The diffusion rate of hydrogen in zirconium oxides is a factor in both the steam oxidation and the hydriding of zirconium alloys. It has been suggested that the measured rates of hydrogen uptake in zircaloys exposed to high-temperature steam can be explained by the diffusion of protons through the surface oxide layers, since the measured uptake and diffusion of neutral hydrogen species in zirconium oxides is very low. This paper investigates the diffusion of protons in tetragonal zirconia at 1500K using denstity functional theory based molecular dynamics and metadynamics simulations. A mean calculated diffusion rate of 5×10-9 / m2s-1 is obtained, which compares well with the value of 3.2×10-10 / m2s-1 obtained by fit to experimentally determined diffusivities of hydrogen in yttrium stabilised zirconia. The simulations show that the "proton" is present as the hydrogen atom in a hydroxide ion and analysis of the electronic structure reveals that the diffusion of the proton is mediated by two-electron-three-centre bonds that form between hydroxide and adjacent oxide ions.

RABONE Jeremy;  VAN UFFELEN Paul; 

2015-01-19

ELSEVIER SCIENCE BV

JRC89211

0022-3115,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC89211,   

10.1016/j.jnucmat.2015.01.002,