Stabilization of Silicon Carbide Via Nano-Structured ALD Thin Films

Producing hydrogen fuel via solar thermal water splitting is an energy-intensive reaction, requiring temperatures up to 1500°C. When operating at such extreme temperatures, it is imperative to have robust materials for reactor vessels and heat exchangers. Silicon Carbide (SiC) is an ideal material for these types of high temperature applications, however it is oxidized by steam at high temperatures and corrodes over time. The use of environmental barriers is well established to prevent oxidation and corrosion of materials. By depositing nano-structured thin films via atomic layer deposition (ALD), this work shows that it is possible to significantly improve the oxidation resistance of SiC. Alumina (Al₂O₃ ) and mullite, an aluminosilicate sensitive to stoichiometry, were investigated as possible coatings to protect SiC. Alumina is known to be stable at high temperatures and chemically inert to the active materials used to catalyze water splitting, however alumina cracks very easily when exposed to large temperature swings like those observed during cloud cover when using concentrated solar power. Mullite has been shown to be a promising material for oxidation resistance and also has similar thermal properties to SiC. In particular, Mullite has a coefficient of thermal expansion close to that of SiC, which would provide resistance to cracking during operation. SiC particles were coated via atomic layer deposition (ALD) and thermogravimetric analysis (TGA) was used to expose these materials to steam at high temperature to determine the effectiveness of the film for protecting the substrate against oxidation.