Oxidation behavior of an 11Cr ferritic–martensitic steel after Ar-ions irradiation in supercritical water

Oxidation Processes and Involved Chemical Reactions of Corrosion-Resistant Alloys in Supercritical Water

“…They then react with oxygen (see reaction ), high-temperature water, and anions to form oxides and hydroxides, and finally precipitate on the alloy surface. As for Cr, Ni, and Fe, reaction can further be expressed by reactions –. ,, The second stage takes place in some of the reactions among the oxides and hydroxides mentioned. The two reaction stages can be explained by the solid-state growth mechanism and the metal dissolution/oxide precipitation mechanism .…”

“…At the initial stage of oxidation, dissolved oxygen diffuses to the metal interior through short circuit paths (e.g., micropores and grain boundaries), and then preferentially reacts with Cr to form Cr-rich oxides (mainly Cr 2 O 3 ) at the initial metal/H 2 O interface through reaction . ,,− This can be attributed to the higher oxygen affinity of Cr than that of Fe and Ni. − As a result, a continuous compact inner layer is formed due to the high lattice diffusion coefficient of Cr ion in Cr 2 O 3 and the high diffusion rate of O along grain boundaries . In addition, Cr 2 O 3 , CrO 3 , and Cr 2 O 7 2– may also be produced via reactions – ,,,,− in the processes above.…”

“…Although the alloy with a high Cr content tends to form a dense, continuous, and protective Cr 2 O 3 layer than does the alloy with a low Cr content, the optimum Cr content is approximately 20 wt % commonly. , However, Cr 2 O 3 can evaporate in the forms of CrO 3 , CrO 2 (OH), and especially CrO 2 (OH) 2 in SCW with a high oxygen content . More specifically, Cr 2 O 3 and CrO 3 can react with water and oxygen to form an oxide hydroxide (i.e., CrO 2 (OH) 2 (chromium­(VI)) by reactions ,,,,,,,− and . CrO 2 (OH) 2 is an active volatile species and probably formed in the metal wastage process in high-temperature and high-pressure water on the oxide/substrate interface .…”

“…Besides, NiO can also be formed by the reactions of Ni and H 2 O/oxygen based on reactions –. ,− NiO is stable in mildly basic oxidizing SCW and acts as a barrier to inhibit ion diffusion, whereas it is unstable in a neutral oxidizing SCW. Owing to the reduction of the oxygen partial pressure on the interface of oxide film and alloy substrate, the decomposition of NiO can occur via reactions and ., Ni 2+ can also react with high temperature water and OH – derived from water ionization to form Ni hydroxide through reactions –. ,, Herein, the ionization of water is realized via reactions and . However, Ni­(OH) 2 can be decomposed and reduced into NiO and Ni in SCW by reactions and , respectively. where n = 1, 2 The surface treatment process affects chemical reactions of elements in alloys.…”

Early oxidation of Super304H stainless steel and its scales stability in supercritical water environments

“…For thin scales on thick substrates, the stress produced in an intact, adherent scale by a temperature change, DT, can be adequately approximated by Ref. [28] …”