Who made that bomb?

In work that may help law enforcement officials better identify terrorists, researchers at the University of Missouri-Rolla are using glass microspheres to trace explosives back to their manufacturers.

‘With explosives we want to find out who is using them illegally by having some way to track them,’ said Dr. Delbert Day, Curators’ Professor emeritus of ceramic engineering. ‘If you know where and when the explosive was made, you can narrow down the number of suspects that might have purchased this explosive.’

The glass microsphere’s chemical composition becomes a signature and can provide the name of company, the plant location, and the day it was manufactured. ‘By controlling the chemical composition you can put this information inside the glass microsphere and only the manufacturer of the explosive has the code,’ Day said.

The tag’s safety is a big concern as explosives are made of dangerous materials, said Dr. Paul Worsey, professor of mining engineering at UMR. Any material added to an explosive is carefully evaluated for fear that it may cause it to detonate prematurely or make it more dangerous.

‘Our idea of using glass microspheres was based on the premise that they are already deliberately added to explosives to improve performance and have not caused a safety problem so they must be safe to use, so why not use them for a tag?’ said Day.

Glasses are durable materials with a high melting temperature. Day said it’s unlikely that glass would react in a dangerous way because it’s an inorganic material – unlike polymers – which makes it less reactive. Polymers are currently used to tag some explosives, but Day said they are less durable than glass microspheres.

‘A glass is stable to much higher temperatures than most polymers, so there is a higher likelihood that a glass microsphere will survive an explosion compared to most polymers,’ said Day.

The glass spheres already added to explosives are hollow, whereas the tags would be solid. Day said there is no evidence that using a solid sphere instead of a hollow one would cause any additional risk. The hollow glass spheres, or ‘microballoons,’ are added to emulsion explosives because they make the explosive more effective, Days said.

After an explosive detonates, the tags – solid glass microspheres – are found in and around the explosion site. The microspheres are then detected using a variety of methods depending on what was added to the spheres when they were formed. For example, if a certain chemical is added, the microspheres will glow when exposed to low-level radiation. They can also be made magnetic so a magnet can be used at the explosion site to pick up the microspheres, said Worsey.

‘In the field of taggants there are a lot of applications, with tagging explosives being just one. There is more interest in it now because of the terrorist activity,’ said Day. Other possible applications include tagging the chemicals used to make drugs, land mines, credit cards, jewellery and electronic products.