Vanadium dioxide

Vanadium dioxide, VO2 is dark blue (V2O5 plus SO2) but is readily reduced further to Vo.i86-V,.6a. VO2 gives the (VO) ion with acids and vanadates(IV) with alkalis and as mixed metal oxides. 

Vanadium(IV) Oxide. Vanadium(IV) oxide (vanadium dioxide, VO2) is a blue-black solid, having a distorted mtile (Ti02) stmcture. It can be prepared from the reaction of V20 at the melting point with sulfur or carbonaceous reductants such as sugar or oxaUc acid. The dioxide slowly oxidizes in air. Vanadium dioxide dissolves in acids to give the stable (VO) " ions and in hot alkaUes to yield vanadate(IV) species, eg, (HV20 ) . 

Vanadium forms numerous oxides, the most important of which are vanadium monoxide, vanadium sesquioxide, vanadium dioxide and vanadium pentoxide. In the earlier examples (e.g., oxides of chromium and of niobium) the enthalpy values for the aluminothermic reduction of each of the oxides was given for the purpose of illustration. Normally, the consideration can be restricted to only those oxides which are readily obtained and which can be handled freely without any special or cumbersome precautions. In the case of vanadium for example, it is sufficient to consider the reduction of the sesquioxide (V203) and the pentoxide (V2Os). The pertinent reactions are ... 

In addition to the foregoing, Gain 4 has prepared a large number of alkali vanadyl sulphites in which the proportions of basic oxide, vanadium dioxide, and sulphur dioxide vary considerably ... 

Oxides Vanadium monoxide VO, gray solid vanadium trioxide V2O3, black solid vanadium dioxide VO2, dark blue solid vanadium pentoxide V2O5, orange to red solid. The last is the most important oxide formed by the ignition in an of vanadium sulfide, 01 othei oxide, 01 vanadium used as a catalyzer, e.g., the reaction SO2 gas plus oxygen of air to form sulfur tnoxide. and the oxidation of naphthalene by air to form phthalie anhydride. 

Casalot, A. andM. Pouchard. 1967. New nonstoichiometric phases of the silver oxide-vanadium pentoxide-vanadium dioxide system. I. Chemical and chrystallographic study. Bull. Soc. Chim. 10 3817-3820. 

The authors react Fe with a low-grade, acid, sub-bituminous coal (SBC) slurry to produce carbon dioxide and Fe. The latter ion can then be harnessed as the anode of the cell, with the oxidation reaction Fe to Fe coupled to the reduction of vanadium dioxide at the cathode of the fuel cell. The first primitive device is said to be 7% efficient, but that is based on the fuel calorific value, asserted to be irrational in this book and in (Barclay, 2002). An alternative catalyst is mooted to start the path to improvement. The fate of the used slurry is not discussed. It could be burnt or buried, depending on economics. 

Kimizuk N., Ishii M., Kawada I., Saeki M. and Nakahira M., Behavior of vanadium dioxide single crystals synthesized under the various oxygen partial pressures at 1500 K. J. Solid State Chem. 9 (1974) pp. 69 - 77. 

Results of investigations of vanadium dioxide thin films obtained by the electron-beam evaporation method are considered. Structural and surface morphology of VO., thin films on silicon substrates are presented. Analysis of electrical characteristics of the studied samples is given. A hysteresis of temperature dependences of capacitance and resistance, as well as the phase transition at 58 °C are obtained. 

For the aquisltion of vanadium dioxide thin films one needs to solve such a problem that together with the growth of VO2, additional compounds as V2O3, V3O5, V2O5 can be formed. Therefore a precise control of deposition process parameters is required. 

Thermal treatment of the films was carried out at 300-500 "C during 10-130 min. An oxidation of vanadium films was performed in a stream of Ar+02 gas mixture. A high-temperature processing of the films was carried out in a recovering medium Ar+4%H2 at 350 °C with a goal of the recovery of vanadium pentoxide down to lower phase of vanadium dioxide. 

The obtained vanadium dioxide films are characterized by a homogeneous finegrained nanostructure with grain size not exceeding 160 nm. The phase transition temperature was about 58 °C. All the samples are characterized by hysteresis of resistance and capacitance. The obtained results give evidence that there are an unoxidized vanadium and its lower oxides in the VO2 films as a separate scattered nanoinclusions. 

Y. Kaneko and H. Kojima, Dissociation Behaviour of Vanadium Dioxide and Basicity in Fused Alkali Metal Sulphate Mixtures, Proceedings of the First International Symposium on Molten Salts Chemical Technology, 1983) pp. 441-444. 

For this reason, a perspective alternative may be a photonic crystal based on opal-vanadium dioxide (VO2) composite, with a semiconductor- metal phase transition in VO2. Experiments on pump-probe measurements of the VO2 phase transition, which use pulses from mode-locked lasers, have shown that this transition occurs for a period of several hundreds of femtoseconds [6]. 

Figure 3. SEM image of a vanadium dioxide photonic crystal with inverted opal structure [10]. 

Vanadium dioxide, VO2 fi = 1.8 (calcd. 1.8), A = 225°. The Weiss constant here is unusually high. The composition was, however, a little difficult to obtain stoichiometrically. The sample studied had an apparent formula V02.os 0.17H20. 

Batista C,Teixeira V, Ribeiro RM. Pulsed DC reactive magnetron sputtering of vanadium dioxide thermochromic thin films. Mater. Technol. 2011 26(l) 35-39. DOI 10.1179/175355511X12941605982307. 

Warwick, M. E. A., Ridley, I. and Binions, R. (2011) Electric Fields in the Chemical Vapour Deposition Growth of Vanadium Dioxide Thin Films. Journal of Nanoscience and Nanotechnology 11,8158-62. 

Turov, V.V, Gorbik, P.P., Ogenko, V.M., Shulga, O.V., and Chuiko, A.A. 2001. Characteristic properties of metal-semiconductor phase transitions of vanadium dioxide in a polyethylene glycol medium containing tetraethylammonium bromide. Colloids Surf. A Physicochem. Eng. Aspects 178 105-112. 

Very recently, vanadium dioxide hybrid fiber mats (PVPA 02) were prepared for the first time and their diffuse reflectance was investigated [36]. 

Warwick, M.E.A., Binions, R., 2014. Chemical vapour deposition of thermochromic vanadium dioxide thin films for energy efficient glazing. Journal of Sohd State Chemistry 214 (0), 53-66. 

Yin D.C., Xu N.K., Zhang J.Y., Zheng X L. Vanadium dioxide films with good electrical switching property. J. Phys. D 1996 29 1051-1057... 

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