Fha. Abdalla et al., EFFECT OF SODIUM-OXIDE DOPING ON SOLID-SOLID INTERACTIONS BETWEEN V2O5 AND AL2O3, Journal of thermal analysis, 47(6), 1996, pp. 1777-1785
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.