Permeation von Wasserstoff durch Metallmembranen

Experiments show that the permeant flux of hydrogen through a metal membrane at low driving pressures ( $\le$ 1 mbar typically) becomes directly proportional to the pressure and not to the square root of it as it is expected from Richardson's equation. The validity of this equation is usually used for the interpretation of permeation experiments and the determination of the diffusion constant. The observations can well be described in terms of a model which takes into account that the concentrations of the hydrogen atoms in the surface near layers show a time evolution and that the rate of molecules released to the outside increases quadratically with the concentration. Thus, additionally to the diffusion constant D, the release rate constant k$_{r}$ is introduced into the model as a new material constant and the rate equations are given. After the description of the wall pump effect, a variety of different limiting cases are discussed for a symmetrical permeation membrane. This is modified to the asymmetric case and to the influence of particle implantation. The permeation number W turns out to be a dimensionless quantity which characterizes the permeation range andpredicts the permeant flux in steady state