1. State Key Laboratory of Solidification Processing Centre of Advanced Lubrication and Seal Materials Northwest Polytechnical University Xi'an Shaanxi 710072 P. R. China
2. Qingdao Centre of Resource Chemistry and New Materials Qingdao Shandong 266100 P. R. China
3. State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of Science Lanzhou Gansu 730000 P. R. China
4. Yantai Zhongke Research Institute of Advanced Materials and Green Chemical Engineering Yantai Shandong 264006 P. R. China