Helium permeability of coated aramid papers

Materials and technologies for cryogenic tanks design are still in the developmental stage. New design concepts demand that composite structure not only carries mechanical loads but provides hermetism. This paper aims at defining a cryogenic tank concept design and developing a barrier layer with impregnated aramid paper to prevent permeation of gases through a composite sandwich wall of the tank. A number of aramid fiber paper sheets have been coated with different resin systems and tested for helium permeability. Permeation kinetics show that there are at least two mass transport mechanisms running simultaneously: diffusion and hydrodynamic flow through micro-porous media. The long period of unsteady permeability was determined. Despite some technological imperfections of the laboratory-made samples, a low level of permeability was achieved, which satisfied the official requirements. Both steady level of permeability and kinetics of unsteady period can be used for quality control purposes.