Mechanism of Na2 SO 4 Induced Corrosion at 600°–900°C

The kinetics of corrosion were measured by accelerated oxidation tests on Co‐30Cr and Ni‐30Cr as a function of temperature from 600°–900°C, in the environment and deposit composition. The alloys were rapidly attacked at temperatures between 650° and 750°C when a liquid sulfate phase was obtained from an initially pure solid deposit. The rapid rate of attack resulted from sulfation of the transient surface nickel or cobalt oxides and the dissolution of these transition metal sulfates into to yield a liquid phase. This retarded the formation of a protective scale. The exposure conditions under which liquids could form from mixtures were calculated from thermodynamic considerations.