STRUCTURES ACCOMPANYING THE SOLID-SOLID INTERACTIONS IN THE V2O5-MGO SYSTEM

Magnesium hydroxide samples were treated with solutions containing different proportions (0.5-50 mol%) of ammonium metavanadate (AMV), dried at 80 degrees C, and then calcined in air at temperatures of 400, 550 and 700 degrees C for 4 h. The solid-solid interactions between the resulting mixed oxides were investigated using DTA, TG, IR and XRD techniques. The results obtained revealed that AMV and Mg(OH)(2) decompose readily at 300 and 375 degrees C respectively to produce V2O5 and MgO solids. The presence of the support enhances the decomposition to V2O5 while the presence of V2O5 retards the decomposition of Mg(OH)(2). With ratios of less than 20 mol% AMV, no peaks in the DTA curves related to the decomposition of AMV were found. However, the two oxides interacted at a composition of 20 mol% AMV above 500 degrees C to form Mg3V2O8 spinel, but this decreased on increasing the percentage content of AMV. Moreover, samples containing 20 or 30 mol% AMV calcined at 700 degrees C mainly led to the formation of Mg3V2O8, whereas an MgV2O6 spinel was the predominant product formed on increasing to 50 mol% AMV.