Manufacture and Characterization of Nanoparticles for Energetic Applications

Abstract

It is established nowadays in combustion science and technology that every flame can pro-duce particles, even when it appears to be particle-free. Starting from this assumption, flames are considered no longer only as a reactive flow with internal energy transfer, but also as a reactor for synthesizing gaseous and solid species. Traditional combustion aerosol technology is focused on studying nanosized particulate matter formation during combustion of hydrocarbons, considered as unwanted pollutants, in order to understand the onset of their formation and minimize their emis-sions. On the other hand, in flame aerosol synthesis nanoparticles are desired products, and the knowledge of their formation is the starting point to set up cheap flame reactors. The main objective of this Ph.D. thesis is the development and control of specific aerosol flame synthesis (AFS) systems for the production and the subsequent characterization of engineered nanomaterials. The work was focused on metal oxides based nanomaterials, carbonaceous nano-materials and carbon-metal oxides nanocomposite. The flame reactors used for the synthesis of carbon nanomaterials were constituted by un-doped flat laminar ethylene/air premixed flame, operated in fuel-rich condition, in which vapor car-bon precursors are given by the unburned fuel. Different carbonaceous particles were produced by changing flame equivalent ratio and particle residence time (i.e, sampling position). Properties of synthesized nanoparticles, such as 2D/3D character, optical features, chemical structure, electrical behavior and interaction forces, were characterized with respect to the flame reactor characteristics. Regarding the production of metal oxides nanoparticles and carbon-metal oxides nanocom-posites, an Aerosol Flame Synthesis (AFS) system was developed and successfully operated in VAFS mode to produce pure, monodisperse nanoparticles of magnesium oxide and titanium diox-ide, by feeding magnesium and titanium precursors to a fuel-lean hydrocarbon flame reactor. Finally, the AFS system was operated in fuel-rich flame reactor conditions, in order to syn-thesize pure TiO2 and carbon-TiO2 nanoparticles with similar dimension and compositions. A char-acterization of nanoparticle health effects, for personal care products applications, in terms of Reac-tive Oxygen Species (ROS) production was performed, showing that flame-synthesized titania pro-duces a lower amount of ROS with respect to commercial TiO2. The presence of carbon induces a further decrease of ROS production, leading to a reduction of nanopowder skin toxicity.