Pyrophoric Materials

Pyrophoric materials are those that are capable of spontaneous combustion in the presence of air. Spontaneous ignition or combustion takes place when these substances reach ignition temperature without application of external heat. Ignition may be delayed or only occur if the material is finely divided or spread as a diffuse layer (titanium powder is an example in the first case, and mixed tributyl phosphine isomers is an example in the second). Or, on the other hand, ignition could be essentially instantaneous, the time delay being measured in milliseconds as with trimethylaluminum. The following classes of compounds are prone to pyrophoricity.

Classes of Pyrophoric Compounds

• finely divided metals

  (calcium, zirconium)
  

• alkali metals

  (sodium, potassium)
  

• metal hydrides or nonmetal hydrides

  (germane, diborane, sodium hydride, lithium aluminum hydride)
  

• Grignard reagents

  (compounds of the form RMgX)
  

• partially or fully alkylated derivatives of metal and nonmetal hydrides

  (diethylaluminum hydride, trimethylphosphine)
  

• alkylated metal alkoxides or nonmetal halides

  (diethylethoxyaluminum, dichloro(methyl)silane)
  

• Metal carbonyls

  (pentacarbonyliron, octacarbonyldicobalt, nickel carbonyl)
  

• used hydrogenation catalysts

  (especially hazardous because of the adsorbed hydrogen)
  

• phosphorus (white)

A more extensive list of pyrophoric compounds can be found in Bretherick's Handbook of Reactive Chemical Hazards. Pyrophoric materials should be stored in tightly closed containers under an inert atmosphere or liquid. All transfers and manipulations of them must also be carried out under an inert atmosphere or liquid. These materials may not be disposed of in a landfill because of their characteristic reactivity.

Copyright © 1996 by College of Science, Texas A&M University