A NEW MECHANISM FOR THE THERMAL-DECOMPOSITION OF AMMONIUM HEXAVANADATE - FORMATION OF N2O

The thermal decomposition of the ammonium hexavanadate (AHV) under var ious atmospheres leads to vanadium oxides with oxidation states compri sed between +5 and +3. The mechanisms are complex and involve diffusio n of the gases between the grains, catalytic decomposition on the surf ace of the oxides and several reduction steps. The formation condition s of VO2 are clearly established and an interpretation of the transfor mation AHV --> VO2 is proposed. For high heating rates and low heating temperatures, using evolved gases analysis (FT-IR/EGA) the formation of nitrous oxide N2O was observed. The formation of this gas is discus sed and correlated with the reduction of the vanadium 5+.