45
ganic dye is a fascinating pyrotechnic problem. The military II. Potassium chlorate, KC1O 3
45
1
and the fireworks and entertainment industries rely on this tech-Naphthalene, C 10 H8
40
nique for the generation of copious quantities of brilliantly-col-Charcoal
15
ored smoke.
The requirements for an effective colored-smoke composition III. Potassium perchlorate, KC10 4
56
2
include
Sulfur
11
Anthracene, C1,,H 10
33
1. The mixture must produce sufficient heat to vaporize the IV. Hexachloroethane, C 2C16
62
2
dye, as well as produce a sufficient volume of gas to dis-Magnesium
15
perse the dye into the surrounding space.
Naphthalene (or anthracene)
23
2. The mixture must ignite at a low temperature and continue to burn smoothly at low temperature (well below 1000°C).
If the temperature is too high, the dye molecules will decompose and the color quality as well as volume of the smoke will deteriorate. Metal fuels are not used in col-in the vaporized material. The vaporized component, which was ored smoke mixtures because of the high reaction tempera-part of the original mixture, then condenses as fine, solid parti-tures they produce.
cles upon leaving the reaction zone and a smoke is created. Or-3. Although a low ignition temperature is required, the smoke ganic dyes, ammonium chloride, and sulfur can be used to create mixture must be stable during manufacturing and storage, smokes using this method.
over the expected range of ambient temperatures.
Alternately, the pyrotechnic reaction can occur in a separate 4. The molecules creating the colored smoke must be of low container, and the heat that is produced volatilizes a smoke-form-toxicity (including low carcinogenicity). Further, they ing component contained in an adjacent compartment. The vapor-must readily sublime without decomposition at the tem-ization and dispersion of heavy oils to create white smoke uses perature of the pyrotechnic reaction to yield a dense this technique.
smoke of good color quality [3].
Finally, a product of a pyrotechnic reaction may vaporize from the reaction zone and subsequently condense as fine particles in air, creating a smoke. Potassium chloride (boiling point 1407°C) When requirements that include low ignition temperature and produces smoke in many potassium chlorate and potassium per-reliable propagation of burning at low reaction temperature are chlorate compositions, although smoke is usually not a goal sought considered, the choice of oxidizer rapidly narrows to one candi-from these mixtures.
date - potassium chlorate, KC10 3 . The ignition temperature of A good white smoke can be obtained by the formation of zinc potassium chlorate combined with sulfur or many organic fuels chloride, ZnC1
is below 2500C. Good heat production is achieved with such mix-2, from a reaction between zinc metal and a chlorinated organic compound (the chlorine-containing species serves tures, in part due to the exothermic decomposition of KC1O 3 at a as the oxidizer). Reaction products that strongly attract mois-temperature below 400°C, forming KCl and oxygen gas.
ture (such as ZnCl
A mixture consisting of 70% KC1O
2 ) will have an enhanced smoke effect in humid 3 and 30% sugar ignites at
atmospheres. The burning of elemental phosphorus, producing 220°C and has a heat of reaction of approximately 0. 8 kcal /gram
170
Chemistry o f Pyrotechnics
Smoke and Sound
171
[5]. Both chlorate-sulfur and chlorate-sugar mixtures are used TABLE 8.2
Colored Smoke Compositions
in commercial colored smoke compositions. Sodium bicarbonate (NaHCO 3) is added to KC1O 3 /S mixtures to neutralize any acidic
% by
impurities that might stimulate premature ignition of the compo-Composition
weight
Reference
sition, and it also acts as a coolant by decomposing endothermi-cally to evolve carbon dioxide gas (CO 2) . Magnesium carbonate Green smoke
(MgCO 3 ) is also used as a coolant, absorbing heat to decompose Potassium chlorate, KC1O 3
25.4
8
into magnesium oxide (MgO) and C0 2. The amount of coolant Sulfur
10.0
can be used to help obtain the desired rate of burning and the Green dye
40.0
correct reaction temperature - if a mixture burns too rapidly, Sodium bicarbonate, NaHCO
more coolant should be added.
3
24.6
The ratio of oxidizer to fuel will also affect the amount of Red smoke
heat and gas that are produced. A stoichiometric mixture of Potassium chlorate, KC1O 3
29.5
8
KC1O
Lactose
18.0
3 and sulfur (equation 8.1) contains a 2.55:1 ratio of oxidizer to fuel, by weight. Colored smoke mixtures in use today Red dye
47.5
contain ratios very close to this stoichiometric amount.
The
Magnesium carbonate, MgCO 3
5.0
chlorate /sulfur reaction is not strongly exothermic, and a New yellow smoke