In-situ laser diagnostic of nanoparticle formation and transport behavior in flame aerosol deposition

Abstract

In this work, we investigate the flame aerosol deposition of TiO2 nanoparticles in a well-defined premixed stagnation flame based on two-dimensional phase-selective laser-induced breakdown spectroscopy (PS-LIBS). The deposited nanoparticles are in anatase phase with an average size of ∼10 nm. In PS-LIBS measurement, atomic emissions of titanium near the wavelength of 500 nm are extracted by spectral filter lenses and imaged for demonstrating the particle volume fraction distributions. The PS-LIBS signals can well depict the whole process of particle formation and transport, including the rapid gas-to-particle conversion near the flame front, dilution and concentrating of the nanoparticles induced by gas density variations, and dropping of particle volume fractions near the substrate. A quantitative model has been proposed to describe convection, thermophoresis, and diffusion of the nanoparticles. Combining the PS-LIBS measurement and the numerical simulation, it is found that, the nanoparticles concentrate outside the boundary layer at low substrate temperatures due to a joint effect of gas compression and thermophoresis. Further parametric analysis indicates that substrate temperatures and precursor loading rates can strongly affect the particle concentration boundary layer and the particle deposition rate.