Tritium diffusion in rutile (TiO2)

Abstract

The diffusivity of tritium in rutile single crystals has been measured parallel to the a and c axes in the temperature range 250–900 °C. Raman-scattering measurements were also made to aid in identifying a nonpolar tritium species involved in the diffusion process. Two species, OT− ions and T2 molecules, are involved in tritium migration. The OT− ions dissociate preceding each tritium jump. Along the a axis the T2 molecules diffuse four orders of magnitude slower than the T+ ions associated with OT−. No dependency of the tritium diffusivity upon the rutile defect structure was observed.

Oxygen and Hydrogen Diffusion in Minerals

“…Radioactive tritium is sometimes used as a tracer for hydrogen diffusion (e.g., Shaffer et al 1974). The tritium concentration in the run products can be determined using autoradiography (e.g., Caskey 1974) or liquid scintillation counting (e.g., Cathcart et al 1979) but requires serial sectioning (i.e., successive grinding and polishing) to obtain the diffusion profile.…”

“…They also noted a significant anisotropy, with rates parallel to the c-axis an order of magnitude or more greater than parallel to the a-axis over the temperature range of their experiments, and there is a factor of two lower activation energy (57 vs. 124 kJ/mol) parallel to the c-axis compared to parallel to the a-axis. Cathcart et al (1979) determined tritium diffusion rates in synthetic rutile crystals along the a-and c-directions. The samples were annealed in a tritium gas source at 254-700 °C (parallel to c experiments) and 500-910 °C (parallel to a experiments).…”

“…The tritium concentration profiles were measured by serial sectioning and liquid-scintillation counting of the tritium β-decay emissions (Gruzin method). Cathcart et al (1979) reported two species, O 3 H − ions and 3 H 2 molecules, are involved in tritium (hydrogen) migration in rutile, with 3 H + ions associated with the O 3 H − ions diffusing four orders of magnitude faster than the 3 H 2 molecules, along the a-axis.…”

Effect of Oxide Layers on the Absorption Kinetics of Hydrogen by Metals at Room Temperature*

“…In reaction models, transport of molecular hydrogen through oxide scales via channels in the oxide structure [17] or through cracks [18] is sometimes discussed, mostly in order to explain a v~p law. Molecular H2 diffusion through cracks as the rate-determining step in a reactive metaloxygen system with fast oxide layer formation seems to be a somewhat unrealistic assumption since the bare metal surface at the end of a crack will be covered instantaneously by a new oxide skin.…”

First-principles study of H intercalation in rutileTiO2

“…2 Intercalation is thought to proceed through dissociative adsorption at surface defects 3,4 although there is some evidence for molecular intercalation in the near surface region. 5 As the insertion of H into rutile is fully reversible up to 10 19 /cm 3 , and is easily controlled and monitored, it provides a useful probe for the variation of optical, electronic, and thermodynamic properties with donated electron concentration. [6][7][8][9] Electrochemical insertion allows intercalation to much higher H concentrations, the exact maximum insertion concentration is not known.…”