Numerical Studies of Hydrogen Outgassing from Copper Electrodes
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Results of hydrogen diffusion in copper are obtained based on molecular dynamics simulations. Temperature dependent diffusion coefficient values obtained here from the simulations agree well with experimental reports in the literature over a wide range spanning 300 K to 1330 K. Simulations with and without a grain boundary have also been carried out to probe their role on hydrogen outgassing from copper, a typical material for electrodes in high pulsed power systems. The results obtained show increased out-diffusion in the presence of a grain boundary (GB), and anisotropic transport, with increases parallel to the GB plane and reduction in the normal direction. The behavior likely arises from distortion of atoms in the GB region which provide alternate paths for atomic hops within the GB core. This result suggests that capping the metal surface, by a few nanolayers of a suitable coating or an oxide, may help reduce outgassing from the grain boundaries inherent in the copper material. In this research, a thin tungsten layer (a few monolayers thick) was added to arrest the outgassing from the metallic copper. It was observed that with inclusion of the tungsten layer, the diffusion rate became very negligible compared to the situation without the tungsten layer.