In Situ Raman Spectroscopic Investigation of Nickel Hydrothermal Corrosion
James E. Maslar, Wilbur S. Hurst, Walter J. Bowers Jr., Jay H. Hendricks, M I. Aquino
A nickel coupon was exposed to air-saturated water at a pressure of 25.4 MPa and temperatures ranging from 21 C to 460 C in an optically accessible flow cell. In situ Raman spectra were collected at a number of temperatures as the coupon was heated and then cooled. The coupon also was characterized ex situ with Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, and X-ray diffraction. Corrosion species were observed in situ at temperatures above 249 C during heating and under all conditions during cooling. The species were identified as NiO and α-CrOOH. The α-CrOOH originated as a corrosion product released from the optical cell and/or flow system. The NiO Raman features are more intense during cooling than at the corresponding temperatures during heating, indicating that NiO is present in greater amounts and/or is more crystalline during cooling.