Vanadium impurity

A colorless mineral known as corundum (composed of aluminum oxide) is colorless. A red variety of corundum known as ruby, a precious stone, owes its color to impurities of chromium within the crystal structure of corundum. Blue and violet varieties of corundum are classified as sapphires, the blue being the result of iron and titanium impurities, and the violet of vanadium impurities within the corundum crystal structure. Another colorless mineral is beryl (composed of beryllium aluminum silicate) but blue aquamarine, green emerald, and pink morganite, are precious varieties of beryl including different impurities aquamarine includes iron, emerald chromium and vanadium, and morganite manganese. 

DFCC mixtures containing 40% sepiolite and 60% GRZ-1 are equally effective in passivating high (10,000 wtppm) levels of vanadium impurities (1 ). In both cases, metakaolin microspheres do not... 

Organophosphorus acids were among the first extractants to be used in the commercial recovery of uranium from solutions obtained by the leaching of low-grade ores with sulfuric acid. In the so-called Dapex process,70 114 the leach liquor is extracted with a solution of about 0.1 M D2EHPA in kerosene, and the pH value of the aqueous phase is adjusted to close to 1.0 in order to prevent the coextraction of vanadium impurities. Since iron(III) also extracts under these conditions, the leach liquor is reduced with metallic iron prior to extraction to convert any iron(III) present to the iron(II) state. 

ESR is known to be a very sensitive tool and can therefore be used in studying structural features of nanosized semiconductor particles doped with paramagnetic metal ions. In many studies vanadium impurities inside the Ti02 matrix or on the particle s surface were used as dopants. Moreover, V4+ ions are very convenient ESR probes since the 51V nuclei have a large magnetic moment leading to informative hyperfine structures (S = 1/2 / = 7/2). At low vanadium concentration, the EPR spectrum has well resolved sharp lines (Fig. 8.10) allowing precise measurement of spin-Hamiltonian parameters. 

In the last few years Schneider and co-workers have performed a number of experiments on various SiC polytypes which exhibit a characteristic infrared emission in the 1.3 to 1.5 pm spectral range [98]. They have assigned this emission band to vanadium impurities substituting the various silicon sites in the lattice. In their extensive work they found three charge states of vanadium which act as an electrically amphoteric deep level in SiC. They also suggest that vanadium may have an important role in the minority-carrier lifetime in SiC-based optoelectronic devices [98,99], Recently, trace amounts of vanadium impurities have been detected in 3C-SiC grown by the modified-Lely technique [100]. 

ABC extractant properties provide an alternative process for the recovery of the sulfuric acid and of the Ti02 values and for removal of chromium and vanadium impurities (see Fig. 10). The waste stream is combined with a recycled stream and concentrated by removing about 40% of its water content. Part of the salt content crystallizes and is separated by centrifugation. The solution, containing the acid and the rest of the salts, is extracted by a coupled extractant. The extract is back-extracted by water to form the back-extract, a solution of H2SO4, which is concentrated in an evaporator to provide the recovered acid. The raffinate of the extraction can be treated for extraction of chromium and vanadium and for titanium recovery and is then recycled to evaporation and crystallization. 

Compared to the relatively young history of the pure metal, aluminium compounds have been known for ages from the above-cited alum class to the more exclusive transition metal-doped aluminium oxides like ruby and sapphire (corundum varieties with chromium for the former and titanium and iron impurities for the latter) or aluminosilicate-like emeralds (a beryl type with chromium and vanadium impurities). However, to the synthetic chemist, aluminium chloride, is de facto one of the first jewels of the aluminium family. Aluminium trichloride (together with titanium tetrachloride, tin tetrachloride and boron trifluoride) is an exemplary Lewis acid that finds many applications in organic synthesis It is extensively used for instance in Friedel-Crafts alkylations and acylations, in Diels-Alder-type cycloadditions and polymerisation reactions. Its involvement in a wide range of reactions has been documented in many reviews and book chapters. ... 

Semi-insulating 6H-SiC crystals have been achieved by using controlled doping with deep-level vanadium impurities (107). The resistively is 10 Q cm at room temperature and 10 Q cm even at 300°C. The semi-insulating behavior is attributed to compensation of residual acceptors by the deep-level vanadium W+(3(i ) donor located near the middle of the band gap. 

Scandinavian goddess, Vanadis) Vanadium was first discovered by del Rio in 1801. Unfortunately, a French chemist incorrectly declared that del Rio s new element was only impure chromium. Del Rio thought himself to be mistaken and accepted the French chemists s statement. 

