Preliminary analysis of physical and chemical phenomena occurring in droplet at solution precursor plasma spraying of zirconia coatings

The study describes the physical and chemical phenomena occurring in a droplet at the solution precursor plasma spraying (SPPS) coating deposition. The analysis followed the process stages leading to obtain zirconia coatings from zirconium acetate precursor. The coatings were sprayed and characterized in our previous study. A simple mathematical model was developed to describe the phenomena occurring during the spray process. The results obtained with the model were correlated with the experimental data. The data were obtained by the characterization of the splats obtained at impact of particles on the substrate. In particular, the diameters of zirconia particles before these impacts were calculated from the splats images. The modeling required the knowledge of plasma jet 2-D velocity and temperature fields at the experiments. These data were obtained by using the GENMIX numerical code. Consequently, the heat and momentum transfer between plasma gas and droplets and particles was described and enabled predicting their velocities, trajectories and temperatures in-flight. The model estimates the duration of the chemical phenomena inside droplets and particles in-flight including evaporation of solvents, the homogeneous nucleation and the phases' transformations prior to zirconia particle melting. The simplified model was useful to predict whether the particles were liquid at impact with substrate and helped in optimizing the liquid feedstock injection pressure.