Pyrotechnic

Pyrotechnics are materials that differ from explosives and propellants in their lower reaction rate and less gas production. P5o-otechnics usually consist of a mixture of two ingredients a fuel and an oxidizer. Generally, the fuels are metals and the oxidizers are either salts or metal oxides. 

In both explosives and propellants the materials are relatively non-porous. The binders and plasticizers used effectively fill the pore spaces. Pyrotechnics are porous and the heat transfer related to the hot gas permeation into the reactant material mixture becomes important. In many pyrotechnics no binders or plasticizers are used. The explosives and propellants have burning (or detonation) rates that depend on density, temperature, and pressure. However, the burning rates of pyrotechnics are, in addition, affected by porosity, particle sizes, purity, homogeneity (degree of mixing), and stoichiometry (fuel or oxidizer ratio). 

The big environmental and health concerns led to the avoidance of many substances that have been used in the past in p5TOtechnic mixtures. These include beryllium, cadmium, mercury, chromates, lead compounds, and many others. 

Pyrotechnics are divided into five major production categories sound, light, heat, smoke, and delay. 

The term pyrotechnics is defined in the Explosive Control Law in Japan as those items manufactured with propellants or explosives to meet a certain purpose 5). The materials having pyrotechnical effects are called pyrotechnics in general. Pyrotechnical effects refer to the emission of heat, light, flame, sound, gas or smoke. The terms pyrotechnic compositions or pyrotechnic mixtures are broadly used. These terms refer to the raw materials for the production of pyrotechnics. Recommendations on the Transport of Dangerous Goods of United Nations c defines pyrotechnic substance as follows  

The term pyrotechnics in English also means the technology of pyrotechnics and is defined as technology to utilize chemically-generated light, heat or sound for amusement, utility or warfare 7).  

Pyrotechnic compositions or mixtures, which are usually combinations of oxidizing and combustible materials, generate heat when they react The material or mixture which generates a large amount of heat through such reaction is called an energetic material or an energetic mixture . 

The fuels consist of resins, charcoal, and sulfur. A typical aerial display shell used in fireworks is shown in Fig. 14.1. The black powder is the propellant which fires the shell to suitable heights. A fuse ignites and fires the various compartments to provide the colors and flashes in sequence. 

See Iron Pigments, inorganic Sulfur Sulfuric acid and sulfur trioxide. 

Pyrotechnics is based on the estabflshed principles of thermochemistry and the more general science of thermodynamics. There has been Httle work done on the kinetics of pyrotechnic reactions, largely due to the numerous chemical and nonchemical factors that affect the bum rate of a pyrotechnic mixture. Information on the fundamentals of pyrotechnics have been pubflshed in Russian (1) and English (2—6). Thermochemical data that ate useful in determining the energy outputs anticipated from pyrotechnic mixtures are contained in general chemical handbooks and more specialized pubHcations (7-9). 

A pyrotechnic composition contains one or more oxidizers in combination with one or more fuels. Oxidizers used in pyrotechnics, such as potassium nitrate, KNO, are soflds at room temperature and release oxygen when heated to elevated temperatures. The oxygen then combines with the fuel, and heat is generated by the resulting chemical reaction. Chemicals that release fluorine or chlorine on heating, such as polytetrafluoroethylene (Teflon) 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Other typical pyrotechnic fuels include charcoal, sulfur, boron, siUcon, and synthetic polymers such as poly(vinyl alcohol) and poly(vinyl chloride). Extensive use has been made of natural products such as starches and gums, and the use of these materials continues to be substantial in the fireworks industry. MiUtary pyrotechnics have moved away from the use of natural products due to the inherent variabiUty in these materials depending on climatic conditions during the growth of the plants from which the compounds are derived. 

Fuel Formula Specific impulse with different oxidizers /N s kg-1  

The name pyrotechnic is derived from the Greek words pyr (fire) and techne (an art), which describes the effect observed from a burning pyrotechnic composition. These effects include the production of coloured smoke, noise, and the emission of bright-coloured light. Pyrotech- 

Pyrotechnics are very similar to explosive and propellant compositions. Explosives perform at the highest speed of reaction producing gaseous products, propellants are gas generators and perform at a slower speed than explosives, and pyrotechnics react at visibly observable rates with the formation of solid residues. 

Pyrotechnic compositions contain a fuel and an oxidizer which is specifically formulated to produce a lot of energy. This energy is then used to produce a flame or glow (i.e. a matchstick), or combined with other volatile substances to produce smoke and light (i.e. fireworks), or to produce large quantities of gas (firework rockets and bangers). 

The materials which are used in this field may be classified from the standpoint of use and storage as follows  

Sporting ammunition describes rifle and handgun ammunition for hunting and target practice. Commercial hunting bullets, ranging in size from around 6 to 12mm, may differ from the conical shape of military bullets in that they 

Artillery ammunition for guns, howitzers, cannons, and mortars ranges upwards in calibre from the 20mm limit that generally divides it from small-arms ammunition. Artillery ammunition is divided into three types  

Large-calibre artillery ammunition permits a more complex payload including high explosives, bursters, shrapnel, bursting charges, fuzes, incendiaries, etc. 

In addition to catalysts, stabilizers, opacifiers (to reduce heat radiation ahead of the flame), flash depressants, plasticizers, and binders, the main fuel and oxidizers for rocket propellants include 

While the term missile can apply to any projectile ammunition, guided missiles describes those rockets whose course or trajectory is controlled electronically by computers and communications equipment. 

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Amorphous boron is used in pyrotechnic flares to provide a distinctive green color, and in rockets as an igniter. 

Strontium is softer than calcium and decomposes in water more vigorously. It does not absorb nitrogen below 380oC. It should be kept under kerosene to prevent oxidation. Freshly cut strontium has a silvery appearance, but rapidly turns a yellowish color with the formation of the oxide. The finely divided metal ignites spontaneously in air. Volatile strontium salts impart a beautiful crimson color to flames, and these salts are used in pyrotechnics and in the production of flares. Natural strontium is a mixture of four stable isotopes. 

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