On the other hand in Ti-Si system, silicon nucleates, and the vapors of titanium and silicon condense on the silicon nuclei simultaneously. Critical diameters as well as homogeneous nucleation rates are strongly dependent on the supersaturation ratios and the surface tensions. The fewer nuclei with the larger sizes are produced in Ti-Si system. An amount of the vapors consumed per one nucleus to grow is larger since a smaller number of the larger nuclei are produced in Ti-Si system. As the result, the obtained particle diameters in Ti-Si system show larger than those in Ti-B system. The boron content in the boride nanoparticles shows a wide range since condensations of- titanium and boron occur at the different positions. The silicon content in the silicide nanoparticles shows a narrow range since condensations of titanium and silicon occur simultaneously