THIN ALUMINA AND SILICA FILMS BY CHEMICAL VAPOR DEPOSITION (CVD)

Alumina and silica coatings have been deposited by MOCVD (Metal Organic Chemical Vapor Deposition) on alloys to protect them against high temperature corrosion. Aluminium Tri-lsopropoxide (ATI) and DiAcetoxyDitertiaryButoxySilane (DAOBS) have been used as metal organic precursors to prepare these ceramic coatings. The influence of several process steps on the deposition rate and surface morphology is discussed. The deposition of SiO 2 at atmospheric pressure is kinetically limited below 833 K and is a mixed first and second order reaction with an activation energy of 155 kJ.mole −1 . The deposition of Al 2 O 3 is kinetically limited below 673 K and is a first order reaction with an activation energy of 30 kJ.mole −1 at atmospheric pressure. The deposition of Al 2 O 3 is kinetically limited below 623 K and is a second order reaction at low pressure (3 torr) with an activation energy of 30 kJ.mole −1 . The decomposition of both precursors involves a B-hydroge n elimination reaction by which DADBS decomposes to acetic acid anhydride, 2-methyl propane, SiO 2 and H 2 O, while ATI decomposes to 2-propanol, propane, Al 2 O 3 and H 2 O.