Storage and Handling - hdbk10810042

PYROPHORIC METALS

DOE-HDBK-1081-94

Spontaneous Heating and Pyrophoricity

micron-diameter dust have ignited when heated to 190 C (374 F).

Combustion of zirconium dust in air is stimulated by the presence of limited

amounts of water (5 to 10%). When very finely divided zirconium powder is

completely immersed in water, it is difficult to ignite, but once ignited it burns

more violently than in air.

Massive pieces of zirconium do not ignite spontaneously under ordinary

conditions, but ignition will occur when an oxide-free surface is exposed to

sufficiently high oxygen concentrations and pressure. The explanation for this

reaction is the same as that cited for a similar titanium reaction. Zirconium

fires (like fires involving titanium and hafnium) attain very high temperatures,

but generate very little smoke.

Explosions have occurred while zirconium was being dissolved in a mixture of

sulfuric acid and potassium acid sulfate. Zirconium has exploded during and

following pickling in nitric acid, and also during treatment with carbon

tetrachloride or other halogen-containing materials. Spontaneous explosions

have occurred during handling of moist, very finely divided, contaminated

zirconium scrap.

Hafnium

Hafnium has similar fire properties to zirconium. Hafnium burns with very

little flame, but it releases large quantities of heat. Hafnium in sponge form

may ignite spontaneously.

Hafnium is generally considered to be somewhat more reactive than titanium or

zirconium of similar form. Damp hafnium powder reacts with water to form

hydrogen gas, but at ordinary temperatures this reaction is not sufficiently

vigorous to cause the hydrogen to ignite. At higher temperatures, however,

ignition of the hydrogen may be expected to proceed explosively.

Storage and Handling

Special storage precautions are not required for zirconium castings because of the very

high temperatures that massive pieces of the metal can withstand without igniting.

Zirconium powder, on the other hand, is highly combustible; consequently, it is

customarily stored and shipped in 3.78-L (1-gal) containers with at least 25% water by

volume. For specific details, refer to NFPA 482, Standard for the Production,

Processing, Handling, and Storage of Zirconium.

Zirconium powder storerooms should be of fire-resistive construction equipped with

explosion vents. Cans should be separated from each other to minimize the

possibility of a fire at one can involving others and to permit checking of the cans

Pyrophoricity

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