Characterization of the oxidation and oxidation-sulfidation of chromium niobium alloys

Materials in mixed corrosion environments, such as those in coal gasification processes or other energy conversion systems, may be exposed to both oxygen and sulfur. Alloys that exhibit simultaneous oxidation and sulfidation resistance are sought for these applications. Alloys containing sufficient Al or Cr readily form a protective oxide scale but generally have high sulfidation rates. Refractory metals, such as Nb or Mo, form protective sulfides but oxidize at catastrophic rates. Materials containing additives of one of these groups have been studied for their complex corrosion resistance. A binary alloy containing components from each group (Cr and Nb) has been investigated in mixed oxidants .Isothermal thermogravimetric measurements give overall scale growth kinetics but do not give details for complex scales or substrates. Multiple layers, different growth regimes and preferential corrosion can complicate interpretation. The environmental SEM with a hot stage attachment allows the observation of scale development at temperature.