A Combined Numerical and Experimental Investigation of Droplet Transport in Solution Precursor Plasma Spray Process (SPPS)

The Solution Precursors Plasma Spray (SPPS) is an emerging thermal spray process that utilizes a solution as a liquid feedstock suitable for the deposition of sub-micron-sized particles for applications in thermal barrier coatings and super-icephobic coatings. During the SPPS process, the droplet undergoes several thermo-physical stages, including an aerodynamic breakup, solvent vaporization, and precipitation of the dissolved solute to form a particle. Several parameters such as droplet size, solute concentration, thermophysical characteristics of the precursor, velocity, and temperature field of plasma affect the final morphology of the particle forming the coatings. In this study, droplets are composed of zirconium acetate as the solute dissolved in a mixture of water and ethanol. To address the challenging problem of particle morphologies by SPPS, the present work develops a numerical approach to model solvent evaporation and shell formation based on coupled heat and mass transfer equations within a single droplet in a plasma field. Subsequently, the calculated shell thickness is validated against a carefully designed experiment in a radio frequency plasma reactor using a droplet generator. Additionally, the effects of different heating rates, droplet size, and residence time on particle morphology are investigated, paving the way for a better understanding of SPPS.