Happy New Year Everyone! I apologize for the wait, but we’re
back again, and with the New Year come new resolutions, so expect consistent
updates! In celebration of the New Year, today I’ll be discussing fireworks.
They light up the sky on special occasions creating colors and shapes to amaze,
but what is it that produces this brilliance? From sparklers to aerial
fireworks, it’s a wide world of bright lights!
From sparklers to aerials, all fireworks are made up of the
same few components: an oxidizing agent, a reducing agent, a coloring agent and
binders. In order to burn the mixture and create the various colors and
patterns, fireworks need a fuel source: the oxidizer. Oxidizers, usually
composed of nitrates (NO3-), chlorates (ClO3-) or perchlorates (ClO4-) release oxygen by reacting and exchanging
electrons with metal ions (an example of this is shown below).
4KNO3 -------> 2K2O + 2N2 + 5O2
Of these oxidizers, nitrates are the least reactive but also
the most controllable. As such, nitrates are used as the major component of
black powder, the compound responsible for thrusting the firework high into the
sky. The less stable chlorates, react more intensely, producing an explosion
upon reaction rather than a consistent burn. Although chlorates are used in
fireworks, they are relatively unstable, giving them limited use. Their most
stable counterparts, however, perchlorates, are more stable and produce more
oxygen, making them ideal to produce the brilliant explosions found in
fireworks.
The oxygen released from the oxidizing agents then quickly
reacts with the reducing agents, typically either sulfur and carbon (charcoal).
These reactions produce hot and rapidly expanding gases, either sulfur dioxide
or carbon dioxide respectively, adding to the explosive force of the
reaction. It is the heat and force
generated from this reaction that produces the loud explosions and bright
colors characteristic of fireworks.
The colors of fireworks are created by heating metal salts
such as strontium carbonate, barium chloride, and copper(I) chloride, each of
which produces a unique color. Energy from the combustion of the reducing
agents excites electrons within the metal atoms into a higher energy state. The
electron then falls back to its ground state, emitting a characteristic
wavelength of light with a specific color. Depending on the salt used, a wide
range of colors can be produced!
Red | strontium salts, lithium salts lithium carbonate, Li2CO3 = red strontium carbonate, SrCO3 = bright red |
Orange | calcium salts calcium chloride, CaCl2 calcium sulfate, CaSO4·xH2O, where x = 0,2,3,5 |
| Gold | incandescence of iron (with carbon), charcoal, or lampblack |
Yellow | sodium compounds sodium nitrate, NaNO3 cryolite, Na3AlF6 |
| Electric White | white-hot metal, such as magnesium or aluminum barium oxide, BaO |
| Green | barium compounds + chlorine producer barium chloride, BaCl+ = bright green |
Blue | copper compounds + chlorine producer copper acetoarsenite (Paris Green), Cu3As2O3Cu(C2H3O2)2 = blue copper (I) chloride, CuCl = turquoise blue |
| Purple | mixture of strontium (red) and copper (blue) compounds |
| Silver | burning aluminum, titanium, or magnesium powder or flakes |
courtesy of about.com
The anatomy of a firework is relatively simple. A fuse runs
out of the firework allowing an observer to ignite the ignition charge from a
safe distance. Once lit, the fuse, composed of a fast action and time delay
fuse, quickly ignites the lift-off mixture. As mentioned before, the power
needed to thrust the firework into the air is provided by black powder, a
combination of sulfur, charcoal (carbon) and potassium nitrate. As the firework rockets into the sky and
reaches its apex, the time delay fuse ignites a burst charge, similar in
composition to black powder, which creates a large explosion. This explosion
propels small clay like balls, known as stars, flying. These stars contain the
oxidizing-reducing-metal salt combination that produces the colorful patterns
we all enjoy! Who knew that so much went into lighting up the night sky!
References:
- http://library.thinkquest.org/15384/chem/index.htm
- http://chemistry.about.com/od/fireworkspyrotechnics/a/fireworkcolors.htm
- http://science.howstuffworks.com/innovation/everyday-innovations/fireworks.htm
- http://scifun.chem.wisc.edu/chemweek/fireworks/fireworks.htm
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