Crossposted at Politicook.net
I touched on fireworks a little in my series on the electromagnetic spectrum, and it is here.
Since it is topical today, I decided to expound on it a little. The "pyro" term is apt because I spent several years as a pyrotechnician, making everything from better screening smokes, better signaling smokes, better delivery systems, and novel bursting mixes for the Army as a civilian.
Fireworks are ancient, dating back, as best we can tell, to ancient China. That is where black powder, a mixture of potassium nitrate, charcoal, and sulfur, was developed. The Chinese used it in small rockets for display and for warfare for centuries until it, and its formula, made its way to Europe around 1250 C.E., give or take. That is where fireworks got started.
First, some definitions:
"Effect" is one of the following: "Report" is the sound that a bursting firework makes. That is different from the sound of the lifting charge for aerial displays. "Light" is any flash, sparkle, or star produced. "Smoke" is just that, and may be intentional, as in smoke bombs, or incidental because of the black powder used. "Other" includes things like confetti set loose by a bursting payload, or the large ash produced when snake tabs are ignited. Update 2: Maybe it is just me, but the smell associated with fireworks is part of the experience. Unlike a movie character, I do love the smell of the sulfur containing combustion products of fireworks, and I am going to add "smell" to the list of effects.
"Fixed set", or "set piece" is a device that has little report, does not explode, and forms a design. Common are ones that approximate a US flag when ignited. Pretty, but not very exciting. However, they are very hard to make because of coordination of burning in a large one. You want all of the colors to be present at once, unless you are trying an animated one. Possible, but extremely difficult. There is also the problem with the smoke interfering with the image.
"Mortar" is the tube from which an aerial display is launched. Sometimes erroneously applied to the aerial display itself.
"Flash" is the very bright light given off by burning metals, usually aluminum, magnalium (magnesium/aluminum alloy), or iron. Sometimes zinc is used.
"Fuel" is any oxidizible material used to produce energy in a pyrotechnic. Common fuels are charcoal, powdered metals, sulfur, dextrine, and shellac.
"Oxidizer" is any material used to burn the fuel at a suitable rate. For a burst, burning is fast. For lifting, slower. Potassium nitrate is the most common oxidizer, but potassium chlorate is essential for colors. With chlorate, most fireworks would be white or yellow. Other oxidizers are nitrates of other metals that mainly are used to impart color.
"Coolant" is any material used to moderate the speed of reaction between a fuel and an oxidizer. Sodium bicarbonate (baking soda) is commonly used.
"Color" is the material used to impart colors other than white or yellow. This gets very complicated, and is the epitome of the art of pyrotechnics to make good colors. Blue is particularly difficult to attain, but recent fireworks are pretty good.
Now, let us examine a few fireworks in particular. There are so many that it would be impossible to go through all of them, but several are so popular as to gain special mention.
Firecrackers are paper cylinders rolled from a "flash mix" of aluminum powder and an oxidizer, with a little sulfur to accelerate the reaction. Flash mixes are extremely treacherous, and anyone handling them either know what they are doing or get a shrink. The only more dangerous mix is the "whistle" or "chaser" mix, used in chasers that everyone knows. The fuzes on firecrackers are cheap, and often burn faster than desired. By regulations by the Consumer Product Safety Commission, firecrackers are limited to the amount of flash mix that they can contain. Incidentially, the "M-80" firecracker was orginally developed by the Army as a machine gun report simulator, strung together by a stout fuze. They had quite an effect. That mix was so "hot" that they were make remotely: the paper tube had a bottom glued in, then the three components were added to each tube separately. Then the top was glued in, and allowed to dry. Then the unmixed tubes were put in a drum of sawdust and the drum taken to a shaker table. After everyone evacuated the area, the shaker ran for half and hour or so, mixing the components. Then each one was removed, pierced in the side, and a fuze inserted and glued. Real M-80's are not available.
