Solid State Reactions between V_2O_5 and C during Mechanochemical Processing and Heating of V_2O_5/C Composite Powders

摘要

Solid state reactions between V_2O_5 and C activated by mechanical milling and by heating the high energy mechanically milled V_2O_5/C composite powders have been investigated. It has been found that during both milling and heating processes, the reduction of V_2O_5 by carbon proceeds in three steps: Step 1: V_2O_5 → VO_2, Step 2: VO_2 → V_2O_3 and Step 3: VO_2 → V_4C_3. Mechanical milling is capable of activating the first two step reactions, although at different times. Heating of the mechanically milled powders activates the different step reactions at different temperature. The first step reaction occurs at around 400°C, the second step reaction occurs at approximately 720°C, while the third step reaction occurs at about 1000°C. The V_2O_5/C mole ratio in the starting powder has little effect on the first two step reactions, but significantly enhances the kinetics of the third step reaction. It is believed that this enhancement was due to a large area of V_2O_5/C interface formed with increasing amount of carbon in the powder. It has also been observed through thermal analysis using DTA and TGA that the third step reaction is highly endothermic which explains why it cannot be activated by mechanical milling.