【作者】 史跃岗；

【导师】 陈石；

【作者基本信息】 大连理工大学 ， 工程热物理， 2009， 硕士

【摘要】 纳米TiO₂是一种应用非常广泛的纳米材料,其具有的光催化性在太阳能电池,光催化合成等诸多方面显示出十分诱人的前景。而二氧化钛光催化活性与其粒径密切相关,并且颗粒粒径特性对颗粒产品的性能产生极大的影响,这就要求对颗粒粒径的影响因素有很好的了解和控制。采用火焰CVD法,在丙烷/空气扩散火焰中氧化前驱物（TiCl₄）制备纳米二氧化钛颗粒,研究进气条件对TiO₂纳米颗粒粒径的影响,并初步研究了进气条件对颗粒晶型的影响。本文共讨论了4种不同的进气条件,结果发现:丙烷与空气流速决定火焰的温度;丙烷流速越大,颗粒粒径则越大;而空气流速越大,颗粒粒径却越小;TiCl₄流速越高,颗粒粒径越大;而载气流速的升高对颗粒粒径大小几乎没有影响。应用CFD商业软件fluent,引入颗粒动力学模型（Pratsinis,1998）,模拟表面氧化反应、稀释作用以及热迁移现象对颗粒粒径的影响,结果表明:包含表面氧化反应的颗粒粒径要大于相同位置不包含表面氧化反应的颗粒粒径,而且表面氧化只是发生在反应的初期,在离燃烧室入口较近处对颗粒粒径有着较大的影响,在出口处由于先驱物和氧化剂浓度的关系对颗粒粒径几乎没有影响;气体稀释作用在火焰区域影响很大,明显抑制了颗粒粒径的增长,而在非火焰区域,湍流稀释作用很小,对颗粒粒径增长几乎不再发生抑制作用;如果同时考虑稀释作用与表面氧化作用,会发现气体对氧化产物TiO₂的稀释作用,明显抑制了颗粒的增长速度,对出口颗粒粒径的影响起决定性作用,而表面氧化反应仅在中心轴附近区域对颗粒粒径有较大的影响;热迁移作用对颗粒粒径的影响较小,仅在火焰内部对颗粒粒径有一定的影响。更多还原

【Abstract】 As an important nanosized material, TiO₂ nano-particle is applicable to production and living widely.Its photocatalytic activity is widely used for solar battery and photocatalytic synthesization and so on.Particle characteristics like size and size distribution mainly influence the final product quality and photocatalytic activity of TiO₂.This emphasizes the need for discussion and control for the influencing factor of particle size.The CVD method is used to produce TiO₂ nano-particle in the propane-air diffusion flame. The effect of different operating conditions on particle size and crystal form is investigated. There are four different operating conditions analyzed. The results show that temperature is influenced mainly by the rate of propane and air; the higher the rate of propane is, the bigger particle size is, while the higher the rate of air is, the less particle size is; besides particle size is consistent with the rate of TiCl₄; while the influence of the rate of carried gas on particle size is negligible.Using the commercial CFD-code FLUENT and the additional fluid-particle dynamics （Pratsinis, 1998）, the simulation of the effect of surface oxidation reaction , dilution and thermophoretic on particle size is performed. The result show that, mean particle diameter with surface oxidation reaction considered is bigger at the same position. Meanwhile the influence of surface oxidation reaction on particle size is obvious at the beginning of reaction but negligible at the outlet because of the relation between precursor and oxidant concentration. The increase of particle size is evidently restrained by dilution in the flame region, but hardly in the non-flame region due to the little effect of dilution. If we take the surface oxidation reaction and dilution into consideration, the dilution restrains obviously the velocity growth and affects deeply the particle size, while surface oxidation reaction effect merely particle size near the centerline.we also find that thermophoretic just have a little influence on particle size inside the flame.更多还原