Suspension plasma spraying of YPSZ coatings: Suspension atomization and injection

Among processes evaluated to produce some parts of or the whole solid-oxide fuel cell, Suspension Plasma Spraying (SPS) is of prime interest. Aqueous suspensions of yttria partially stabilized zirconia atomized into a spray by an internal-mixing co-axial twin-fluid atomizer were injected into a DC plasma jet. The dispersion and stability of the suspensions were enhanced by adjusting the amount of dispersant (ammonium salt of polyacrylic acid, PAA). A polyvinyl alcohol (PVA) was further added to the suspension to tailor its viscosity. The PVA also improved the dispersion and stability of the suspensions. The atomization of optimized formulations is described implementing Weber and Ohnesorge dimensionless numbers as well as gas-to-liquid mass ratio (ALR) value. Drop size distributions changed from monomodal distributions at low We to multimodal distributions when We number increases. The viscosity of the suspensions has a clear influence on the drop size distribution and suspension spray pattern. The secondary fragmentation of the drops due to the plasma jet was evidenced and the final size of the sheared drops was shown to depend on the characteristics of the suspension. Rather dense zirconia coatings have been prepared, which is a promising way to produce electrolyte.