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Pyrophoric

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Pyrophoric

Not to be confused with Porphyria.


A pyrophoric substance (from Greek πυροφόρος, pyrophoros, "fire-bearing") is a substance that ignites spontaneously in air at or below 54.55 °C (130.19 °F)".[1] Examples are iron sulfide and many reactive metals including uranium, when powdered or thinly sliced. 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, and pyrophoric alloys are made for this purpose.[2] 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 (Teflon)-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.

Pyrophoric materials

Solids

Liquids

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

Gases

Notes

External links

  • US Dept. of Energy Handbook, "Primer on Spontaneous Heating and Pyrophoricity" (archived)
  • List of pyrophoric materialssv:Självantändning#Pyrofora ämnen

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