EFFECTS OF ALKALI-METAL IONS ON THE THERMAL-DECOMPOSITION OF AMMONIUM METAVANADATE SUPPORTED ON ALUMINA

The thermal decomposition of ammonium metavandate (AMV) supported on gamma-alumina (1 : 1 mol) and treated with alkali-metal ions was investigated using differential thermal analysis (DTA), thermogravimetric analysis (TGA), infrared (i.r.) absorption spectroscopy and X-ray diffraction (XRD). The results revealed that the presence of alkali-metal ions did little to affect the thermal decomposition processes of AMV supported on alumina. However, these ions enhanced creation of V4+ ions by heating the samples in air at 400-degrees-C. The oxides produced underwent a solid-solid interaction at 500-700-degrees-C, forming alkali-metal vanadates. The formation of these spinels was found to be strongly dependent on the degree of diffusion and the concentration of the alkali-metal ions. Moreover, the addition of a higher concentration of alkali-metal ions inhibits the formation of aluminium vanadate while enhancing the crystallinity of gamma- to delta-alumina.