Pyrophoric powder

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). 

If stored at ambient temperature, the complex decomposes to a dark pyrophoric powder. 

A brown pyrophoric powder is produced if the carbonyl is dissolved in acetic acid containing above 5% of water. 

Schmitz-Dumont, O., Angew. Chem., 1955, 67, 231 A pyrophoric powder. 

The amorphous form, prepared by dehydration at low temperature, is a pyrophoric powder. 

As already stated it is a specially active form of nickel and is prepared from a nickel-aluminium alloy sodium hydroxide is added to dissolve the aluminium and nickel is left as a black pyrophoric powder. 

Heat of combustion, thermal conductivity, surface area and other factors influencing pyrophoricity of aluminium, cobalt, iron, magnesium and nickel powders are discussed [4], The relationship between heat of formation of the metal oxide and particle size of metals in pyrophoric powders is discussed for several metals and alloys including copper [5], Further work on the relationship of surface area and ignition temperature for copper, manganese and silicon [6], and for iron and titanium [7] was reported. The latter also includes a simple calorimetric test to determine ignition temperature. 

Tetrameric [MeLi]4 (1), [EtLi]4 (2) and [t-BuLi]4 (3) are white pyrophoric powders. While methyllithium is soluble only in polar solvents like diethyl ether, the two others are soluble even in non-polar hydrocarbons like hexane. In non-donating solvent the tetrameric aggregation is retained. Each of the four U3 triangles is /ra-capped by a Ca atom above the center of the equilateral metal triangle. Even in the solid-state none of the three tetramers adopts ideal symmetry (Figure 6). 

An active form of the hydride obtained as a solvated pyrophoric powder and used as a reducing agent is prepared by the reaction of dibutylmagnesium (C4H9)2Mg with phenylsdane, CeHBSiHs in ether-heptane solvent mixture. 

A common problem of this synthesis is the decomposition of the product to a black insoluble and pyrophoric powder (presumably metallic Mo), which is possibly caused by the use of an impure starting material, to the adventitious introduction of air, to excessive exposure to light, or to a combination of those factors. If a black powder is formed, this can be removed at the end of the reaction by filtration through a glass frit the subsequent workup is as described above. Such decomposition reduces the yield but does not lead to a less pure product. If larger amounts of Mo(CO)6 are used, the sublimation of larger quantities of Mo(CO)6 to the condenser occurs, which may require interruption of the procedure and manual scraping of the sublimed solid back into the flask with a spatula under a flow of N2. 

The pyrophoric powders were cooled in an ammonia atmosphere, and... 

Acetic Acid and Water. Forms brown pyrophoric powder in acetic acid containing more than 5% water.4... 

The flask is tapped gently in order to free the magnetic stirring bar, and the white solid is converted to a fine, air-sensitive and pyrophoric powder by careful yet vigorous agitation of the flask. The flask is heated to 60° for 4-6 hr with constant pumping, after which time the salt is considered to be dry. 

Chloroethynyl complexes of Mo and W are obtained from [M(CO)3Cp]-(M = Mo, W) with C2C12, with only trace amounts of W(CC1= CHCl)(CO)3Cp and W(CO)3Cp 2(p-C=C) being isolated.162 Pale brown Cr(CO)3Cp 2(p-C=C) (45/Cr) is the major product obtained with M = Cr, together with a black pyrophoric powder containing Cr. With C2X2 (X = Br, I), only MX(CO)3Cp was formed. The dark yellow tungsten complex 45/W is also obtained from the reaction of LiC2H with WCl(CO)3Cp.163... 

Magnesium hydride is obtained by interaction of Mg and H2 at ca. 500°C. An active form is readily made by interaction of PhSiH3 and Bu"Mg in ether-heptane solvents in presence of tmen. The solvated pyrophoric powders are used as reducing agents and hydride sources.13 The hydrides of Ca, Sr, and Ba are also made by direct interaction (Section 2-13). For Ca, Sr, and Ba the structure is of the PbCl2 type, whereas MgH2 has the rutile structure.14... 

A very dangerous fire and moderate explosion hazard when exposed to heat or flame can react vigorously with oxidizing materials. Warning pyrophoric in air. Mixtures with nitrogen oxide explode above 50°C. Violent reaction with zinc + transition metal halides (e.g., cobalt halides, rhodium halides, ruthenium halides). Mixtures with acetic acid + water produce a pyrophoric powder. To fight fire, use water, foam, CO2, dr " chemical. See also CARBONYLS and IRON COMPOUNDS. 

If the acetic acid contains more than 5% of water, the reaction yields only a brown pyrophoric powder. 

Properties White to tan, free-flowing, pyrophoric powder. Moderately soluble in toluene and benzene slightly soluble in ethyl ether stable indefinitely in sealed containers. 

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