Sesquioxide, chromium

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

The total heat requirement is thus around 599.98 kj, which is about 548.81 kj more than the heat available from the reaction. This calculation, however, does not take into account the inevitable heat losses due to the nonadiabatic conditions in the reactor. An estimate of these heat losses can be made by considering the industrial practice for aluminothermic chromium metal production. The charge is preheated to about 500 °C before loading into the aluminothermic crucible. This operation adds about 96.65 kj (i.e., 48.9 cal deg-1 475) of heat to the system. It, therefore, appears that around 41.84 kj (96.65 kj - 54.81 kj) of heat is lost due to radiation and convection for every mole of chromium sesquioxide reduced to the metal by the aluminothermic process. 

Hopper, J.T., J.W. Holloway, and W.T. Butts, Jr. 1978. Animal variation in chromium sesquioxide excretion patterns of grazing cows. Jour. Anim. Sci. 46 1096-1102. 

Synonyms chromic oxide chromia chromium sesquioxide green cinnabar chrome green chrome oxide green oil green leaf green ultramarine green Cl 77288... 

Chromium Pyroarsenate, Cr4(As207)3, is produced when a small quantity of chromium sesquioxide is fused at a low temperature with sodium or potassium dihydrogen arsenate.12 It yields green transparent... 

Texaco 18 asphal 8, Amm perchlorate 73, cetyl acetamide 3, dibutyl sebacate 5.5, castor oil modified glycerol sebacate 3 chromium sesquioxide (serving as a combustion accelerator) 2.5 parts (Ref 2a Ref 8, p 114)... 

Atomic chlorine is highly reactive, combining slowly with sulphur and red phosphorus, rapidly with copper and chromium sesquioxide. It also can be shown to start the long chains in a mixture of hydrogen and chlorine. 

O. If the sulphuric acid is hot and concentrated, oxygen is evolved as gas if dilute, substances present in solution, if they are capable of being oxidised, are attacked by the oxygen. When chromic anhydride is heated, it is converted into chromium sesquioxide, Cr2Os, with evolution of oxygen. 

Synonym(s) Hexaaquachromium (III) chloride Chromite Chromium sesquioxide dichromium trioxide Chromumorthophos-phate phosphoric acid, chromium (III) salt... 

Preparation.—Metallic chromium is usually obtained by reduction of the sesquioxide, CtjOj, the chief source of which is chrome iron ore (p. 7). The latter, after separation from gangue, is powdered, washed, mixed with lime and potassium carbonate, dried, and then roasted, the mass being continually stirred. The potassium chromate produced is extracted with water and converted into the dichromate by treatment with sulphuric acid. After recrystallisation the potassium dichromate is reduced by heating wth sulphur, starch, or other suitable material, and finally washed with water the chromium sesquioxide remains undissolved. 

A solution of chromic chloride is readily obtained by the action of dilute hydrochloric acid on chromic hydroxide, or on chromium sesquioxide which has not been ignited this solution on evaporation yields an amorphous, deliquescent, green mass, soluble in water and in alcohol. The product on heating in hydrogen chloride or chlorine at temperatures above 250° C. becomes anhydrous, at the same time assuming the usual colour of the anhydrous salt. Basic chlorides are formed by... 

Chromic Oxide, Chromium Sesquioxide, CrgOg, which occurs naturally in chrome ochre (see p. 8), exists in both amorphous and crystalline forms. The amorphous form may be obtained by calcination of a mixture of three parts of potassium chromate with two parts of sal-ammoniac by heating potassium dichromate with sulphur . ... 

Amorphous chromium sesquioxide is a green powder, the tint of which depends upon the method of preparation the colour becomes brownish on heating. The crystalline oxide forms very dark green hard crystals belonging to the trigonal system (ditrigonal scaleno-hedral) ... 

Chromates are usually yellow or red in colour, and, except those of ammonium, the alkali metals, calcium, strontium, and magnesium, are practically insoluble in w ater. They are obtained by oxidation of chromites, by fusion of chromium sesquioxide with the appropriate base in presence of air or of an oxidising agent by oxidation of chromium salts in solution or by double decomposition. Normal, di-, and tri-clrromates, etc., are derived from one and the same acid oxide KaCrOj behaves like an alkali torvards CrOg, since it is quantitatively converted into dichromate. A large number of complex double chromates are known. 

Chromates, dichromates, etc., are readily reduced, e.g. by hydro-clrloric acid (with evolution of chlorine), by sulphurous acid (ivith formation of sulphate and dithionatc), by hydrogen sulf>hide (ivith separation of sulphur), by ferrous salts, by alcohol, etc., the solution simultaneously becoming green owing to the formation of a chromic salt. The chromates of the more feebly electro-positive elements decompose w hen strongly heated, with formation of chromium sesquioxide dichromates of other metals yield normal chromates, chromium sesquioxide, and oxygen. ... 

Moissan, he. cit. Wedekind and Horst, Ber., 1915, 48, 105. Traube, Annalen, 1848, 66, 98, states that the pyrophoric residue obtained on heating to redness chromic sulphate in hydrogen consists of a mixture of chromous sulphide and chromium sesquioxide. Of. Kopp, Oompt. rend., 1844, 18, 1156. 

Chromium Tetrasulphide, Cr3S4, is prepared by heating a mixture of chromium sesquioxide and sulphur in hydrogen. It is a greyish-black powder, insoluble in Avater and sulphuric acid, but easily soluble in nitric acid. ... 

Chromic sulphide is a broAvnish-black, lustrous amorphous powder, of density 3-538 at 14° C. When heated in air it gives sulphur dioxide and chromium sesquioxide, Avhile in hydrogen it yields chromous sulphide. It is attacked and oxidised by nitric acid, aqua regia, and fused potassium nitrate. Compounds of chromic sulphide with sulphides of other metals haA-e been described. Regarding chromic sulphide as the thioanhydride of thiochromous acid, H2Cr2S4, these compounds may be described as thiochromites. 

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