Corrosion of Mullite by Molten Salts

Abstract

The interaction of molten salts of different Na 2 O activities and mullite is examined with furnace and burner tests. The more‐acidic molten salts form small amounts of Al 2 O 3 ; the more‐basic molten salts form various Na 2 O–Al 2 O 3 –SiO 2 compounds. The results are interpreted using the Na 2 O–Al 2 O 3 –SiO 2 ternary phase diagram, and some possible diffusion paths are discussed. The generally higher melting points of Na 2 O–Al 2 O 3 –SiO 2 compounds lead to better behavior of mullite in molten salts, as compared to SiO 2 ‐protected ceramics such as SiC. Mullite‐coated SiC is discussed, and the corrosion behavior is evaluated.