Preparation of Vanadium Dioxide by Reduction of Vanadium Anhydride with Ammonia
Abstract Generated abstract
This study examines the preparation of vanadium dioxide by reducing powdered vanadium anhydride with a constant flow of ammonia, seeking a faster alternative to previously used oxidation, solid-state heating, and vanadyl oxalate decomposition methods. The reduction was carried out for 30 minutes over 300 to 500°C, with carbon dioxide used during heating and cooling, and the products were evaluated by permanganatometric determination of vanadium content. The results indicate that conditions near 390°C give a product consistent with vanadium dioxide, with 61.0% vanadium compared with the theoretical 61.42%, while higher temperatures lead to further reduction and formation of lower-valence vanadium oxides.
Full Text
Production of Vanadium Dioxide by Reduction of Vanadium Anhydride with Ammonia
G. N. Khodalevich, L. P. Gevlich
(Presented by the seminar of the Department of Inorganic Chemistry, KhTF)
The present work considers a method for obtaining vanadium dioxide, \(\mathrm{VO_2}\), by reducing vanadium anhydride with ammonia at various temperatures. Vanadium dioxide can be obtained by the following methods:
1) by careful oxidation of vanadium sesquioxide with atmospheric oxygen according to Cook [1];
2) by prolonged heating of a mixture of vanadium sesquioxide with vanadium anhydride [2];
3) by decomposition of vanadyl oxalate upon heating [2].
Obtaining vanadium dioxide by the first two methods is inconvenient, since it involves a large expenditure of time, respectively 3–8 days. The third method, given in Brauer’s handbook, was used by us in a previous work, in which the conditions for synthesizing the dioxide by this method were specified.
In the present work, vanadium dioxide was obtained by reducing powdered vanadium anhydride with ammonia. The reduction was carried out in the temperature range 300–500°C under a constant flow of ammonia. Gaseous ammonia was obtained from a 25% ammonia solution (chemically pure), which was added dropwise to a Wurtz flask containing dry potassium hydroxide.
Conditions of preparation
A weighed portion of vanadium anhydride, thoroughly ground in a porcelain mortar, was poured into a porcelain boat and placed in a quartz tube, which was inserted into an electric furnace. Until the prescribed reduction temperature was reached, a stream of carbon dioxide was passed through the tube. Upon reaching the corresponding temperature, the carbon dioxide flow was stopped and ammonia was passed at a rate of 15 l/hour for 30 min.
After the reduction time had elapsed, the ammonia feed was stopped, and the resulting product was cooled in a stream of carbon dioxide to 80°C. Final cooling of the resulting product was carried out in a desiccator. Reduction of vanadium anhydride in a stream of ammonia was carried out in the temperature range 300–500°C, within which the temperature conditions were varied every 15–25°C.
The best percentage of reduction of vanadium anhydride to vanadium dioxide was achieved at a temperature of 390°C (Table 1). End-
product \( \mathrm{VO_2} \)—vanadium dioxide—is a blue-black powder. Quantitative determination of vanadium in the product obtained was carried out by the permanganatometric method.
Table 1
| \(t\ ^\circ\mathrm{C}\) | Reduction time, min | Charge of vanadium anhydride | Weight of reduction product | Vanadium content in the reduction product, % |
|---|---|---|---|---|
| 305° | 30 | 0,4497 | 0,4269 | 39,4 |
| 325° | 30 | 0,4554 | 0,4276 | 46 |
| 350° | 30 | 0,4505 | 0,4172 | 53,8 |
| 375° | 30 | 0,4545 | 0,4160 | 56,8 |
| 390° | 30 | 0,4550 | 0,4148 | 61 |
| 405° | 30 | 0,4499 | 0,4099 | 61,8 |
| 410° | 30 | 0,4551 | 0,4158 | 62,1 |
| 420° | 30 | 0,4499 | 0,3969 | 74 |
| 450° | 30 | 0,4551 | 0,4026 | 121 |
The vanadium content in vanadium dioxide obtained at a temperature of 390°C is 61.0%; the theoretical value is 61.42%. At higher temperatures, reduction proceeds with the formation of vanadium oxides of lower valencies.
Conclusions
A method has been developed for reducing vanadium anhydride to vanadium dioxide.
The optimum temperature conditions for the reduction of vanadium anhydride with ammonia have been found.
References
- O. A. Cook, J. Amer. Chem. Soc. 69, 331, 1947.
- Handbook of Preparative Inorganic Chemistry, edited by I. L. Brauer, Moscow, 1956.
- B. V. Nekrasov, Fundamentals of General Chemistry, Moscow, 1967.