Effect of sodium oxide doping on solid-solid interactions between V2O5 and Al2O3

A V2O5/Al2O3 mixed solids sample was prepared with a molar ratio of 0.4:1 Na2O (4 and 10 mol%) was added in the form of sodium nitrate prior to calcination in air in the temperature range 500-1000 degrees C. Solid-solid interactions between V2O5 and Al2O3 were studied using DTA and TG curves and their derivatives together with XRD techniques. The results obtained showed that Na2O interacted with V2O5 at temperatures starting from 500 degrees C to yield a sodium/vanadium compound, Na0.3V2O5 which remained stable and decomposed in part by heating at 1000 degrees C. V2O5 exists in orthorhombic and monoclinic forms in the case of pure mixed solids and those containing 4 mol%, of Na2O and preheated at 500 degrees C, and in monoclinic form in the case of the mixed solid doped with 10 mol% of Na2O. Heating of pure and doped mixed oxide solids at 650 degrees C resulted in the conversion of most of the V2O5 into AlVO4. Doping with sodium oxide enhanced the solid-solid interaction between V2O5 and Al2O3 at 650 degrees C to produce AlVO4. The produced AlVO4 decomposed completely on heating at 700 degrees C to form alpha-Al2O3 and V2O5, (orthorhombic and monoclinic forms). The presence of Na2O was found to decrease the relative intensity of the diffraction lines of alpha-Al2O3 (corundum) produced at 750 degrees C which indicated some kind of hindrance of the crystallization process. Heating of pure and doped mixed solids at 1000 degrees C resulted in a further crystallization of alpha-corundum together with V2O5 and sodium vanadate, Na0.3V2O5. However, the intensities of diffraction lines relative to those of the sodium vanadium compound were found to decrease markedly by heating at 1000 degrees C, indicating partial thermal decomposition into vanadium and aluminium oxides.