Peaks of hydrogen thermal desorption: simulation and interpretation

Different models of hydrogen thermal desorption peaks have been analyzed. The model of volume-averaged concentration dynamics with a continuum parameter makes it possible to integrally take into consideration the dominance of limiting factors: diffusion and recombination of atoms into desorbing molecules. An analytical symmetry criterion for peaks versus the method of expanding a composed spectrum into a series of Gaussian curves is suggested. Modifications of (i) the Kissinger method to estimate the activation energy of desorption in experiments with several material heating rates and (ii) a procedure for solving the inverse problem of unimodal peak parametrical identification from one heat rate are presented. Comparison with the diffusion model with dynamic boundary conditions has been carried out. It has been shown that local peaks may arise not only because of release of hydrogen atoms with different binding energies captured by volume traps, but also because of interaction between volume and surface processes and heat-induced surface structure modifications. The parameters of deuterium thermal desorption from ISO-880U graphite have been estimated.