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

V2O5/Al2O3 solids of varying compositions were prepared, dried at 100 degrees C and calcined in air at 400-1000 degrees 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 degrees C, respectively, to yield an ammonium vanadium intermediate compound and Al2O3 as solids. The intermediate compound readily decomposed at 360 degrees 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 A1VO(4) took place at 750 and 900 degrees C. These solids decomposed entirely at 1000 degrees C, producing V2O5 and alpha-corundum. The pure Al2O9 samples employed existed as amorphous solids even when heated in air at 750 degrees C, but in the presence of V2O5 (7-18 wt. %) they crystallized to theta-alumina at 600 degrees C. The pure solid alumina crystallized at 1000 degrees 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 degrees C.