In Situ Raman Spectroscopic Investigation of Stainless Steel Hydrothermal Corrosion
James E. Maslar, Wilbur S. Hurst, Walter J. Bowers Jr., Jay H. Hendricks
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.