【作者】 欧阳欣；

【导师】 李晓杰； 闫鸿浩；

【作者基本信息】 大连理工大学 ， 工程力学， 2009， 博士

【摘要】 气相爆燃与爆轰法是通过引爆由可燃气体、气相氧化剂和前驱体所组成的混合气体来制备纳米氧化物的一种新型的合成技术。此方法不仅具有爆轰法操作简单,易于控制,高效、经济和节能等优点,而且生成物产量高、无杂质,并且易于进行工业化生产。本文利用气相爆燃与爆轰法制备出了纳米级的二氧化钛颗粒,并对其合成反应机理进行了研究,主要工作内容与成果如下:1.对氢气与空气混合气体的爆燃和氢氧混合气体爆轰过程中的爆炸压力进行了测量实验,通过高速摄影机拍摄了氢气与空气爆燃和氢气与氧气爆燃转爆轰过程中火焰面的传播过程。氢气与空气的实验中,反应是爆燃反应,从观察窗口观察得到其最大火焰速度在250 m/s左右,最大爆炸压力约为0.5 MPa。氢气与氧气的爆轰实验中,反应在初始端处在爆燃转爆轰的过程中,由于湍流的影响,火焰面产生了畸变,导致了燃烧速度加快,最终在管尾发展形成气相爆轰。距离起爆端0.46 m处,火焰面速度为1300 m/s,其后仍在不断加速,最大爆炸压力约为2.0 MPa。环境温度的改变对氢氧气体爆轰的最大爆炸压力和爆炸压力上升速率的影响较小;而氢气空气混合气体爆燃的最大爆炸压力和爆炸压力上升速率随着环境温度的增加而增加。2.对密闭管道中氢气与空气和氢氧混合气体的反应过程进行了数值模拟,发现氢气与空气反应属于爆燃反应,而氢氧反应属于爆轰反应。氢气与空气反应过程中,管道内压力和温度随着时间增加而升高,火焰阵面前出现压缩波,火焰面后的气体密度降低。随着反应的进行,火焰在管道中从点火点向另一端传播,传播到管尾时反应结束。氢氧爆炸反应中,反应由爆燃反应逐步的转化为了爆轰反应,模拟结果与实验结果比较吻合。3.通过调整初始氢气与空气混合气体的初始环境温度、注入的前驱体的量等参数,从而对爆燃合成的纳米二氧化钛晶粒尺度、组成与形貌进行主动控制,实现了选择性合成二氧化钛纳米粉体。根据克劳修斯—克拉佩龙方程推出了四氯化钛的蒸汽压与温度的关系曲线。在环境温度未达到前驱体的气化温度时,注入的前驱体一部分气化,而另一部分在反应器的内管壁形成气溶胶状态或吸附于内管壁,这对气相爆燃和爆轰合成产物的组成、晶粒尺度分布和形貌有着较大的影响。4.以氢气与氧气的混合气体为爆炸源,以四氯化钛为前驱体,进行了气相爆轰合成二氧化钛纳米粉的研究,并对产物的结构和性质进行了表征。我们发现相对氢气与空气混合气体的爆燃合成,相同工况下氢氧混合气体的爆轰合成反应速度更快,释放的热量也更大,爆轰合成出来的二氧化钛颗粒形态更趋于球形,而且控制好四氯化钛的浓度时,产物的分散性也较好。这说明气相爆轰法相对于气相爆燃法有一定的优势,是一种有前景的制备纳米二氧化钛粉体的方法。5.利用反应热力学理论分析了爆轰过程中纳米二氧化钛的成核、长大过程。分析了在化学反应、晶核形核、晶粒生长、晶粒间吸附凝聚等过程中的一系列影响因素。改进了kruis模型,推导出了气相爆燃合成和爆轰合成的晶核扩散生长模型,计算结果和实验结果比较符合。分析和讨论了气相爆燃和爆轰合成中颗粒的相变机理,结合理论公式和实验结果得出部分二氧化钛颗粒是在氢氧燃烧反应区外水解生成的结论。更多还原

