In situ Raman spectroscopic investigation of chromium surfaces under hydrothermal conditions

• Published in: Applied surface science Vol. 180; no. 1; pp. 102 - 118
• Main Authors: Maslar, J.E, Hurst, W.S, Bowers, W.J, Hendricks, J.H, Aquino, M.I, Levin, I
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-08-2001; Elsevier Science
• Subjects: Analytical chemistry; Aqueous corrosion; Chemistry; Chromium; Chromium oxide; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Hydrothermal oxidation; In situ Raman spectroscopy; Materials science; Metals, semimetals and alloys; Oxidation; Physics; Specific materials; Spectrometric and optical methods; Surface treatments; 82.80.Ch; Aqueous corrosion; Hydrothermal oxidation; 81.05.Bx; Chromium oxide; Chromium; 81.65.Mq; In situ Raman spectroscopy; Raman spectra; Inorganic compounds; Transition element compounds; Surface treatments; XRD; Experimental study; Transition elements; Chromium oxides; Corrosion products; Oxidation; SEM; X-ray emission spectra; Hydrothermal condition
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/S0169-4332(01)00338-5

Three chromium coupons were exposed to air-saturated water at pressures of ca. 25
MPa and temperatures up to 545°C in an optically accessible flow cell. In situ Raman spectra were collected at different temperatures as the coupons were heated and then cooled. Coupons were also characterized ex situ with Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry, and X-ray diffraction. Coupons heated to either 374 or 505°C exhibited the same corrosion product, tentatively identified as α-CrOOH that originated as corrosion product released from the optical cell and/or flow system. A coupon heated to 545°C exhibited a variety of Cr
III, mixed chromium valence Cr
III/Cr
VI, and/or Cr
VI species during heating. During cooling, the same corrosion product was observed at all temperatures on this coupon and was tentatively identified as Cr
2O
3 with Cr
VI incorporated into the Cr
2O
3 Cr
III–oxygen network. The difference in observed corrosion processes among the three coupons was attributed to a difference in water purity to which they were exposed.