tion, is a critical step in the manufacturing process. The sol-The number of possible organic fuels is enormous. Considera-vent is evaporated following granulation, leaving a dry, homoge-tions in selecting a candidate are:
neous material.
Dextrine is widely used as a binder in the fireworks industry.
Water is used as the wetting agent for dextrine, avoiding the 1. Extent of oxidation: This will be a primary factor in the cost associated with the use of organic solvents.
heat output /gram of the fuel.
Other common binders include nitrocellulose (acetone as the 2. Melting point: A low melting point can aid in ignitibility solvent), polyvinyl alcohol (used with water), and Laminae (an and reactivity; too low a melting point can cause produc-unsaturated polyester crosslinked with styrene -- the material tion and storage problems. 100°C might be a good mini-is a liquid until cured by catalyst, heat, or both, and no sol-mum value.
vent is required). Epoxy binders can also be used in liquid 3. Boiling point: If the fuel is quite volatile, the storage form during the mixing process and then allowed to cure to life of the mixture will be brief unless precautions are leave a final, rigid product.
taken in packaging to prevent loss of the material.
In selecting a binder, the chemist seeks a material that will 4. Chemical stability: An ideal fuel should be available com-provide good homogeneity with the use of a minimum of polymer.
mercially in a high state of purity, and should maintain Organic materials will reduce the flame temperatures of compo-that high purity during storage. Materials that are easily sitions containing metallic fuels, and they can impart an orange air-oxidized, such as aldehydes, are poor fuel choices.
color to flames if incomplete combustion of the binder occurs and 5. Solubility: Organic fuels frequently double as binders, carbon forms in the flame. A binder should be neutral and non-and some solubility in water, acetone, or alcohol is re-hygroscopic to avoid the problems that water and an acidic or quired to obtain good binding behavior.
basic environment can introduce. For example, magnesium-containing mixtures require the use of a non-aqueous binder/sol-Materials that have been used in pyrotechnic mixtures include vent system, because of the reactivity of magnesium metal to-nitrocellulose, polyvinyl alcohol, stearic acid, hexamethylenetetra -
wards water. When iron is used in a composition, pretreatment mine, kerosene, epoxy resins, and unsaturated polyester resins of the metal with wax or other protective coating is advisable, such as Laminae. The properties of most of these fuels can be especially if an aqueous binding process is used.
80
Chemistry of Pyrotechnics
Components of High-Energy Mixtures
81
RETARDANTS
3.
U.S. Army Material Command, Engineering Design Handbook, Military Pyrotechnic Series, Part Three, "Proper-Occasionally, a pyrotechnic mixture will function quite well and ties of Materials Used in Pyrotechnic Compositions,"
produce the desired effect, except for the fact that the burning Washington, D.C., 1963 (AMC Pamphlet 706-187).
rate is a bit too fast. A material is needed that will slow down 4.
R. C. Weast (Ed.), CRC Handbook o f Chemistry and the reaction without otherwise affecting performance. This can Physics, 63rd Ed., CRC Press, Inc., Boca Raton, Fla., be accomplished by altering the ratio of ingredients (e.g., re-1982.
ducing the amount of fuel) or by adding an inert component to 5.
H. Ellern, Military and Civilian Pyrotechnics, Chemical the composition. Excess metallic fuel is less effective as a "cool-Publ. Co., Inc., New York, 1968.
ant" because of the ability of many fuels - such as magnesium -
6.
T. J. Barton, et al. , "Factors Affecting the Ignition Tem-to react with the oxygen in air and liberate heat. Also, metals perature of Pyrotechnics," Proceedings, Eighth Interna-tend to be excellent heat conductors, and an increase in the tional Pyrotechnics Seminar, IIT Research Institute, metal percentage can speed up a reaction by facilitating heat Steamboat Springs, Colorado, July, 1982, p. 99.
transfer through the composition during the burning process.
7.
J. H. McLain, Pyrotechnics from the Viewpoint of Solid Materials that decompose at elevated temperatures with the State Chemistry, The Franklin Institute Press, Philadelphia, absorption of heat (endothermic decomposition) can work well Penna., 1980.
as rate retardants.
Calcium and magnesium carbonate, and so-
8.
U.S. Department of Transportation, "Hazardous Materials dium bicarbonate, are sometimes added to a mixture for this pur-Regulations," Code of Federal Regulations, Title 49, Part pose.
173.
P
heat
9.
U.S. Army Material Command, Engineering Design Hand-CaCO 3 (solid)
CaO (solid) + CO 2 (gas)
book, Military Pyrotechnic Series, Part One, "Theory and 2 NaHCO
Application," Washington, D.C., 1967 (AMC Pamphlet 706-3
(solid) --> Na 20 (solid) + H 2O (gas) + 2 CO 2 (gas) 185).
However, gas generation occurs that may or may not affect the 10.
D. Price, A. R. Clairmont, and I. Jaffee, "The Explosive performance of the mixture.
Behavior of Ammonium Perchlorate," Combustion and Flame, Although endothermic, these reactions are thermodynamically 11, 415 (1967).
spontaneous at high temperature due to the favorable entropy 11.
R. Lancaster, Fireworks Principles and Practice, Chemical change associated with the formation of random gaseous prod-Publ. Co., Inc., New York, 1972.
ucts from solid starting materials.
12.
U.S. Consumer Product Safety Commission, "Fireworks De-Inert diluents such as clay and diatomaceous earth can also vices," Code of Federal Regulations, Title 16, Part 1507.
be used to retard burning rates. These materials absorb heat J. E. Rose, "The Role of Charcoal in the Combustion of I
13.
and separate the reactive components, thereby slowing the py-Black Powder," Proceedings, Seventh International Pyro-rotechnic reaction.
technics Seminar, IIT Research Institute, Vail, Colorado, July, 1980, p. 543.
REFERENCES
1.
A. A. Shidlovskiy, Principles of Pyrotechnics, 3rd Ed., Moscow, 1964. (Translated by Foreign Technology Division, Wright-Patterson Air Force Base, Ohio, 1974.) 2.
T. Shimizu, Fireworks - The Art, Science & Technique,
pub. by T. Shimizu, distrib. by Maruzen Co. , Ltd., Tokyo, 1981.
a