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In this presentation tribological investigations on steels, polymers and coatings in gaseous and liquid hydrogen are shown. For steels the results of show that although martensitic steel may suffer from hydrogen embrittlement, application e.g. in roller bearings is possible. On the other hand, martensitic transformation of austenitic steels may cause problems in the application of these materials. Furthermore, the tribological performance of polymer composites with and without solid lubricant fillers in gaseous and liquid hydrogen was investigated. In particular, PEEK- and PTFE-matrix compounds showed low friction and sufficient low wear under these conditions. Among the solid lubricants, carbon-based materials are appropriate for hydrogen applications. Several variants of DLC and ta-C materials were tested. Beside the results for hydrogen, also a comparison with CH4-environment is shown.
A modified composite membranes (PVA/SiOH/SiOC) were made via solution-casting process using different 1:1, 1:2, 1:3 and 1:4 volume ratios of polyvinyl alcohol (PVA):methoxytrimethylsilane (MTMS). Moreover, FT-infrared and energy-dispersive X-ray spectroscopy (EDX) were mesured to account for the network structural rearrangements involving silicon within PVA matrices. The addition of MTMS has improved the thermal and mechanical properties of the composite membranes as compared to pristine PVA. In addition, the crystallinity and the morphological changes of PVA/MTMS composites was studied using X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Three structures were suggested based on trimethyl silanol (I) wet out condensation (II and III) with the dopped PVA followed by and H-bonding interactions (IV). The outcomes of B3LYP/6-31G(d) frequency calculations favors a three-dimensional SiOC linked network (III). Nevertheless, EDX reveals, the 3D SiOC links are not observed on the surface of composite membranes, however, is found dominant in the bulk, [(CH3)3SiOCH2CH2CH2O]n. Moreover, the solubility, density, and refractive index of the synthesized composites were measured and found depended on the ratio of PVA in the composite membranes. The current results are compared with that published earlier including dimethoxydimethylsilane at the same conditions.
This chapter deals with the development of polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE)-based composites, optimized for low friction and low wear performance under extreme environments. It is demonstrated that the incorporation of a harder polymer component into PTFE (such as PEEK particles), a short fiber reinforcement (e.g. carbon fibers (CFs)) and internal lubricants (e.g. PTFE particles) helps to reduce the friction and to improve the wear resistance over a very wide temperature range.
The tribological behaviour of polyetheretherketone (PEEK) and polyimide (PI) composites was investigated in air, vacuum and hydrogen environments. Polymers were filled with graphite, submicron particles or carbon nano-tubes. Experiments reveal that hydrogen environment has a major influence on both polymer structure and fillers during sliding. The sliding behaviour of these polymer composites is much improved in hydrogen compared to air. In particular, graphite and nano-particles have a remarkable effect on friction and wear, respectively.