Study of Alkali- and Sulfur-Enhanced Corrosion of Advanced Energy Systems. Final Report

摘要

The initial stage of MHD anode corrosion process appears to be dominated by out-diffusion of metallic species into the powder deposit. In addition, K and S appear to diffuse into the native oxide and underlying metal substrate. The out-diffusion process clearly leads to a loss of metal species from either the native oxide or metal substrate, while in-diffusion leads to the formation of sulfides and possibly to the accumulation of K containing compounds which may ultimately flux the protective oxide scale. The results for MHD anodes may be compared with those from previous studies of alkali-sulfur enhanced corrosion of turbine alloys. Although the specific details of these studies differ, both agree that rapid or catastrophic corrosion is preceded by a variable length induction period. During this period, relatively small changes in weight are observed. However, the protective metal oxide scale is breached which establishes the condition for rapid direct attack by condensed corrosive deposits. Thus, the mechanisms and kinetics of processes associated with the induction period are of great interest in understanding the survivability of various alloys. In the corrosion modeling effort, it was found that a simple model which considered only the diffusion-limited corrosion of iron did not correctly predict the iron corrosion product species for iron-based alloys. This lack of agreement was due to the absence of the treatment of other metal constituents in the alloy which form corrosion products. A more detailed model which includes equilibrium and diffusion relations for all metal species is required for accurate modeling of the corrosion product composition. 14 refs. (ERA citation 10:044510)