Chromites

Chromite is a member of the spinel group. Spinels have the general formula, R 0 R2 03. R represents a divalent metal ion, such as Fe++, Mg++, Mn++, and so forth. R is a trivalent ion. Some examples are AF++, and Ci ++. The chemical formula for chromite is FeO Cr203. The characteristics of this group of minerals are as follows  

The only significant chromium ore mineral is chromite, a member of the spinel group, with the formula (Fe,Mg)0(Fe,Al,Cr)203. The important ore variables are Cr203 content, Cr Fe ratio, Si02 content, amount and ratio of AI2O3 and 

and sulfur and phosphorus content. In some operations high-grade ore is selectively mined, hand sorted and screened, and sold as lump and fines. More commonly the high-grade lump material is removed by hand, and the reminder is crushed and ground before beneficiation. LIBS may be used for chromite sorting and Mg, Al, Si contents evaluation (Fig. 8.12). 

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Neutral refractory materials include graphite, charcoal, coke, chromite and various carbides. 

Sodium dichromate is prepared on the large scale by heating powdered chromite with sodium carbonate, with free access of air the sodium chromate first formed is treated with acid ... 

The principal ore is chromite, which is found in Zimbabwe, Russia, Transvaal, Turkey, Iran, Albania, Finland, Democratic Republic of Madagascar, and the Phillippines. The metal is usually produced by reducing the oxide with aluminum. 

The refractory industry has found chromite useful for forming bricks and shapes, as it has a high melting point, moderate thermal expansion, and stability of crystalline structure. 

However, compounds known to be double oxides in the solid state are named as such for example, Cr2Cu04 (actually Cr203 CuO) is chromium(III) copper(II) oxide (and not copper chromite). 

With various catalysts, butanediol adds carbon monoxide to form adipic acid. Heating with acidic catalysts dehydrates butanediol to tetrahydrofuran [109-99-9] C HgO (see Euran derivatives). With dehydrogenation catalysts, such as copper chromite, butanediol forms butyrolactone (133). With certain cobalt catalysts both dehydration and dehydrogenation occur, giving 2,3-dihydrofuran (134). 

Reduction. Hydrogenation of dimethyl adipate over Raney-promoted copper chromite at 200°C and 10 MPa produces 1,6-hexanediol [629-11-8], an important chemical intermediate (32). Promoted cobalt catalysts (33) and nickel catalysts (34) are examples of other patented processes for this reaction. An eadier process, which is no longer in use, for the manufacture of the 1,6-hexanediamine from adipic acid involved hydrogenation of the acid (as its ester) to the diol, followed by ammonolysis to the diamine (35). 

The result is the formation of a dense and uniform metal oxide layer in which the deposition rate is controlled by the diffusion rate of ionic species and the concentration of electronic charge carriers. This procedure is used to fabricate the thin layer of soHd electrolyte (yttria-stabilized 2irconia) and the interconnection (Mg-doped lanthanum chromite). 

Fig. 1. Global distribution of seabed mineral deposits, where x represents chromite + barite titanium, zirconium, hafnium, and thorium tin I gold, platinum, and silver 3 sand and gravel shell, calcium carbonate gems marine polymetaUic sulfides phosphorites Cl cobalt cmsts S sulfur and B...

Hydrolysis of primary amides cataly2ed by acids or bases is very slow. Even more difficult is the hydrolysis of substituted amides. The dehydration of amides which produces nitriles is of great commercial value (8). Amides can also be reduced to primary and secondary amines using copper chromite catalyst (9) or metallic hydrides (10). The generally unreactive nature of amides makes them attractive for many appHcations where harsh conditions exist, such as high temperature, pressure, and physical shear. 

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