stoichiometric mixture is needed to generate the heat necessary Potassium chlorate, KC1O
to volatilize the dye.
3
22.0
4
Sucrose
15.0
2 KC1O
Chinoline yellow dye
42.0
3 + 3 S -> 3 SO 2 + 2 KC1
(8.1)
Magnesium carbonate, MgCO 3
21.0
grams
245
96
%
71.9
28.1
(a 2.55 to 1.00 ratio)
The reaction of potassium chlorate with a carbohydrate (e.g. , lactose) will produce carbon monoxide (CO), carbon dioxide (CO2 ) or a mixture depending on the oxidizer:fuel ratio.
The balanced
equations are given as equations 8.2 and 8. 3. (Lactose occurs The amount of heat can be controlled by adjusting the KC1O 3 : as a hydrate - one water molecule crystallizes with each lactose sugar ratio. Excess oxidizer should be avoided; it will encourage molecule.)
oxidation of the dye molecules. The quantity (and volatility) of CO
the dye will also affect the burning rate. The greater the quan-2 Product
tity of dye used, the slower will be the burning rate - the dye 8 KC10 3 + C12H22011'H20 - 8 KCI + 12 C0 2 + 12 H2O (8.2) is a diluent in these mixtures. Typical colored smoke compositions grams
980
360.3
contain 40-60% dye by weight. Table 8. 2 shows a variety of colored smoke compositions.
%
73.1
26.9
(2.72 to 1.00 ratio)
In colored smoke compositions, the volatile organic dye sub-Heat of reaction = 1.06 kcal /gram .[ 1 ]
limes out of the reacting mixture and then condenses in air to form small solid particles. The dyes are strong absorbers of CO Product:
visible light. The light that is reflected off these particles is 4 KC1O
missing the absorbed wavelengths, and the complementary hue 2 + C12H22O11 • H ZO -
4 KCl + 12 CO + 12 H 2O (8. 3)
is perceived by observers. This color-producing process is dif-grams
490
360.3
ferent from that of colored flame production, where the emitted
%
57.6
42.4
(1.36 to 1.00 ratio)
wavelengths are perceived as color by viewers. Table 7.6 lists the complementary colors for the various regions of the visible Heat of reaction = 0.63 kcal/gram [1]
spectrum.
172
Chemistry of Pyrotechnics
Smoke and Sound
173
A variety of dyes have been used in colored smoke mixtures; TABLE 8.3 Dyes for Colored Smoke Mixtures
many of these dyes are presently under investigation for carcinogenicity and other potential health hazards because of their mo-Orange 7
Solvent green 3
lecular similarity to known "problem" compounds [4]. The ma-a-xylene-a zo- S-naphthol
1, 4-di-p -toluidino-anthraquinone
terials that work best in colored smokes have several properties in common, including
1. Volatility: The dye must convert to the vapor state on heating, without substantial decomposition. Only low molecular weight species (less than 400 grams/mole) are usually used - volatility typically decreases as molecular weight increases. Salts do not work well; ionic species generally have low volatility due to the strong inter-ionic attractions present in the crystalline lattice. Therefore, functional groups such as -COO - (carboxylate ion) and
- NR +
3
(a substituted ammonium salt) can not be present.
2.
Chemical stability: Oxygen-rich functional groups (-NO 21
-SO3H) can't be present.
At the typical reaction tem-
peratures of smoke compositions, these groups are likely Disperse red 9
Violet
to release their oxygen, leading to oxidative decomposi-1-methylamino-anthraquinone
1,4-diamino-2,3-dihydroanthraquinone
tion of the dye molecules. Groups such as -NH and -NHR
2
(amines) are used, but one must be cautious of possible oxidative coupling reactions that can occur in an oxygen-rich environment.
Structures for some of the dyes used in colored smoke mixtures are given in Table 8.3.
WHITE SMOKE PRODUCTION
Chinoline yellow
Vat yellow 4
The processes used to generate a white smoke by means of a pyro-2-( 2-quinolyl)-1 , 3-indandione
dibenzo(a,h)pyrene-7,14-dione
technic reaction include:
0
1. Sublimation of sulfur, using potassium nitrate as the oxidizer: A 1:1 ratio of sulfur to KNO 3 is used in such mixtures. Caution: some toxic sulfur dioxide gas will be formed. Ignition of these mixtures must be done in a well-ventilated area.