Heat and Delay Compositions
141
Shuttle.
The pyrotechnic boosters used for these launches typi-4.
U.S. Army Material Command, Engineering Design Handbook, cally contain
Military Pyrotechnic Series, Part One, "Theory and Application, " Washington, D . C . , 1967 (AMC Pamphlet 706-185).
1.
A solid oxidizer:
Ammonium perchlorate (NH,,C1O,,) is the
5.
J. R. Partington, A History of Greek Fire and Gunpowder, current favorite due to the high percentage of gaseous W. Heffer & Sons, Ltd., Cambridge, England, 1960.
products it forms upon reaction with a fuel.
6.
G. D. Barrett, "Venting of Pyrotechnics Processing Equip-2.
A small percentage of light, high-energy metaclass="underline" This
ment," Proceedings, Explosives and Pyrotechnics Applica-metal produces solid combustion products that do not aid tions Section, American Defense Preparedness Assn. , Los in achieving thrust, but the considerable heat evolved by Alamos, New Mexico, October, 1984.
the burning of the metal raises the temperature of the 7.
"Military Explosives, " U.S. Army and U.S. Air Force Tech-other gaseous products. Aluminum and magnesium are nical Manual TM 9-1300-214, Washington, D.C. , 1967.
the metals most commonly used.
8.
R. F. Gould (Ed.), Advanced Propellant Chemistry, American 3.
An organic fuel that also serves as binder and gas-former: Chemical Society Publications, Washington, D.C. , 1966.
Liquids that polymerize into solid masses are preferred, for simpler processing, and a binder with low oxygen content is desirable to maximize heat production.
A negative oxygen balance is frequently designed into these propellant mixtures to obtain CO gas in place of CO 2 .
CO is
lighter and will produce greater thrust, all other things being equal.
However, the full oxidation of carbon atoms to CO 2 evolves more heat, so some trial-and-error is needed to find the optimum ratio of oxidizer and fuel [8].
Propellant compositions are also used in numerous "gas generator" devices, where the production of gas pressure is used to drive pistons, trigger switches, eject pilots from aircraft, and perform an assortment of other critical functions. The military and the aerospace industry use many of these items, which can be designed to function rapidly and can be initiated remotely.
REFERENCES
1.
F. L. McIntyre, A Compilation of Hazard and Test Data for Pyrotechnic Compositions," Report ARLCD-CR-80047, U.S.
Army Armament Research and Development Command, Dover, NJ, 1980.
2.
J. H. McLain, Pyrotechnics from the Viewpoint of Solid State Chemistry, The Franklin Institute Press, Philadelphia, Penna., 1980
3.
A. A. Shidlovskiy, Principles of Pyrotechnics, 3rd Ed., Moscow, 1964. (Translated by Foreign Technology Division, Wright-Patterson Air Force Base, Ohio, 1974.)
A "weeping willow" aerial shell bursts high in the sky and leaves its characteristic pattern as the large, slow-burning stars descend to the ground. Charcoal is frequently used to produce the attractive gold color, with potassium nitrate selected as the oxidizer to achieve a slow-burning mixture. (Zambelli Internationale)
7
COLOR AND LIGHT PRODUCTION
The production of bright light and vivid color is the primary purpose of many pyrotechnic compositions. Light emission has a variety of applications, ranging from military signals and highway distress flares to spectacular aerial fireworks. The basic theory of light emission was discussed in Chapter 2, and several good articles have been published dealing with the chemistry and physics of colored flames [1, 21.
The quantitative measurement of light intensity (candle power) at any instant and the light integral (total energy emitted, with units of candle-seconds/gram) can be affected by a variety of test parameters such as container diameter, burning rate, and the measuring equipment. Therefore, comparisons between data obtained from different reports should be viewed with caution.
WHITE LIGHT COMPOSITIONS
For white-light emission, a mixture is required that burns at high temperature, creating a substantial quantity of excited atoms or molecules in the vapor state together with incandescent solid or liquid particles. Incandescent particles emit a broad range of wavelengths in the visible region of the electromagnetic spectrum, and white light is perceived by the viewer. Intense emission from sodium atoms in the vapor state, excited to higher-energy electronic states by high flame temperature, is the principal light source in the sodium nitrate /magnesium /organic binder flare compositions widely used by the military [3, 41.
143
144
Chemistry of Pyrotechnics
Color and Light Production
145
Magnesium or aluminum fuels are found in most white-light com-fireworks mixtures. Several published formulas for white light positions. These metals evolve substantial heat upon oxidation, compositions are given in Table 7.1.
and the high-melting magnesium oxide (MgO) and aluminum oxide The ratio of ingredients, as expected, will affect the perform-
(A1203 ) reaction products are good light emitters at the high re-ance of the composition. Optimum performance is anticipated near action temperatures that can be achieved using these fuels. Ti-the stoichiometric point, but an excess of metallic fuel usually in-tanium and zirconium metals are also good fuels for white-light creases the burning rate and light emission intensity. The addi-compositions.
tional metal increases the thermal conductivity of the mixture, In selecting an oxidizer and fuel for a white-light mixture, a thereby aiding burning, and the excess fuel - especially a vola-main consideration is maximizing the heat output. A value of 1.5
tile metal such as magnesium (boiling point 1107°C) - can vapor-kcal/gram has been given by Shidlovskiy as the minimum for a ize and burn with oxygen in the surrounding air to produce extra usable illuminating composition [5]. A flame temperature of less heat and light. The sodium nitrate/magnesium system is exten-than 2000°C will produce a minimum amount of white light by emis-sively used for military illuminating compositions. Data for this sion from incandescent particles or from excited gaseous sodium system are given in Table 7.2.
atoms.
The anticipated reaction between sodium nitrate and magnesium Therefore, the initial choice for an oxidizer is one with an is
exothermic heat of decomposition such as potassium chlorate (KC1O
5 Mg + 2 NaNO 3 -> 5 MgO + Na2O + N 2
3). However, mixtures of both chlorate and perchlorate salts with active metal fuels are too ignition-sensitive for commer-grams 121.5