【Abstract】 Gas-phase Deflagration and Detonation method is a new synthesis technology for preparing nanomaterials by detonating the combustible gases, gas-phase oxidants and precursors. Not only is it simple operation, easy control, high efficiency, low costs and energy efficiency, but also it is high output, high purity and easy for industrialization. In this paper, TiO₂ nanoparticles were produced by gas-phase deflagration and detonation method, and the synthesis mechanism had also been studied. The main work and results are as follows:1. The detonation pressure of hydrogen-air deflagration and hydrogen oxygen detonation were measured. The flame propagation processes of deflagration and detonation were photographed by high speed cameras. In the deflagration reaction of H₂ and air, the maximum flame velocity is about 250 m/s in the obserbing window, and the maximum detonation pressure is about 0.5 MPa. In the initial stage of the reaction H₂ and O₂, it is under transition from deflagration to detonation. Then the frame front produced distortion due to the turbulence, which leads to the increase of combustion velocity. Finally the reaction is up to detonation at the tail of pipe. The flame velocity is about 1300 m/s at the distance of 0.46 m from the initiation, and the velocity becomes higher. The maximum detonation pressure is about 2.0 MPa when the reaction finished. The ambient temperature has less influence on the maximum pressure and the pressure rising rate in the detonation reaction of H₂ and O₂. With the ambient temperature increase, the maximum pressure and the pressure rising rate rise in the deflagration reaction of H₂ and air.2. The numerical simulation processes of hydrogen-air reaction and hydrogen-oxygen reaction are studied. It can be proved that the hydrogen-air reaction is deflagration reaction, and the hydrogen-oxygen reaction is under detonation. In the reaction of H₂ and air, the pressure and temperature rise with time. Furthermore, compression wave appears ahead of flame front. Otherwise, gas density decreases behind of flame front. With the process of reaction, the flame propagates from the ignition to another end until the reaction finished. In the reaction of H₂ and O₂, the deflagration reaction gradually turns to the detonation reaction. Compared with the experimental results, the numerical simulation results are identical.3. With changing the ambient temperature and the content of precursor, we could selectively synthesize TiO₂ nanoparticles by controlling the particle size and shapes of TiO₂ particles. According to Clausius-Clapeyron equation, we deduced the relation curve between vapor pressure of titanium tetrachloride and gasification temperature. When the ambient temperature did not reach the gasification temperature of titanium tetrachloride, the titanium tetrachloride turned into aerosol, which would change to foggy droplets nearby the inner wall of pipe. In the above case, it would have great influence on the particle size and the shapes of TiO₂ particles.4. Using titanium tetrachloride as the source of TiO₂, the experiments for synthesizing TiO₂ nanoparticles were carried out by detonating the premixed gas of H₂ and O₂. The structures and properties of the as-prepared TiO₂ nanoparticles were also characterized. Compared with the reaction of H₂ and air, the reaction of H₂ and O₂ more easily reach detonation which react faster and order more heat in the same conditions. The shapes of TiO₂ nanoparticles which were synthesized by gas-phase detonation tend to sphere, and it could have good dispersibility. The results indicated gas-phase detonation synthesis method was a promising method for industrial production in the future.5. Based on the reaction thermodynamics theory, the nucleation and growth processes of TiO₂ nanoparticles were analyzed in the detonation. The influencing factors of chemical reaction, crystal nucleation, grain growth and intercrystalline adsorption-condensation were studied. Moreover, the kruis model was improved. And the growth model of crystal nuclear proliferation for gas deflagration and detonation synthesis was derived. The calculation results are close to the experimental results. The phase transition mechanism of grains synthesized by gas deflagration and detonation was analyzed and discussed. In the end, combining with experimental results and theoretical formulas, it is found that some TiO₂ particles are formed by pyrohydrolysis outside the combustion reaction.更多还原