Pyrophoric components

Pyrophoricity is a property of metals and oxides of lower oxidation states, including radioactive ones, in which they spontaneously ignite during or after stabilization. If the waste also contains other combustible matter, it will burn. For a waste form to be safe from spontaneously igniting, the metals and oxides of lower oxidation states must be fully oxidized. To determine whether a particular waste is pyrophoric or not, one must identify the pyrophoric components within the waste. Such identification is done by analytical methods such as X-ray diffraction. 

The acid-base reaction that forms the Ceramicrete waste forms also creates an oxidizing environment in which species of lower oxidation states are automatically converted to their fully oxidized states. Hence, pyrophoric components (such as PU2O3) should be converted to their most stable and fully oxidized forms (such as PUO2) that are no longer pyrophoric. Wagh et al. [10] have demonstrated such transformations in the Ceramicrete process by using surrogates of Pu (see the case study in Section 17.5.4). 

Cerium is a component of misch metal, which is extensively used in the manufacture of pyrophoric alloys for cigarette lighters. While cerium is not radioactive, the impure commercial grade may contain traces of thorium, which is radioactive. The oxide is an important constituent of incandescent gas mantles and is emerging as a hydrocarbon catalyst in self cleaning ovens. In this application it can be incorporated into oven walls to prevent the collection of cooking residues. 

Gr. neos, new, and didymos, twin) In 1841, Mosander, extracted from cerite a new rose-colored oxide, which he believed contained a new element. He named the element didymium, as it was an inseparable twin brother of lanthanum. In 1885 von Welsbach separated didymium into two new elemental components, neodymia and praseodymia, by repeated fractionation of ammonium didymium nitrate. While the free metal is in misch metal, long known and used as a pyrophoric alloy for light flints, the element was not isolated in relatively pure form until 1925. Neodymium is present in misch metal to the extent of about 18%. It is present in the minerals monazite and bastnasite, which are principal sources of rare-earth metals. 

Properties. Uranium metal is a dense, bright silvery, ductile, and malleable metal. Uranium is highly electropositive, resembling magnesium, and tarnishes rapidly on exposure to air. Even a poHshed surface becomes coated with a dark-colored oxide layer in a short time upon exposure to air. At elevated temperatures, uranium metal reacts with most common metals and refractories. Finely divided uranium reacts, even at room temperature, with all components of the atmosphere except the noble gases. The silvery luster of freshly cleaned uranium metal is rapidly converted first to a golden yellow, and then to a black oxide—nitride film within three to four days. Powdered uranium is usually pyrophoric, an important safety consideration in the machining of uranium parts. The corrosion characteristics of uranium have been discussed in detail (28). 

Metallic components of zinc, aluminium and magnesium (or their alloys) are unsuitable for service with bromomethane because of the formation of pyrophoric Grig-nard-type compounds. The Case History attributes a severe explosion to ignition of a bromomethane-air mixture by pyrophoric methylaluminium bromides produced by corrosion of an aluminium component. 

The carbaalanes [8, 9] possess clusters formed by aluminum and carbon atoms. They represent a new class of compounds which, in some respects, may be compared to the important class of carbaboranes. Usually, they were obtained by the reaction of aluminum alkynides with aluminum hydrides (hydroalumination) and the release of trialkylaluminum derivatives (condensation). The first carbaalane, (AlMe)g(CCH2Ph)5H 3 [10], was synthesized by the treatment of dimethylalumi-num phenylethynide with neat dimethylaluminum hydride. The idealized stoichiometric ratio of the components is given in Eq. (2), which also shows a schematic drawing of the molecular structure. Compound 3 was isolated in the form of colorless crystals in 60% yield. While 3 is only slightly air-sensitive, the less sterically shielded propynide derivative 4, also shown in Eq. (2), is highly pyrophoric [11],... 

In the catalyst preparation area where the fire occurred, aluminum alkyl and isopentane are mixed in a batch blending operation in three 8000-gallon kettles. The flow rates of components are regulated by an operator at the control room. Temperature, pressure, and liquid level within the kettles are monitored by the control room operator. The formulated catalyst is stored in four 12,000-gallon vertical storage tanks within this process unit. Aluminum alkyl is a pyrophoric material and isopentane is extremely flammable. Each vessel was insulated and equipped with a relief valve sized for external fire. 

