Vanadium sulphates

The general constitutional formula for the vanadium alums is [V(H402)6](S04)(S04R), which differs from the formulas for other double vanadium sulphates in that the sulphato groups are not attached to the nuclear vanadium atom. 

Electronic Raman Spectrum of Guanidinium Vanadium Sulphate... 

Based on their early fundamental research of all-VRFBs, Skyllas-Kazacos et al. [25] also first developed some commercial products, for example, a 1 kW vanadium redox battery (VRB) cell stack. By employing 1.5-2 M vanadium sulphate, sulphuric acid in both half-cells, over 85% of theoretical capacity and 70-80% energy efficiency was obtained. Then in 1994, a 4 kW/12 kWh vanadium battery was evaluated in a demonstration solar house by Thai Gypsum Products Ltd. in Thailand under a license lirom the UNSW [26]. 

When grape plants were sprayed with vanadium sulphate at the time of massive flowering and with grapes about the size of peas, AA concentration in leaves and berries increased appreciably Sugars accumulated in greater con centrations, ripening was accelerated and yield was increased ... 

The data were fitted to a second-order polynomial (Equation 10.1) and the values of the second-, first- and zero-order coefficients were calculated for each solution as shown in Table 10.2. The second-order coefficient is reported as an indicator of the solute-solute interactions in the solution. The first-order coefficient is proportional to the variation in the solution density (molar volume) with the addition of vanadium sulphate and the last coefficient is the density of the acid-water mixture. The values of these coefficients at different acid concentrations do not show any trends. This might be due to the fact that the variations might be too small and lie within experimental error. 

To calculate the value of the measured relative viscosity from experimental results, the viscosity of dilute sulphuric acid solutions was used as the viscosity of the solvent. The fact that the concentration of the acid was kept constant for each set of solutions allows it to be considered as the solvent. The validity of this assumption is based on the fact that the addition of the acid (up to 2.0 M) did not cause significant changes in the viscosity of water compared to the addition of vanadium sulphates. It is also assumed that the contribution of sulphuric acid to the increase in the viscosity of the solution is independent of the addition of vanadium (111) sulphate. Nevertheless, the accuracy of the parameters calculated below should always be treated with caution. 

Figure 10.16 shows the corrected specific conductance values for vanadium sulphate solution in 2.0 M sulphuric acid at different temperatures. The corrected values show a wave-like curve however, the shape of the curve seems to differ between different temperatures. The degree of scattering in the data seems to be higher at the higher concentration range. This is most likely due to the abnormality in the viscosity behaviour especially at higher concentrations. 

Except for the curve at 15°C, the change in the corrected conductivity of the solutions follows the wave shape. A slight drop in the conductivity is initially observed at concentrations below 0.8 M, which is followed by an increase in the conductance to a maximum around 1.3 M. Similar behaviour was reported for a number of ternary systems MX-HX-H2O, where MX is the salt and HX is the acid. Zinc sulphate-sulphuric acid-water mixture in particular was reported to show similar curves when the concentration of the salt was increased at constant acid concentration. The measured conductivity values were correlated to the concentration of different species in the solution. The calculation of different species concentrations was based on a set of equilibria with known equilibrium constant values. Unfortunately it was not possible to carry out similar calculations on vanadium sulphate solutions due to the lack of values of equilibrium constants. 

The conductivity-viscosity curves were also obtained for vanadium sulphate and glycerol solutions at 15°C and 40°C to confirm the validity of this assumption over the whole temperature range. Similar behaviour is observed as shown in Figures 10.18 and 10.19. 

Temperature has a significant effect on the sulphate/bisulphate equilibrium and on the concentration of the hydronium ions in the soluhons as well. However, the lack of information on the temperature effects on the formation of vanadium-sulphate ion pairs makes it difficult to explain the effect of the temperature on the solution conduchvity. 

