The Fourth of July fireworks display in my family always has a bit of a nerdy side to it. Cries of "Strontium Nitrate!" punctuate the brilliant red burst of a skyrocket. Unified shrieks of "Barium Nitrate!" as brilliant green sparks shower out of the sky. All of this stems from my experimentation as a teenager with different combinations of chemicals to produce a rainbow of colors in home-made fireworks, but this scientific 4th of July exuberance at my household may soon change. Some of the most colorful fireworks may be outlawed because of the toxic pollution they cause.
One rarely gives much thought to the toxic environmental pollution that accompanies a fireworks display. Amidst the choking black-powder smoke and sulfurous stench of a pyrotechnic Independence Day celebration, pounds of volatile compounds and heavy metals go up in smoke to make colorful explosions that pollute the air and contaminate ground water. Potassium perchlorate, an essential oxidant in many fireworks, is under scrutiny by the US Environmental Protection Agency because it promotes thyroid dysfunction and causes birth defects. Barium nitrate is a noxious heavy metal with toxic effects on the heart and lungs. But the skies will not go dark in future Independence Day celebrations if scientists can find more environmentally friendly substitutes. The answer to this environmental dilemma, like fireworks themselves, may come from adapting the horrible explosives of war for use in the festive celebration of Independence Day.
Jared Moretti, Jesse Sabatini and Gary Chen, writing in the current edition of the scientific journal Angew. Chem. Int. are looking for "greener" alternatives to toxic barium in periodates as explosives. These researchers work for the US Army, Pyrotechnics Technology and Prototyping Division, in New Jersey where every day is the Fourth of July. Their primary concern is in reducing environmental pollution caused by the Army's signal flares and incendiary devices, but their labors are likely to come to the rescue in the environmental battle over fireworks as well.
The researchers are working to make a greener 50 caliber M8 armor-piercing incendiary bullet. Upon impact with an armored vehicle or aircraft, the M8 bursts into flames with a blinding incandescent flash that burns through metal and ignites fuel vapors in the target. Currently, the explosive inside this bullet combines both toxic components the EPA would like to eliminate: barium nitrate and potassium perchlorate oxidizers, together with 50% magnesium-aluminum alloy. In their spectacular chemistry experiments they tried replacing the nasty perchlorates and barium with a strontium nitrate, potassium periodate or sodium periodate instead; all of which have less toxicity issues.
Some mixtures were duds, failing to ignite at all, but their efforts eventually found a mixture of these components in just the right proportion that produced explosions with the same armor piercing kick and an even brighter flash plume than the original formula. Periodate salts, if used in correct proportions, could replace the more toxic perchlorates. Sodium periodate produced a brilliant yellow white flash that would be perfect for fireworks. An added benefit of periodates over perchlorates is that they attracted less water from the air, which helps keep the powder dry and extend the shelf life of the explosive.
If you are a teen-age avid reader of Scientific American, like I was, please don't be foolish. Fingers are nice. So is vision. A burn-scarred face won't help your social life and burning down your home would be more than an inconvenience. Many people are harmed and homes go up in flames from accidents using even the safest commercial works. Experimenting with the chemistry of pyrotechnics as an amateur is extremely dangerous and foolish. Instead, take this article to your chemistry teacher and ask him or her to consult this new scientific study and use it to safely learn about the chemistry of fireworks. Write out the chemical reactions and discuss oxidation and exothermic reactions. Ask your teacher to explain what Gibbs free energy is and why it matters for skyrockets. With countless chemicals to choose from, how did the scientists know, from a glance at the periodic chart, which chemicals to substitute for the more toxic ingredients? Why did sodium nitrate produce a brilliant yellow flash rather than say purple? And why is the light from a streetlamp yellowish? Have a safe and fun 4th, and start learning the new chemical names to call out next year!
Reference: Jared D. Moretti, Jesse J. Sabatini, and Gary Chen (2012) Periodate salts as pyrotechnic oxidizers: Development of barium- and perchlorate-free incendiary formulations. Angew. Chem. Int. Ed. 2012, 51, 1-4.