A new model for puffing and micro-explosion of single titanium(IV) isopropoxide/p-xylene precursor solution droplets

•A new model for the puffing and micro-explosion of precursor solution droplets is presented.•The puffing occurs if the inner part of the droplet reaches the boiling temperature of the higher volatile component of the droplet whereas the lower volatile component builds up a liquid shell at the droplet surface.•Micro-explosion occurs if the pressure inside the droplet exceeds the ambient pressure.•The model can capture situations in which puffing followed by micro-explosion is found as well as puffing throughout the final stage of droplet lifetime.•TTIP/p-xylene droplets are studied in a convective air flow and conditions typical for flame spray pyrolysis are presented.•The number of puffs depends on the initial droplet size, the relative velocity, the precursor loading, and the ambient gas temperature. In flame spray pyrolysis, the precursor solution droplet undergoes heating and evaporation, followed by gas phase combustion and generation of nanoparticles. Depending on the precursor solution, the precursor/solvent droplet may experience puffing and micro-explosion. A new one-dimensional model is developed to describe these processes in the spherically symmetric droplet interior with emphasis on the puffing and the micro-explosion. After the initial droplet heating, the preferential evaporation of the higher volatile component causes the accumulation of the lower volatile precursor at the droplet surface and thus forms a liquid shell that hinders the evaporation process. In the droplet interior away from the liquid shell, the higher volatile component accumulates and when the temperature reaches the boiling point of that liquid, puffing occurs. If the pressure inside the droplet exceeds the ambient pressure, the droplet undergoes micro-explosion. The present study concerns single precursor/solvent droplets of titanium(IV) isopropoxide (TTIP) in p-xylene at room temperature in hot convective air at atmospheric pressure. A parameter study is performed to show the dependence of the puffing and the micro-explosion on the initial precursor loading, the initial droplet size, the ambient gas temperature, and the relative velocity between the droplet and the ambience. There are situations where micro-explosion follows the puffing or puffing repeats until the end of the droplet lifetime with no micro-explosion. This is the first model to successfully describe the puffing in precursor solution droplets and the micro-explosion which may follow the puffing.