A comparative study of nanoparticles in premixed flames by scanning mobility particle sizer, small angle neutron scattering, and transmission electron microscopy

Scanning mobility particle sizer (SMPS) and transmission electron microscopy (TEM) studies were conducted for TiO2 and soot particles. The TiO2 particles were produced from a premixed stagnation ethylene–oxygen–argon flame (ϕ = 0.36) doped with titanium tetraisopropoxide. Soot was generated from a burner-stabilized premixed ethylene–oxygen–argon flame (ϕ = 2.5). The close agreement among SMPS, TEM, and X-ray diffraction results for TiO2 nanoparticles demonstrates that the probe sampling/mobility measurement technique is accurate for on-line analysis of the size distribution of particles as small as 3 nm in diameter. In the case of soot, notable disagreement between the SMPS and TEM sizes was found and attributable to the fact that the soot taken from the flame studied herein is liquid-like and that upon deposition on the TEM grid, the primary particles do not retain their sphericity. This interpretation is supported by measurements with photo ionization aerosol mass spectrometry, small angle neutron scattering, and thermocouple particle densitometry.