Plastic composite materials for cryogenic storage of hydrogen

A series of experiments were carried out, to describe the properties of selected plastic composite materials in relation to their potential use in containers for liquid hydrogen. The experiments were concerned with the measurement of gas diffusion through the composite materials and with their mechanical properties at low temperatures. Hydrogen diffusion into the materials was measured by gravimetry in an ultra-microbalance. For the majority of materials no uptake could be detected at room temperature. A test at 77 K for one material showed no uptake at that temperature as well. In one case, PEEK, an uptake was measured at room temperature, but the rate was so low that it is not considered to represent a hazard. The mechanical properties of 7 composite samples were measured by tensile testing and simultaneous measurement of the accumulated acoustic emission caused by crack formation. In one measurement the acoustic emission indicated crack formation at relatively low stresses (i.e, below 150 MPa). The other samples only showed negligible acoustic emission up to 150 MPa, which is considered to be sufficient for application of the material in a liquid hydrogen container. The work done indicates that plastic composites are suitable for application in low temperature gas containers. More exhaustive measurements of hazard-related physical and chemical materials properties are needed though, before a pilot container can actually be designed. In particular the reaction of the materials to long-term gas exposure needs to be characterised, and also more dedicated diffusion experiments should be carried out, recommendably done in a diffusion cell, where the material to be tested can be suspended as a diaphragm separating a pressure difference.