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論文題目「Synthesis of Titanium Boride Nanoparticles by Induction Thermal Plasmas」
Cheng Yingying
An experimental study has been conducted for boride functional nanoparticles fabrication in RF plasma reactor in this paper. Titanium-based boride was selected as model of investigation. In the thermal plasma, the mixed powders of titanium with boron were evaporated immediately and nanoparticles were produced through the cooling process. The experimental parameters of plasma gas, powder feed rate, boron content in the feed powders and carrier gas flow rate investigated played an important role in the producing of titanium boride nanoparticles. The nanoparticles were characterized based on phase composition in the product and crystalline diameter. X-ray diffractometry and transmission electron microscopy were used to characterize and measure the particles. The nanoparticles of titanium-based boride produced on the reactor wall had the average crystalline diameter from 10 to 45 nm. The diameter of TiB was smaller than that of TiB2. The mass fraction of TiB had the range from 0% to 99.58%.
Helium used as a secondary gas with argon enhances heat transfer from the plasma to heavy particles. The crystalline diameter of as-prepared particles increases with the powder feed rate; the mass fraction of TiB decreases in the product of TiB and TiB2 with the increase of the powder feed rate. When a larger amount of boron is included in the feed powders, nanoparticle provide a smaller diameter and the mass fraction of TiB decreases in the product of TiB and TiB2. Increasing carrier gas flow rate, the mass fraction of TiB in product of TiB and TiB2 becomes larger, and the crystalline diameter of TiB2 decreases. These results provided evidence to suggest that boride nanoparticles can be produced by RF-ICP and also the crystalline diameter and composition were controllable.
The detailed mechanism of boride nanoparticle collective growth remains poorly understood. Because it is impossible to observe every process using experimental approaches directly; only the characteristics of the final products can be evaluated.
In the future work, theoretical/numerical approach as a powerful tool has to be carried out to clarify the titanium boride nanoparticle growth and to predict the profiles of nanoparticles that will be synthesized. In numerical simulation, the temperature and flow profile of the induction thermal plasma, the precursory powders trajectory and temperature history in the plasma flow and the nanoparticle formation will be investigated. The numerical results will be compared with the experimental results.
The formation of metastable boride nanoparticle in Ti-B, Al-B, Si-B, Mo-B, and Ta-B systems will be investigated in the future work. The synthesis of metastable materials requires quench process. In phase diagrams, Ti3B4, AlB10 and AlB12 have been shown to be a line compound. They are not stable, and difficult to synthesize by conventional synthesis methods. RF plasma is possible to synthesize these metastable materials due to the rapid quenching rate.
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