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Exposition of sol‐gel alumina‐coated P92 steel to flue gas: Time‐resolved microstructure evolution, defect tolerance, and repairing of the coating
Author(s) -
Wollschläger Nicole,
Nofz Marianne,
Dörfel Ilona,
Schulz Wencke,
Sojref Regine,
Kranzmann Axel
Publication year - 2018
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.201709712
Subject(s) - chromia , coating , materials science , flue gas , microstructure , diffusion barrier , spall , diffusion , metallurgy , layer (electronics) , chemical engineering , porosity , composite material , oxide , chemistry , physics , organic chemistry , engineering , thermodynamics
Technically relevant P92 steel (9% Cr) was coated with a micron‐thick porous alumina layer prepared by sol‐gel technique and treated with flue gas (60 CO 2 ‐30 H 2 O‐2 O 2 ‐1 SO 2 ‐7 N 2 (mole fraction in %)) at 650 °C to mimic an oxyfuel‐combustion process. Local defects in the coating were marked using focused ion beam (FIB) technique and were inspected after exposition to hot flue gas atmosphere at 300, 800, and 1300 h, respectively. Local defects like agglomerated alumina sol particles tend to spall off from the coating uncovering the underlying dense chromia scale. Re‐coating was found to restore the protection ability from oxidation when repeatedly treated with hot flue gas. Cracks and voids did not promote the local oxidation due to the formation of crystalline Mn/S/O species within and on top of the coating. The protective character of the steel‐coating system is a result of (i) the fast formation of a dense chromia scale at the surface of sol‐gel alumina‐coated P92 steel bars in combination with (ii) the porous alumina coating acting as diffusion barrier, but also as diffusion partner in addition with (iii) fast Mn outward diffusion capturing the S species from flue gas.