Vanadium IV) forms blue VOSO4, (0, 3 and 5H2O), vanadyl sulphate, which forms ranges of double salts, Prepared by SO, reduction of V2O5 in H2SO4. 

NaCl, interact with the sulphur and vanadium oxides emitted from the combustion of technical grade hydrocarbons and die salt spray to form Na2S04 and NaV03- These conosive agents function in two modes, either the acidic mode in which for example, the sulphate has a high SO3 thermodynamic activity, of in the basic mode when the SO3 partial pressure is low in the combustion products. The mechanism of coiTosion is similar to the hot coiTosion of materials by gases widr the added effects due to the penetration of tire oxide coating by tire molten salt. 

Sulphates, which form part of the ash from the combustion of many fuels, are not harmful to high-alloy steels, but can become so if reduction to sulphide occurs. This leads to the formation of low melting point oxide-sulphide mixtures and to sulphide penetration of the metal. Such reduction is particularly easy if the sulphate can form a mixture of low melting point with some other substance. Reduction can be brought about by bad combustion, as demonstrated by Sykes and Shirley , and it is obviously important to avoid contact with inefficiently burnt fuels when sulphate deposits may be present. Reduction can also be brought about in atmospheres other than reducing ones and the presence of chlorides or vanadium pentoxide has been shown to be sufficient to initiate the reaction. It has also been shown that it can be initiated by prior cathodic polarisation in fused sodium sulphate. The effect of even small amounts of chloride on oxidation in the presence of sulphate is illustrated in Fig. 7.33 . 

Reactions of contaminants in the fuel or air in the combustion zone can result in the formation of compounds which can condense as molten salts onto cooler components in the system. This type of process can occur when fuels containing sulphur or vanadium are burnt. In the case of sulphur contaminants, alkali sulphates form by reactions with sodium which may also be present in the fuel or in the combustion air, and for vanadium-containing fuels low-melting-point sodium vanadates or vanadium pentoxide are produced, particularly when burning residual oils high in vanadium. Attack by molten salts has many features in common which will be illustrated for the alkali-sulphate-induced attack, but which will be subsequently shown to be relevant to the case of vanadate attack. 

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... 

Discussion. Molybdates [Mo(VI)] are quantitatively reduced in 2M hydrochloric acid solution at 60-80 °C by the silver reductor to Mo(V). The reduced molybdenum solution is sufficiently stable over short periods of time in air to be titrated with standard cerium(IV) sulphate solution using ferroin or /V-phenylanthranilic acid as indicator. Nitric acid must be completely absent the presence of a little phosphoric(V) acid during the reduction of the molybdenum(VI) is not harmful and, indeed, appears to increase the rapidity of the subsequent oxidation with cerium(IV) sulphate. Elements such as iron, copper, and vanadium interfere nitrate interferes, since its reduction is catalysed by the presence of molybdates. 

With the exception of iron(II) and uranium(IV), the reduced solutions are extremely unstable and readily re-oxidise upon exposure to air. They are best stabilised in a five-fold excess of a solution of 150g of ammonium iron(III) sulphate and 150 mL of concentrated sulphuric acid per litre [approximately 0.3M with respect to iron] contained in the filter flask. The iron(II) formed is then titrated with a standard solution of a suitable oxidising agent. Titanium and chromium are completely oxidised and produce an equivalent amount of iron(II) sulphate molybdenum is re-oxidised to the Mo(V) (red) stage, which is fairly stable in air, and complete oxidation is effected by the permanganate, but the net result is the same, viz. Mo(III)- Mo(VI) vanadium is re-oxidised to the V(IV), condition, which is stable in air, and the final oxidation is completed by slow titration with potassium permanganate solution or with cerium(IV) sulphate solution. 

Large amounts of chloride, cobalt(II), and chromium(III) do not interfere iron(III), nickel, molybdenum)VI), tungsten(VI), and uranium(VI) are innocuous nitrate, sulphate, and perchlorate ions are harmless. Large quantities of magnesium, cadmium, and aluminium yield precipitates which may co-precipitate manganese and should therefore be absent. Vanadium causes difficulties only... 

