Functionally Graded Aluminum Nitride - Oxide Coatings for Hot Pipe Protection

75080S Corrosion is a significant problem in pipelines exposed to corrosive and oxidizing conditions at high temperatures. Mild steel is the desired material for constructing these pipelines; however, mild steel corrodes very quickly compared to more expensive alloys. A new low-cost coating method is needed to deposit a corrosion resistant coating on the interior surface of mild steel pipes. This project will develop a low cost chemical vapor deposition method to deposit functionally graded aluminum-nitride/aluminum-oxide coatings onto the surface of mild steel. Aluminum nitride provides a strong chemical bond to the steel surface and aluminum oxide provides a high-temperature corrosion and oxidation-resistant surface. In Phase I, aluminum chloride molten salt and ammonia complexes were prepared. The aluminum chloride ammonia complex was then used to deposit aluminum nitride on the surface of mild steel using chemical vapor deposition techniques. By controlling deposition conditions, a functionally-graded aluminum- nitride/aluminum-oxide layer was shown to adhere well to mild steel substrates. In Phase II, deposition conditions will be optimized for controlling the density, composition, and thickness of functionally graded corrosion resistant coatings. Coated steel samples will be tested for corrosion/oxidation resistance and mechanical strength. Finally, the low-cost deposition process will be scaled-up to demonstrate commercial potential. Commercial Applications and Other Benefits as described by the awardee: The new coating technology should be applicable to the prevention of corrosion in high temperature pipelines, which are utilized in such key industries as power plants, petrochemical plants, and paper mills. A related application would involve the prevention of steam-promoted, heavy-metal-cation migration in stainless steel steam pipes, found in coal gasification power plants.