EFFECTS OF PYROLYTIC CARBON STRUCTURE ON DIFFUSIVITY OF TRITIUM

The release behavior and diffusivity of tritium were studied as a function of the degree of the preferred orientation utilizing pyrolytic carbons deposited on alumina substrates. The release spectra of tritium during a constant rate annealing shifted to a higher temperature with an increase in the extent of anisotropy of the carbon structure. The amounts of tritium retained in a sample after annealing depended strongly on the anisotropy factor. Furthermore, a great discrepancy was observed between the diffusion coefficients obtained from isotropic and from anistropic pyrolytic carbons. These experimental results were attributed to an anisotropic diffusion of tritium in carbon materials, that is, tritium atoms or ions diffuse mainly between basal planes.