Gas-driven hydrogen isotopes permeation through different carbon materials

Hydrogen gas driven permeation through the fine-grain graphites MPG-8 and R5710, and through CFC NB31 in two main directions has been investigated for sample thicknesses of 1–7 mm and pressures from 10−2–10 Pa. The gas driven permeation occurs through the carbon-base materials by the hydrogen molecular gas flow through the internal porosity network rather than hydrogen atom diffusion through the graphite lattice. The permeabilities of MPG-8 and Nb31 are of the same order, while the permeability of R5710 is two orders of magnitude less. The specific bulk conductivity is about 5 × 1015 molecules s−1 m−1 Pa−1 for MPG-8; 8 × 1013 molecules s−1 m−1 Pa−1 for R5710; 1 × 1016 molecules s−1 m−1 Pa−1 for Nb31 along ex-pitch (x) fibers after taking into account the perforated surface layer and 0.8 × 1016 molecules s−1 m−1 Pa−1 for Nb31 along needled (z) fibers.