Kinetics and mechanism of solid-state reaction between bismuth(III) oxide and molybdenum(VI) oxide

Abstract

The mechanism of the following solid-state reactions between bismuth(III) oxide and molybdenum(VI) oxide was investigated within the temperature range 400–650°C. (i) Bi 2O 3 + MoO 3 → Bi 2MoO 6, (ii) Bi 2O 3 + 2MoO 3 → Bi 2MO 2O 9, (iii) Bi 2O 3 + 3MoO 3 → Bi 2(MOO 4) 3, (iv) Bi 2MoO 6 + MoO 3 → Bi 2MO 2O 9, (v) Bi 2Mo 2O 9 + MoO 3 → Bi 2(MoO 2)3. Two types of experiments, capillary and particle size, were performed to ascertain whether MoO 3 diffuses into Bi 2O 3 or vice versa. These show that molybdenum trioxide diffuses into bismuth oxide grains. If α is the fraction of molybdenum trioxide reacted, the kinetics in all five cases are found to be governed by the equation α n = kt throughout the temperature range, where n and k are constants at a given temperature and t is the time. Both n and k are temperature dependent. The characteristic feature of these reactions is that they proceed to completion. Results are also fitted by the relation α = k 2t 1 2 − k 3t , where k 2 and k 3 are constants, which shows that the reactions occur by bulk diffusion through grain boundary contacts. The number of grain boundary contact points decreases with time in the course of reaction.