Sulfur in the Corrosion of Superalloys.
Abstract
Radiotracer sulfur-35 has been diffused into single crystals of nickel oxide as a function of oxygen pressure, doping additions of lithium or chromium and temperature (1000 to 1250 C). The measured data were found to deviate markedly from the error function complement dependence for diffusion from a constant source. The deviation is attributed to the migration of sulfur by the 'double mode simultaneous diffusion mechanism.' The faster mode is suggested to be via nickel vacancies and the slower mode via oxygen vacancies. The diffusivities are: D(fast) = 2.94 exp (-86.6 kcal/RT) and D(slow)= 1.08 x 10 to the -9th power exp(-32.8 kcal /RT). These data show that sulfur migrates through nickel oxide by two different mechanisms at two different rates. A concurrent study was performed on the SO2-O2 corrosion of Ni and Ni-2 1/4% Cr alloy between 900 and 1050 C. Constant oxygen pressure (20%) was used and 0, 2, 5 and 10% SO2 with the balance argon. The rates of corrosion increased as the percent SO2 increased, attaining an apparent maximum between 5 and 10%. No sulfides were found at the nickel-nickel oxide interface. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1977
- Accession Number
- ADA047652
Entities
People
- J. Bruce Wagner Jr.
Organizations
- Northwestern University