1. Key Laboratory of Coal Science and Technology, Ministry of Education and Shanxi Province, Taiyuan University of Technology, No. 79 Yingze West Street, Taiyuan 030024, China
2. Lignite Fly Ash Institute of Engineering & Technology, Xilingol Vocational College, Xilinhot, Inner Mongolia 026000, China
3. Division of Nanoscale Measurement and Advanced Materials, National Institute of Metrology, No. 18, Bei San Huan Dong Lu, Chaoyang Dist, Beijing 100029, China