  In this paper the determination of material properties such as Sieverts'
constant (solubility) and diffusivity (transport rate) via so-called gas
release experiments is discussed. In order to simulate the time-dependent
hydrogen fluxes and concentration profiles efficiently, we make use of an
analytical method, namely we provide an analytical solution for the
corresponding diffusion equations on a cylindrical specimen and a cylindrical
container for three boundary conditions. These conditions occur in three phases
-- loading phase, evacuation phase and gas release phase. In the loading phase
the specimen is charged with hydrogen assuring a constant partial pressure of
hydrogen. Then the gas will be quickly removed by a vacuum pump in the second
phase, and finally in the third time interval, the hydrogen is released from
the specimen to the gaseous phase, where the pressure increase will be measured
by an equipment which is attached to the cylindrical container. The
investigated diffusion equation in each phase is a simple homogeneous equation,
but due to the complex time-dependent boundary conditions which include the
Sieverts' constant and the pressure, we transform the homogeneous equations to
the non-homogeneous ones with a zero Dirichlet boundary condition. Compared
with the time consuming numerical methods our analytical approach has an
advantage that the flux of desorbed hydrogen can be explicitly given and
therefore can be evaluated efficiently. Our analytical solution also assures
that the time-dependent boundary conditions are exactly satisfied and
furthermore that the interaction between specimen and container is correctly
taken into account.
