Chemistry labs typically contain a number of potential hazards ranging from chemicals to lasers and beyond. Pyrophoric materials are among the most dangerous, as they spontaneously and violently ignite when exposed to mere water, or even air! Dealing with pyrophoric materials safely requires significantly more protection than that offered by traditional safety attire like eye protection and lab coats. As a chemistry doctoral student at Indiana University, I work with pyrophoric materials all the time and I have not once created a catastrophically destructive fireball.
To better understand how can we can prevent pyrophoric disasters, we first need to understand what causes them. Pyrophoric materials ignite spontaneously when exposed to water or air. The probability of this reaction increases exponentially with the amount of exposed surface area, which makes pyrophoric materials in the form of small filings or fine powder particularly risky. Their dramatic reactivity can be traced back to the material’s desire to be oxidized or lose electrons. Many pyrophoric elements are alkali metals, which lie in group one of the periodic table. These metals have one more electron than their preceding, very stable, noble gas which has a stable electron configuration. For example, sodium (Na), an alkali metal, has one more electron than neon (Ne), a noble gas. This lone, unpaired electron is what makes sodium very reactive.
Oxygen, which is present in oxygen gas (O2) and water (H2O), is a great partner for pyrophoric materials. Oxygen needs two additional electrons to create the same stable electron configuration present in neon. Therefore, if sodium and oxygen were to react, the ‘extra’ electron in sodium would be donated to oxygen. And if two sodium atoms were to react the more stable compound sodium oxide (Na2O) could be formed – allowing all atoms involved to have the stable octet electron configuration.
Thus, the key to working with pyrophoric materials is to not expose them to water or air as these will cause them to be readily oxidized. In the laboratory, we can create environments filled only with an inert gas such as nitrogen (N2) or argon (Ar) which are unreactive toward pyrophoric materials. Laboratories that use many pyrophoric or air sensitive materials use glove boxes, which cost thousands of dollars, while working with the materials. As shown in the picture to the right, glove boxes consist of a large sealed box with holes for gloves to allow the researcher to work in the box. The pressure in the box is maintained higher than atmospheric pressure – this makes sure that air never flows into the box.
Items can be transferred in and out of the glove box using a small antechamber. Once the antechamber is filled the several cycles of pulling vacuum followed by purging with nitrogen gas are completed to eliminate any air. Once completed the antechamber can be opened from within the glove box and the items transferred inside.
Pyrophoric materials, due to their high reactivity, are used in lighters to allow us to quickly make fire. However, they can also make great catalysts such as described in my previous post Fuel for the future: The evolving process of making hydrogen. Their uses are endless – how many more uses for can you think of?
The purpose of this post is not to provide safety guidelines for working with pyrophoric materials. Please refer to material safety data sheets when working with chemicals and adhere to all recommended precautions.