Although many variations of the cyclohexane oxidation step have been developed or evaluated, technology for conversion of the intermediate ketone—alcohol mixture to adipic acid is fundamentally the same as originally developed by Du Pont in the early 1940s (98,99). This step is accomplished by oxidation with 40—60% nitric acid in the presence of copper and vanadium catalysts. The reaction proceeds at high rate, and is quite exothermic. Yield of adipic acid is 92—96%, the major by-products being the shorter chain dicarboxytic acids, glutaric and succinic acids,and CO2. Nitric acid is reduced to a combination of NO2, NO, N2O, and N2. Since essentially all commercial adipic acid production arises from nitric acid oxidation, the trace impurities patterns ate similar in the products of most manufacturers. 

Germanium tetrachloride refined for use in making optical fibers is usually specified to contain less than 0.5 to 5 ppb of each of eight impurities vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. Limits are sometimes specified for a few other elements. Also of concern are hydrogen-bearing impurities therefore, maximum limits of 5 to 10 ppm are usually placed on HCl, OH, CH2, and CH contents. 

Ferrophosphoms is produced as a by-product in the electrothermal manufacture of elemental phosphoms, in which iron is present as an impurity in the phosphate rock raw material. The commercial product contains ca 23—29% P and is composed primarily of Fe2P [1310-43-6] and Fe P [12023-53-9] along with impurities such as Cr and V. Ferrophosphoms is used in metallurgical processes for the addition of phosphoms content. Low concentrations (up to - 0.1%) of phosphoms in wrought and cast iron and steel not only increases the strength, hardness, and wear resistance but also improves the flow properties. In large stmctural members and plates, it is desirable to use a type of steel that does not need to be quenched or tempered, and thus does not exhibit weld-hardening. This property is afforded by the incorporation of a small quantity of phosphoms in steel. Ferrophosphoms from western U.S. phosphoms production is used as a raw material for the recovery of vanadium (see Vanadiumand vanadiumalloys). 

Impurities that form volatile chlorides leave as gases at the top of the furnace together with the TiCl. By cooling those gases, most impurities, with the exception of vanadium and siUcon chlorides can be separated from the titanium tetrachloride [7550-45-0]. Vanadium chlorides can be reduced to lower oxidation state chlorides that are soHds highly volatile SiCl can be removed from TiCl by fractional distillation. 

Physical and Chemical Properties. Titanium dioxide [13463-67-7] occurs in nature in three crystalline forms anatase [1317-70-0] brookite [12188-41 -9] and mtile [1317-80-2]. These crystals are essentially pure titanium dioxide but contain small amounts of impurities, such as iron, chromium, or vanadium, which darken them. Rutile is the thermodynamically stable form at all temperatures and is one of the two most important ores of titanium. 

The red cake can be further purified by dissolving it in an aqueous solution of Na2C02- The iron, aluminum, and silicon impurities precipitate from the solution upon pH adjustment. Ammonium metavanadate then precipitates upon the addition of NH Cl and is calcined to give vanadium pentoxide of greater than 99.8% purity. 

The vanadium alloy is purified and consoHdated by one of two procedures, as shown in the flow diagram of the entire aluminothermic reduction process presented in Figure 1. In one procedure, the brittle alloy is cmshed and heated in a vacuum at 1790°C to sublime most of the aluminum, oxygen, and other impurities. The aluminum faciHtates removal of the oxygen, which is the feature that makes this process superior to the calcium process. Further purification and consoHdation of the metal is accompHshed by electron-beam melting of pressed compacts of the vanadium sponge. 

Because no process has been developed for selectively removing impurities in vanadium and vanadium alloys in the metallic state, it is essential that all starting materials, in aggregate, be pure enough to meet final product purity requirements. In addition, the consoHdation method must be one that prevents contamination through reaction with air or with the mold or container material. 

Because of the effects of impurity content and processing history, the mechanical properties of vanadium and vanadium alloys vary widely. The typical RT properties for pure vanadium and some of its alloys are hsted in Table 4. The effects of ahoy additions on the mechanical properties of vanadium have been studied and some ahoys that exhibit room-temperature tensile strengths of 1.2 GPa (175,000 psi) have strengths of up to ca 1000 MPa (145,000 psi) at 600°C. Beyond this temperature, most ahoys lose tensile strength rapidly. 

For direct precipitation of vanadium from the salt-roast leach Hquor, acidulation to ca pH 1 without the addition of ammonia salts yields an impure vanadic acid when ammonium salts are added, ammonium polyvanadate precipitates. The impure vanadic acid ordinarily is redissolved in sodium carbonate solution, and ammonium metavanadate precipitates upon addition of ammonium salts. Fusion of the directly precipitated ammonium salts can yield high purity V20 for the chemical industry. Amine solvent extraction is sometimes used to recover 1—3 g/L of residual V20 from the directly precipitated tail Hquors. 

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