Mechanical Stabilization. Four methods may be considered for stabilizing heterogeneous fuels mechanically. The use of the metals in the form of sols is not practical because the powders, when subdivided to the required degree, are expensive and hazardous to handle. If they are allowed to become coated with the metal oxide, to eliminate their pyrophoricity, their metal content is reduced to an unacceptable level. Another approach involves the use of a liquid whose density equals that of the solid phase. Such an approach is also impractical because there are few liquid materials that have appropriate densities, and those that do are inappropriate as fuel components for chemical or thermodynamic reasons. Furthermore, the density equivalence is lost at reduced and elevated temperatures, causing settling or floating of the solid phase. 

Cerium, Ce at wt 140.13,at No 58 one of the "rare earth elements gray, ductile, maleable metal which tarnishes in moist air d 6.78 mp 645°, bp 1400° sol in dil acids insol in cold w slowly oxidizes in hot w forms numerous alloys salts. It occurs in monazite sand which is an orthophosphate of thorium and rare earths. Ce-Fe pyrophoric alloys are used as sparking flints for lighters, tracer bullets for military signalling. Ce metal is used as component of some rocket proplnts and in alloys for jet engines. Toxicity, fire expln hazards of Ce are discussed in Ref 5- Ce alloy, called Misch Metal Ce 52, Nd 18, Pr 5, Sm 1 other substances(such as La, Ca, Al, C, Si Fe) 24%, has many applications. Mixt of Ce ... 

Isohexides exhibit excellent properties as plasticizers for polyvinyl alcohol polymers.2 Compounds obtained from isosorbide and trialkylaluminum proved to be highly active cocatalysts for polymerization of alkenes. Such derivatives, which were supposed to be oligomeric O-aluminum-isosorbides, are of glass-like appearance and exhibit pyrophoric properties.255 Isosorbide is a component of mixtures used for water-based pigment inks, having excellent dispersion stability, which is necessary for ink-jet printing.256 257... 

Impregnation of Supports and Drying. Most obvious is incipient wetness impregnation of a support with a solution of an active precursor and subsequent drying and calcination of the thus loaded support [6], Incipient wetness or pore-volume impregnation is especially attractive with preshaped support bodies. When the active component has to be in the metallic state, reduction can be carried out after the calcination step. Often, the catalyst is reduced after loading into the reactor to prevent a separate passivation step, in which the surface of the pyrophoric reduced catalyst is carefully oxidized. However, to achieve reproducible catalysts the catalyst manufacturer usually reduces the catalyst and delivers the passivated catalyst, which then only needs a short additional reduction. 

NOTE Flammable components do not cover pyrophoric, self-heating or water-reactive substances and mixtures because such components are never used as aerosol contents. 

Trichlorosilane DPR from the Dow Coming Midland Plant was analyzed for composition, flash point, pyrophoricity, etc. New test methods were developed to quantify the shock-sensitive nature of the hydrolyzed gels which commonly form when handling this stream. This testing was performed on individual fractionated DPR species, and the hazards of each component were quantified. It was determined that SiH-containing chlorosiloxanes had played a key role in several past safety incidents. 

Catalysts in which a metal is the active component are, however, pyrophoric after thermal treatment of the metal precursor in a reducing gas flow. Grinding of a reduced catalyst in an inert atmosphere without intermediate exposure to atmospheric air has been performed with nickel fat-hardening catalysts. After the grinding procedure the small catalyst particles are taken up in hardened fat, which protects the nickel against oxidation. The procedure is, however, tedious and cannot be readily executed with the small batches of catalyst usually used in the fine-chemical industry. 

Analysis by x-ray diffraction showed the strongest reflections for the hexagonal close-packed cobalt metal with no other components present. The cobalt powder was not pyrophoric at room temperature, but burned with an orange flame when placed on a hot plate. 

Catalysts in which the active component is a finely divided metal are often pyrophoric. The catalyst can be better handled after surface oxidation of the active component (passivation). Reactivation is then carried out in the start-up phase under process conditions. 

Alkali metal alloys and alkaline earth metal alloys have a wide range of applications. The degree to which the alloys retain the pyrophoric or water-reactive properties of their parent metals depends on their concentration in the alloy, the modifying nature of the alloyed components, and the state of subdivision. Many commercial alloys of this type, present no hazard. Others, such as the potassium-sodium alloys used in heat exchangers, present significant concern. Other alkali and alkaline earth metal alloys include... 

Articles, Pyrophoric Articles which contain a pyrophoric substance (capable of spontaneous ignition when exposed to air) and an explosive substance or component. The term excludes articles containing white phosphorus. UN App. B, ICAO A2, US 173.59, lATA App. A... 

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