Ion-driven permeation of hydrogen through surface-coated iron

The coating effect on ion-driven permeation has been investigated with an incident energy of 750-3000 eV and an incident flux of (0.42-4.26) x 10(17) H-2(+) m(-2) s. Pure Fe (above 99.95%) discs were coated with thin films of Pd or SiO2 by r.f. sputtering on the front side or the back side or both sides. For iron coated with palladium on the front side, no ion-driven permeation was observed. The permeation was determined to be limited by the recombination-recombination regime (recombination on both sides) under the experimental conditions. The permeation ratio, therefore, can be controlled by coating with a thin film on either of the two surfaces. The incident energy dependence of permeation ratio varies with different front surface. The chemisorption energy of hydrogen on the oxide surface was estimated to be 24 kJ mol(-1) for the naturally oxidized Fe surface and 27 kJ mol(-1) for the SiO2 surface.