The Formation of Combustion Generated Particles: Using In situ Electron Microscopy to Advance our Understanding and Modeling

燃烧产生的纳米颗粒的形成无论是作为一种污染物，如煤烟，还是作为一种材料，如炭黑，都是重要的。最近，我已经能够将我的煤烟专业知识转化为炭黑的材料合成。炭黑(CB)本质上是一种纯煤烟，在复合材料、橡胶、塑料、电池和涂料等领域有着广泛的应用。这些纳米颗粒的聚集体和内部结构很重要，因为它们分别决定了烟尘和碳黑的健康效应和材料特性。这项研究计划的长期目标是对碳颗粒燃烧生成的增长有一个基本的了解，利用这种了解来开发详细的预测模型，并将这些模型应用于解决实际问题，如预测碳黑和碳烟的颗粒大小和聚集结构。这项提议将基于我们在煤烟形成方面的丰富经验，以及我们最近率先成功地使用环境透射电子显微镜(ETEM)以亚纳米分辨率实时可视化纳米级碳颗粒，因为它们因引入的气体而氧化和/或其内部结构因加热而变化；这项工作最近获得了两个奖项。这项提议将率先使用电子显微镜来探索粒子生长对初级粒子的桥接和包络的影响。目前的模型忽略了这一影响，通过假设不断增长的粒子的点接触高估了表面积。放置在埃特姆中的粒子将从我们的火焰或碳黑生产商那里获得。当纳米粒子与引入的碳氢化合物气体发生反应时，电子显微镜可以拍摄到它们的单个聚集体的图像。据信，还没有人使用ETEM来研究煤烟或碳黑颗粒的生长。此外，飞行时间二次离子质谱仪(TOF-SIMS)将提供一种新的方法来鉴定碳烟表面反应或吸附的物种的分子结构。短期目标是：(1)使用ETEM观察颗粒生长过程如何影响颗粒聚集和分子结构；(2)使用TOF-SIMS测量从我们的同流火焰或ETEM反应器中采样的颗粒表面的分子结构；(3)通过纳入第一和第二个目标的研究结果，改进我们的颗粒形成模型。这些模型将更好地预测颗粒的生长和表面性质；然后将用火焰的实验数据进一步验证它们。燃烧衍生纳米颗粒形成的多学科性质使其成为热科学研究领域的学生的极好培训。我最近毕业的所有博士生都进入了与论文研究相关的具有挑战性的职位，我的三名博士生最近也开始了终身教授的职位。

The formation of combustion-derived nanoparticles is important both as a pollutant such as soot and as a material such as carbon black. Recently I have been able to translate my soot expertise to the material synthesis of carbon black. Carbon black (CB), which is essentially a pure form of soot, has a wide range of applications such as in composites, rubbers, plastics, batteries and paints. The aggregate and internal structure of these nanoparticles is important as they determine the health effects and material properties of soot and carbon black, respectively. The long-term goals of this research program are to develop a fundamental understanding of the combustion-generated growth of carbon particles, to use this understanding to develop detailed predictive models and to apply these models to solve practical problems such as predicting particle size and aggregate structure of carbon black and soot. This proposal will be based on our deep experience in soot formation and our recent success in pioneering the use of an Environmental Transmission Electron Microscope (ETEM) to visualize, in real time, nanoscale carbon particles, with a sub-nanometer resolution, as they oxidize due to an introduced gas and/or as their internal structure transforms due to heating; this work recently won two awards. This proposal will pioneer the use of the ETEM to explore the effect of particle growth on bridging and enveloping the primary particles. Current models ignore this effect, overestimating the surface area by assuming point contact of growing particles. The particles placed into the ETEM will be obtained from our flame or from carbon black producers. The ETEM can image individual aggregates of nanoparticles as they react to introduced hydrocarbon gases in the electron microscope. It is believed that no one has used an ETEM to study the growth of soot or carbon black particles. Also, a TOF-SIMS (Time of flight secondary ion mass spectrometry) will provide a new method to identify the molecular structure of the species reacting or adsorbed on the soot surface. The short term objectives are we will: (1) use ETEM to look at how particle growth processes both affect and are affected by the particle aggregate and molecular structure; (2) measure the molecular structure of the surface of particles sampled from our coflow flame or our ETEM reactor using a TOF-SIMS; (3) improve our particle formation models by incorporating the findings of the first and second objectives. The models will better predict the particle's growth and surface properties; they will then be further validated with experimental data from flames. The multidisciplinary nature of combustion-derived nanoparticles formation makes it excellent training for students in the thermo-sciences research area. All my recent graduated PhD students have gone on to challenging positions related to their thesis research and three of my PhD students have recently begun tenure track professor positions.