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[15.0] Incendiaries, Miscellaneous Pyrotechnics, & Fireworks

v1.3.0 / chapter 15 of 15 / 01 jun 16 / greg goebel

* In addition to explosives, there's a wide range of other pyrotechnics, including incendiaries, a wide range of miscellaneous specialized pyrotechnic devices, and last but not least the diverse and entertaining field of fireworks. This chapter completes the survey of pyrotechnics.

fireworks


[15.1] INCENDIARIES
[15.2] MISCELLANEOUS PYROTECHNIC DEVICES
[15.3] FIREWORKS
[15.4] COMMENTS, SOURCES, & REVISION HISTORY

[15.1] INCENDIARIES

* Incendiary weapons have long been used in combat, for example, the "flaming arrows" used by Apaches to set wagons on fire in Western movies. In the 7th century CE, Byzantine Greek alchemists found that a mix of pitch, naphtha, sulfur, and petroleum would burst violently when ignited, and named the mixture "Greek Fire". The empire's military used it to defend Constantinople from invading Saracens. Later, in naval fighting during the age of sail, cannonballs were often heated red-hot before firing in hopes of setting an enemy vessel on ablaze.

Modern military incendiary munitions consist of "napalm", "fuel-air explosives (FAE)", and metallic compositions. Napalm is simply gasoline to which a thickener has been added to make the burning fluid viscous and sticky. The original World War II form of napalm used a thickener named "sodium palmitrate", leading to the name "na-palm". Modern "napalm B" uses polystyrene plastic beads as a thickener. Homemade napalm can use liquid or powder soap, or styrofoam packing peanuts, as a thickener. FAEs spray out an aerosol cloud of a hydrocarbon liquid, and then ignite it to create an explosive fireball over a wide area.

Aluminum has already been mentioned as an incendiary metal. Other incendiary metals include zirconium, magnesium, titanium, and depleted uranium. They all burn at very high temperatures. A particularly useful metallic incendiary is "thermite", which is a mix of ferrous oxide (Fe2O3, essentially rust) and aluminum. The thermite reaction is as shown below:

   Fe2O3 + 2Al -> Al2O3 + 2Fe

The reaction burns very hot and releases a tremendous amount of energy. Sometimes boosters such as sulfur or barium nitrate are added to thermite to make it easier to ignite and enhance its effect, the mix then being referred to as "thermate". Thermite / thermate is often used in demolition grenades to burn or melt down military gear that has to be abandoned to an enemy.

One modern scheme uses a "combustible foil" based on pyrotechnic metals to perform emergency welds. The foil contains ultrathin alternating layers of metals such as nickel and aluminum. The foil is ignited by a match or a 9 volt battery, and instantly ignites over its entire surface. Varying the thickness and composition of the layers provides control over the speed, temperature, and total energy of the reaction. It works in a vacuum or underwater, and can be used by soldiers for emergency field repairs. The combustible foil can also be used for detonators and heating devices.

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[15.2] MISCELLANEOUS PYROTECHNIC DEVICES

* White phosphorus was also once used as a military incendiary. Elemental phosphorus comes in two forms, a "red" amorphous form, and a "white" form arranged as tetrahedral units of four atoms. Red phosphorus is relatively easy to handle, but white phosphorus ignites spontaneously at room temperature. White phosphorus is now mainly used to generate smoke.

White phosphorus also serves a role in the most common pyrotechnic device, the safety match. The match was invented by an English chemist named John Walker (1781:1859) in 1826, when he was mixing chemicals with a small stick and accidentally scraped the stick on a rough surface. It caught fire. Walker followed up the lucky accident by developing and selling the first matches.

The basic design of the match remains much the same as Walker's original invention:

Other pyrotechnic materials are used as heating fuels, in fuzes or flares, to create smoke, fill up automotive airbags, or propel rockets. Some common pyrotechnic devices include:

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[15.3] FIREWORKS

* While fireworks may not seem like high technology, they are a highly refined art. There are two basic schools for fireworks fabrication, the Oriental and the Italian. In the US, fireworks are manufactured by a few concerns, most of which run in Italian families, such as the Zambellis and the Gruccis. Nearly all pyrotechnic materials except for high explosives are used in fireworks. The basic constituent of many fireworks is, as mentioned earlier, black powder, but flash powders and smoke-generating pyrotechnics are used as well.

Simple firecrackers and rockets are made from black powder in paper cases. Sparklers are made from a thick slurry consisting of fuels, binders, and oxidizers into which wires are dipped. Whistling fireworks use gas-generating pyrotechnics that are packed into narrow tubes that create the whistle when the gas escapes. Roman candles consist of a set of bright "stars" that generate light and color, packed into a paper tube in layers of black powder. As the black powder burns down from the top of the tube, it ignites each layer of black powder in turn, spitting out a star.

roman candle

The stars are made of mixes of pyrotechnic metals, salts, and binders such as resin and gum. Stars in oriental fireworks are rolled into shape, while Italian stars are generally made from cakes and cut into cubes. The round Oriental stars can have multiple layers, causing their appearance to change as they burn. Early stars and other illuminating elements could only obtain white and gold effects, using saltpeter. Modern stars obtain a wide range of color effects, such as:

Clever chemistry has to be employed to get the desired effects. The strontium and barium compounds aren't stable in storage, for example, and have to be synthesized through chemical reactions during the pyrotechnic process. Copper compounds will break down if the pyrotechnic process is too hot, destroying the color, so the firework has to be carefully designed to burn at a low temperature.

