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. So lid-solid interactions between V2O5 and Al2O3 were studied using DTA a nd TG curves and their derivatives together with XRD techniques. The r esults obtained showed that Na2O interacted with V2O5 at temperatures starting from 500 degrees C to yield a sodium/vanadium compound, Na0.3 V2O5 which remained stable and decomposed in part by heating at 1000 d egrees C. V2O5 exists in orthorhombic and monoclinic forms in the case of pure mixed solids and those containing 4 mol%, of Na2O and preheat ed at 500 degrees C, and in monoclinic form in the case of the mixed s olid 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 V2O 5 into AlVO4. Doping with sodium oxide enhanced the solid-solid intera ction between V2O5 and Al2O3 at 650 degrees C to produce AlVO4. The pr oduced AlVO4 decomposed completely on heating at 700 degrees C to form alpha-Al2O3 and V2O5, (orthorhombic and monoclinic forms). The presen ce of Na2O was found to decrease the relative intensity of the diffrac tion lines of alpha-Al2O3 (corundum) produced at 750 degrees C which i ndicated some kind of hindrance of the crystallization process. Heatin g of pure and doped mixed solids at 1000 degrees C resulted in a furth er crystallization of alpha-corundum together with V2O5 and sodium van adate, Na0.3V2O5. However, the intensities of diffraction lines relati ve to those of the sodium vanadium compound were found to decrease mar kedly by heating at 1000 degrees C, indicating partial thermal decompo sition into vanadium and aluminium oxides.