In situ Raman spectroscopy was employed to investigate corrosion of 304L stainless steel in air-saturated water at a pressure of 25.2 Mpa and temperatures up to 496 C in an optically accessible flow cell. The steel also was characterized ex situ with Raman spectroscopy and scanning electron microscopy. After exposure, the steel surface consisted of a NiFe2O4 film with an overlayer of α-CrOOH Crystallites. Α-CrOOH originated as a corrosion product released from the optical cell and/or flow system. NiFe2O4 was first identified after the coupon was heated to 247 C and was observed under all subsequent conditions. At 247 C, the NiFe2O4 was probably disordered, however, upon heating to 326 C the crystallinity and possibly the thickness increased significantly. Α-CrOOH was first identified after the coupon was heated to 326 C and was observed under all subsequent conditions. In situ Raman spectra indicated that NiFe2O4 was present in greater amounts and/or was more crystalline during cooling, while there was probably less α-CrOOH present in the Raman scattering volume during cooling than during heating.
Issue: No. 9
Pub Type: Journals
agueous corrosion, corrosion product release, hydrothermal oxidation, in situ optical spectroscopy, NiFe<sub>2</sub>O<sub>4</sub>, Raman spectroscopy, spinel, stainless steel