You may have noticed recently that we've been talking a lot about hydrogen- gaseous hydrogen as well as liquid. We're looking toward the future and we can see that it is a key component in green energy. We've already spoken about the lack of reactive properties in PTFE and PEEK, but that's not the only useful aspect of these materials over others, like stainless steel. These materials suffer from long-term exposure to permeation by absorbed hydrogen, and will have decreased tensile strengths over time.
INCREASED PERMEATION RESISTANCE TO HYDROGEN
PEEK has been tested for permeation resistance to hydrogen. Permeability, diffusivity, and solubility are used to describe the dissolution and transport of a gas through a material. Low permeability is generally required in static and dynamic sealing solutions to reduce emissions. PEEK is advantaged in low permeability applications due to its relatively high Tg and semicrystalline solid-state structure. This helps prevent absorbed hydrogen from weakening the container it's in, and preventing tensile stress.
In 2011, a study was completed to measure the permeation resistance of PEEK to hydrogen at ambient conditions. A range of nearly 20 Permeability, diffusion, and solubility coefficients were measured on two grades of VICTREX PEEK-based extruded films and compression and injection moulded specimens from VICTREX PEEK. All PEEK samples exhibited generally low permeability which can be attributed in part to the glassy state as the ambient temperature was below Tg. Compounded with the increased tensile strength a PEEK coating would provide metals like stainless steel, this dramatically reinforces the eligibility of PEEK as a gaseous sealing material for use in hydrogen storage, compression and delivery equipment.
PEEK against Hydrogen Embrittlement
Aside sealing applications, other less conventional uses of PEEK have been tested with great success in replacing metallics in solid engineered components; the issue with metallic solutions is the risk of hydrogen embrittlement. Hydrogen embrittlement is a term used to describe the process by which metals, for example steel, become brittle and fracture due to the ingress and diffusion of hydrogen. A significant consequence of this exposure can lead to a substantial reduction in ductility and load bearing capacity. So machined mechanical components can suffer drastically reduced strength and life expectancy/usability. Materials such as high strength steels, titanium and aluminium alloys are the most vulnerable to this phenomenon which, beyond the risk of hydrogen embrittlement, would likely have been the backbone of mechanical structures and machinery within the hydrogen processing and production equipment due to their tensile strengths.
However, PEEK and other polymers are NOT expected to be permanently affected by exposure to hydrogen and consequently can be considered to extend the lifetime and reliability of components in hydrogen service across many applications including sealing solutions and compressors. Additionally, machined PEEK can be used to replace traditional machined metallic components without suffering too much tensile stress. We're looking forward to applying our knowledge in PEEK and fluoropolymers to help solve the obstacles on the road to greener energy.
