Potassium

Spontaneous Heating and Pyrophoricity

DOE-HDBK-1081-94

PYROPHORIC METALS

slightly above its melting point (98 C or 208 F) has been ignited by placing

sodium oxide particles on its surface. This indicates the possibility of ignition

at temperatures below the boiling point. Once ignited, hot sodium burns

vigorously and forms dense white clouds of caustic sodium oxide fumes.

During combustion, sodium generates about the same amount of heat as an

equivalent weight of wood.

The principal fire hazard associated with sodium is the rapid reaction with

water. It floats on water (specific gravity 0.97), reacting vigorously and

melting. The hydrogen liberated by this reaction may be ignited and explode

from the heat of the reaction. Sodium (like other burning, reactive metals)

reacts violently with most chemicals that can oxidize, halogenated

hydrocarbons, with halogens such as iodine, and with sulfuric acid.

Potassium

The fire hazard properties of potassium (K) are very similar to those of sodium

with the difference that potassium is usually more reactive. For example, the

reaction between potassium and the halogens is more violent, and, in the case

of bromine, a deflagration/detonation can occur. There is an explosive reaction

with sulfuric acid. Unlike sodium, potassium forms some peroxides and

superoxides during combustion. These peroxides may react violently with

organic contaminants (oils, etc.). Peroxides and superoxides may also react

explosively with metallic potassium (see NaK below).

NaK (Sodium-Potassium Alloys)

NaK is the term used when referring to any of several sodium-potassium

alloys. The various NaK alloys differ from each other in melting point, but all

are liquids or melt near room temperature. NaK alloys possess the same fire

hazard properties as those of the component metals except that the reactions

are more vigorous. Under pressure, NaK leaks have ignited spontaneously.

The potassium in NaK will react with atmospheric oxygen to form three

different oxides, potassium oxide (K2 O), potassium peroxide (K2 O2 ), and

potassium superoxide (KO2 ). These oxides form a crust over the NaK surface.

If this crust is permeated and the superoxide (KO2) is allowed to mix with the

potassium in the NaK, a very high temperature thermite-type reaction can

occur. This reaction may take several minutes to develop if the NaK is stored

under an inert atmosphere or it may occur instantly if stored under atmospheric

oxygen.

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Pyrophoricity