Corrosion resistant coatings (Al2O3) produced by metal organic chemical vapour deposition using aluminium-tri-sec-butoxide

Abstract

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 aluminiumtri-sec-butoxide (ATSB). The effect of the deposition temperature (within the range 290-420 °C), the precursor vapour pressure (5.33 x 10-3_2.67 x 10-2 kPa), and the gas flow (6.5-12.5 1 mint) of the MOCVD process have been studied in relation to corrosion properties at high temperatures. The corrosion experiments were performed at 450 °C in a gas atmosphere containing 1% H2S, 1% H20, 19% H2, 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.

Al2O3 coatings against high temperature corrosion deposited by metal-organic low pressure chemical vapour deposition

“…This means that uniform coatings can be deposited at higher deposition temperatures. In our case the slopes of the plots were 65 + 2 kJ mo1-1 at low and 83___ 5 kJ mol -~ [6] at atmospheric pressure. But a shift of the critical temperature to a lower value (from 370°C (atmospheric pressure) to 300 °C (low pressure)) was observed.…”

“…The slopes of the plots in the reaction rate limitation regime were calculated to be 65 + 2 kJ mol -~. This value is lower than the one obtained from atmospheric pressure CVD (83 +5 kJmol -~) [6]. Furthermore, the growth rates are about 10 times lower at 0.17 kPa and the coatings have less variations in colour, so they are more uniform.…”

“…The application of metal aikoxides as precursors has several advantages: (1) these compounds can be purified to a high degree; (2) they contain enough oxygen for the formation of the desired oxide, which means that no additional compounds have to be added to the gas stream--this is an advantage over the use of trimethyl aluminium (TMA) with oxygen or nitrous oxide [7]; (3) the deposition temperature is much lower than for the formation of AI203 from AICI3, CO2 and H 2 [8,9]. ATSB has until recently been used only as a precursor for the deposition of AI203 at atmospheric pressure [5,6]. From the results obtained it was clear that more research was necessary to produce crack-and pore-free A1203 coatings.…”

“…In recent years A1203 has also been investigated for application as a protective coating against high temperature corrosion in coal gasification environments. The A1203 coatings were produced by MOCVD using the metal alkoxides alurninium tri-isopropoxide (AI(OC3H7)3) [4] and aluminium tri-sec-butoxide (ATSB) (Al(OC4Hg)3) [3,5,6] as precursors. The application of metal aikoxides as precursors has several advantages: (1) these compounds can be purified to a high degree; (2) they contain enough oxygen for the formation of the desired oxide, which means that no additional compounds have to be added to the gas stream--this is an advantage over the use of trimethyl aluminium (TMA) with oxygen or nitrous oxide [7]; (3) the deposition temperature is much lower than for the formation of AI203 from AICI3, CO2 and H 2 [8,9].…”

High-temperature oxidation of an alumina-coated Ni-base alloy

“…Alumina has been deposited by several techniques including atomic layer epitaxy (4), pyrolytic decomposition (5,6) spray pyrolysis (7), ion assisted deposition (8,9), laser physical vapor deposition (lo), reactive sputter deposition (2), air plasma spray (11) and chemical vapor deposition (12)(13)(14)(15)(16)(17)(18)(19)(20)(21). The alumina coatings in the present work were deposited by a recently developed open-air CVD process called combustion chemical vapor deposition (22).…”