Liquid lubricants and greases used in space applications are generally susceptible to degradation or aging. Depending on the specific material combination and storage conditions, aging effects are also relevant for long-term storage (LTS). An overview on both physical and chemical aging processes for liquid lubricants and greases is given and processes which are seen as relevant for LTS and may impact the long-term performance of these materials are identified. Individual degradation processes as well as causes and potential risks are discussed, providing complementary data for two liquid perfluoropolyether (PFPE) lubricants (Fomblin Z25 and Brayco 815Z) and a PFPE grease (MAPLUB PF 100-b), focussing on thermo-oxidative and catalytic degradation. For these lubricants, monitoring of degradation effects is done indirectly by their mass loss at different temperatures and in the presence of a catalyst over a total duration of 1000 h. An increased mass loss during accelerated thermo-oxidative aging at temperatures above 200 °C is observed, with overlapping effects of thickener degradation for the investigated grease. Noticeable catalytic degradation effects are further seen for accelerated thermo-oxidative aging in the presence of Al2O3 above 200 °C.
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This research work was performed at the Polymer Competence Center Leoben GmbH (PCCL, Austria) under a programme of, and funded by, the European Space Agency (contract number 4000125239/18/NL/KML/va). PCCL is funded by the Austrian Government and the State Governments of Styria, Upper and Lower Austria. However, the views expressed herein can in no way be taken to reflect the official opinion of the European Space Agency and are not intended to endorse particular technologies, companies, or products.
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Wolfberger, A., Hausberger, A., Schlögl, S. et al. Assessment of the chemical degradation of PFPE lubricants and greases for space applications: implications for long-term on-ground storage. CEAS Space J (2021). https://doi.org/10.1007/s12567-021-00348-6
- Liquid lubricants
- Chemical degradation
- Long-term storage