Tribology of engineering and coated materials in the presence of environmentally friendly refrigerant

Aromatic Thermosetting Poyester (ATSP);Polymeric Coatings;Tribofilm;Boundary Lubrication;Tribology;Hydrofluoroolefins (HFO-1234yf);Environmentally Friendly Refrigerant

Akram, Mohammad

关键词: Aromatic Thermosetting Poyester (ATSP);    Polymeric Coatings;    Tribofilm;    Boundary Lubrication;    Tribology;    Hydrofluoroolefins (HFO-1234yf);    Environmentally Friendly Refrigerant;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/78320/Akram_Mohammad1.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

In recent years, considerable effort has been devoted towards finding of alternative refrigerants due to environmental issues related to high global warming potential (GWP).Specifically, developing a system-compatible alternative refrigerant is of prime concern in order to reduce costs associated with design modifications.Among the candidate refrigerants, newly developed HFO-1234yf is considered as a direct substitution for the current R-134a refrigerant for possessing similar thermo -physical properties. However, in an actual system, a refrigerant circulates through different tribo-components where it interacts with the interfacial components (such as surface materials andlubricants), altering their tribological behavior. Therefore, the tribological performance of a refrigerant must be evaluated prior to widely used in refrigeration/ air-conditioning systems. Along this line, we have investigated the tribological performance of HFO-1234yf refrigerant under aggressive boundary lubrication conditions. Specifically, we have performed controlled tribo-experiments, simulating actual automotive air-conditioning compressor systems, to measure in-situ friction and near-contact temperature.Interestingly, we have observed a run-in instability in the frictional behavior for the case of HFO-1234yf refrigerant, unlike R-134a refrigerant. This intermediate instability is associated with decomposition of the reactive HFO-1234yf refrigerant at the contact interface under specific loading conditions. However, beneficial anti-wear tribofilms were shown to evolve throughout this process as revealed via Scanning Electron Microscopic (SEM) analysis. Energy Dispersive Spectroscopy (EDS) in conjunction with X-ray Photoelectron Spectroscopic (XPS) analysis identified the existence of Fluorine on these boundary films, attributing the fluorinated interaction at the contact zone. This fluorination, thus, facilitates formation of FeF3- enriched tribofilms over the cast iron based interface. In addition, we have demonstrated the influence of the loading conditions and state-or-art lubricants on the tribological compatibility of HFO-123yf refrigerant. Finally, the tribological performance of newly synthesized aromatic thermosetting polyester (ATSP), blended with 5% polytetrafluoroethylene (PTFE), namely ATSP/PTFE, has been evaluated under unlubricated and boundary lubricated conditions. Current state-of-art polymeric coatings have also been considered for comparative purposes. Tribological and morphological investigations revealed superior tribological performance for ATSP/PTFE. The better performance is attributed to segregated surface morphology associated with ATSP/PTFE