Pyrophoricity

Pyrophoricity is the tendency of a substance to ignite spontaneously when exposed to air, often because rapid oxidation releases heat faster than it can dissipate.

Oxidation: A chemical process in which a substance loses electrons, often by reacting with oxygen. Rapid oxidation in air supplies the heat that can ignite a pyrophoric substance.
Pyrophoric materials: Substances that ignite spontaneously when exposed to air under specified conditions. This category includes the solids, liquids, and gases whose handling requires air exclusion.
Flammability: The ability of a material to ignite and sustain burning under specified conditions. Flammable materials generally need an ignition source; pyrophoric materials can ignite upon air exposure.
Oxygen: A reactive chemical element that makes up about 21 percent of Earth's atmosphere. Atmospheric oxygen is the oxidizer that initiates many pyrophoric reactions.
Autoignition temperature: The lowest temperature at which a substance ignites in air without an external flame or spark. It distinguishes heat-driven ignition from pyrophoric ignition initiated by air exposure.
Organolithium reagent: An organometallic compound containing a carbon–lithium bond, widely used in synthesis. Some organolithium reagents ignite on air exposure and require inert-atmosphere techniques.
Hypergolic propellant: A pair of propellants that ignite spontaneously when brought into contact with each other. Hypergolic ignition follows contact between chemicals, not exposure to air.
Oxidizing agent: A substance that accepts electrons from another substance in a chemical reaction. Air acts as the oxidizing environment for many pyrophoric materials.
Passivation: The formation of a protective surface layer that slows further chemical reaction. Passivation prevents continuing oxidation that could otherwise sustain spontaneous ignition.
White phosphorus: A reactive allotrope of phosphorus that ignites in air at ordinary temperatures. Its spontaneous ignition is a well-known example of pyrophoricity.

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