Mechanistic understanding of the roles of hydrogen in modification of oxide film of alloy 600 in high temperature high pressure water environment

The roles of H in the modification process of the oxide film of alloy 600 was investigated through a dual-exposed oxidation experiment with an in-situ H-charging method in a high temperature high pressure water environment. The selective dissolution of the NiO modified the oxide film into a defective and porous, single-layered Cr₂O₃ skeleton after oxidation with H charging. The modification process depended on three different chemical states of H with a varied distribution: i) H₂ molecule in water, ii) neutral H in the grain boundary of the oxide film, and, iii) proton (H⁺) in the lattice of the oxide film.