In situ Raman spectroscopic investigation of zirconium–niobium alloy corrosion under hydrothermal conditions

In situ Raman spectroscopy was employed to investigate corrosion of a zirconium–niobium alloy in air-saturated water at a pressure of 15.5 MPa and temperatures ranging from 22 to 407 °C in an optically accessible flow cell. Monoclinic ZrO2 (m-ZrO2) was identified under all conditions after the coupon was heated to 255 °C for 19 h. Cubic ZrO2 (c-ZrO2) was tentatively identified in situ during heating at temperatures between 306 and 407 °C, but was not observed under any other conditions. Species tentatively identified as α-CrOOH and a CrVI and/or CrIII/CrVI compound were observed in situ during heating at temperatures between 255 and 407 °C, but were not observed under any other conditions. The chromium compounds were identified as corrosion products released from the optical cell and/or flow system.