Industrial surfaces behaviour related to the adsorption and desorption of hydrogen at cryogenic temperature [in LHC vacuum system ]

The determination of the hydrogen adsorption capacity on different industrial surfaces has been carried out by measuring isothermal adsorption. First results show that the adsorption capacity is mainly determined by surface porosity. Therefore, the samples may be classified into two categories: smooth and porous surfaces. Thermal desorption spectra reveal two adsorption energy levels for hydrogen physisorbed on porous materials, but only a single one on smooth samples. The value of the lowest energy level seems to be independent of the substrate nature. The physisorption process studied at low coverage, well below a monolayer, shows that these two levels are not well defined but an energy distribution exists for each of them. The influences of the isotherm temperature and an annealing at 7 K of an adsorbed monolayer on hydrogen adsorption capacity have been studied. (16 refs)