Wednesday, July 4, 2018

Speaking of Science: True blue fireworks

Speaking of Science
Sarah Kaplan and Ben Guarino on Science

Macy's Fourth of July fireworks display in New York on July 4, 2017. (Alba Vigaray/EPA)

If blue fireworks in recent years have looked a little bluer, thank a chemist.

Fireworks explode thanks to the gunpowder in their shells. But the pyrotechnics get color from different chemical salts, specifically, metal chlorides. Electrons in the salts, flooded with energy as the payload heats up, have to release their excess energy somewhere. They do so as light. You might see reds from lithium salts, or oranges from calcium. Blues come from copper salts.

But the deepest blues were, historically, among the most difficult colors to produce. Blue fireworks need to hit just the right temperature. The copper compound emits blue at a high heat, but if the temperatures rocket too high, the heat destroys the metal and the colors are lost.

The introduction of an alloy of magnesium and aluminum has infused better blues into the explosions. "People may think colors look brighter; well, they're correct," emeritus chemistry professor at Washington College John A. Conkling told Chemical & Engineering News last year.

Chemists continue to tinker with the blue formula. In 2015, researchers in Munich developed new type of blue firework using bromine instead of not chlorine. Bromides are less toxic than chlorides, the chemists said, but burn as brilliantly blue. They estimated it would take five to 10 years to perfect the blue flares, but perhaps their work will light up future Fourths.


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