THERMAL-DECOMPOSITION OF SODIUM OXALATE IN THE PRESENCE OF V2O5 - MECHANISTIC APPROACH OF SODIUM OXIBRONZES FORMATION

The thermal decomposition of sodium oxalate in the presence of vanadiu m pentoxide in 1:2 molar ratio affords the vanadium bronze alpha'-NaV2 O5. Complementary techniques such as thermogravimetry (TG), differenti al thermal analysis (DTA), gas analysis (GC), X-ray powder diffraction (XRD) and infrared spectroscopy (IR) were applied to provide informat ion on the operative mechanism. A promotive effect of vanadium pentoxi de on the decomposition of sodium oxalate takes place. Carbonate speci es and carbon monoxide could not be detected as intermediates during t he decomposition which occurs over a wide range of temperatures, typic ally between 200 and 525-degrees-C. The progressive formation of NaxV2 O5 bronzes with x increasing up to unity with temperature leads us to propose that the carbon-carbon bond cleavage of the oxalate is promote d by electron transfer between the oxalate anion and the vanadium pent oxide matrix. Such behaviour is dependent on the redox potential of th e metal ion initially present in the oxalate and of vanadium pentoxide .