cussions of materials and factors that affect performance tion of the degree of confinement. Increased confinement leads to accelerated burning. Shimizu reports a burning 1. The composition produces the desired effect and is efficient rate in air of .03-.05 meters/second for black powder paste both in terms of effect /gram and effect /dollar.
impregnated in twine. The same material, enclosed in a
9 4
Chemistry of Pyrotechnics
Pyrotechnic Principles
95
2. The composition can easily and safely be manufactured, large quantities of bulk powder are present in one location, and handled, transported, stored, and used, assuming nor-if accidental ignition should occur, there is a good chance that mal treatment and the expected variations in temperature.
an explosive reaction rate may be reached.
3. Storage lifetime is acceptable, even in humid conditions, For this reason, mixing and drying operations should be iso-and there is reasonably low toxicity associated with both lated from all other plant processes, and remote control equip-the starting materials and reaction products.
ment should be used wherever and whenever possible. All high-energy manufacturing facilities should be designed with the idea in mind that an accident will occur at some time during the life These requirements seem rather simple, but they do restrict of the facility. The plant should be designed to minimize any or eliminate a number of potential starting materials. These com-damage to the facility, to the neighborhood, and most impor-pounds must either be deleted from our "acceptable" list or spe-tantly, to the operating personnel.
cial precautions must be taken in order to use them. Examples The manufacturing operation can be divided into several include
stages
1. Preparation of the individual components: Materials to be Potassium dichromate (K 2Cr2O ): This is a strong oxidizer, used in the manufacturing process may have to be dried, as well 7
but it only contains 16% oxygen by weight. It has a cor-as ground or crushed to achieve the proper particle size, or rosive effect on the mucous membranes, and its toxicity screened to separate out large particles or foreign objects. Ox-and suspected carcinogenicity suggest the use of alternate idizers should never be processed with the same equipment used oxidizers.
for fuels, nor should oxidizers and fuels be stored in the same Ammonium perchlorate (NH,,ClO,,): This is a good oxidizer, and area prior to use. All materials must be clearly labeled at all can be used to make excellent propellants and colored times.
flames. However, it is a self-contained oxidizer-fuel sys-2. Preparation o f compositions:
This step is the key to
tem (much like ammonium nitrate). The mixing of NH +
proper performance. The more homogeneous a mixture is, the 4
(fuel) and C1O -
greater its reactivity will be. The high-energy chemist is al-a
(oxidizer) occurs at the ionic level. The
potential for an explosion cannot be ignored. Conclusion: ways walking a narrow line in this area, however. By maxi-if this material is used, it must be treated with respect mizing reactivity - with small particle sizes and intimate mix-and minimum quantities of bulk powder should be pre-ing - you are also increasing the chance of accidental ignition pared.
during manufacturing and storage. A compromise is usually Magnesium metal ( Mg) : This is an excellent fuel and produces reached, obtaining a material that performs satisfactorily but is brilliant illuminating mixtures. The metal is water-reactive reasonably safe to work with. This compromise is reached by however, suggesting short shelf-life and possible sponta-careful specification of particle size, purity of starting materi-neous ignition if magnesium-containing mixtures become als, and safe operating procedures.
wet. Conclusion: replace magnesium with the more stable A variety of methods can be used for mixing. Materials can aluminum (or possibly titanium) metals. If magnesium gives be blended through wire screens, using brushes. Hand-screen-the best effect, coat the metal with an organic, water-re-ing is still used in the fireworks industry, but should never be pelling material.
used with explosive or unstable mixtures. Brushes provide a safer method of screening the oxidizer and fuel together. Materials can also be tumbled together to achieve homogeneity, and PREPARATION OF HIGH-ENERGY MIXTURES
this can (and should) be done remotely. Remote mixing is strongly recommended for sensitive explosive compositions such as the The most hazardous operations in the high-energy chemistry field
"flash and sound" powder used in firecrackers and salutes and involve the mixing of oxidizer and fuel in large quantities, and the the photoflash powders used by the military.
subsequent drying of the composition (if water or other liquid is 3. Granulation : Following mixing, the powders are often used in the mixing and granulating processes). In these operations, granulated, generally using a small percentage of binder to aid
9 6
Chemistry of Pyrotechnics
in the process. The composition is treated with water or an organic liquid (such as alcohol), and then worked through a large-mesh screen. Grains of well-mixed composition are produced which will retain the homogeneity of the composition better than loose powder.
Without the granulation step, light and dense materials might segregate during transportation and storage. The granulated material is dried in a remote, isolated area, and is then ready to be loaded into finished items. Remember: Sizable quantities of bulk powder are present at this stage, and the material must be protected from heat, friction, shock, and static spark.
4.
Loading:
An operator, working with the minimum quantity of bulk powder, loads the composition into tubes or other containers, or produces pellets for later use in finished items. The making of "stars" - small pieces of color-producing composition used in aerial fireworks - is an example of this pelleting operation.
5.
Testing:
An important final step in the manufacturing process is the continual testing of each lot of finished items to ensure proper performance. Significant differences in performance can be obtained by slight variation in the particle size or purity of any of the starting materials, and a regular testing program is the only way to be certain that proper performance is being achieved.
REFERENCES
1.
T. L. Davis, The Chemistry of Powder and Explosives, John Wiley & Sons, Inc. , New York, 1941.
2.
U.S. Army Material Command, Engineering Design Handbook, Military Pyrotechnic Series, Part One, "Theory and Application," Washington, D.C. , 1967 (AMC Pamphlet 706-185).
3.
A. A. Shidlovskiy, Principles of Pyrotechnics, 3rd Ed. , A magnesium-containing flare burns with a brilliant white flame in Moscow, 1964. (Translated by Foreign Technology Division, the test tunnel of the Applied Sciences Department, Naval Weapons Wright-Patterson Air Force Base, Ohio, 1974.) Support Center, Crane, Indiana. Special instrumentation can mea-4.
T. Shimizu, Fireworks from a Physical Standpoint, Part One, sure the intensity of the light output as a function of wavelength.
( trans. by A. Schuman), Pyrotechnica Publications, Austin,
"White light" compositions emit throughout the visible region of the Texas, 1982.