5 Things You Didn’t Know About the Science of FireworksScience, Technology Wednesday, July 4th, 2012
(Smithsonian.com) Fireworks, a centuries-old technology, are an iconic symbol of Independence Day celebrations—but they’re also a marvel of modern science and engineering. Read on to discover the science behind the fireworks you’ll see all around the country tonight.
1. The chemical formula for fireworks was invented by accident. Sometime during the 10th century, the Chinese began making fireworks with gunpowder (the first-known chemical explosive had only recently been discovered). But scholars believe that the inventors hit upon the chemical formula for gunpowder—sulfur, coal and potassium nitrate, or saltpeter—during attempts to create an elixir of immortality. Over time, the Chinese developed a wide variety of fireworks that produced different types of visual effects, and the pyrotechnician became a respected profession in Chinese society.
2. Fireworks are designed not to explode. Counterintuitively, chemists design fireworks to burn as slowly as possible, rather than explode rapidly. A slower burn means that a firework will produce a visual effect for a longer duration that covers a greater area of the sky. To achieve this, the fuel and oxidizer chemicals used—typically metals such as aluminum or magnesium for fuel, and percholates, chlorates or nitrates for oxidizers—are relatively large-grained, in the range of 250 to 300 microns, about the size of a grain of sand. Additionally, chemists avoid mixing the fuel and oxidizer together thoroughly, making it more difficult for them to burn.
3. Different colors are produced by different chemicals. The bright colors visible when fireworks explode are a result of pyrotechnic stars—pellets of chemicals that generate certain colors or produce sparking effects when burned. When the bursting charge is ignited, the main fuel explodes first, transferring energy to the colorant chemicals, which prompts these chemicals’ electrons to move into an excited state. Then, moments later, when the colorant chemicals cool and the electrons fall back to their base state, they release the extra energy as colorful radiation when they are flying through the sky.
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