Air-plasma spraying colloidal solutions of nanosized ceramic powders

Coatings prepared from nanosized powders were obtained by spraying ethanol-based colloidal solutions into a plasma plume. The powders investigated included 40 nm -Al₂O₃, 75 nm 8 wt% Y₂O₃-ZrO₂, and 750 nm 25 wt% CeO₂-ZrO₂. Spray distances from approximately 50 to 63 mm were required to achieve significant coating deposition. As observed in the TEM, the typical lamella morphology of air plasma sprayed oxide coatings was not observed in coatings fabricated from 40 nm -Al₂O₃, which was comprised of spherical powders that had partially sintered. However, lamellae were observed in the coatings prepared with both nanosized zirconia powders. The characteristic size of the lamella and the grains that comprised the zirconia coatings were nominally a few nanometers.