HEAT PRODUCTION
The use of incendiary mixtures in warfare can be traced back to ancient times, when it provided an effective means of assaulting well-fortified castles. Naval warfare was revolutionized by the use of flaming missiles to attack wooden ships, and much effort was put into improving the heat output, portability, and accuracy of these thermal weapons.
As both weaponry and the use of explosives for blasting developed, the need for a safe, reliable way to ignite these devices became obvious, and the concept of a pyrotechnic "delay" emerged. A variety of terms are used for materials that either ignite or provide a delay period between ignition of a device and the production of the main explosive or pyrotechnic effect. These include
1. Fuse: A train of slow-burning powder (usually black pow- der), often covered with twine or twisted paper. Fuses are lit by a safety match or other hot object, and provide a time delay to permit the person igniting the device to retreat to a safe distance.
2. Electric Match (Squib) : A metal wire is coated with a dab of heat-sensitive composition. An electric current is passed through the wire, and the heat that is produced ignites the match composition. A burst of flame occurs that ignites a section of fuse or a charge of pyrotechnic composition. Squib compositions usually contain potassium chlorate (low ignition temperatures! ). Lead mononitroresorcinate (LMNR) is also included in many squib mixtures. Several squib formulas are listed in Table 1.
TABLE 1. Electric Match (Squib) Compositions
3. First Fire: An easily-ignited composition is placed in limited quantity on top of the main pyrotechnic mixture. The first fire is reliably ignited by a fuse or squib, and the flame and hot residue that is produced then ignites the main charge. Black powder moistened with water containing a binder such as dextrine is used in the fireworks industry as a first fire, and also secures the fuse to the item. First fires are often referred to as "primes" - a term similar to another with a distinct meaning).
4. Delay Composition: A general term for a mixture that burns at a selected, reproducible rate, providing a time delay between activation and production of the main effect. A fuse containing a core of black powder is an example of a delay. Highly-reproducible delay mixtures are needed for military applications, and much research effort has been put into developing reliable compositions.
5. Primer: A term for the device used to ignite smokeless powder in small arms ammunition. An impactsensitive composition is used. When struck by a metal firing pin, a primer emits a burst of flame capable of igniting the propellant charge. Several typical primer mixtures are given in Table 2.
TABLE 2. Typical Primer Mixtures
6. Friction Igniter: A truly "self-contained" device should be ignitible without the need for a safety match or other type of external ignition source. Highway flares (fusees), other types of distress signals, and some military devices use a friction ignition system. The fusee uses a two-part igniter; when the two surfaces are rubbed together, a flame is produced and the main composition is ignited. Typically, the scratcher portion of these devices contains red phosphorus and the matchhead mixture contains potassium chlorate (KC1O 3 ) and a good fuel. Several friction igniter systems are given in Table 3.
TABLE 3. Friction Igniter Mixtures