Numerical Analysis of an Isovolumetric Thermal Desorption Experiment

Abstract

Our research group is currently investigating a new kind of thermal desorption experiment (TDE), which uses a hydrogen isotope by loading-unloading process yielding transport parameters. Safety issues are limiting the hydrogen loading content to 3 % at 105 Pa, while former experiments are using pure hydrogen for the loading process at nearly same pressure e. g. [1]. Especially the thermal elongation coefficient (TDE operating conditions 300° to 500 °C compatibility to stainless steel) forces to think about an alternative material of boron silicate glass for specimen containment, in this paper copper will be discussed. The analysis of TDE concerns the amount of hydrogen stored in the specimen, stored in the time variable gas phase as well as stored in the containment material. These three phases are coupled by phase equilibrium. The here developed analysis procedure can currently only be performed numerically for a two dimensional geometry. However a two dimensional analytical solution regarding the same boundary condition is currently under investigation. One part of the solution results of this problem can be compared to an additional analytical solution with simpler boundary conditions, e.g. a vanishing hydrogen amount inside the specimen containment observed in steady state. The numerical results will be used to check the suitability of several experimental scenarios, for example the usability of a copper based specimen containment. The approach currently practiced in many experiments is to simply subtract the zero rate of hydrogen without considering the phase equilibrium between the three mentioned phases. The main goal of this analysis procedure consists in the solution of the inverse problem, namely the extraction of the transport parameters like Sieverts ́-and diffusion-constant from a measured time dependent desorption pressure increase.