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 750-3000eV and an incident flux of (0.3-6.0) x 1017 ionsm-2s-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 750-1500eV, but changes little in the range 2000-3000eV. 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. (orig.)