Synthesis and physicochemical properties of ammonium tetravanadate for obtaining VO2

Abstract

In order to develop a technological process for obtaining vanadium dioxide by the thermal decomposition, we developed the method of synthesis of highly dispersed vanadium(IV) salt as a precursor. It comprises vanadium pentoxide interaction with the oxalic acid in the solution, which gives intermediate oxovanadium solution, following precipitation of the product (ammonium tetravanadate) by adding ammonium hydroxide to oxovanadium, rinsing and drying the product. With the use of photocolorimetry and potentiometric titration the intermediate product was identified as H2[VO(C2O4)2] and the final product as (NH4)2V4O9. Kinetic constants and activation energy of limiting reaction (Ea = 73.0 kJ/mol) were found, as well as the standard heat of the product formation (ΔН0f = –3494.5 kJ/mol), its solubility and density. It is shown that after high temperature treatment the substance transforms into vanadium dioxide of high quality with a typical semiconductor-metal transition.