Pyrophoric carbide

A small-scale process has been described by Scaife and Wylie in which thorium carbide is used as the feed material. This is made by pelletting a mixture of finely divided thorium oxide with graphite and heating in a carbon resistance tube furnace above 2000°C, in an argon atmosphere. The rather pyrophoric carbide is then reacted with iodine at 500 C and 4 to 200 mm pressure, and sublimed under vacuum to give a yellow thorium tetra-iodide. This is then thermally decomposed on a tungsten filament at high temperature in the normal manner. 

Whereas finely divided cobalt is pyrophoric, the metal in massive form is not readily attacked by air or water or temperatures below approximately 300°C. Above 300°C, cobalt is oxidized by air. Cobalt combines readily with the halogens to form haUdes and with most of the other nonmetals when heated or in the molten state. Although it does not combine direcdy with nitrogen, cobalt decomposes ammonia at elevated temperatures to form a nitride, and reacts with carbon monoxide above 225°C to form the carbide C02C. Cobalt forms intermetallic compounds with many metals, such as Al, Cr, Mo,... 

The products of decomposition of metal carboxylates vary to some extent with the constituent cation and the final residue is usually either the metal or an oxide, occasionally the carbide and sometimes some elemental carbon deposit. Dollimore et al. [94] have described the use of Ellingham diagrams for the prediction of the composition of the solid products of oxalate decompositions. The complete characterization of residual material can be difficult, however, since the solids may be finely divided, pyrophoric [1010], metallic and amorphous to X-rays. 

Schmitt, C. R., J. Fire Flamm., 1971, 2, 163 The finely divided carbide is pyrophoric. 

Fire hazards and pyrophoricity of mixed charges for preparing titanium carbide are discussed. 

Chemicals that are water or air reactive pose a significant fire hazard because they may generate large amounts of heat. These materials may be pyrophoric, that is, they ignite spontaneously on exposure to air. They may also react violently with water and certain other chemicals. Water-reactive chemicals include anhydrides, carbides, hydrides, and alkali metals (e.g., lithium, sodium, potassium). 

Oxycarbides have also been described (176). They are of interest for catalysis because oxophilic metals may not form carbides easily in preparations from metal oxides by treatment with methane, oxycarbides rather than carbides may form. Furthermore, carbides and nitrides are usually passivated after preparation they are slowly exposed to oxygen or air to form a thin protective oxide layer on the metal carbide surface. In this passivated form, these materials are not pyrophoric and can be transported through the air. After insertion into a catalytic reactor, they must be reactivated either by methane or ammonia treatment, as used in their preparation, or by reduction with hydrogen. In these cases, pure carbide or nitride is not always reformed at the surface an oxycarbide or oxynitride is often formed instead. 

Pyrophoric carbonyl metals Carbonylithium Phosphine Calcium carbide Uranium carbide mixo-T ributylborane Tributylphosphine ... 

High-purity UC and UCj can be prepared by arc melting the elements. Annealing below 1700°C, preferably under pressure, is required - to form UjCj. Because of the high reactivity of the powdered carbides, all studies should be done with material that is as coarse as possible. The finely divided carbides are pyrophoric and aquire any oxygen in an otherwise inert atmosphere at RT. 

Thorium carbides (ThC, ThC2) and uranium carbides (UC, UC2) exhibit metallic properties, but in other properties differ significantly from the carbides of the subgroups of the IVth, Vth and Vlth groups of the periodic table. Their hardnesses are substantially lower (see Table 5.6-1), they are pyrophoric and are easily hydrolyzed in water or weak aeids. Their only economic importance is as carbidie fuels in nuelear technology, particularly for high temperature and breeder reactors which are currently in the evaluation phase. 

BENSULFOID (7704-34-9) Combustible solid (flash point 405°F/207°C). Finely divided dry materia forms explosive mixture with air. The vapor reacts violently with lithium carbide. Reacts violently with many substances, including strong oxidizers, aluminum powders, boron, bromine pentafluoride, bromine trifluoride, calcium hypochlorite, carbides, cesium, chlorates, chlorine dioxide, chlorine trifluoride, chromic acid, chromyl chloride, dichlorine oxide, diethylzinc, fluorine, halogen compounds, hexalithium disilicide, lampblack, lead chlorite, lead dioxide, lithium, powdered nickel, nickel catalysis, red phosphorus, phosphorus trioxide, potassium, potassium chlorite, potassium iodate, potassium peroxoferrate, rubidium acetylide, ruthenium tetraoxide, sodium, sodium chlorite, sodium peroxide, tin, uranium, zinc, zinc(II) nitrate, hexahydrate. Forms heat-, friction-, impact-, and shock-sensitive explosive or pyrophoric mixtures with ammonia, ammonium nitrate, barium bromate, bromates, calcium carbide, charcoal, hydrocarbons, iodates, iodine pentafluoride, iodine penloxide, iron, lead chromate, mercurous oxide, mercury nitrate, mercury oxide, nitryl fluoride, nitrogen dioxide, inorganic perchlorates, potassium bromate, potassium nitride, potassium perchlorate, silver nitrate, sodium hydride, sulfur dichloride. Incompatible with barium carbide, calcium, calcium carbide, calcium phosphide, chromates, chromic acid, chromic... 

DINITROGEN MONOXIDE (10024-97-2) May form explosive mixture with flammable and reactive gases, including anhydrous ammonia, carbon monoxide, chlorine trifluoride, hydrogen, hydrogen sulfide, nitryl fluoride, phosphine. Nonflammable but supports combustion as temperature increases above 572°F/300°C, it becomes both a strong oxidizer and self-reactive. Pyrophoric at elevated temperatures. Reacts, possibly violently, with aluminum, ammonia, boron, hydrazine, lithium hydride, sodium, tungsten carbide. 

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