1. National Engineering Laboratory for Vacuum Metallurgy, Kunming University of Science and Technology, Kunming 650093, P. R. China
2. Panzhihua School of Vanadium and Titanium, Panzhihua University, Panzhihua, People’s Republic of China
3. Sichuan Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization, Panzhihua University, Panzhihua, People’s Republic of China