Particle Image Velocimetry Diagnostics for Suspension Plasma Spraying

In order to achieve SOFC with reduced costs, suspension plasma spray process (SPS) could be an attractive technique. This process uses atomized suspensions which penetrate the plasma: a bi fluid injector ensures the atomization of the suspension with argon at controlled flow rate and the radial injection of the spray into the plasma plume.

Understanding the relationships between suspension characteristics (particle size, surface tension, and viscosity), atomization (gas and suspension flow behaviour), operating plasma spray conditions and properties of the deposited layers is crucial to optimize coatings. In this study, the particle image velocimetry (PIV) diagnostic was first implemented to analyse the spray produced by the two-fluid atomizer. The design of the atomizing nozzle was changed in order to achieve high speed spray with narrow droplet size distributions and the resultant spray was characterized. As the particle states in the plasma play a critical role in the impact behaviour of the drop on the substrate and in turn on the coating morphology, the PIV diagnostic was adapted to the constraints of suspension plasma spraying. Both aqueous and ethanol suspensions of yttria stabilized zirconia (YSZ) powders were injected into the plasma using various injection parameters and operating conditions. The velocities and directions of the particles have thus been determined and correlated with coating morphologies.