Abstract
Characteristics of burning and non-burning sprays generated by a coaxial air-assistnozzle, previously used for the synthesis of ceramic nanoparticles by flame spraypyrolysis (FSP), are studied using phase Doppler anemometry. Also, the effectof droplet interaction on the overall combustion behavior of the spray (groupcombustion) and, consequently, on the characteristics of flame-made ceramic particlesis investigated. A physical model is proposed which correlates the formation ofinhomogeneous mixtures of micron-sized hollow particles and solid nanoparticles to thecombustion mode: the precursor droplets which entirely evaporate in the hot flame areresponsible for the formation of nanoparticles. The vapor species react, formingintermediate and product molecules and clusters that quickly grow to nanosized ceramicparticles. On the other hand, under certain conditions, a small number of thedroplets, particularly with large initial sizes, escape from the spray boundaries andbecome extinguished, producing large hollow ceramic particles. It is also possiblethat some of the large droplets, which lie within the spray core, do not entirelyevaporate. These surviving droplets then form large particles which are usuallyhollow but can collapse to solid particles at sufficiently high temperatures. Also, acriterion for the formation of homogeneous ceramic nanoparticles is presented.
Published Version
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