Chromium III Oxide

Reduction with ammonium salts provides chromium(lll) oxide with a particularly low sulfur content 

Chromiutti(lII) oxide is obtained by reducing sodium dichromate with organic materials, charcoal or sulfur in an exothermic reaction  

These reactions are carried out continuously in furnaces. The reacted mixture is leached with water to remove soluble products, filtered, dried and ground. Very pure chromium(III) oxide (99%) of pigment quality is thereby obtained. 

Chromium(III) can also be obtained by reacting sodium dichromate with ammonium salts such as ammonium chloride or sulfate  

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. 

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Chromium Removal System. Chlorate manufacturers must remove chromium from the chlorate solution as a result of environmental regulations. During crystallization of sodium chlorate, essentially all of the sodium dichromate is recycled back to the electrolyzer. Alternatively, hexavalent chromium, Cr, can be reduced and coprecipitated in an agitated reactor using a choice of reducing agents, eg, sodium sulfide, sulfite, thiosulfate, hydrosulfite, hydrazine, etc. The product is chromium(III) oxide [1333-82-0] (98—106). Ion exchange and solvent extraction techniques have also... 

The dry gas has been made by direct reduction of a solid mixture of nitrite and nitrate with chromium(III) oxide (3KNO2 4- KNO3 4-Cr203 —4NO 4- 2K2Cr04) but is now more conveniently obtained from a cylinder. 

Chromi-nydroxyd, n. chromic hydroxide, chro-mium(III) hydroxide, -oxyd, n. chromic oxide, chromium(III) oxide, -rhodanwasser-stoffsMure, /. chromithiocyanic acid, thio-cyanatochromic(III) acid, -salz, n. chromic salt, chromium(III) salt, -suifat, n. chromic sulfate, chromium(III) sulfate, -suifocyan-saure, /. chromithiocyanic acid, thiocyana-tochromic(III) acid, -verbindung,/. chromic compound, chromium(III) compound. 

The ammonium dichromate resembles a tiny volcano as it bums, emitting hot gases, sparks, and a voluminous green dust of chromium(III) oxide. 

The +3 state of chromium is best represented by chromium(III) oxide, Cr2Os, which is a green, inert solid used as a green pigment. It can be made in rather spectacular fashion by heating ammonium dichromate. Once started, the reaction... 

A detailed study of the dehydrogenation of 10.1 l-dihydro-5//-benz[6,/]azcpinc (47) over metal oxides at 550 C revealed that cobalt(II) oxide, iron(III) oxide and manganese(III) oxide are effective catalysts (yields 30-40%), but formation of 5//-dibenz[7),/]azepinc (48) is accompanied by ring contraction of the dihydro compound to 9-methylacridine and acridine in 3-20 % yield.111 In contrast, tin(IV) oxide, zinc(II) oxide. chromium(III) oxide, cerium(IV) oxide and magnesium oxide arc less-effective catalysts (7-14% yield) but provide pure 5H-dibenz[b,/]azepine. On the basis of these results, optimum conditions (83 88% selectivity 94-98 % yield) for the formation of the dibenzazepine are proposed which employ a K2CO,/ Mn203/Sn02/Mg0 catalyst (1 7 3 10) at 550 C. 

C04-0102. Write the balanced redox reactions for the formation of each of the following oxides from the reaction of molecular oxygen with pure metal (a) strontium oxide (b) chromium(III) oxide (c) tin(IV) oxide. 

Pure chromium metal is made by a two-step reduction sequence. First, sodium dichromate is reduced to chromium(III) oxide by heating in the presence of charcoal ... 

Chromium (III) oxide gave rise to a very violent reaction with lithium heated to 180 C. The temperature exceeds 1000 C. It is a typical thermite reaction during which a more electropositive metai violentiy reduces an oxide by forming a metal, which is chromium in this particular case. However, the mixture needs to reach a high temperature to be able to react. 

The enthalpy of decomposition, which is rather low compared with criterion C, in the CHETAH programme (see p.117), was determined by DSC and corresponds to 0.76 KJ/g at 230-260°C. In a confined atmosphere the decomposition conditions would be explosive. This reaction has been used many times because of its spectacular aspect. This is why it is called Vesuvius fire by artificers and green volcano by lecturers. These demonstrations should be stopped because of the detonation risks they represent as well as chromium (III) oxide toxicity. 

Cuprous oxide is also reduced violently by electropositive metals as discovered in an accident which occurred with aluminium. With chromium (III) oxide the reaction enables one to make copper chromite, which is a very common catalyst. The activity of copper chromite is such that it frequently combusts at the end of the reaction. 

Arsenic is violently oxidised by strong oxidants. This applies to potassium superoxide (incandescence of the element), dichlorine oxide (the released heat causes the chlorinated derivative to detonate), chromium (III) oxide Oncande-scence), potassium or silver nitrates (ignition), potassium permanganate or sodium peroxide (detonations). 

Chromium (III) oxide hydrate had been introduced into acetic anhydride causing a very violent hydrolysis of acetic anhydride and the spreading of the products. 

Iron(III) oxide and chromium(III) oxide react exothermally, and lead oxide explosively. Copper oxide and manganese dioxide react at 350°C incandescently. 

Lithium is used to reduce metallic oxides in metallurgical operations, and the reactions, after initiation at moderate temperatures, are violently exothermic and rapid. Chromium(III) oxide reacts at 185°C, reaching 965° similarly molybdenum trioxide (180 to 1400°), niobium pentoxide (320 to 490°), titanium dioxide (200-400 to 1400°), tungsten trioxide (200 to 1030°), vanadium pentoxide (394 to 768°) also iron(II) sulfide (260 to 945°), and manganese tclluridc (230 to 600°C)... 

The kinetics of chromium (III) oxide deposition from solution during the leaching of skeletal copper has been studied, and a linear rate was found that is not affected by chromate concentration but decreases with increasing hydroxide concentration [55], The total amount deposited was greater as the chromate concentration increased. 

Caesium trioxide, 4263 Calcium oxide, 3937 Chromium(II) oxide, 4241 Chromium(III) oxide, 4251... 

Eary LE, Rai. 1987. Kinetics of chromium (III) oxidation to chromium (VI) by reaction with manganese oxide. Environmental Science and Technology 21 1187-1193. 

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