Thermal Aging of Combustion Chemical Vapor Deposited Oxide Coatings

Abstract

Zirconia coatings containing yttria were deposited onto sapphire substrates using liquid fuel combustion chemical vapor deposition (CCVD^sm ) and subsequently aged in air at 1,200°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°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 micro structural! changes occur in these coatings at 1,200° C.