Pyrophoricity

pyrophoricity can cause it to look like a glowing ember under certain conditions.]]

A pyrophoric substance (from Greek πυροφορος, purophoros, "fire-bearing") is a substance that will ignite spontaneously in air. Examples are iron sulfide and many reactive metals including uranium, when powdered or sliced thinly. 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.

Uses

The creation of sparks from metals is based on the pyrophoricity of small metal particles. 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.

Handling

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).

Pyrophoric materials

Solids

Alkylated metal alkoxides or nonmetal halides (diethylethoxyaluminium, dichloro(methyl)silane)

Alkali metals (sodium, potassium, rubidium, cesium)

Copper fuel cell catalysts, e.g., Cu/ZnO/Al₂O₃

Grignard reagents (compounds of the form RMgX)

Finely divided metals (iron, 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, triethylboron)

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.

Metal carbonyls (dicobalt octacarbonyl, nickel carbonyl)

Methane tellurol (CH₃TeH)

Phosphorus (white, or yellow)

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.

Gases

Arsine

Diborane

Phosphine

Silane

Liquids

Metalorganics of main group metals (e.g. aluminium, gallium, indium, zinc and cadmium etc.)

Triethylborane

Hydrazine is hypergolic with oxidants like dinitrogen tetroxide, not truly pyrophoric.

Notes

External links

US Dept. of Energy Handbook, "Primer on Spontaneous Heating and Pyrophoricity"

List of pyrophoric materials

Category:Chemical properties