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 vanadium pentoxide in 1:2 molar ratio affords the vanadium bronze alpha'-NaV2O5. Complementary techniques such as thermogravimetry (TG), differential thermal analysis (DTA), gas analysis (GC), X-ray powder diffraction (XRD) and infrared spectroscopy (IR) were applied to provide information on the operative mechanism. A promotive effect of vanadium pentoxide on the decomposition of sodium oxalate takes place. Carbonate species and carbon monoxide could not be detected as intermediates during the decomposition which occurs over a wide range of temperatures, typically between 200 and 525-degrees-C. The progressive formation of NaxV2O5 bronzes with x increasing up to unity with temperature leads us to propose that the carbon-carbon bond cleavage of the oxalate is promoted by electron transfer between the oxalate anion and the vanadium pentoxide matrix. Such behaviour is dependent on the redox potential of the metal ion initially present in the oxalate and of vanadium pentoxide.