Phases Transition and Consolidation Mechanism of High Chromium Vanadium-Titanium Magnetite Pellet by Oxidation Process

Based on the fundamental characteristics of high chromium vanadium-titanium magnetite (HCVTM), the effects of roasting temperature and roasting time on the phase transition and oxidation consolidation during the oxidation were investigated systematically. It was shown that the oxidation of HCVTM pellet was not a simple process but complex. With increasing roasting temperature and time, the compressive strength of oxidized pellet was improved. The phase transition during oxidation was hypothesized to proceed as follows: (1) Fe3O4 -> Fe2O3; (2) Fe2.75Ti0.25O4 -> Fe9TiO15 + FeTiO3 -> Fe9TiO15 + Fe2Ti3O9; (3) Fe2VO4 -> V2O3 -> (Cr0.15V0.85)(2)O-3; (4) FeCr2O4 -> Cr2O3 -> Cr1.3Fe0.7O3 + (Cr0.15V0.85)(2)O-3. The oxidation consolidation process was divided into three stages: (1) oxidation below 1,173 K; (2) recrystallization consolidation at 1,173 - 1,373 K; (3) particle refining recrystallization-consolidation by the participation of liquid phase at 1,373 - 1,573 K. To obtain the HCVTM oxidized pellet with good quality, the rational roasting parameters included a roasting temperature of 1,573 K and a roasting time of 20 min.