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

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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.