A pyrophoric substance (from Greek πυροφορος, purophoros, "fire-bearing") is a substance that will ignite spontaneously in air (cf. hypergolic). Examples are iron sulfide and many reactive metals including uranium, when powdered or sliced thin. Pyrophoric materials are often water-reactive as well and will ignite when they contact water or humid air. They can be handled safely in atmospheres of argon or (with a few exceptions) nitrogen. Most pyrophoric fires should be extinguished with a Class D fire extinguisher for burning metals.
The creation of sparks from metals is based on the pyrophoricity of small metal particles, and pyrophoric alloys are made for this purpose. This has certain uses: the sparking mechanisms in lighters and various toys, using ferrocerium; starting fires without matches, using a firesteel; the flintlock mechanism in firearms; and spark-testing ferrous metals.
Small amounts of pyrophoric liquids are often supplied in a glass bottle with a PTFE-lined septum. Larger amounts are supplied in metal tanks similar to gas cylinders, designed so a needle can fit through the valve opening. A syringe, carefully dried and flushed of air with an inert gas, is used to extract the liquid from its container.
Pyrophoric solids require the use of a sealed glove box flushed with inert gas. Glove boxes are expensive and require maintenance. Thus, many pyrophoric solids are sold as solutions, or dispersions in mineral oil or lighter hydrocarbon solvents. Mildly pyrophoric solids (such as lithium aluminium hydride and sodium hydride) can be handled in the air for brief periods of time, but the containers must be flushed with inert gas before storage.
Small amounts of pyrophoric materials and empty containers must be disposed of carefully, by quenching the residue. Less-reactive substances can be disposed of by diluting heavily with an unreactive solvent like hexane, placing the container in a cooling bath, and adding water dropwise. More reactive substances can be quenched by slowly adding the dilute solution to dry ice, then adding a mildly reactive substance that does not freeze in dry ice to the mixture (wet diethyl ether, acetone, isopropyl alcohol, and methanol are often used).
- Alkylated metal alkoxides or nonmetal halides (diethylethoxyaluminium, dichloro(methyl)silane)
- Alkali metals (lithium, sodium, potassium, rubidium, caesium)
- Copper fuel cell catalysts, e.g., Cu/ZnO/Al2O3
- Grignard reagents (compounds of the form RMgX)
- Finely divided metals (iron, aluminium, magnesium, calcium, zirconium, uranium, titanium, bismuth, hafnium, thorium, osmium)
- Used hydrogenation catalysts such as Raney nickel (especially hazardous because of the adsorbed hydrogen)
- Metal hydrides or nonmetal hydrides (germane, diborane, sodium hydride, lithium aluminium hydride, uranium trihydride)
- Iron sulfide: often encountered in oil and gas facilities where corrosion products in steel plant equipment can ignite if exposed to air.
- Partially or fully alkylated derivatives of metal and nonmetal hydrides (diethylaluminium hydride, trimethylaluminium, triethylaluminium, butyllithium), with a few exceptions (i.e. dimethylmercury and tetraethyllead)
- Lead & Carbon Powders produced from decomposition of Lead Citrate
- Uranium is pyrophoric, as shown in the vaporization of depleted uranium penetrator rounds into burning dust upon impact with their targets. In finely divided form it is readily ignitable, and uranium scrap from machining operations is subject to spontaneous ignition.
- Methane tellurol (CH3TeH)
- White phosphorus
- Plutonium: several compounds are pyrophoric, and it causes some of the most serious fires occurring in United States Department of Energy facilities.
- Petroleum hydrocarbon (PHC) sludge.
- Metalorganics of main group metals (e.g. aluminium, gallium, indium, zinc and cadmium etc.)
- National Research Council (U.S.). Committee on Hazardous Substances in the Laboratory (1983), Prudent practices for disposal of chemicals from laboratories, National Academies, p. 240, http://books.google.com/books?id=tzcrAAAAYAAJ&pg=PA240.
- N. Pradeep Sharma, Dictionary Of Chemistry, http://books.google.co.uk/books?id=tz5dh8VoIfQC&pg=PA259
- C.W. Corti et al. / Applied Catalysis A: General 291 (2005) 257
- Angelo & Subramanian (2008), Powder metallurgy: science, technology and applications, p. 48, "Powders of aluminium, iron and magnesium are highly pyrophoric in nature"
- Pyrophoric lead composition and method of making it
- The Reaction of Pyrophoric Lead with OxygenTemplate:Registration required
- DOE | Office of Health, Safety and Security | Nuclear Safety and Environment | Uranium
- DOE | Office of Health, Safety and Security | Nuclear Safety and Environment | Plutonium