Researchers Use Glass Spheres to Tag and Trace Explosives

Dr. Delbert Day, Curators’ Professor emeritus of ceramic engineering and Dr. Paul Worsey, professor of mining engineering at UMR, are combining their talents in materials and explosives to create a more effective way for munitions manufacturers to identify where and when their explosives are made.

“With explosives we want to find out who is using them illegally by having some way to track them,” says Day. “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 says.

The tag’s safety is a big concern as explosives are made of dangerous materials, Worsey says. 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?” says Day.

Glasses are durable materials with a high melting temperature. Day says 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 -- tiny chips of plastic -- are currently used to tag some explosives, but Day says 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,” says Day.

The glass spheres already added to explosives are hollow, whereas the tags would be solid. Day says 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 says.

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. Then a magnet can be used at the explosion site to pick up the microspheres, says 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,” says Day. Other possible applications include tagging the chemicals used to make drugs, land mines, credit cards, jewelry and electronic products.