FLAME SYNTHESIS OF METAL NANOPARTICLES

Nanosized materials are playing a crucial role across a wide range of applications. New advanced techniques for the production of engineered nanoparticles and their characterization are in great demand. The aim of this work is the development and control of a high temperature reactor for the production of engineered nanoparticles taking advantage from our previous studies on combustion-generated fine carbonaceous particles. The reactor consists of a laminar premixed flame, homogenously doped with monodisperse droplets of precursor metal dissolved or dispersed in volatile solvents. The droplets are generated by a vibrating orifice aerosol generator, and injected into the burner composed by a stainless steel tube with Mullite Zirconia placed on its top. The burner is heated above 100 °C to ensure solvent evaporation and the feeding of the precursor metal particles directly in the high-temperature environment generated by the flame. By changing the flame stoichiometry from fuel-lean to fuel-rich conditions it is possible to obtain pure metal particles or mixtures of metal and organic materials. Particles are collected by thermophoresis, inserting a cold substrate in the flame by means of a pneumatic actuator. Morphological and dimensional analysis are performed on the collected particles by Atomic Force Microscopy (AFM), Raman Spectroscopy and Scanning Electron Microscopy (SEM). The latter technique is coupled with Energy-Dispersive X-Ray Spectroscopy measurements, in order to obtain the chemical composition of the generated nanoparticles. Scanning probe microscopy and AFM allows inferring both qualitative and quantitative information on many physical properties including size, morphology, surface texture and roughness and electrical conductivity. Preliminary results have been obtained by inserting in a premixed stoichiometric flame of ethylene/air 50 micron droplets of metal nitrate solutions (nickel, cadmium, lead and magnesium) at different concentrations. Collected particles show sizes ranging from more than 100 nm down to less than 10 nm having a wide range of morphologies and chemical compositions. The nanoparticle characteristics depend on the precursor concentrations, the flame temperature and the rate of heat transferred from the hot burnt gases of the flame to the precursor metals.