The observation of the reactions V6O13+V2O3→4V2O4 and V2O5+V2O3→2V2O4 by using high temperature x-ray diffraction technique

Two reactions, V6O13+V2O3→4V2O4 and V2O5+V2O3→2V2O4, both of which form V2O4, were studied by using high temperature X-ray diffraction technique, under a reduced air pressure of Pair = 10-1--100 mmHg by continuous evacuation. Isothermal experiments were carried out in vacuum ampoule (Pair = 10-2 mmHg closed system and 5x10-2 mmHg continuous evacuation) and DTA (Pair = 10-1--100 mmHg continuous evacuation) was also employed in order to compare the reactions. According to the experimental results obtained, it was found that V2O3 was oxidized to V2O4 by V6O13 and V2O5. In V2O5-V2O3 system, the reaction started at 3400C and proceeded slowly with an increase in the temperature, while in V6O13-V2O3 system, it started at 4500C with a high reaction rate. Different products appeared during the reaction in correspondence to the atmosphere; in V2O5-V2O3 system, three products of V4O9, V6O13 and V2O4 were observed in the case of isothermal reactions of continuous evacuation, but only V2O4 were formed in the case of closed ampoule experiments. In high-temperature X-ray analysis of pure samples of V2O3 and V2O4, no reactions were observed under continuous evacuation condition. In the cases of the systems of V6O13-V2O3 and V2O5-V2O3, V2O4 appeared at 4500C and 3000C, respectively. On the other hand, pure V6O13 and V2O5 samples were observed to decompose at 3000C and 4500C to form V2O4 and V4O9, and V6O13, respectively. V2O3, therefore, was considered to be oxidized by the oxygen formed from V6O13 and V2O5, but as to whether the oxygen is in molecular state or ionic remains uncertain. The initiation temperature of decomposition of V2O5 and V6O13 were independent of whether they were heated together with V2O3 or heated without it; which led to an assumption that the formation of V2O4 starts at the temperature where V2O5 and V6O13 begin to decompose. (auth.)