1. Faculty of Metallurgical and Energy Engineering Kunming University of Science and Technology Yunnan Kunming 650093 P. R. China
2. The Key Laboratory of Vacuum Metallurgy of Non-ferrous Metals of Yunnan Province Yunnan Kunming 650093 P. R. China
3. School of Science and Technology Pu'er University Yunan Puer 665000 P. R. China