Chromium impurity

Once the green, nonalum modifications of the chromium ion have formed, reversion to the hexaaquo form on cooling is sufficiendy slow that on chilling to 5°C a cmde ferrous ammonium sulfate can be crystallised, removing neady all the iron from the system. This cmde iron salt is treated with makeup ammonium sulfate, heated again to retain the chromium impurities in the green noncrystallisahle form, and then cooled to separate the bulk of the iron as a technical ferrous ammonium sulfate, which is sold for fertiliser and other purposes. The mother Hquor from this crystallisation is returned to the filtration step. 

The use of radioactivated discs of aluminum and steel to estimate fragment erosion in solid targets at very high velocities was found to be feasible. Activation of discs was accomplished by slow neutron irradiation in a nuclear reactor at a flux of 8 x 1012 neutrons per cm2 per sec for 3 days for the aluminum discs (4g, 2.5cm diam x 0.3cm thick), and for 4 hrs for the steel discs (5g, 2.5cm diam x 0.15cm thick). Gamma-ray spectrometry indicated the presence of 59Fe (half-life 46 days) and 51Cr (half-life 28 days) in ratios 0.5 for aluminum and 1.3 for steel. The radioactivities in the aluminum arose solely from impurities, whereas in the steel they were contributed by the major component, iron, and only supplemented by the chromium impurity. The radioactivity was found by successive acid soln determinations to be distributed evenly in both metals... 

Alumina is a widespread component of siliceous minerals. It occurs as single crystals in the form of sapphire, and with chromium impurity as ruby, and in large deposits as the hydrated oxide bauxite (A1203-2H20). The dehydration of this and other hydrated oxides at temperatures below 1000°C leads to the formation of y-Al203 which is converted to a-Al203 above 1000 °C. The transformation is irreversible and the a-polymorph is stable from absolute zero to its melting point at 2050 °C. 

At this point, it is important to remove as much of the blue chromium impurities from the organic phase as possible. 

Decarburization occurs in steels and cast irons in hydrogen gas by the reaction of H with C in the steel. The decarburization rate is primarily dependent on the diffusion rate of C in the steel, but is also affected by the carbon content of the steel, alloying elements in the steel, such as chromium, impurities in the hydrogen, and of course time and temperature. Carburization of steels, the reverse of decarburization, is usually conducted at temperatures of about 900°C, but decarburization can occur at temperatures as low as 800°C. " ... 

Chromium impurities in the a-alumina phase fluoresce under laser irradiation of appropriate wavelength. For materials exhibiting the piezo-spectroscopic effect, the wave number, v, of the fluorescence line depends on the stress state. In the case of alumina, the line shift, Av, is approximately proportional to the stress for stresses up to a few GPa... 

Defects in crystalline solids are important because they modify important properties. For example, just a trace of chromium impurity changes colourless aluminium oxide into ruby. Metals are ductile when linear defects called dislocations are free to move. Crystals dissolve and react at increased rates at points where dislocations intersect the surface of the crystal. Thus, it is necessary to have an idea of the types of defect that form and the role that they play in the control of properties in order to understand the behaviour of solids. 

Beryllium is a rare element that s found mainly in a mineral called beryl, which is a complex aluminosilicate (Be3Al2SigO,. When beryl contains chromium impurities, it s known as an emerald when it has iron impurities, it s an aquamarine. 

Chemical data presented in Table 4.20 demonstrate that the alexandrite samples which exhibit only one type of chromium luminescence in its lattice, namely Cr " m, are characterized by low concentrations of chromium impurity. Figure 5.41a presents time-resolved luminescence spectra at 300 K after very long delay of 5 ms of alexandrite from Siberia which is characterized by the highest chromium. It is structurally complicated emission composed of two narrow lines peaking at 690.3 and 695.9 nm superimposed by the broad emission band. All those narrow lines and structured broad band combination remains the same under different excitations. 

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. 

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. 

Solid-State Lasers. Sohd-state lasers (37) use glassy or crystalline host materials containing some active species. The term soHd-state as used in connection with lasers does not imply semiconductors rather it appHes to soHd materials containing impurity ions. The impurity ions are typically ions of the transition metals, such as chromium, or ions of the rare-earth series, such as neodymium (see Lanthanides). Most often, the soHd material is in the form of a cylindrical rod with the ends poHshed flat and parallel, but a variety of other forms have been used, including slabs and cylindrical rods with the ends cut at Brewster s angle. 

Materials of Construction. Resistance of alloys to concentrated sulfuric acid corrosion iacreases with increasing chromium, molybdenum, copper, and siUcon content. The corrosiveness of sulfuric acid solutions is highly dependent on concentration, temperature, acid velocity, and acid impurities. An excellent summary is available (114). Good general discussions of materials of constmction used ia modem sulfuric acid plants may be found ia References 115 and 116. More detailed discussions are also available (117—121). For nickel-containing alloys Reference 122 is appropriate. An excellent compilation of the relatively scarce Hterature data on corrosion of alloys ia Hquid sulfur trioxide and oleum may be found ia Reference 122. 

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. 

Chromium oxide is mixed with aluminum powder, placed in a refractory-lined vessel, and ignited with barium peroxide and magnesium powder. The reaction is exothermic and self-sustaining. Chromium metal of 97—99% purity is obtained, the chief impurities being aluminum, iron, and silicon (Table 4). Commercial chromium metal may also be produced from the oxide by reduction with silicon in an electric-arc furnace. 

Cr C Cr C chromium iton(l l) [12052-89-0] CrFe (c phase), and chromium iron molybdenum(12 36 10) [12053-58-6] Cr 2F 36 o Q phase), are found as constituents in many alloy steels Ct2Al23 and CoCr ate found in aluminum and cobalt-based alloys, respectively. The chromium-rich interstitial compounds, Ci2H, chromium nitrogen(2 l) [12053-27-9] Ct2N, and important role in the effect of trace impurities on the... 

When Cr202 is introduced as an impurity into the a-Al202 lattice, as occurs in the semiprecious mineral mby, the color is red rather than the normal green. This color anomaly is the result of ligand field splitting of the Cr(III) ion (51,52). Chromium (ITT) also colors other minerals (53). 

Modem manufacturing processes quench the roast by continuous discharge into the leach water held in tanks equipped with agitators. At this point the pH of the leach solution is adjusted to between 8 and 9 to precipitate aluminum and siHcon. The modem leaching operations are very rapid because no or htde lime is used. After separation of the ore residue and precipitated impurities using rotary vacuum filters, the cmde Hquid sodium chromate may need to be treated to remove vanadium, if present, in a separate operation. The ore residue and precipitants are either recycled or treated to reduce hexavalent chromium to Cr(III) before disposal. 

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