CORROSION-RESISTANT COATINGS (AL2O3) PRODUCED BY METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION USING ALUMINUM-TRI-SEC-BUTOXIDE

The metal organic chemical vapour deposition (MOCVD) of amorphous alumina films on steel was performed in nitrogen at atmospheric pressure. This MOCVD process is based on the thermal decomposition of aluminium-tri-sec-butoxide (ATSB). The effect of the deposition temperature (within the range 290-420-degrees-C), the precursor vapour pressure (5.33 x 10(-3)-2.67 x 10(-2) kPa), and the gas flow (6.5-12.51 min-1) of the MOCVD process have been studied in relation to corrosion properties at high temperatures. The corrosion experiments were performed at 450-degrees-C in a gas atmosphere containing 1% H2S, 1% H2O, 19% H-2, and balanced Ar. It was found that the amount of corrosion products on an alumina film (0.20 +/- 0.05 mg cm-2)-AISI 304 combination decreased with increasing deposition temperature of the coating. This was more pronounced for the products formed through the coating owing to a certain porosity. The crack density, where products were also formed, was almost unaffected.