A substance is pyrophoric (from
Greek: πυροφόρος, pyrophoros, 'fire-bearing') if it ignites spontaneously in air at or below 54 °C (129 °F) (for gases) or within 5 minutes after coming into contact with air (for liquids and solids).[1] Examples are
organolithium compounds and
triethylborane. 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.
Class Dfire extinguishers are designated for use in fires involving pyrophoric materials. A related concept is
hypergolicity, in which two compounds spontaneously ignite when mixed.
Uses
The creation of
sparks from metals is based on the pyrophoricity of small metal particles, and pyrophoric alloys are made for this purpose.[2] Practical applications include 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
polytetrafluoroethylene-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.
When working with pyrophoric solids, researchers often employ a sealed
glove box flushed with inert gas. Since these specialized glove boxes are expensive and require specialized and frequent maintenance, many pyrophoric solids are sold as solutions, or dispersions in
mineral oil or lighter
hydrocarbon solvents, so they can be handled in the atmosphere of the laboratory, while still maintaining an oxygen- and moisture-free environment. 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 the material is returned to the container for storage.
Uranium, as shown in the disintegration 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[7]
^
abcAngelo & Subramanian (2008), Powder metallurgy: science, technology and applications, p. 48, Powders of aluminium, iron and magnesium are highly pyrophoric in nature
^C.W. Corti et al. / Applied Catalysis A: General 291 (2005) 257
"Pyrophoric Chemicals Guide"(PDF). Environmental Health and Safety. University of Minnesota. Archived from
the original(PDF) on 31 October 2014. Retrieved 27 March 2021.