Thermal decomposition of ammonium metavanadate

Ammonium metavanadate is subjected to thermal treatment in the range 180–550°C and structural and surface area changes are studied by X-ray diffraction and N₂ adsorption. DTA and TGA show the existence of a large endotherm (260°C) possibly composed of several stages, and a much smaller one (340°C) which is responsible for evolution of the molecule of water associated with the V₂O₅ initially formed. Three exotherms also appear and explanations for their presence are given. The phases formed, as well as the specific surface areas, are determined for the products obtained in a vacuum and in the presence of water vapour, and changes in surface areas are related to the phase transformations and dehydration of the products formed during thermal treatment.