Rockets are essentially a firecracker on a stick, with a lifting mix (black powder) to lift them and a payload, usually, such as stars or a flash mix. The stick provides the flight stabilization. Bottle rockets are miniature rockets. The fuzes on them are usually cheap and unreliable, so be careful. The fuze ignites the lifting charge, which, when it burns up the the "report" charge, ignites it with a bang and some light. Mrs. Translator and I used to, along with nephews, cousins, and friends would have bottle rocket wars. We would take pipes (we used aluminum tent poles) and separate into two person teams, an "aimer" and a "loader". The aimer would target an opposing team and say go, and then the loader would start the fuze and push the bottle rocket into the pipe. It was great fun, and no one ever got hurt. We did all wear safety glasses. I got some holes burned in a shirt or two, and once someone got a burn on his hand, but nothing serious. While I do not recommend it, it was great fun.
Chasers are essentially bottle rockets without a stick, with the port hole carefully regulated. The lifting mix is replaced with a whistle mix. Notice the next time you listen to one: the pitch changes from high to low. This has nothing to do with the Doppler Effect, but is a consequence of the resonant chamber getting larger as the mix occupying it getting burnt. The longer the resonance cavity, the lower the pitch.
Sparklers are pieces of steel wire coated with a dazzle mix, which is an oxidizer, usually potassium nitrate, a fuel (often shellac, which is also a binder), and aluminum or iron flake, which supply the sparkle effect. Colored ones have other metal nitrates to impart that quality. My only serious firework injury came from sparklers, and I had extremely deep and painful burns on my hand on account of lighting three at once. That was back when I was ignorant about how fireworks work. The channel formed between the three of them allowed pressure to build, and with any gassy pyrotechnic, as pressure increases, so does the burn rate. The flame ran down the channel and burnt me before I could react. Never light more than one at a time.
Most commercial displays use mortar-launched effects, since it is hard to make rockets with the degree of control necessary for large displays, but mortar-launched payloads are easy to control, in timing of firing, height of travel, and time delay for activation. Large displays can take a long time to set up, and are controlled by firing panels for what may be thousands of mortar tubes. Almost all large displays are fired electrically and some are computer controlled. There are a number of consumer market mortar-launched fireworks, most of which shoot out a payload that produces a shower of sparks or colored stars, often with a report. The humble Roman candle is perhaps the most well known mortar-launched firework.
Before this gets too long, let me talk about colors. All firework colors are caused by electrons, excited by high temperature, falling into lower, unoccupied orbitals and emitting light then. See the link above for the technical description.
Using Roy G. Biv as a model, we have red first. Red is usually caused by strontium, a member of the calcium group of elements. It has a strong red emission in one of its transitions, and is a deep red, sometimes described as scarlet. Lithium also is sometimes used, and it gives a crimson color. Both are used as their nitrates, which are oxidizers. Potassium chlorate is used as the main oxidizer, because nitrate burns too hot and washes out the colors. Our founding fathers and mothers saw only white and yellow fireworks. The colorant and oxidizer are mixed with a fuel, usually sugar or something similar, and a binder to keep it together after formation of the pellet.
Orange is uncommon in fireworks, except for orange dazzle from iron powder. I am not familiar with a true orange flame.
Yellow is easy, but not very popular. Any sodium salt (usually sodium nitrate) can form it, as can calcium salts. The calcium ones are a orangy-yellow.
Green is almost always produced by barium. It, like strontium, is a member of the calcium group of metals. Barium produces an intense green emission, and is usually used as the nitrate or the chloride. Chlorides have an advantage in that they are relatively volatile and so produce more bang for the buck. It is always used with potassium chlorate as the oxidizer, and usually sugar as the fuel.
Blue is the most difficult color to produce. No element has a really strong blue emission line, and the human eye is not very sensitive to the blue. In old formulations, arsenic was used, but it did not make a very good blue, and obviously its toxicity was a problem. Now days, copper with a chlorine donor is used, usually copper nitrate and powdered polyvinyl chloride. The temperature has to be controlled very carefully, because the color producing species is not an atom, but the CuCl+ ion, which is very delicate compared with an atom. Sugar, chlorate, and coolant must be balanced very carefully to get a good, deep color that burns long enough to see.
Update: I intentionally stopped this diary because it was getting too long. I would be happy to try to field any question or respond to any comment about fireworks. If I had gone into the possible detail, it would have run many, many pages. Warmest regards, Doc.