Ammonium dichromate

HUMAN CARCINOGEN AS DUST, CONTACT WITH COMBUSTIBLE MATERIAL MAY CAUSE FIRE, FLAMMABLE 

Self-sustaining decomposition occurs at 225°C with swelling and release of heat and nitrogen gas, leaving Cr203. Extinguish with water.2 

Decomposes and ignites on heating to 190°C. Green Cr203 is emitted and explosion occurs if confined.3 

The dust irritates the respiratory tract and eyes. Swallowing causes internal irritation and damage. Prolonged exposure to the dust may cause ulceration, liver and kidney damage, and ultimately cancer. Avoid inhaling dust. Avoid contact with eyes and skin.4 TLV- 

Wear nitrile rubber gloves, laboratory coat, and eye protection. Avoid breathing dust. Cover spill with a 1 1 1 mixture by weight of sodium carbonate or calcium carbonate, clay cat litter (bentonite), and sand. Scoop mixture into a container of water. Add 3 M sulfuric acid (prepared by cautiously adding 10 mL of concentrated acid to 50 mL of cold water) to neutralize the solution, and then add a further 20 mL for each 1 g of dichromate (to give a pH of 1). While stirring, add sodium thiosulfate crystals until the solution becomes blue colored and cloudy (approximately 10 g/g dichromate). Slowly and cautiously neutralize the solution with sodium carbonate (approximately 3.2 g/mL of 3 M 

The simplified thermal decomposition of (NHA)2Cr207 has often been represented by the equation 

In a comprehensive thermal analysis study, Mahieu et al. (66) showed that 

The first transition, A - B, began at 235°C and involved a mass-loss of 20% or 153 g when normalized at the second transition, B C, at 260°C the 

A - B Transition. Reduction of Cr(VI) to Cr(V) occurs with loss of ammonia and nitrogen according to the equation 

C - D Transition. Dehydration of the compound, [(Cr02)6H20], occurs, or 

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Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

Manufacture The primary iadustrial compounds of chromium made directly from chromite ore are sodium chromate, sodium dichromate, and chromic acid. Secondary chromium compounds produced ia quantity include potassium dichromate, potassium chromate, and ammonium dichromate. 

Potassium and ammonium dichromates are generally made from sodium dichromate by a crystallization process involving equivalent amounts of potassium chloride or ammonium sulfate. In each case the solubiHty relationships are favorable so that the desired dichromate can be separated on cooling, whereas the sodium chloride or sulfate crystallizes out on boiling. For certain uses, ammonium dichromate, which is low in alkaH salts, is required. This special salt may be prepared by the addition of ammonia to an aqueous solution of chromic acid. Ammonium dichromate must be dried with care, because decomposition starts at 185°C and becomes violent and self-sustaining at slightly higher temperatures. 

A number of manufacturers around the world are using the decomposition of ammonium dichromate to produce chrome oxide (eq. 5) (78). Generally, an excess of finely ground ammonium sulfate is mixed with sodium dichromate, and the dry mixture is heated to form chrome oxide and sodium sulfate, evolving nitrogen and steam. 

Chromia—alumina catalysts are prepared by impregnating T-alumina shapes with a solution of chromic acid, ammonium dichromate, or chromic nitrate, followed by gentie calciaation. Ziac and copper chromites are prepared by coprecipitation and ignition, or by thermal decomposition of ziac or copper chromates, or organic amine complexes thereof. Many catalysts have spiael-like stmctures (239—242). 

The procedure described is that of Wille and Saffer. Propiolaldehyde has also been prepared by the oxidation of propargyl alcohol using ammonium dichromate or manganese dioxide in 10% sulfuric acid. Propiolaldehyde has also been prepared by warming the dimethyl or diethyl acetal with dilute sulfuric acid. ... 

Ammonium dichromate Barium chlorate Calcium chlorate/hypochlorite Chromium trioxide (chromic acid)... 

A. Tanuary 17, 1986 explosion at a Diamond Shamrock Chemical plant near Ashtabula, Ohio, killed two employees, critically injured another, and caused lesser injuries to at least a dozen other workers. The blast involved 2,000 lb of ammonium dichromate in the unit for its production at the plant,... 

The compound ammonium dichromate, (NH C Oy, has a reddish-orange color owing to the presence of the Cr2072- ion. 

The Cr2072- ion can act as an oxidizing agent in the solid state as well as in water solution. In particular, it can oxidize the NH ion to molecular nitrogen. When a pile of ammonium dichromate is ignited, a spectacular reaction occurs (Figure 20.12). 

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... 

I-A1ON0-2-NAPHIH0L-4-SULE0NIC acid, 11, 72 16, 91 17, 91 Aminonaphtholsulfonic acids, coupling to form azo dyes, 16,16 p-Aminophenol, 16, 39 Aminopiperole, 16, 6 /3-Ahinopropionic acid, 16, 1 4-Aminoveratrole, 16, 4 Ammonium dichromate, 16, 74 Ammonium formate, 17, 77 Ammonium thiocyanate, 16, 74 Ammonium vanadate, 13, 1 to w-Amyl alcohol, IS, 17 hri.-Amyl alcohol, 13, 68 -Amylbenzene, 10, 4 -Amyl borate, 13, 17 -Amyl bromide, 16, 41 iso-Amyl iodide, 13, 62 n-Amyl iodide, 13, 62 n-Amybnagnesium bromide, 16, 41... 

Modification of the burning rates, pressure exponents, and temp coefficients of burning rate of the fluorocarbon composites has been accomplished with copper, lead, tin, sodium, ammonium and potassium fluoborates sodium, potassium, lithium, lead, copper and calcium fluorides potassium and ammonium dichromate lead and zinc stearate cesium carbonate potassium and ammonium sulfate copper chromite oxides of magnesium, copper and manganese boron zinc dust and carbon black (Ref 75)... 

In the previous examples, the calculated enthalpies of decomposition are taken. The enthalpies of formation of the decomposition substances come from the corresponding chapters in Part Two. The published values of enthalpies of formation are favoured and use of the values estimated is only made when there is no experimental data. A few inorganic compounds have been added which are noted for their instability eg ammonium dichromate and ammonium nitrate. 

The results obtained using this criterion are very close to reality. Two of the compounds that are known to be unstable and appear in this series, ie nitroaniline and ammonium nitrate, which have an expiosophoric group without necessarily being noted for being explosive, are classified medium risk . There are still two anomalies the far too severe classification for 1,2-dichiorobenzene, which is obviously due to the endothermic nature of the aromatic cycle Crt would be better to analyse 1,2-dichlorocyclohexane using the technique mentioned before) and on the other hand, the underestimated risk of ammonium dichromate, which is, incidentally, overestimated in the regulations as will be seen later. 

When analysing the resulte it is noticed this time that criterion C4 is the least severe of the four CHETAH criteria. It emphasises the unstable property of nitroaniline but under mates the instability of ammonium nitrate and ammonium dichromate for which there is no indication of danger whatsoever. 

They are strong oxidants especially when they are combined with sulphuric acid. Ammonium dichromate or chromate (less used) have an oxygen balance(C3= 0 g% for the first one) that makes them likely to be very unstable thermodynamically. This is confirmed by the labelling code 1 (explosive in the dry state) provided by the regulations and attested by a number of accidents. 

Ammonium dichromate decomposes at a temperature starting at 170-190 C to give the following reaction ... 

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