Chromium pyrophoric

Chromium (II) also forms sulfides and oxides. Chromium (II) oxide [12018-00-7], CrO, has two forms a black pyrophoric powder produced from the action of nitric acid on chromium amalgam, and a hexagonal brown-red crystal made from reduction of Cr202 by hydrogen ia molten sodium fluoride (32). Chromium (II) sulfide [12018-06-3], CrS, can be prepared upon heating equimolar quantities of pure Cr metal and pure S ia a small, evacuated, sealed quartz tube at 1000°C for at least 24 hours. The reaction is not quantitative (33). The sulfide has a coordination number of six and displays a distorted octahedral geometry (34). 

Compact chromium is not dangerous. The meteil powder ( pyrophoric ) obtained by the amalgam evaporation is the only one that represents risk. As far as chromium... 

Evaporation of mercury from mercury amalgam leaves pyrophoric chromium [1]. Increasing the temperature at which hexacarbonylchromium is thermally decomposed increases the surface area and pyrophoricity of the chromium powder produced [2],... 

The black powder ignites if ground or heated in air [1], The oxide obtained by oxidation of chromium amalgam is pyrophoric [2],... 

Mellor, 1940, Vol. 8, 436 1943, Vol. 11, 162 1942, Vol. 12, 32 Pyrophoric chromium attains incandescence in the oxide, while calcium, potassium and uranium need heating before ignition occurs, when combustion is brilliant in the 53% oxygen content. 

Finely divided (pyrophoric) chromium incandesces in sulfur dioxide [1], while pyrophoric manganese bums brilliantly on heating in the gas [2], Molten sodium reacts violently with the dry gas or liquid, while the moist gas reacts as vigorously as water with cold sodium [3],... 

Copper chromite catalyst, after use in high-pressure hydrogenation of fatty acids to alcohols, is pyrophoric, possibly owing to presence of some metallic copper and/or chromium. Separation of the catalyst from the product alcohols at 130°C in a non-inerted centrifuge led to a rapid exotherm and autoignition at 263°C. 

During the preparation of the complexes of chromium, molybdenum and tungsten from K[M(CO)3C5H5] and bromosilane, the residues from sublimation of the products are all pyrophoric. 

Caution. Chromium(VI) oxide, Cr03, is carcinogenic. Especially after the drying procedure, inhalation of the fine powder must be avoided by working in a well-ventilated hood. Also the use of the toxic CO gas makes an efficient hood absolutely necessary. The final Cr(II) catalyst is extremely pyrophoric and should never be allowed to get into contact with air. 

WarningI Tris(acetonitrile)chromium tricarbonyl is highly pyrophoric and degrades rapidly when exposed to oxygen, but is reasonably stable in THF solution. Best yields are obtained when this intermediate is as free of acetonitrile as possible while avoiding formation of the green colored [Cr(lll)] decomposition product, which develops on contact with air. 

Caution. Chromium (VI) oxide is carcinogenic. Inhalation of the fine CrO 3-silica powder must be avoided by working in a well-ventilated fume hood. The reduction of this powder with CO also necessitates the use of an efficient fume hood. The final Cr (II) catalyst is pyrophoric and should not be allowed to come into contact with air. 

They did not measure the dissociation press, at higher temp., and added that the dissociation does not proceed until a definite dissociation press, has been attained and then ceases as is commonly the case rather does the dissociation press, exhibit a continuous slow change. This is explained by assuming that chromium and its nitride form not two phases, but only one variable phase. J. Feree made the nitride contaminated with a little oxide by heating pyrophoric chromium in a current of nitric oxide and he also obtained this nitride by the action of ammonia on heated chromium. 

Pyrophoric chromium attains incandescence in the oxide, while calcium, potassium... 

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