The dynamics behaviors of nanoparticles in flames, including coagulation, coalescence and deposition, are the basic physical process in a wide range of heterogeneous combustion systems, e.g. the vapor phase synthesis of TiO2, SiO2, carbon black nanoparticles; the combustion of Al nanoparticles; the formation of urtrafine particles in coal combustion. Based on the system of flame synthesis using a stagnation-swirl flame, the present work studies the coagulation, coalescence and depsotion of nanoparticles in stagnation flames. By the means of synthesis experiments, in-situ laser diagnostics and molecular dynamics(MD) simulation, the present work investigates the growth of nanoparticles in flames and deposition in boundary layers at a flow field scale, as well as particle or molecular scale issures such as the interaction force between particles, the collision rate enhanced by attractive forces and the nano-scale coalescence process influenced by high surface curvature, which are crucial for the understanding of nanoparticle transport phenomenonna. The manucript also reports a novel in-situ laser diagnostics phenonmon called low-intensity phase-selective laser-induced breakdown spectroscopy and related technique.

High purity anantase nanoparticles below 10nm and nano-porous films are successfully synthesized by stagnation-swirl flames. Parametric study shows that the precursor concentration and strain rate are the controlling parameters for the synthesis of nanoparticles in stagnation flames. The precursor concentration dominates when final particle size stays below the critical sintering size. When the final particle size exceeds the critical sintering size, the residence time becomes important, which can be controlled by strain rate in stagnation flames. The experimental measurement of deposition rate and theoretical analysis indicates that the boundary layer can be divided into three regimes: convection-controlled regime, transition regime and thermophoresis-controlled regime. The gas transport in convection-controlled regime and thermophoretic Peclet number in thermophoresis-controlled regime jointly determine the deposition rate. As for the property of nano-porous film formed by the deposition of nanoparticles, the simultaneously influence from Brownian motion and thermophoresis is crucial, resulting a smaller porosity for larger depositing particles.

The interaction force between two anastase particles are studied by MD simulation, showing a permanent dipole arising from the asymmetric distribution of ions at the surfaces. The dipole-dipole interaction is comparable to van der Waals force and remarkablely enhances the collsion rate, by enlarging the capture radius. The dipole effect decays at high temperatures due to the large fluctuations. The simulation of coalescence process of nanoparticles indicates a viscous flow mechanism for particles below the critical diameter, which appear to be amorphous due to the strong influence from surface curvatures. As for the particles above the critical diameter, the coalescence process is controlled by surface diffusion at the initial stage and recrystallization in the final stage, since the grain structure consists of a crystalline core and an amorphous shell.

A novel low-intensity laser-induced breakdown spectroscopy (LIBS) is discovered during the study of in-situ laser dignotics for nano-aerosols. While the laser energy is large than the breakdown threshold of gas phase and smaller than the breakdown threshold of particles phase, the breakdown only happens at each indivual nanoparicle without visible spark and the gas phase is not broke down. Meanwhile the atomic emission from the particle is collected, revealing information on particle elementary composition, volume fraction and size.