Thermal Aging of Combustion Chemical Vapor Deposited Oxide Coatings

Zirconia coatings containing yttria were deposited onto sapphire substrates using liquid fuel combustion chemical vapor deposition (CCVDSM) and subsequently aged in air at 1,200 degrees C. Toluene solutions, containing 2.5 and 7.5 mole percent Y 2-ethylhexanoate (Y 2-EH) (balance Zr 2-EH) and total metal concentrations (Zr + Y) of 0.005 M and 0.02 M, were used. All coatings were polycrystalline with those produced from the higher Y 2-EH solutions displaying complex microstructures, including dendrites at the higher molarity. Gas temperatures measured with a thermocouple during deposition near the substrate surfaces were between 1,200 and 1,400 degrees C. Thermal aging produced significant effects on the coatings' morphologies and x-ray diffraction . patterns. Diffusional processes during annealing caused particle coalescence, and smoothed and densified the coatings. The x-ray diffraction data indicate that substantial microstructural changes occur in these coatings at 1,200 degrees C.