High-temperature stability of amorphous A_l2O₃ deposited on Si and CeO₂-stabilized ZrO₂ by metalorganic chemical vapor deposition

Aluminum acetylacetonate and water vapor were used to deposit an amorphous Al₂O₃ seal coating on Si and CeO₂-stabilized ZrO₂ (CSZ) produced by air plasma spray. The Al₂O₃ coating prepared at ∼500°C was ∼2.5μm thick, uniform, and non-porous. The crystallization and adhesion characteristics of the Al₂O₃ coating were examined by thermally annealing the Al₂O₃-coated Si and CSZ substrates in air. The amorphous coating crystallized to metastable Al₂O₃- phases within 20 hours at temperatures as low as 700°C. The coating on Si spalled upon annealing whereas the coating on CSZ did not spall, but microcracked extensively due to the significant volume shrinkage associated with crystallization.