Vanadium pentoxide, decomposition

Violence of reaction depends on concentration of acid and scale and proportion of reactants. The following observations were made with additions to 2-3 drops of ca. 90% acid. Nickel powder, becomes violent mercury, colloidal silver and thallium powder readily cause explosions zinc powder causes a violent explosion immediately. Iron powder is ineffective alone, but a trace of manganese dioxide promotes deflagration. Barium peroxide, copper(I) oxide, impure chromium trioxide, iridium dioxide, lead dioxide, manganese dioxide and vanadium pentoxide all cause violent decomposition, sometimes accelerating to explosion. Lead(II) oxide, lead(II),(IV) oxide and sodium peroxide all cause an immediate violent explosion. 

Vanadium pentoxide is an intermediate in recovering vanadium from minerals (See Vanadium). Sodium polyvanadate, obtained as a red cake in one of the steps in extracting vanadium from its ores is calcined at 700°C in air to form a melt of vanadium pentoxide. Pentoxide is prepared in purified form by dissolving red cake in sodium carbonate solution followed by addition of an aqueous solution of ammonia and ammonium chloride. Ammonium metavanadate is precipitated which on decomposition at 320 to 430°C forms vanadium pentoxide. 

Pyrovanadates, R 4V207 or 2R a0.Va05.—The alkali pyrovana-dates are prepared by dissolving the equivalent quantity of vanadium pentoxide in solutions of alkalis, or by the spontaneous decomposition in solution of the alkali orthovanadates. Pyrovanadates of other metals are obtained by fusing vanadium pentoxide with the salts or hydroxides of the metals in molecular proportions, or, when they are sufficiently insoluble, by double decomposition between an alkali pyro-vanadate and a salt of the metal required. 

DOT CLASSIFICATION 6.1 Label Poison SAFETY PROFILE A poison by several routes. Can react violently with (Ca -i S + H2O), CIF3, Li. When heated to decomposition it emits toxic fumes of VOx. See also VANADIUM PENTOXIDE (dust). 

A possible softening mechanism ia illustrated schematically in Figure 4A. Temperature excursions at the extrudate surface may accelerate the fluxing of vanadium pentoxide (ref. 10) and increase its interaction with other deposited nretals. Aliunlnuin sulfate, absent in the fines, may have decomposed at the particle surface due to the high temperature conditions. If decomposition did occur, temperatures would have been in excess of about 1400 F, and such conditions covild promote the collapse or sintering of the catalyst mesopores (refs. 11,12). Within the extrudate interior, however, conditions were apparently such to stabilize vanadium pentoxide, aluminum sulfate, and the catalyst mesopotes. 

In tile production of formaldehyde by most of the methods which have been described up to this point, relatively pure materials and temperatures up to 400° C. or higher are required. If, however, vanadium pentoxide is used as the catalyst the claim has been made84 that it is possible to produce better yields of formaldehyde, that the catalyst is not affected by poisons such as acetone and water, that the reaction takes place at a sufficiently low temperature to be below the decomposition point of formaldehyde, and that, moreover, a large excess of air is beneficial to the reaction, thus minimizing the danger from explosions which take place only at certain concentrations of the alcohol-air mixtures. A temperature as low as 225° C. has been claimed to be used and methanol which contains as much as 5 per cent acetone is said to give satisfactory results.38... 

It may be seen from comparison of results on ethylene oxidation over silver and vanadium pentoxide that with both catalysts the oxidation of unsaturated hydrocarbons will proceed by the same mechanism. C02 generation is not accelerated in the presence of aldehydes and these cannot be intermediates in ethylene combustion. When aldehydes are introduced into the reactant mixture, the ratio of ethylene oxide to C02 formation rates undergoes a change, due to strong adsorption of aldehydes on the catalyst surface. Ethylene oxide will form on silver and is in fact absent on vanadium oxides. It was shown experimentally that the absence of acetaldehyde and formaldehyde in the products of oxidation over silver, and the low absolute content of these substances for vanadium oxides is due to the fact that they are not formed at all, or formed at a low rate, and not to their oxidation or decomposition. 

This equilibrium has been studied. Using a catalyst consisting of 73 per cent charcoal and 27 per cent nickel, which resulted from carbonizing a mixture of sugar and nickel acetate, the decomposition of carbon monoxide into carbon and carbon dioxide was entirely suppressed and the catalyst maintained its activity for months in producing methane. Ferric oxide, vanadium pentoxide, and cerium oxide are promoters for the nickel-charcoal catalyst. Studies have also been made of the various reactions involved in the reduction of carbon monoxide and dioxide. ... 

The composition of vanadium pentoxide dissociation products in thermal plasma is shown in Fig. 7-26 as a function of plasma temperature and specific energy input (Nester et al., 1988). The process is considered at atmospheric pressure the composition is presented in moles per kilogram of mixture (initially 6.67 mol/kg). Decomposition with formation of VO2 starts at relatively low temperatures however, formation of vanadium atoms requires... 

Cassaine is a tertiary base that can be satisfactorily titrated with methyl red, bromophenol green, or iodoeosin as indicators it gives a yellow-colored solution in sulfuric acid which in the presence of vanadium pentoxide becomes green. The bisulfate, B H2SO4 2H2O, melts with decomposition at 290° and the hydrochloride, B-HC1-H20, melts at 212-213° (17). 

Franc and Dvoracek showed that some functional groups and bond types may be identified by degradation of the sample in a microreactor, and gas chromatographic separation of the volatile reaction products. Details of the method and apparatus are given, and results are presented for the degradation of alkyl- aryl- and chloralkyl-silanes and siloxanes (with concentrated sulphuric acid saturated with vanadium pentoxide) of alkoxysilanes (with hydriodic acid at 75 C) and of vinylsilanes (by saturation with chlorine on a water bath followed by decomposition with concentrated sulphuric acid at 175°C). Alkyl, chloroalkyl, phenyl, chlorophenyl, alkoxyl and vinyl groups, and s Si-Si s and =Si-H bonds were all detected by these procedures. 

In thermal decomposition the polyvanadates first lose their crystal water, and then at 370-500°C dissociate to orthovanadate and vanadium pentoxide (Mokhosoeva et al., 1972). 

For solvent extraction of pentavalent vanadium as a decavanadate anion, the leach solution is acidified to ca pH 3 by addition of sulfuric acid. Vanadium is extracted in about four countercurrent mixer—settler stages by a 3—5 wt % solution of a tertiary alkyl amine in kerosene. The organic solvent is stripped by a soda-ash or ammonium hydroxide solution, and addition of ammoniacal salts to the rich vanadium strip Hquor yields ammonium metavanadate. A small part of the metavanadate is marketed in that form and some is decomposed at a carefully controlled low temperature to make air-dried or fine granular pentoxide, but most is converted to fused pentoxide by thermal decomposition at ca 450°C, melting at 900°C, then chilling and flaking. 

The pentoxides of vanadium, niobium, and tantalum react with hydrogen peroxide to produce per-acids of the general formula HR04. H20. These per-acids increase in stability with increase in atomic weight. Pertantalic acid is a white solid which can be heated to 100° C. without undergoing decomposition. The oxyfluorides of these metals also take up active oxygen to yield peroxyfluorides, which are much better defined in the case of niobium and tantalum than with vanadium. 

Figure 7-26. Vanadium production by direct decomposition of pentoxide (V2O5) in atmospheric-pressure thermal plasma. Composition of products (1) VO2 (2) VO (3) O2 (4) [O] X 0.1 (5) V+ (6) V...

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