Thermodynamic model for grain boundary effects on hydrogen solubility, diffusivity and permeability in poly-crystalline tungsten

Abstract

A thermodynamic model to evaluate effects of grain boundary (GB) on hydrogen behaviors in poly-crystalline tungsten is established. With this model, the effective solubility, diffusivity and permeability of hydrogen in tungsten equilibrated with surrounding H2 gas can be calculated as a function of grain size, temperature and H2 partial pressure. By setting 1.0eV to the binding energy of hydrogen to GBs and 0.4eV to the diffusion barrier of hydrogen along GBs, the model reasonably reproduces some experimental data on the effective diffusivity and permeability. Comparisons between calculation results by the model and available experimental data show that GBs significantly affect the hydrogen behaviors up to around 1000K or higher in practical materials. Therefore, the effects of GBs need to be considered in analysis of experimental results, for which the present model can be utilized, and in prediction of tritium inventory and leakage in fusion reactors.