Pyrotechnics heat-producing

Heat-producing pyrotechnic compositions are used in a variety of applications, for example, as first fires in pyrotechnic devices to ignite other materials, as primers, as heat generators in pyrotechnic heaters, as propellants in gas generators and rocket motors, and as incendiary devices. 

Pyrotechnic compositions which are used in primers or first fires are very sensitive to initiation, whereas compositions which are used in heat-generating devices are less sensitive. The sensitivity of the compositions can be controlled by reducing the amount of oxidizer and choosing a less sensitive oxidizer. 

---

An electric match consists of a high resistance bridge wire surrounded by a heat sensitive pyrotechnic composition. When an electric current is appiied through the leg wires, the bridge wire heats up and ignites the pyrotechnic composition. This produces a small burst of fire, not unlike that from a safety match. 

In a manner that closely parallels the creation of aerosols for obscuration or signaling, one can also form aerosols of definite chemical entities. As a rule, the substance that is to be evaporated and recondensed is mixed with the heat- and gas-producing pyrotechnic mixture. Exceptionally, the evaporated substance derives from a chemical chaise within the heat-producing system. Arrangements where a gaseous heat source or gas itself furnishes a physically separate dispersing force fall under a subject treated in the next chapter on nonspecific gases. 

Direct creation of steam within dj pyrochemical system seems to belong in the category of unsolved p/oblems because of the enormous cooling effect of the evaporating water. The term direct creation out of the pyrotechnic-system ptx>per is used, since the application encased high heat producers to create steam for driving underwater projectiles, for instance, is quite another matter and has been proposed and patented. ... 

The thermodynamics of these metathesis reactions are well illustrated by further consideration of the M0S2 system. The large amount of heat produced in this reaction, emphasized by the accompanying pyrotechnic display (iO), can be quantified from a Hess s law calculation where the heat of the reaction is -213 kcal/mole 11). (Bomb calorimetry... 

Propellants and explosives are chemical compounds or mixtures that rapidly produce large volumes of hot gases when properly initiated. Propellants bum at relatively low rates measured in centimeters per second explosives detonate at rates of kilometers per second. Pyrotechnic materials evolve large amounts of heat but much less gas than propellants and explosives (see Pyrotechnics). 

Strontium Peroxide. Commercial strontium peroxide contains about 85% Sr02 and 10% active oxygen. It can be made by heating strontium oxide ia the preseace of oxygea gas uader 20 MPa (200 atm) pressure, or by reactiag a soluble stroatium salt with hydrogea peroxide. The only substantial appHcation for this compound is ia pyrotechnics (qv). Strontium peroxide [1314-18-7] produces a red color ia flames. 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

Pyrotechnics which burn to produce heat, smoke, light and/or noise. 

To produce this type of atomic emission in a pyrotechnic system, one must produce sufficient heat to generate atomic vapor in the flame, and then excite the atoms from the ground to various possible excited electronic states. Emission intensity will increase as the flame temperature increases, as more and more atoms are vaporized and excited. Return of the atoms to their ground state produces the light emission. A pattern of wavelengths, known as an atomic spectrum, is produced by each element. This pattern - a series of lines - corresponds to the various electronic... 

Alternatdy, the pyrotechnic reaction can occur in a separate container, and the heat that is produced volatilizes a smoke-forming component contained in an adjacent compartment. The vaporization and dispersion of heavy oils to create white smoke uses this technique. 

Volatilization of oil A pyrotechnic reaction produces the heat needed to vaporize high molecular weight hydrocarbons. The subsequent condensation of this oil in air creates a white smoke cloud. The toxicity of this smoke is probably the least of all the materials discussed here. 

The pyrotechnic phenomena of heat, smoke, noise, and motion are reasonably easy to comprehend. Heat results from the rapid release of energy associated with the formation of stable chemical bonds during a chemical reaction. Smoke is produced by the dispersion in air of many small particles during a chemical reaction. 

In addition to an oxidizer, pyrotechnic mixtures will also contain a good fuel - or electron donor - that reacts with the liberated oxygen to produce an oxidized product plus heat. This heat will enable the high-energy chemist to produce any of a variety of possible effects - color, motion, light, smoke, or noise. 

All pyrotechnic compositions evolve heat upon ignition, and this release of energy can be used to produce color, motion, smoke, and noise. There are applications as well for the chemically-produced heat itself, and these will be addressed in this chapter. 

Pyrotechnic mixtures An oxidizer/fuel mixture that produces bright or colored lights, heat, fogs, or acoustic effects. 

---