Vanadates properties

Several forms of magnesium vanadates have been characterized. Some physical properties ate summarized in Table 27 (28—30) (see also Vanadium AND VANADIUM ADLOYS). 

In the calciaation process, a mixture of corresponding oxides and an optional modifier, eg, molybdic acid, are milled together to achieve a homogenous mixture. The mixture is calciaed at 750—950°C and milled to a desired particle size. Wet milling ia an alkaline medium is recommended to remove any unreacted vanadium salts that ate beheved to degrade the pigmentary properties of bismuth vanadate (39). 

Vanadium-Sodium Compounds Most Corrosive. Physical property data for vanadates, phase diagrams, laboratory experiments, and numerous field investigations have shown that the sodium vanadates are the lowest melting compounds and are the most corrosive to metals and refractories. These compounds are thought to form by either the vapor phase reaction of NaCI and V2O5 or by the combination of fine droplets of these materials upon the cooler parts of combustion equipment. 

Cheng Z, Zha S, Aguilar L, and Liu M. Chemical, electrical, and thermal properties of strontium doped lanthanum vanadate. Solid State Ionics 2005 176 1921-1928. 

Bismuth tritelluride, 4 24 physical properties of, 4 20t Bismuth trithiocyanate, 4 25 Bismuth Vanadate Yellow, 19 405-406 pigment for plastics, 7 370t Bismuthyl carbonate hemihydrate, 4 25 Bismuthyl nitrate hemihydrate, 4 25 Bismuthyl nitrite hemihydrate, 4 25 Bis(lV-maleimidomethyl) ether (BME), hemoglobin modifier, 4 113 Bisoprolol fumarate, molecular formula and structure, 5 156t Bis(pentafluorophenyl)borane, 13 638 Bis(pentafluorophenyl)tri-4-tolylbismuth, 4 35... 

A. Kudo, K. Omori, H. Kato, A novel aqueous process for preparation of crystal form-controlled and highly crystalline BiV04 powder from layered vanadates at room temperature and its photocatalytic and photophysical properties,/. Am. Chem. Soc. 121 (1999) 11459-11467. 

Moriyama, Y., and Nelson, N., 1988, Purification and properties of a vanadate- and N-ethylmaleimide- sensitive ATPase from chromaffin granule membranes. J. Biol. Chem., 263 8521-8527. 

Fotiev, A. Slobodin, B. V. Hodos, M. Y. Vanadates, their Synthesis, Composition and Properties, Nauka Moscow (in Russian), 1988. 

Konta R, Kato H, Kobayashi H, Kudo A (2003) Photophysical properties and photocatalytic activities under visible light irradiation of silver vanadates. Phys Chem Chem Phys 5 3061-3065... 

Ziolkowski, J. (1983a). Catalytic properties of defective brannerite-type vanadates. II. A model of sites active in oxidation of propylene on the (201) and (202) planes J- Catal. 81, 311-27. 

The production process for bismuth vanadate pigments consists usually of a precipitation reaction followed by a calcination step. This calcination leads to an appreciable increase in particle size as demonstrated in Figure 30. The calcination step is different from producer to producer and can be completely absent depending on the precipitation process and the desired product properties. 

Hypovanadous oxide resembles the metal in many of its properties. It is insoluble in water, but dissolves in acids without evolution of hydrogen to yield the lavender-coloured solutions which are characteristic of solutions of hypovanadous salts. These salts are, however, most conveniently prepared in solution by electrolytic reduction in an inert atmosphere of solutions of vanadium pentoxide in the various acids.7 Hypovanadous salts are isomorphous with salts of divalent iron, chromium, and manganese. On being treated with caustic alkalis, a brown precipitate of hypovanadous hydroxide, V(OH)a, is obtained, which rapidly oxidises to the greyish-green vanadous hydroxide, V(OH)s. 

The yellow, amorphous variety is unstable and its identity is a little doubtful. It is stated to be obtained sometimes from the red, amorphous form by evaporation of a solution of the latter in hydrochloric acid, and it may also result from the ignition of ammonium meta-vanadate or from the decomposition of vanadates by acids. According to Bleecker it is most conveniently prepared by the electrolytic decomposition of copper vanadate.5 It becomes brick red on being heated, and is similar to the red variety in its general properties, except that it appears to be less hygroscopic and less soluble its saturated aqueous solution contains between 300 and 400 mgm. per litre.6... 

Bismuth Vanadate, The use of lead chromate pigments has been slowly phased out of many applications. Thus a search for more environmentally acceptable relatively inexpensive yellow pigments having excellent coloristic properties has been ongoing. 

Point defects in the form of cation vacancies () were introduced by Aykan et al. (93-95) into molybdates, tungstates, and vanadates with scheelite-type crystal structures. The authors studied the catalytic properties of more than 30 scheelite-structure phases represented by the formula A1 x< xM04 (M = molybdenum, tungsten, and/or vanadium and A may include Li, Na, K, Ag, Ca, Sr, Ba, Cd, Pb, Bi, and/or arare earth element in quantities appropriate to achieve charge balance for the normal oxidation states). It was found that the defects can be introduced... 

VO(OR)3 — the alkoxides of vanadyl (V) or otherwise the esters of vanad-ic acid — belong to the most easily available derivatives and can be easily purified by distillation under low vacuum. The synthesis of these derivatives — from ethoxide to t-amyloxide—via alcoholysis of V2Os was first described at the beginning ofthe twentieth century by Prandtl and Hess [1313,743], The same work contained the first description ofthe hydrolysis of VO(OR)3, which laid basis for the numerous studies of the processes of formation of sols and gels of vanadic acid. The studies of the low-valent derivatives of vanadium that are very sensitive to oxidation were started in the 1960s by the works of Bradley on V(OR)4 and V(OR)3 [226]. The preparation, structure, and magnetic properties of vanadium(II) alkoxides were investigated only quite recently. 

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