In-situ Surface Enhanced Raman Spectroscopy Investigation of Surface Film Formed on Nickel and Chromium in High-temperature and High-pressure Water

In-situ surface enhanced Raman spectroscopy (SERS) was used to characterize surface films formed on Ni and Cr in high-temperature and high-pressure water. NiO shows a Raman peak at 540 cm^-1 due to crystal defects. Below -0.75 V, Ni-SERS has a very weak peak at 540 cm^-1, which is associated with air-formed oxide. Above -0.7 V, a stable NiO film is formed. Cr-SERS shows a strong peak at 540 cm^-1 and a weak peak at 610 cm^-1, which can be associated with a formation of CrOOH, or Cr₂O₃, or a mixture of two. The intensity of 610 cm^-1 peak decreases as the potential is raised and CrOOH is converted to Cr₂O₃. The identification on the surface films formed on Ni-Cr alloy in high-temperature and high-pressure water was discussed.