Coating effect on plasma-driven permeation of hydrogen in iron

The coating effect on plasma-driven permeation has been investigated with an incident energy of 750–3000 eV and an incident flux of (0.3–6.0) × 1017 ions m−2 s−1. Pure Fe (more than 99.95%) discs were coated with thin films of Pd or Au by r.f. sputtering on the front or the back. A good linear relationship was observed between the permeation flux and incident flux for all specimens. As temperature increases, the permeation flux through non-coated Fe decreases rapidly, while that through Fe coated with Pd on the back remains almost constant. The permeation flux increases with increasing incident energy in the range 750–1500 eV, but changes little in the range 2000–3000 eV. The permeation spike reappears after the specimen has been left in vacuum overnight, but no spike appears when the specimen is left in a hydrogen atmosphere overnight.