Z 1 Niobium 1 Nitrate 1 Osmium 73 a. I Perchlorate Phenols u a o Platinum o 0. 1 5 u 1 Rhodium 1 Rubidium Ruthenium Scandium 1 Selenium Silver I Sodium 1 Strontium 1 Sulphate Sulphides, organic Sulphur dioxide 1 Tantalum 1 Tellurium 1 Thallium Thorium e H 1 Titanium a u ab a 1- I Uranium 1 Vanadium 1 Yttrium 1 Zinc Zirconium... 

Strongly acidic vanadium(V) oxidises bromide in a sulphate ion medium . The reaction is first-order in both oxidant and sulphuric acid. The dependence of the rate on bromide ion concentration is complex and a maximum is exhibited at certain acidities. A more satisfactory examination is that of Julian and Waters who employed a perchlorate ion medium and controlled the ionic strength. They used several organic substrates which acted as captors for bromine radical species. The rate of reduction of V(V) is independent of the substrate employed and almost independent of substrate concentration. At a given acidity the kinetics are... 

Analysis of the dynamics of SCR catalysts is also very important. It has been shown that surface heterogeneity must be considered to describe transient kinetics of NH3 adsorption-desorption and that the rate of NO conversion does not depend on the ammonia surface coverage above a critical value [79], There is probably a reservoir of adsorbed species which may migrate during the catalytic reaction to the active vanadium sites. It was also noted in these studies that ammonia desorption is a much slower process than ammonia adsorption, the rate of the latter being comparable to that of the surface reaction. In the S02 oxidation on the same catalysts, it was also noted in transient experiments [80] that the build up/depletion of sulphates at the catalyst surface is rate controlling in S02 oxidation. 

The production of sulphuric acid by the contact process, introduced in about 1875, was the first process of industrial significance to utilize heterogeneous catalysts. In this process, SO2 was oxidized on a platinum catalyst to S03, which was subsequently absorbed in aqueous sulphuric acid. Later, the platinum catalyst was superseded by a catalyst containing vanadium oxide and alkali-metal sulphates on a silica carrier, which was cheaper and less prone to poisoning. Further development of the vanadium catalysts over the last decades has led to highly optimized modem sulphuric acid catalysts, which are all based on the vanadium-alkali sulphate system. 

The structures of the anhydrous vanadiumfiii) sulphates, 2(804)3, yellow (monoclinic) and green (rhombohedral), have been investigated, and a new double sulphate, (NH4)3V(S04)3, has been prepared and extensively characterized. Single-crystal magnetic susceptibility studies (1.5—20 K) of guanidi-nium vanadium(iii) sulphate have been reported, and the zero-field splitting has been estimated as 3.74 cm . ... 

The purification of the alkali hydroxides.—Numerous impurities have been reported in commercial sodium and potassium hydroxides. Several have commented on the presence of peroxide, particularly in caustic potash.19 Various salts—carbonate, sulphate, nitrate, nitrite, chloride, and phosphate—as well as alumina, silica, organic matters, and metal oxides—e.g. arsenic, vanadium, iron, etc., have been reported. More or less of the other alkalies may also be present. 

Trivalent Compounds.—In trivalent vanadium compounds the basic character of the element is well developed, and both normal and oxy-salts of the sesquioxide V203 are well defined, e.g. vanadous sulphate, V2(S04)3, and vanadium oxymonochloride, VOC1. It has been previously mentioned that resemblances between the elements of the A and B Subdivisions of Group V. are mainly restricted to the pentavalent compounds it is of interest to note that the oxychloride has analogues in the trivalent antimony and bismuth basic chlorides, SbOCl and BiOCl. Trivalent vanadium also displays considerable analogy, however, with other trivalent transitional elements, as shown by the following —... 

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