AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Collisional Growth, Charging and Measurement of Molecular Clusters to Sub-10 nm Particles in High Temperature Flame Environment
GIRISH SHARMA, Rajan K. Chakrabarty, Pratim Biswas, Washington University in St Louis
Abstract Number: 554 Working Group: Meet the Job Seekers
Abstract It is important to understand the early stages of particle formation and growth in high temperature combustion systems for both nanoparticle synthesis and environmental applications. According to conventional understanding, at high flame temperatures, the particles collide with each other and coagulate to form larger particles. Contrary to this understanding, our previous work shows that during the early stages of particle formation and growth (< 2 nm), charged particle fraction is very high (> 95%), suggesting that in addition to neutral particle interactions, there are charged particle, and ion-particle interactions as well.
My PhD work can be divided into three major chapters viz. collisional growth, measurement, and charging of sub-10 nm particles. First, collisional growth of titania nanoparticles is studied at moderately high temperatures from 400 – 800 C; and it was found that the collisional growth rate is found to be higher than predicted by kinetic theory of gases. Experiments show that there is higher enhancement in the collisional growth as compared to theories based on Hamaker constant. Following this, molecular dynamics simulations are performed to understand the interatomic forces that lead to this enhancement in collisional growth.
Second, the commonly used equipment for sub 2 nm particle measurement, half-mini differential mobility analyzer is characterized. The working section of the half-mini DMA is simulated using commercial software COMSOL. Comparison of the simulated transfer function with existing models from Knutson-Whitby and Stolzenburg is also elucidated. It is found that the former model overestimates the resolution; whereas the latter is close to the simulation results for aerosol flow to sheath flow above 0.067. This work provides a useful method to study the flow regimes and transfer function of a high flow DMA.
Third, the well characterized half-mini DMA is used to study the early stages of particle formation and growth mechanism for titania nanoparticle synthesis from TTIP precursor in a flame aerosol reactor as well as soot nanoparticles from McKenna burner. The insights from the total and charged particle size distribution, starting from molecular clusters to sub-10 nm particle size provides new insights into the particle formation and growth mechanism. To further understand the role played by charge, a model for simultaneous charging and coagulation is developed using the method of moments.