I’ve been an organic chemist now for over fifteen years, and I can tell you, chemists have their share of job dangers. We’re expected to deal with extremely toxic chemicals, flammable solvents, even materials which burst into flame if exposed to regular air. I’ve had numerous occasions in the lab where a chemical I was using could very likely kill me if mishandled. Organotins, for example – complexes that mix both carbon atoms and tin into the same complex, and have a “4” out of “4” for toxicity levels. Fluoride salts, which can kill through bone loss. Heavy metal catalysts which slowly accumulate over time before poisoning symptoms become apparent, silica gel which can lead directly to lung cancer – the organic chemistry lab is a fundamentally hazardous environment. We chemists are expected to deal with these dangers by virtue of our training; we learn which compounds pose a particular threat, and take steps to reduce our exposure. The real danger, and the materials that I have nightmares about, are compounds which are dangerous but appear to be innocent. They take me off guard, and I always wonder if I’m being sufficiently cautious.
One prime example of this are so called “nanomaterials”. A nanometer is a very small distance – a thousandth of a thousandth of a millimeter. On this scale, which is the size regime of individual atoms and molecules, materials have an extremely high surface area. That’s the key to their high reactivity and it’s what makes them interesting for a wide variety of applications; there is an intense amount of interest in nanochemistry. However, along with this high reactivity towards other chemicals comes a high reactivity towards oxygen gas, and that’s what makes these compounds so dangerous. One of the most surprising aspects of chemistry is the effects of surface area on the rate of a chemical reaction. A molecule can only react with another molecule if the two can come into intimate contact, at precisely the right distance and orientation. If most of the molecule is trapped deep within a solid or underneath the surface, it won’t be able to react; it really is that simple. Take the example of an ice cube. If the ice is in a solid chunk and you drop it into a warm drink, it’ll take a while to dissolve – perhaps as much as 30 minutes. If you take the same amount of ice and finely shave it into a powder before adding it to the drink, it’s going to melt within a few minutes. It’s the same process occurring (ice melting), but the increased surface area makes it happen much faster.
Take the same principle and apply it to metal powders, which normally react very slowly with oxygen when the metal is in a clump. Finely separated metal powders, however, react fiercely with oxygen, often spontaneously combusting. How substantial is the danger? A team of chemists from Canada recently studied this subject, and published their results in the journal named Industrial & Engineering Chemistry. What they found confirms my own experiences over the years of powders catching flame. Explosions from nanomaterials – those on the scale of nanometers – require only a small amount of energy in order to spark. Less than 1 mJ is required, which is a very small amount; just a tiny spark from static or improper thermal storage could easily set off an explosion. The researchers gave a list of suggestions for the proper handling of these materials which can help to lower the danger inherent in fine powders. Many of them were common sense, but all of them drove home the importance of caution when handling even seemingly innocent compounds. The article was an interesting read. From the standpoint of a chemist, it gave me some practical tips on how to work in a safer fashion. From the standpoint of a layman, it gives a nice glimpse into the fascinating (but occasionally dangerous) job of an organic chemist.
The source of this article can be found at:
Worsfold, S., et al. “Review of the explosibility of non-traditional dusts”. Ind. Eng. Chem. Res., Article ASAP 2012. DOI: 10.1021/ie201614b.