2. Combustion of phosphorus: White or red phosphorus burns to produce various oxides of phosphorus, which then attract moisture to form dense white smoke. Research and
174
Chemistry of Pyrotechnics
Smoke and Sound
175
TABLE 8.4 White Smoke Compositions
4.
Formation of zinc chloride ("HC Smokes"): A reaction of
the type
by
Refer-
C x Cly + y/2 Zn } x C + y/2 ZnC1 2 + heat
Composition
weight
Note
ence
produces the zinc chloride vapor, which condenses in air I.
Hexachloroethane, C
and attracts moisture to create an effective white smoke.
2C1 6
45.5
HC type C
6
Zinc oxide, ZnO
47.5
These mixtures have been widely used for over forty years Aluminum
7.0
with an excellent safety record during the manufacturing process.
However, ZnC1 2 can cause headaches upon con-II.
Hexachlorobenzene, C 6 C1 6
34.4
Modified HC
6
tinued exposure and replacements for the HC smokes are Zinc oxide, ZnO
27.6
actively being sought due to health concerns relating to Ammonium perchlorate, NH,,C10,,
24.0
the various reaction products.
Zinc dust
6.2
The original HC smoke mixtures (Type A) contained Laminac
7.8
zinc metal and hexachloroethane, but this composition is III.
Red phosphorus
63
Under de-
extremely moisture- sensitive and can ignite spontaneously 8
if moistened.
An alternative approach involves adding a
Butyl rubber, methylene
37
velopment
small amount of aluminum metal to the composition, and chloride
zinc oxide (ZnO) is used in place of the moisture-sensi-IV.
Red phosphorus
51.0
4
tive metal.
Upon ignition, a sequence of reactions en-
Magnesium
10.5
sues of the type [6]
Manganese dioxide, MnO,
32.0
Magnesium oxide, MgO
1.5
2 Al + C 2 C1 6 } 2 AIC1 3 + 2 C
(8.4)
Microcrystalline wax
5.0
2 A1C1 3 + 3 ZnO -> 3 ZnC1 2 + A1 2 0 3
(8.5)
V.
Potassium nitrate, KNO 3
48.5
Contains
9
ZnO + C -* Zn + Co
(8.6)
Sulfur
48.5
arsenic
Arsenic disulfide, As
3 Zn + C
2 S 2
3.0
2 C1 6 - 3 ZnCl 2 + 2 C
(8.7)
Alternatively, the original reaction has been proposed to be [ 7]
2 Al + 3 ZnO - 3 Zn + A1 2O 3
(8.8)
In either event, the products are ZnCl
development work relating to red phosphorus-based smoke 2 , CO, and A1 20 3 .
The zinc oxide cools and whitens the smoke by consuming mixtures is actively being pursued to find substitutes for atomic carbon in an endothermic reaction that occurs spon-the zinc chloride smokes. A typical red phosphorus mix-taneously above 1000°C (equation 8.6). The reaction with ture is given in Table 8.4. An explosive bursting charge aluminum (equation 8.4 or 8.8) is quite exothermic, and is often used with the very-hazardous white phosphorus.
this heat evolution controls the burning rate of the smoke Caution :
Phosphorus-based smokes generate acidic com-
mixture.
A minimum amount of aluminum metal will yield pounds which may be irritating to the eyes, skin, and the best white smoke. Several "HC" smoke compositions respiratory tract.
are listed in Table 8.4.
3.
Volatilization of oiclass="underline"
A pyrotechnic reaction produces the
5.
"Cold Smoke":
White smoke can also be achieved by non-
heat needed to vaporize high molecular weight hydrocar-thermal means. A beaker containing concentrated hydro-bons. The subsequent condensation of this oil in air cre-chloric acid placed near a beaker of concentrated ammonia ates a white smoke cloud. The toxicity of this smoke is will generate white smoke by the vapor-phase reaction probably the least of all the materials discussed here.