| dc.description.abstract | Abstract
Generation of nonoparticles via gas-phase reaction has many advantages over other methods. This study utilizes thermal plasma as the energy source for nanoparticles synthesis and aims to develop a thermal plasma system to synthesize nanoparticles. Three devices have been developed for the purpose. Although the first one is capable of producing nanoscale particles, a lot of welding slags are produced during the process and the obtained particles are apt to form hard aggregates. Therefore, another system based on non-transferred thermal plasma is developed. Due to small cross section and volume, corresponding to 9.5 cm2 and 0.95 L, the quenching gas and plasma gas cannot be well mixed. Besides, the fact that the quenching gas is injected in one direction causes the cooling performance is not good enough for obtaining narrow particle size distribution. In order to improve the cooling performance, a water cooling steel reactor with larger cross section (900 cm2) and volume (72 L) is designed and constructed and named as APTPR (atmospheric pressure thermal plasma reactor). Compared with the results obtained with the senond system, APTPR can effectively narrow down particle size distribution.
The influences of several operating parameters, including precursor feeding way, feeding rate, plasma power, flow rate of quenching gas and pressure on particle sizes and crystal form are investigated in this study. The experimental results indicate that the TiO2 powder synthesized by TiCl4 fed through plasma torch is mainly rutile. However, the particles size distribution is broader, about 10-40 nm. Amorphous TiO2 particles with uniform size, corresponding to 9 nm, can be obtained while TiCl4 is injected into plasma jet. Moreover, a higher feeding flow rate of TiCl4 results in the smaller specific surface area of the particles. The specific surface area obtained using flow rate of 0.41 and 0.59 lpm are 179 and 93 m2/g, respectively.
To overcome particle agglomeration problem, dispersion of the original particles via supersonic technique is conducted in this study as well. Experimental results indicate the optimal concentration of surfactant DT-760 is 0.5%. Due to the higher strength of cavitation, using audio frequency of 20,000 Hz as the mechanical source is suggested. Dispersion of generated particles is better as a higher energy density is applied. | en_US |