Diffusion and hydration of oxygen confined in Fe(OH)2 nano-cracks at high temperatures

• Published in: The Journal of supercritical fluids 2017-02, Vol.120, p.345-354
• Main Authors: Kallikragas, Dimitrios T., Choudhry, Kashif I., Svishchev, Igor M.
• Format: Article
• Language: English
• Subjects: Iron hydroxide surfaces; Molecular oxygen; Nano confinement; Supercritical water
• ISSN: 0896-8446; 1872-8162
• DOI: 10.1016/j.supflu.2016.06.011

[Display omitted] •Confinement of supercritical water.•Diffusion and hydration of oxygen in nano-cracks.•Implications for stress corrosion cracking.•Atomic density profiles between Fe(OH)2 surfaces. Molecular dynamics simulations were conducted of an oxygen molecule in high temperature water confined between parallel iron hydroxide surfaces spaced at 10, 20 and 80Å apart. Radial distribution functions, coordination numbers, diffusion coefficients, and density profiles across the gap are provided. At supercritical conditions, the oxygen was found to be most likely situated in the centre region of the gap. Hydration numbers increased as the spacing of the surfaces increased and the mean diffusion coefficients for both oxygen and water were seen to be lower than their values in the bulk systems. However, the lateral diffusion coefficients of oxygen through the nano-cracks at supercritical water conditions were greater than the mean diffusion coefficients in the bulk. The effect of confinement on the water structure was seen to diminish with 20Å of surface spacing and was absent with 80Å of separation.