Abstract
Aluminum oxide and chromium oxide were deposited onto untreated and pre-oxidized Ni coupons by metal–organic chemical vapor deposition. Oxidizing the surface prior to the deposition of the ceramic coating has been studied to determine the effect of the intermediate oxide layer. The metal oxide coatings were obtained from their respective metal acetylacetonate precursors. The pyrolysis reactions were carried out under atmospheric conditions. Amorphous Al 2O 3 was obtained at a deposition temperature of 500 °C and crystalline Cr 2O 3 with the corundum structure was obtained at 450 °C. The effectiveness of the metal oxide coatings as barriers were evaluated by oxidation experiments at 800 °C for 120 h. Samples coated with Al 2O 3 exhibited a significant decrease in oxidation rate. However, Cr 2O 3 coated on both untreated and pre-oxidized samples were not effective barrier coatings. Samples involving Cr 2O 3 deposited on untreated Ni showed an increase in oxidation rate whereas samples with Cr 2O 3 on heat-treated Ni showed a similar oxidation rate as uncoated Ni. The microstructures were investigated with scanning electron microscopy. Composition and crystalline structures were determined with X-ray diffraction and elemental analysis.
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