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ABSTRACT
In this work, lithium and diurea greases formulated by poly-alpha-olefin were aged up to 1,200 h in an oven at 120°C and periodically taken out for testing. Scanning electron microscopy (SEM) and infrared (IR) spectra proved that both physical and chemical degradation occurred during the thermal aging process, such as a decrease in apparent viscosity, thickener destruction, and change in chemical species. Diurea grease showed much better anti-oxidation performance during thermal aging than lithium grease. A dual effect of thermal aging on the grease lubricity was observed and analyzed. Results showed that early oxidation might reduce grease lubricity due to the formation of ketones and aldehydes, and the decrease in grease viscosity and oil bleeding due to thickener destruction would contribute to better replenishment.
Acknowledgement
The authors thank Shenzhen Hecheng Lubricant Material Co. Ltd. for supplying the greases.
Funding
This work is financially supported by the International Science &Technology Cooperation Project (Grant No. 2011DFA70980) and National Natural Science Foundation of China (Grant No. 51375255) and by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51321092).