grams of glucose consumes 1.00 grams of oxygen. The proper weight ratio of potassium chlorate to glucose is therefore 2.55: 0.938, and the stoichiometric mixture should be 73.1% KC10 3 and
76
Chemistry of Pyrotechnics
Components of High-Energy Mixtures
77
I
Equation:
C6 H 12 06 + 6 0 2 -> 6 CO 2 + 6 H2O
of crystallization) will evolve less heat than similar, nonhydrated moles
1
6
6
6
species due to the absorption of heat required to vaporize the wa-grams
1 80
1 92
264
108
ter present in the hydrates.
grams/gram 0
0.938
1.00
Two "hot" organic fuels are shellac and red gum. Shellac, secreted by an Asian insect, contains a high percentage of trihy-
[ Obtained by setting up the ratio
droxypalmitic acid - CH3(CH2)11(CHOH)3COOH [2]. This mole-180
X
cule contains a low percentage of oxygen and produces a high 192
1.00
heat /gram value. Red gum is a complex mixture obtained from an Australian tree, with excellent fuel characteristics and a low and solving
melting point to aid in ignition.
Charcoal is another organic fuel, and has been employed in X = (180)(1.00) = 0.938]
1 92
high-energy mixtures for over a thousand years. It is prepared by heating wood in an air-free environment ; volatile products FIG. 3.1 Calculation of oxygen demand. The quantity of oxygen are driven off and a residue that is primarily carbon remains.
consumed during the combustion of an organic fuel can be calcu-Shimizu reports that a highly-carbonized sample of charcoal lated by first balancing the equation for the overall reaction. Each showed a 91:3:6 ratio of C, 11, and 0 atoms [2].
carbon atom in the fuel converts to a carbon dioxide molecule (C0
The pyrotechnic behavior of charcoal may vary greatly de-2 ),
and every two hydrogen atoms yield a water molecule. The oxy-pending upon the type of wood used to prepare the material.
gen required to burn the fuel is determined by adding up all of The surface area and extent of conversion to carbon may vary the atoms of oxygen in the products and then subtracting the oxy-widely from wood to wood and batch to batch, and each prepara-gen atoms (if any) present in the fuel molecule. The difference is tion must be checked for proper performance [13]. Historically, the number of oxygen atoms that must be supplied by the atmos-willow and alder have been the woods preferred for the prepara-phere (or by an oxidizer). This number is then divided by 2 to tion of charcoal by black powder manufacturers.
obtain the number of
Charcoal is frequently the fuel of choice when high heat and 02 molecules needed. The coefficients can
then be multiplied by the appropriate molecular weights to obtain gas output as well as a rapid burning rate are desired. The ad-the number of grams involved.
dition of a small percentage of charcoal to a sluggish composition will usually accelerate the burning rate and facilitate ignition.
Larger particles of charcoal in a pyrotechnic mixture will produce attractive orange sparks in the flame, a property that is I
often used to advantage by the fireworks industry.
26.9% glucose by weight. An identical answer is obtained if the chemical equation for the reaction between KC1O 3 and glucose is Carbohydrates
balanced and the molar ratio then converted to a weight ratio The carbohydrate family consists of a large number of naturally-occurring oxygen-rich organic compounds. The simplest carbo-C 6H 120 6 + 4 KC1O 3 -> 6 CO2 + 6 H 2O + 4 KC1
hydrates - or "sugars" - have molecular formulas fitting the Moles :
1
4
pattern (C.H 2O)n , and appeared to early chemists to be "hy-Grams:
180
490
drated carbon." The more complex members of the family de-Weight %:
26.9
73.1
viate from this pattern slightly.
Examples of common sugars include glucose (C 6H120 6 ) , lactose The more highly oxidized - or oxygen rich - a fuel is, the (C12H22011) , and sucrose (C12H22011) . Starch is a complex poly-smaller its heat output will be when combusted. The flame tem-mer composed of glucose units linked together. The molecular perature will also be lower for compositions using the highly-ox-formula of starch is similar to (C6H1005)n, and the molecular idized fuel. Also, fuels that exist as hydrates (containing water weight of starch is typically greater than one million. Reaction e
78
Chemistry
Components
79
o f Pyrotechnics
of High-Energy Mixtures
with acid breaks starch down into smaller units. Dextrine, a found in a handbook prepared by the U.S. Army [3]. Table 3.6
widely-used pyrotechnic fuel and binder, is partially-hydrolyzed contains information on a variety of organic compounds that are starch. Its molecular weight, solubility, and chemical behavior of interest to the high-energy chemist.
may vary considerably from supplier to supplier and from batch to batch. The testing of all new shipments of dextrine is required in pyrotechnic production.
BINDERS
The simpler sugars are used as fuels in various pyrotechnic mixtures. They tend to burn with a colorless flame and give off A pyrotechnic composition will usually contain a small percentage less heat per gram than less-oxidized organic fuels. Lactose is of an organic polymer that functions as a binder, holding all of used with potassium chlorate in some colored smoke mixtures to the components together in a homogeneous blend. These bind-produce a low-temperature reaction capable of volatilizing an orers, being organic compounds, will also serve as fuels in the ganic dye with minimum decomposition of the complex dye mole-mixture.
cule. The simpler sugars can be obtained in high purity at mod-Without the binder, materials might well segregate during erate cost, making them attractive fuel choices. Toxicity prob-manufacture and storage due to variations in density and par-lems tend to be minimal with these fuels, also.
ticle size. The granulation process, in which the oxidizer, fuel, and other components are blended with the binder (and usually a suitable solvent) to produce grains of homogeneous composi-Other Organic Fuels