ORNL's iron aluminides (Fe3Al) do not corrode readily in sulfur-containing environments because they form an aluminum oxide coating. "The aluminum oxide (Al2O3) film resists attack by sulfur," says Sikka, "but if the sulfur should break through, Al2O3forms rapidly again to prevent the propagation of any sulfur attack. Our iron aluminide alloy provides higher resistance to sulfidation when exposed to hydrogen sulfide and sulfur dioxide gases than any other iron-based or nickel-based alloy."