Influence of thin silicon films on deuterium and tritium permeation in steels

Samples of 21-6-9, 309S, and 1017 steels were coated with silicon films either by sputter-deposition or by pyrolysis of silane. The tritium/deuterium permeabilities of these samples in the pressure range 1.3 kPa to 100 kPa were then measured from 3200K to 6700K. Some surface layer characteristics were determined by Auger spectroscopy. Sputter-coated silicon films resulted in a lower permeability and a higher activation energy downstream side of the sample although a substantial barrier effect was also observed with silicon on the downstream side. The permeation results for thick and thin silicon films deposited by pyrolysis were qualitatively similar to the behavior of surface oxide coatings; that is, a thin film was a better barrier than a thick film and resulted in a higher activation energy for permeation