Vanadium pentoxide composites

The ash deposits resulting from the combustion of solid and oil fuels often contain appreciable quantities of other corrodants in addition to vanadium pentoxide. One of the more important of these is sodium sulphate, and the effects of this constituent in producing sulphur attack have been mentioned. The contents of sodium sulphate and vanadium pentoxide present in fuel oil ash can vary markedly and the relative merits of different materials depend to a great extent upon the proportions of these constituents. Exposure of heat-resisting alloys of varying nickel, chromium and iron contents to ash deposition in the super-heater zones of oil-fired boilers indicated a behaviour pattern depending on the composition of the alloy and of the ash... 

In practice, the production of vanadium by aluminothermic reduction is also governed by some other considerations. The reduction has to be carried out under an inert atmosphere (helium or argon) to avoid nitrogen pick-up from the air by vanadium metal. The composition of the oxide-aluminum charge has to be so chosen that the thermit (metal obtained by aluminothermic reduction) contains between 11 and 19% aluminum. This is necessary for the subsequent refining step in the vanadium metal production flowsheet. Pure vanadium pentoxide and pure aluminum are used as the starting materials, and the reduction is conducted in a closed steel bomb as shown in Figure 4.17 (C). 

Elemental composition V 56.02%, O 43.98%. An acid solution is analyzed for vanadium (See Vanadium). Pentoxide in sulfuric acid may he converted to vanadyl sulfate hy reduction with SO2 (See Reactions) or ferrous ammonium sulfate (FAS). The excess FAS may he destroyed with ammonium persulfate. Vanadyl sulfate is then titrated with a standard solution of potassium permanganate ... 

Hypovanadic Bromide, vanadium tetrabromide, VBr4, has not hitherto been isolated, but it is of interest to note that a double salt of composition VBr4.SbBr3.7HaO has been obtained by dissolving antimony tribromide and vanadium pentoxide in hydrobromic acid and adding bromine. ... 

Vanadium Oxyiodides.—No definite oxyiodides of vanadium are known, although several substances of varying composition have been obtained by the action of vanadium pentoxide on hydriodic acid.7 Vanadoiodates and vanadoperiodates are described on p. 90. 

Intermediate Oxides.—Oxides which are intermediate between liypovanadic oxide, V02, and vanadium pentoxide, V205, are known. By the partial reduction of vanadium pentoxide, or by the partial oxidation of one of the lower oxides, there have been prepared a number of oxides which are best considered as being formed by the combination of the acidic vanadium pentoxide with a lower basic oxide in varying molecular proportions. These oxides react yvith alkalis, and yield a series of salts called vanadyl vanadates, intermediate in composition between the vanadites and the vanadates. 

Vanadium pentoxide dissolves in acids, both organic and inorganic, to form vanadyl or unstable vanadic salts,7 and in alkalis to produce ortho-, pyro-, meta-, and poly-vanadates. The physico-chemical changes involved when vanadium pentoxide is heated with various basic oxides in the powder state have been investigated by Tammann.8 On being digested with liquid ammonia slow absorption of ammonia takes place the composition of the product has not been definitely established.9 The oxide also dissolves in alcohols to produce esters,10 and combines with methylamine and ethylamine to form compounds of the type 2(R.NHB).V205, where R represents the alkyl radical.11... 

Beryllium Metavanadate, Be(V03)2.4H20.—Addition of solutions of beryllium salts to alkali vanadates gives rise to basic vanadates of indefinite composition. The pure salt is obtained by boiling beryllium hydroxide and vanadium pentoxide in water in the required proportions. The solution is filtered, concentrated to a syrup and poured into alcohol, whereupon isometric cubes, modified by an octahedron, are obtained. The larger crystals polarise light. Density, 2-273. One gram dissolves in a litre of water at 25° C.s... 

By the action of vanadium pentoxide on selenous acid solutions, or by reduction of a solution of vanadium pentoxide in selenic acid, red crystals of a free vanado-selenous acid have been obtained, the composition of which is SV206.4Se02.4H20.j aq. It contains four molecules of water of constitution, and, according to Prandtl, should be formulated H4Ve017.4H2Se03.(aj—2) aq. 

Vanadium Oxysulphides.—No vanadium oxysulphides of definite composition have been prepared. By the action of acids on solutions of vanadium pentoxide in ammonium sulphide, or on solutions of alkali vanadates which have been saturated with hydrogen sulphide, brown precipitates are obtained which consist of oxysulphides of variable composition.1... 

Hypovanadic oxide, V02, and vanadium pentoxide, V205, both dissolve in hydrofluosilicic acid to yield a vanadyl fluosilicate and a vanadium fluosilicate, both of doubtful composition.14... 

W. Muthmann and co-workers also reported that finely divided vanadium reacts with nitrogen at a red-heat. The reaction is so slow that 20-24 hrs. are needed for the increase in weight to become constant nitrogen is also absorbed at dull redness, but the action is still slower. In contradistinction to H. E. Roscoe, the composition of the product approximated vanadium heminitride, V2N. R. E. Slade and G. I. Higson found that vanadium nitride dissociates at 1203° and 02 mm. press. According to N. Whitehouse, at a white-heat vanadium forms the mononitride. The velvety-black powder is unchanged in air when heated in air, however, it forms vanadium pentoxide water, and dil. hydrochloric acid, hot or cold, have no action, but it dissolves in cold dil. nitric acid. G. Gore found that vanadium nitride is insoluble in liquid ammonia. It is not affected by alkali-lye, but with fused potassium hydroxide, ammonia is evolved. 

Both the rate and tire equilibrium conversion of a chemical reaction depend on the tem-peraUire, pressure, and compositionof reactants. Consider,for example, the oxidation of sulfur dioxide to sulfur trioxide. A catalyst is required if a reasonable reaction rate is to be attained. Witli a vanadium pentoxide catalyst the rate becomes appreciable at about 573.15 K (300°C) and continues to mcrease at higher temperatures. On the basis of rate alone, one would operate tire reactorat the highest practical temperature. However, the equilibrium conversion to sulfur trioxide falls as temperature rises, decreasing from about 90% at 793.15 K (520°C) to 50% at about 953.15 K (680°C). These values represent maximum possible conversions regardless of catalyst or reaction rate. The evident conclusion is that both equilibrium and rate must be considered in the exploitation of chemical reactions for commercial purposes. Although reaction rates are not susceptible to thermodynamic treatment, equilibrium conversions are. Therefore, the purpose of this chapter is to detennine the effect of temperature, pressure, and initial composition on the equilibrium conversions of chemical reactions. 

The combustion of vanadium and its oxides, as reported by Mah and Kelley (4), led to two problems (1) the oxide products liquefy before the pentoxide composition is obtained and (2) the oxide products are corrosive and cause a container problem. The combustion of vanadium led to varying mixtures of V O Crutile) and V Og. This was verified by x-ray diffraction. The enthalpy of formation values for VgO and V20g were derived from the same set of experiments ( ). 

B g. 3. The effect of isotopic composition of molecular oxygen on rate of exchange with oxygen of vanadium pentoxide after Jirff and Novakova (21). 

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