Of chromium metal

Alloys./ A substantial amount of chromic oxide is used in the manufacture of chromium metal and aluminum—chromium master alloys. 

Self-Test 12.15B What mass of chromium metal can be obtained from a 1 m solution of CrO- in dilute sulfuric acid, by using a current of 6.20 A for 6.00 h ... 

C02-0102. How many atoms of chromium-53 are there in a 0.123 g sample of chromium metal (Consult Figure 2-17.1... 

Chromium makes up just 0.012% of the Earth s crust, yet it is an important industrial metal. The main use of chromium is in metal alloys. Stainless steel, for example, contains as much as 20% chromium. Nichrome, a 60 40 alloy of nickel and chromium, is used to make heat-radiating wires in electrical devices such as toasters and hair dryers. Another important application of chromium metal is as a protective and decorative coating for the surface of metal objects, as described in Chapter 19. 

The production of chromium metal by the aluminothermic reduction of chromium sesquioxide can be represented by the equation ... 

Each mole of chromium metal plated out from a chrome plating bath (i.e., C1O3 and H2SO4) requires six moles of electrons. 

The complex [Cr(DMF)6][Cl04]3 has been prepared from the reaction of chromium(III) perchlorate with DMF (90 °C, 10 h).951 Solvent exchange and substitution proceed by h mechanisms.947,952 The complex [Cr(DMF)6]Br3-DMF was prepared by the reaction of chromium metal with bromine in DMF 953 the electronic spectrum of this complex was very similar to that of the perchlorate salt. 

Metallurgy aluminothermic production of chromium metal by reaction of aluminum powder and Cr203... 

Sfi F-Tfst 12.13B How many hours are required to plate 12.00 g of chromium metal from a 1 M solution of Cr03 in dilute sulfuric acid, using a current of 6.20 A ... 

In air, the reaction of chromium metal with acids yields chromium(III) because chromium(II) is rapidly oxidized by atmospheric oxygen ... 

FIGURE 20.7 (a) Reaction of chromium metal with 6 M H2S04 in the absence of air gives bubbles of H2 gas and a solution containing the blue chromium(II) ion. (b) Reaction of chromium metal with 6 M HC1 in the presence of air yields a green solution containing chromium(III) species. 

Information regarding genotoxic effects in animals after inhalation exposure to chromium or its compounds is limited. Sprague-Dawley rats that inhaled chromium fumes generated from powders of chromium metal by a plasma flame thrower at 1.84 or 0.55 mg chromium(0)/m3 (5 hours/day,... 

Inc., Ward Hill, Massachusetts (16) chromium potassium sulfate McGean-Rohco, Inc., Cleveland, Ohio and (17) chromium-silicon monoxide Cerac Incorporated, Milwaukee, Wisconsin (SRI 1997). Besides these producers of chromium metal alloys and chromium compounds, Table 4-1 reports the number of facilities in each state that manufacture and process chromium, the intended use of the products, and the range of maximum amounts of chromium products that are stored on site. The data reported in Table 4-1 are derived from the Toxic Release Inventory (TRI) of EPA (TRI97 1999). The TRI data should be used with caution since only certain types of facilities were required to report. Hence, this is not an exhaustive list. 

Abstraction, reductive coupling, electron transfer, bond activation, oxidative addition, n-complexation, disproportionation and metal cluster formation are some of the reactions that occur when metal atoms interact with organic polymers and small molecules. Examples of these reactions are provided from the literature on the organometallic chemistry of free atoms and coordination-deficient molecules. Past uses of model compound studies to understand the early stages of chromium metallization on polyimide are critiqued. New evidence for reactions of chromium atoms with compounds related to polyimides is given. 

Chromium nitrides have been prepared by several routes heating of chromium metal in N2, reaction of chromium borides with NH3, and heating of CrCly in gaseous NH3. The two stable nitrides have the composition Cr2N and CrN see Nitrides Transition Metal Solid-state Chemistry). At very high temperatures, both decompose into the constituent elements (CrN, > 1425 °C CryN, >700 °C). CrN is very stable chemically, while CryN dissolves in dilute acid with liberation OfH2. 

A year later, Vauquelin was able to isolate a small sample of the metal itself He heated charcoal (nearly pure carbon) with a compound of chromium, chromium trioxide (Cr203). When the reaction was complete, he found tiny metallic needles of chromium metal ... 

The chromium(lll) oxide thus obtained has a low sulfur content, particularly when a substoichiometric amount of ammonium salt is used, and can be used for the aluminothermic manufacture of chromium metal. 

Chromium(IIf) oxide utilized in the manufacture of chromium metal by aluminothermic reduction, as a pigment and as a polishing agent. 

Apart from the utilization of large quantities of ferrochrome (produced by reducing chromite with coal) in the manufacture of alloys containing iron and chromium, smaller quantities of chromium metal are used in, for example, the manufacture of turbine blades, the production of iron-free alloys and cermets (metal ceramics e.g. 23% by weight aluminum oxide, 77% by weight chromium). 

The use of stoichiometric quantities of ammonium chloride or slightly under stoichiometric quantities of ammonium sulfate in the reaction mixture yields low sulfur chromium(lll) oxide for the manufacture of chromium metal. 

Preparation. In one method a mixture of 9 g. of chromium metal powder (Fisher) and 100 ml. of 6Af hydrochloric acid was stirred with water cooling to room temperature until the reacllon was complete. A deoxygenated solution of... 

Fig. 11. Cocondensation products of chromium metal vapor and [2.2]paracyclophane (8) [53]...

Fig. 12. Cocondensation product of chromium metal vapor and [3.3]paracyclophane (55) and its oxidation to the corresponding radical cation 56 and 57 [15]...

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