1. Faculty of Metallurgy and Energy Engineering Kunming University of Science and Technology Kunming 650093 P. R. China
2. State Key Laboratory of Complex Nonferrous Metal Resources Clear Utilization Kunming University of Science and Technology Kunming 650093 P. R. China
3. National Engineering Laboratory Center for Vacuum Metallurgy Kunming University of Science and Technology Kunming 650093 P. R. China