Development of an in situ Raman spectroscopic system for surface oxide films on metals and alloys in high temperature water

In order to directly analyze the structure of oxide films on metals and alloys in high temperature water conditions, an in situ Raman spectroscopic system has been developed, utilizing Ar-laser with sapphire/diamond window assemblies as a part of an Alloy 690 autoclave. The performance of the developed in situ Raman spectroscopic system was verified using high purity NiO, NiFe2O4, Cr2O3, and NiCr2O4 powders. Obtained reference Raman spectra in room temperature air environment agreed well with published results. The developed Raman system has been applied for the characterization of the surface oxide films of a nickel-base Alloy 600 in typical primary water conditions of pressurized water reactors (PWRs); water with 1000 ppm boron and 2 ppm lithium at a pressure of 18 MPa and temperatures ranging up to 350 °C. In situ Raman spectra were collected for Alloy 600 in PWR water conditions at different temperatures up to 350 °C, while the specimens were heated and then cooled. In this study, NiO, Cr2O3, and NiCr2O4 phases were observed for Alloy 600 in PWR water conditions, in reasonable agreement with earlier results of ex situ studies.