Hafnium

Flammability

Description of key information

Flammability properties of hafnium highly depend on the form and particular size of the metal.
Two tests were performed following EEC Method A10 on Hf electrolytic crystals (particle size > 0,8 mm) and Hf Shot (particle size <0,8mm), showing that hafnium shot (<0.8mm)  is flammable cat. 1 according to the 1272/2008 regulation (CLP)
hafnium sponge and Hf shot are considered of the same hazards with a view to classification, on the basis of expert judgement.
Massive Hf (bars) and electrolytic crystals (particle size > 0,8 mm) are considered as non flammable
In the powder form, hafnium is pyrophoric.
According to the 1272/2008/CEE regulation (CLP): 
hafnium powder is classified "pyr sol.1" 
Hf Shot (particle size <0,8mm) and sponge are classified flammable solid cat.1
Massive Hf (bars) and electrolytic crystals (particle size > 0,8 mm) are  non flammable

Key value for chemical safety assessment

Flammability:

highly flammable

Additional information

Flammability is usually seen as the ease with which the substance can burn or be ignited. However it also includes spontaneously flammability (pyrophoricity) and ignition on contact with water.

Reactivity of metals is strongly influenced by their state of subdivision: in bulk they often resist chemical combination; in powdered form they may react very rapidly. Thus, as a bulk metal, it is somewhat unreactive, but finely divided material may be pyrophoric. The metal reacts exothermically with compounds having active hydrogen atoms (such as acids and water) to form flammable hydrogen gas and caustic products. The reactions are less vigorous than the similar reactions of alkali metals, but the released heat can still ignite the released hydrogen.

The combustibility of hafnium increases as the average particle size decreases, but other variables, such as moisture content also affect its ease of ignition.

Hafnium metal can be found under different forms:

-  Powder

- Shot

-  Electrolytic crystals

- Sponge

- Van Arken bar (bulk metal)

PYROPHORICITY

POWDER FORM:

Various independent studies show that hafnium in powder form presents a risk of explosion in contact with air according to its particle size.

According to annex VII, section 7.13 column 2 of the REACH regulation on standard information requirements, the study does not need to be conducted when the substance ignites spontaneously with air at room temperature. Hafnium powder presents risks of spontaneous ingnition, therefore, hafnium powder is not tested for pyrophoric properties.

SPONGE:

In the daily use and handling of hafnium sponge during which continuous exposure to air can occur, no spontaneous ignition is observed. The absence of structural alerts furthermore confirms that hafnium sponge is not expected to have pyrophoric properties.

FLAMMABILITY IN CONTACT WITH WATER

Under conditions where hafnium is in contact with water, no ignition and/or liberation of flammable gases is observed. The absence of structural alerts furthermore confirms that it is highly unlikely that hafnium sponge is flammable in contact with water.

However it has to be noted that, In order to avoid explosion when in contact with air, the level of humidity in the metal has to remain lower than 3% or above 25% only. Any other level of humidity is potentially dangerous.

 

FLAMMABILITY

Two tests have been carried out in a GLP laboratory followong EEC method A10, on two different testing material and lead to the following classification:

-         Hf electrolytic crystals (particle size >0.8mm) :non flammable

-         Hf Shot (particle size <0.8mm):flammable solid cat.1

Due to its form, the hafnium bar was considered non hazardous and therefore was not tested.

For sponge, as it is a very porous and friable material, which can generate finely divided and easily flammable particles. On the basis of expert judgment, sponge and Hf shot are considered of the same hazards with a view to classification.

For powder, no tests have been run on this kind of form. However, literature points towards pyrophoric properties, although it is not clear where the powder form starts (i.e. from which particle size down)

Flammability additional key value for CSA: spontaneously flammable in air (pyrophoric)

Justification for classification or non-classification

On the basis of experience and studies presented:

hafnium powder is classified "pyr sol. cat 1" (H250: Catches fire spontaneously if exposed to air)

According to the results of the tests (method A 10, 440/2008/CEE regulation) and on the basis of expert judgment:

hafnium shot (particle size <0,8mm) and sponge are considered as highly flammable (R11) following 67/548/EEC regulation, and "flammable solid" category 1 (H 228) according to the 1272/2008/CEE regulation (CLP).

On the basis of experience and results of conducted test, Massive Hf (bars) and electrolytic crystals (particle size >0.8mm ) are considered as non flammable