(174g) Nano-Structured Ceramic ALD Coatings to Stabilize SiC Against Oxidation in High Temperature Steam Solar Thermal Water Splitting Applications

Silicon Carbide (SiC) is an ideal material for many high-temperature applications due to its resistance to thermal shock and high thermal conductivity. However, SiC degrades in water-rich environments limiting its applications in extreme oxidative environments such as combustion engines, heat exchangers, and high temperature solar thermal reactor materials. Current deposition methods for environmental barrier coating (EBCs) such as plasma spraying and aerosol spraying generate micron-scale films with inherent grain boundaries and cracks. Atomic layer deposition (ALD) generates nano-scale films that are dense, crack-free, and chemically bonded to the surface without the use of excess precursor. We have found that the application of ALD EBCs significantly improves the oxidation resistance of SiC in extreme environments with a film four orders of magnitude thinner than standard applications. We have grown ALD layers of our desired materials on high surface area SiC particles using a fluidized bed particle ALD reactor in order to investigate the chemistry of steam oxidation. Using thermogravimetric analysis, it has been shown that these coatings improve the oxidation resistance of SiC by up to 2/3 at 1000^oC. Isothermal kinetic analysis was used to compare the kinetic effects of the ultra-thin coatings, and based on derived rate expressions, a 10 nm film is predicted to enhance the lifetime of SiC parts by 3X. We have successfully demonstrated the use of ALD coated SiC solar thermal reaction tubes on-sun at NREL’s high flux solar furnace.