Analysis of thermally induced solid-solid interactions in vanadia-alumina system

V₂O₅/Al₂O₃ solids of varying compositions were prepared, dried at 100°C and calcined in air at 400–1000°C. The solid-solid interactions between the mixed oxides were investigated by means of DTA, TG and XRD techniques.The results revealed that ammonium metavanadate and aluminium hydroxide decomposed at 260 and 290°C, respectively, to yield an ammonium vanadium intermediate compound and Al₂O₃ as solids. The intermediate compound readily decomposed at 360°C to give V₂O₅.Solid V₂O₅ generally catalyses the crystallization of Al₂O₃ to an extent proportional to its amount present. The solid-solid interactions between Al₂O₃ and V₂O₃ to produce AlV₂O₄ and AlVO₄ took place at 750 and 900°C. These solids decomposed entirely at 1000°C, producing V₂O₅ and alpha-corundum. The pure Al₂O₃ samples employed existed as amorphous solids even when heated in air at 750°C, but in the presence of V₂O₅ (7–18 wt.%) they crystallized to thetaalumina at 600°C. The pure solid alumina crystallized at 1000°C to a mixture of theta and kappa-alumina. In the presence of V₂O₅, alpha-corundum together with kappa and theta phases was obtained on heating at 900°C.