Single droplet combustion of iron nitrate-based precursor solutions: Investigation of time- and size scales of isolated burning FSP-droplets

Abstract

Flame spray pyrolysis (FSP) is a powerful and versatile technique for the rapid and scalable synthesis of functional nanoparticles. The route of nanoparticle formation depends on the mass transfer of liquid precursor droplets into the gas phase, significantly deciding the quality of generated nanoparticles. Therefore, the study of time- and size scales of isolated burning FSP-droplets plays an important role in better understanding and promoting the use of this technique. Hereby, we have used a low-cost iron nitrate-based precursor-solvent system to investigate the disruptive burning process of single droplets with initial droplet diameters ranging from 48 µm to 125 µm. Different timescales at the level of steady droplet combustion and µ-explosions were correlated to droplet sizes. It has been observed that the total lifetime of a droplet converges towards the duration of the µ-explosion process for small droplet sizes causing the µ-explosion to occur immediately after ignition. In order to study the effect of the solvent composition of ethanol and 2-ethylhexanoic acid (2-EHA), the volumetric fraction of 2-EHA was varied from 20% up to 80%. An increasing fraction of 2-EHA causes the onset of the disruption to occur later and the droplet to become more concentrated with precursor. The results of this work provide fundamental insights into single droplet combustion and contribute to a better understanding of the use of low-cost precursor-solvent systems in FSP.