Functionally Graded Aluminum Nitride-Oxide Coatings for Hot Pipe Protection
DOE Phase II Contract DE-FG02-04ER83939
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. The 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 deposited which adhered well to mild steel substrates.
In the Phase II project 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.
The main application for this technology will be corrosion prevention in high temperature pipeline utilized in key industries such as power plants, petrochemical plants, and paper mills. A related application will be prevention of steam promoted heavy metal cation migration in stainless steel steam pipes found in coal gasification power plants.