How are metal salts used in fireworks?

www.Chemie-im-Alltag.de

Oliver Reiser

With the burning of fireworks on New Year's Eve, millions become hobby chemists. Fun and danger, beauty and environmental pollution are close together.

In Southern Europe on Easter, in the USA on Independence Day on July 4th, in France to commemorate the storm of the Bastille on July 14th, in Great Britain on Guy Fawkes Day on November 5th and in Germany on New Year's Eve on December 31st : The burning of fireworks has been an expression of joy and solemnity for centuries.

Gunpowder

Most fireworks are based on black powder, the discovery of which is attributed to the monk Berthold Schwarz in the 14th century. In China, however, black powder was already known around the year 1000.

The mixture from that time has not changed today either: 75 percent potassium nitrate, 10 percent charcoal, 15 percent sulfur result in a mixture that burns under a bright flame when lit. The charcoal is burned to carbon dioxide, potassium nitrate serves as a highly concentrated oxygen supplier. The addition of sulfur makes the mixture easier to ignite.

A whole series of chemical reactions take place, which can be formulated as follows:


The resulting gases carbon dioxide, nitrogen and sulfur dioxide expand by a multiple of the volume of the black powder with simultaneous high heat generation and thus cause a violent explosion in a closed vessel. That is why paper sleeves are always used for fireworks, and before detonation in other vessels, especially in metal containers, be expressly warned.

The sulfur compounds formed when burning black powder are strong environmental toxins. Especially sulfur dioxide (SO2), a pungent smelling gas, is one of the main causes of acid rain. For this reason, the strictest requirements are imposed on the industry to prevent sulfur-containing exhaust gases from entering the environment. By filling up with low-sulfur, high-octane super-plus gasoline, drivers can help to slow down the dying of forests. On the other hand, no fireworks would withstand the requirements for limiting sulfur emissions.

Splendor of colors through heavy metals and PVC

Red, green, blue, yellow - there is no color that is missing from a fireworks display. But how do the splendid colors with which fireworks burn come about? Metal ions are excited to glow when exposed to great heat, for example in an open flame (the so-called flame ionization). Depending on the metal salt - the nitrates are usually used as a simultaneous oxygen donor - a characteristic color is observed: strontium nitrate glows red, barium nitrate green, barium nitrate / sulfur yellow and copper hydroxide / sulfur blue. Despite the brilliance of the colors, the use of metals, especially the very toxic barium and strontium salts, is very questionable for ecological reasons. If such salts are incurred as waste in a chemistry laboratory, they must be collected separately as hazardous waste (heavy metal waste) and properly disposed of.

Polyvinyl chloride (PVC) is also added to the fireworks to enhance the color, especially with the colors red and blue. Not only since the airport fire in Düsseldorf has been known that burning PVC releases toxic gases and acids and, especially in the presence of metal salts, dioxins.

Are fireworks still in keeping with the times?

From the environmental point of view, fireworks represent a considerable burden, but our society cannot be imagined without them in the future. I therefore consider professionally organized large fireworks to be a suitable solution. Not only because of the environment, but also because of personal safety, however, I would advocate the abolition of individual small fireworks for everyone, and here above all for the ban on firecrackers. At least everyone should be aware that a firecracker is an explosive device that you have to handle with care for yourself and others (figure on the right, click to enlarge). Closed clothing and, in particular, protection for the eyes (protective goggles) are recommended to everyone who wants to work as a pyrotechnician on New Year's Eve. Proper handling - hands off black imports from Eastern Europe - fireworks should always be the top priority, and above all throwing a firecracker at another person must be avoided under all circumstances!

I wish you a happy and healthy start to the new year!

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Oliver Reiser