Silicon Volatility From Alumina and Aluminosilicates Under Solid Oxide Fuel Cell Operating Conditions

Thermodynamic equilibrium modeling indicates that the introduction of H 2 O in oxidizing environments decreases Si stability due to formation of volatile hydroxide and oxy hydroxides. 3 Al 2 O 3 ·2 SiO 2 mullite bond offers only slight improvement over pure silica as the thermodynamic activity of silica in mullite is near unity. In reducing atmospheres Si stability is improved by the presence of H 2 O and Al 2 O 3 , transitioning from SiO and silane as the dominant volatile species to hydroxides, oxy hydroxides, and SiO with increasing water vapor partial pressure. Empirical studies reveal initial rapid releases of Si from stationary solid oxide fuel cell refractory materials followed by slower solid‐state diffusion limited release.