A "setpiece" is an obscure form of fireworks display that is undergoing something of a revival. It consists of hundreds of tubes of color-generating fireworks mounted on a wooden frame in a graphics pattern and linked with a fast-burning black powder fuse taped to the frame. The fuze sets off all the tubes quickly to generate a vivid display, and can also set off pinwheels and other fireworks attached to the display. Centuries ago, setpieces could be very elaborate, including such things as fire-spouting dragons "flying" on wires -- but such tricks are expensive, troublesome, potentially hazardous, and not seen much today.

Large skyrockets are also used in public displays. They use a black powder propellant, sometimes mixed with other pyrotechnic materials so they leave a spectacular trail, and have a payload consisting of stars or other pyrotechnic elements dispersed by a black powder bursting charge. However, the main firework for public spectaculars is the "shell". Shells can be built to produce a variety of effects:

Shells consist of a payload and a "lift charge" of black powder that lifts it into the sky. The shell is stuffed down a PVC pipe mounted in a sandbox, and lit off by an incendiary fuze or, more commonly in big fireworks displays, by an electric spark from a "squib". When the shell is fired, a time-delay fuze, or "spegette", inside the shell is lit, and burns down to set off a black-powder charge that bursts the shell and disperses the stars.

Oriental shells are spherical, while Italian shells are cylindrical. Bursting charges in Oriental shells may consist of rice hulls impregnated with black powder to increase the flash of the burst. Oriental shells are appropriate for generating symmetrical displays, such as chrysanthemums.

oriental-style spherical shell

Italian shells burst in a more irregular fashion, but they can be designed with multiple firework stages or "breaks", connected by spegettes, that detonate consecutively. For example, a three-break Italian shell might consecutively disperse a burst of red, white, and blue stars.

Italian-style cylindrical shells

Multiple-break shells can be very elaborate. The blast charge may ignite a set of stars so the shell's launch is suitably spectacular, and the stages may contain such elements as whistling pyrotechnics as well as stars.

Sophisticated fireworks displays often use elaborate control systems to sequence the ignition of fireworks, and synchronize them with sound and laser effects. One of the more interesting fields in modern fireworks are indoor fireworks displays. Such displays are used in rock concerts and other entertainments, and use conventional fireworks technology, modified with strict safety standards in mind to ensure no toxic emissions and appropriate safety for performers and audience.

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[15.4] COMMENTS, SOURCES, & REVISION HISTORY

* Although I enjoy the sciences, I wasn't fond of my chemistry classes in high school and college. Possibly the emphasis on rote learning turned me off; I recall teaching assistants in my college classes expressing a certain derision for that approach as well. However, once I decided to build a series of documents on the physical sciences, there was simply no way to avoid writing a document on chemistry.

As I worked on this document I began to realize that I didn't want to write something that was much like a conventional chemistry text. There's nothing wrong with such things, of course, but they do tend to be overkill for someone who "doesn't do chemistry for a living", for example myself. A long survey of, say, organic chemistry is pretty useless for non-chemists, involving a lot of wading through factoids that are promptly forgotten. Does anyone except a chemistry professional have the slightest need to know the IUPAC naming schemes for hydrocarbons?

The end result was that I tried to focus on history and applications, making brief references to topics such as chemical equations and organic chemistry, so vital to a formal chemistry class, in footnotes. I generally followed the line of least resistance in writing this document, taking as minimalist as possible an attitude towards topics that seemed laborious and focusing on stuff that was more like fun: "When in doubt, throw it out." It turned out that being lazy was a useful strategy, since it helped keep a focus on a readable end product for nonspecialists, instead of a dry formal text.

I don't claim that this document is a replacement for, much less superior to, a conventional chemistry text. It is targeted for readers who would find a formal text too much trouble. However, I would claim it also provides a useful background supplement for those who are working on a formal chemistry course. I will add more to it in the future as I learn new things and figure out places where I went wrong -- not being a chemist, I am certain there are a few naive statements here and there.

* Sources include:

I surfed quite a few websites for data, too many and too trivial to mention, and even found some information in TV shows on explosives and fireworks broadcast on the HISTORY CHANNEL and the DISCOVERY CHANNEL.

Somewhat to my surprise, different sources gave different, sometimes seriously different, numbers for the properties of the elements, which left me in a quandary over who to believe. I finally decided to buy a CRC HANDBOOK OF CHEMISTRY & PHYSICS to get the data -- I bought a used one, the 70th edition from 1989:1990, there being no reason to shell out the stiff price of a new one when all I wanted was basic data that's been nailed down for decades.

* As concerns copyrights and permissions for this document, all illustrations and images credited to me are public domain. I reserve all rights to my writings. However, if anyone does want to make use of my writings, just contact me, and we can chat about it. I'm lenient in giving permissions, usually on the basis of being properly credited.

* The chapters on plastics, batteries & fuel cells, and explosives & pyrotechnics were originally released as stand-alone documents:

* Revision history:

   v1.0.0 / 01 sep 07 
   v1.0.1 / 01 oct 08 / Minor cosmetic update.
   v1.1.0 / 01 sep 10 / Minor cosmetic update.
   v1.1.1 / 01 aug 12 / Corrections, cleaned up abiogenesis section.
                        Cleaned up global warming & fuels sections.
   v1.2.0 / 01 jul 14 / Climate change enhancements.
   v1.3.0 / 01 jun 16 / Review & polish.
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