Hydrogen isotope exchange via water exposure at oxyhydroxide surfaces of stainless steel and silicon

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The rates at which hydrogen isotopes are exchanged on oxyhydroxide surface films of 304L stainless steel and Si(100) upon exposure to water vapor have been investigated. Surface films were prepared by bombardment with D2O+. The surfaces were then monitored by secondary ion mass spectroscopy and direct recoil spectroscopy as a function of water (H2O or D2O) exposure. A fast and a second much slower process characterize the exchange at both films. The processes are isotopically reversable. The fast process is limited by water exposure, complete in 5–10 Langmuirs (L) for both materials, and is considered to involve terminal hydroxyl groups. The slow process appears to be the bulk diffusion-limited exchange within the oxyhydroxide film. Exchange-diffusion constants have been derived from fits to TRIM calculations for depth-of-origin of sputtered species: Dex ∼10−18 and 10−19 cm2/s for the films on 304L stainless steel (SS) and Si, respectively, at 295 K. Dex for 304L SS is consistent with previous results on FeOOH and SS. Diffusion exchange appears important in understanding tritium decontamination from surfaces.