Mechanochemical treatment (MChT) in various media (water, air, ethanol) of the V2O5/ammonium dimolybdate composition at the ratio V:Mo = 0.7:0.3 has been carried out. Physicochemical transformations in this
system have been studied by means of X-ray powder diffraction (XRD) and thermal analysis as well as FTIR spectroscopy. Ammonium
dimolybdate undergoes hydration with formation of 4-aqueous ammonium paramolybdate during the MChT in water. Changes of phase
and chemical composition at activation are determined first of all by nature of medium in which milling was carried out. Maximal
interaction of components occurs during modification of the studied system in water.