Thermo-physical processes in cerium nitrate precursor droplets injected into high temperature plasma

The thermo-physical phenomena inside a droplet during its flight in a thermal plasma flow have been modeled for SPPS processes using cerium nitrate precursor. The different thermo-physical stages encountered during droplets' flight include aerodynamic breakup, rapid vaporization of solvent and precipitation, internal pressurization with shell rupture and rapid heating of volumetrically precipitated ceramic particle. The effects of injection type (transverse versus axial) and initial size of the droplets on the final deposit layer microstructure have been studied. The results show that for axial injection the heating process is very rapid and smaller droplets (< 10 µm) undergo full pyrolization resulting in favorable microstructure. On the contrary for transverse injection the heating process is slower as the droplets are injected in the outer shear layer of plasma where the temperature and velocity both are much lower than the core of the plasma. The larger droplets (> 20 µm) have better chances of getting pyrolized in the case of transverse injection. It was also observed that the angle of trajectory of the droplets after primary (first) precipitation does not have much effect on the final microstructure.