Materials Science Forum, Vol.386-3, 293-298, 2002
Solid state reactions between V2O5 and C during mechanochemical processing and heating of V2O5/C composite powders
Solid state reactions between V2O5 and C activated by mechanical Milling and by heating the high energy mechanically milled V2O5/C composite powders have been investigated. It has been found that during both milling and heating processes, the reduction of V2O5 by carbon proceeds in three steps: Step 1: V2O5 --> VO2, Step 2: VO2 --> V2O3 and Step 3: VO2 --> V4C3. 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 400degreesC, the second step reaction occurs at approximately 720degreesC, while the third step reaction occurs at about 1000degreesC. The V2O5/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 V2O5/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.