Aerosol Synthesis of Nanostructured Materials
The scientifical and technological interest in nanostructured materials is currently tremendously increasing. 1–3 The basis of this interest is related to the extraordinary properties that powders and materials at the nanometer or subnanometer scale exhibit. 4-6 Such properties result from their structure that distinguish them from conventional polycrystalline materials by the size of the crystallites that compose them as well as a large volume fraction of interface and grain boundaries. The nanostructured materials research efforts emphasize the synthesis routes for the generation of ultrafine powders with control over particle size, shape, composition and morphology as the key issue in advanced materials synthesis.1 The aerosol synthesis route enables the generation of new nanoparticles and nanomaterials either as coatings or powders as single, complex metal oxides, nonoxides or metals by adjusting the precursor chemistry.7 The starting-point of the aerosol synthesis of nanostructured materials is the generation of discrete droplets of the starting solution (aerosol) and control over aerosol decomposition in a high temperature tubular flow reactor.8.9 The successive processes of solvent evaporation, drying, solute precipitation and decomposition proceed through heterogeneous gas-liquid/solid reactions in dispersed system ensuring high surface reaction and limiting any compositional segregation to the droplet level.9 By controlling the precursor solution chemistry, processing parameters and mechanisms of particle formation through either the surface or volume precipitation of droplets it is possible to tailor the powder size, morphology, chemical and phase compositions. The condition for aerosol generation ultrasonically with special emphasis on the various particle morphology synthesis is reviewed in this paper. The importance to model the phenomenon of mass and heat transfer occurring during the evaporation/drying stage is discussed from the viewpoint of the parameters leading to a certain particle morphology. It is demonstrated that aerosol synthesis of nanostructures can be realized in a controlled manner by adjusting the aerosol droplet size and precursor chemistry.
KeywordsSpray Pyrolysis Strontium Ferrite Aerosol Droplet Droplet Coalescence Particle Synthesis
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