pyroforic

Pyrophoric is a term used to describe substances that ignite spontaneously when exposed to air, even at normal ambient temperatures. This ignition occurs without the need for an external ignition source such as a spark or flame. The reactivity is due to the substance's ability to readily undergo oxidation in the presence of oxygen.

Common examples of pyrophoric materials include certain finely divided metals like finely powdered iron, magnesium, and titanium, as well as organometallic compounds such as tert-butyllithium and diethylzinc. Some gases, like phosphine, can also be pyrophoric. The pyrophoric nature of a substance depends on several factors, including its physical form (e.g., particle size), purity, and the presence of any passivating layers that might inhibit oxidation.

Handling pyrophoric substances requires extreme caution. They are typically stored under an inert atmosphere, such as argon or nitrogen, or under a layer of mineral oil or other inert liquid to prevent contact with air. Specialized equipment and procedures are necessary for their transfer and use in laboratory and industrial settings. Accidental exposure to air can lead to rapid combustion, fires, and potentially explosions, making proper safety protocols paramount. Firefighting for pyrophoric materials often involves using dry chemical extinguishers designed for metal fires (Class D) or smothering the flames with sand or other inert materials, as water can exacerbate the situation by reacting with some pyrophoric substances.