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The polymer chemical structure of the polyimide has a major influence on the tribological behaviour. The addition of graphite in PI2 has a beneficial effect in hydrogen on the friction and wear. The low friction of graphite is associated with a lubricant film in hydrogen. The influence of hydrogen on graphite is more effective than humidity. CNTs have a similar effect to that of graphite in PEEK composites. TiO2 particles improve significantly the wear rate both in vacuum and hydrogen environment. In LH2 friction and wear decrease for unfilled polymers. Friction of graphite filled composites increases slightly and wear rate is stable.
The development of hydrogen technologies is a key strategy to reduce greenhouse gas emission worldwide. Power-to-Gas is a challenging solution, in which hydrogen and methane can be used in mobility, industry, heat supply and electriity generation applications. This presentation deals with the tribological behaviour of polymer materials in hydrogen and methane, both in gas and in liquid form.
The influence of hydrogen environment on the friction and wear behavior of polyimide (PI) composites was investigated for two different PI-types (PI1 and PI2) filled with natural or synthetic graphite. Sliding tests were run against AISI 52100 steel and the worn surfaces as well as the transfer film were analyzed by means of SEM, EDX and Infrared Spectroscopy. Results indicate that the chemical structure of the polyimide has a major influence on the tribological behavior. While the friction of PI2 remains rather stable in all environments, PI1 showed very low friction in hydrogen without any lubricant. The lubricity of graphite was found to be more effective in hydrogen than in moist air.
This lecture deals with the sliding behaviour of polymer materials in hydrogen environment. After a short introduction of the hydrogen activities at BAM, the tribological performances of polymer materials in gaseous hydrogen are presented and compared with air and vacuum environment. The second part focusses on the influence of the counterface materials in hydrogen. Finally, the last section is dedicated to experiments liquid hydrogen.
In the development of hydrogen technology, special attention is paid to the technical problems of
hydrogen storage. One possible way is cryogenic storage in liquid form. Generally cryotechnical
machines need components with interacting surfaces in relative motion such as bearings, seals or
valves, which are subjected to extreme conditions. Materials of such systems have to be resistant to
friction-caused mechanical deformation at the surface, low temperatures and hydrogen environment.
Since materials failure can cause uncontrolled escape of hydrogen, new material requirements are
involved for these tribo-systems, in particular regarding operability and reliability. In the past few
years several projects dealing with the influence of hydrogen on the tribological properties of friction
couples were conducted at the Federal Institute for Materials Research and Testing, (BAM), Berlin.
This paper reports some investigations carried out with polymer composites. Friction and wear were
measured for continuous sliding and analyses of the worn surfaces were performed after the
experiments. Tests were performed at room temperature in hydrogen as well as in liquid hydrogen.
This presentation deals with the influence of the counterface materials on the sliding behaviour of some polymer materials in hydrogen. Polyimide (PI), polyetheretherketone (PEEK) and Polytetrafluoroethylene (PTFE) materials were investigated against hardened 52100 martensitic bearing steel and 304 austenitic stainless steel with similar roughness (Ra = 0.2 μm). Results indicate that the friction and wear of PI and PEEK materials depend on the counterface material. This effect wasn’t observed for PTFE composites.
While the tribological performance of polyimide is better against 52100 in hydrogen, improved sliding behaviour of PEEK materials is observed with 304 counterface, particularly at higher sliding speed. Surface analyses of the transfer film reveal that the influence of the counterface is primarily related to the chemical nature of the steel for PI and to the thermal conductivity of the disc for PEEK materials.