Preparation of vanadium dioxide powders by thermolysis of a precursor at low temperature.

A kind of crystal precursor, (NH₄)₅[(VO)₆(CO₃)₄(OH)₉]·10H₂O, less than 12 × 40 μm in dimensions was synthesized by reaction of vanadyl dichloride and ammonium hydrocarbonate in solution. The precursor microcrystals were fined to less than 10 μm with mean size of about 4 μm, by using organic solvents and surfactant in the process of the synthetical technique. Thermolysis of the precursor in a flow of nitrogen gas was investigated by TGA and DTA. The XRD powders patterns for the products from the thermolysis of the precursor show that the VO₂ powder obtained at 350, 365, 380 and 410°C for 30 min were a noncrystalline phase, a monoclinic one named as B phase, a mixed phase of the B and the usual monoclinic A phase, and the pure A phase, respectively. SEM micrographs of VO₂ powders from the fined precursor demonstrated that the particle sizes of these fine powders were less than 2 μm. DSC curve of the VO₂ obtained at 450 °C for 30 min from the fined precursor showed that there was an endothermic phase transition at 71 °C. [ABSTRACT FROM AUTHOR]