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Chapter Seventeen: The Chemistry of Pyrotechnics
Most pyrotechnic mixtures follow a very simple set of chemical
rules. We'll go over those now. Most mixtures contain an oxidizing
agent, which usually produces oxygen used to burn the mixture, and a
reducing agent, which burns to produce hot gasses. In addition, there
can be coloring agents to impart a color to the fire, binders, which
hold the mixture in a solid lump, and regulators that speed up or slow
down the speed at which the mixture burns. These are not all the
possibilities, but they cover most all cases.
Oxidizing agents, such as nitrates, chlorates, and perchlorates
provide the oxygen. They usually consist of a metal ion and the
actual oxidizing radical. For example, Potassium Nitrate contains a
metal ion (Potassium) and the oxidizing radical (the Nitrate).
Instead of potassium, we could instead substitute other metals,
like sodium, barium, or strontium,
and the chemical would still supply oxygen to the burning mixture. But
some are less desirable. Sodium Nitrate, for example, will absorb moisture
out of the air, and this will make it harder to control the speed
at which the mixture will burn.
In the following examples, we'll use the letter "X" to show the
presence of a generic metal ion.
Note that Nitrates are stingy with the oxygen that they give up. They
only give one third of what they have.
Some Some
Nitrate Nitrite Oxygen
2XNO ---> 2XN0 + O
3 2 2
Chlorates are very generous, on the other hand. They give up all
the oxygen they have. Furthermore, they give it up more easily. It
takes less heat, or less shock to get that oxygen loose. Mixtures
using chlorates burn more spectacularly, because a smaller volume of
the mix needs to be wasted on the oxidizer, and the ease with which the
oxygen is supplied makes it burn faster. But the mixture is also MUCH more
sensitive to shock.
Some Some
Chlorate Chloride Oxygen
2XClO ---> 2XCl + 3O
3 2
Perchlorates round out our usual set of oxidizing tools.
Perchlorates contain even more oxygen than Chlorates, and also give it
all up. However, they are not as sensitive as the Chlorates, so they
make mixtures that are "safer". That is, they're less likely to explode
if you drop or strike them.
Some Some
Perchlorate Chloride Oxygen
XClO ---> XCl + 2O
4 2
Reducing agents, like sulfur and charcoal (carbon) simply burn
the oxygen to produce sulfur dioxide and carbon dioxide. It's usually
best to include a mixture of the two in a pyrotechnic mixture, as
they burn at different speeds and temperatures, and the proper
combination will help control the speed of combustion.
Also, when extra fast burning speed is needed, like in
rockets and firecrackers, metal powder is often added. The finer the
powder, the faster the burning rate. The proportions change the
speed, as well. Magnesium powder or dust is often used for speed.
Aluminum dust works, but not as well. Zinc dust is used in some cases.
Powdered metal, (not dust) particularly aluminum or iron, are often
used to produce a mixture that shoots out sparks as it burns. In rare
cases, it is desirable to slow down the burning speed. In this case,
corn meal is often used. It burns, so acts as a reducing agent, but it
doesn't burn very well.
Coloring agents are very interesting. It's long been known
that various metals produce different colored flames when burned in a
fire. The reasons are buried in the realm of quantum physics, but the
results are what matters, and we can present them here. Note that if we
use an oxidizing agent that contains a colorizing metal, it can do a
double job. It can produce oxygen and color.
Barium:
Barium salts give a pleasant green color. Barium Nitrate is most often
used.
Strontium:
Strontium salts give a strong red color. Strontium Nitrate is a very
convenient material for red.
Sodium:
Sodium salts give an intense yellow color. So intense in fact that any
sodium compounds in a mixture will usually wash out other colorizers.
As has been said, Sodium Nitrate absorbs moisture from the air, and so is
not really suitable to impart color. Instead, Sodium Oxalate is
usually used. This does not absorb lots of water, but has the
disadvantage of being very poisonous.
Copper:
Copper salts are used to give a blue color. Blue is the most
difficult color to produce, and it's usually not too spectacular. Usually
Copper Acetoarsenite (Paris Green) is used. This compound contains
arsenic, and is very poisonous. Since it still doesn't produce a very
memorable blue, it's often used with mercurous chloride, which
enhances the color, but is also poisonous, and expensive, to boot.
Potassium:
Potassium salts will give a delicate purple color, if they're very pure.
The cheaper lab grades of potassium nitrate often contain traces of
sodium, which completely obscure the purple color. In order to get the
purple coloring, very pure grades must be used, and you must be very
careful to mix it in very clean vessels, and scoop it from the supply jar
with a very clean scoop. The color is certainly worth the effort, if you
can get it.
Some mixtures that burn in colors also contain binders, that
hold the mixture together in a solid lump. These lumps are usually
referred to as stars. The balls fired from a roman candle or the
colorful showers sprayed from aerial bombs are examples of stars.
Depending on the mixture, the binder is either a starch called dextrin
or finely powdered orange shellac. A shellac-like material called
red gum is also used on occasion. In some mixtures, the shellac
powder also helps produce a nice color. Shellac mixtures are
moistened with alcohol to get them to stick together. Dextrin mixtures
are moistened with water. If the colored mixture is to be used as a
flare, it's just packed into a thin paper tube. If it's to be fired
from a roman candle, it's usually extruded from a heavy tube by
pushing it out with a dowel, and the pieces are
cut off as the proper length pops out. Stars fired from an aerial bomb
are usually made by rolling the moist mixture flat, and cutting it
with a knife into small cubes. Stars that are extruded are often
called "pumped stars" those that are rolled out are "cut stars".
The following are formulas for mixtures that burn with various
colors. Parts are by weight.
Red
Potassium Chlorate 9
Sulfur 2
Lampblack 1
Strontium Nitrate 9
bind with shellac
dissolved in alcohol
Blue
Potassium Chlorate 9 This one is inferior
Copper Acetoarsenite 2 Potassium Chlorate 12
Mercurous Chloride 1 Copper Sulfate 6
Sulfur 2 Lead Chloride 1
bind with dextrin Sulfur 4
in water bind with dextrin in water
Green
Barium Chlorate 8 Barium Nitrate 3
Lampblack 1 Potassium Chlorate 4
Shellac Powder 1 Shellac Powder 1
bind with alcohol Dextrin 1/4
Bind with alcohol
Yellow
Potassium Chlorate 8 Potassium Chlorate 8
Sodium Oxalate 3 Sodium Oxalate 4
Lampblack 2 Shellac Powder 2
Bind with shellac in Dextrin 1
alcohol or dextrin Bind with alcohol
in water
White
Potassium Nitrate 6
Sulfur 1
Antimony Sulfide 2
bind with dextrin in
water
Orange
Strontium Nitrate 36
Sodium Oxalate 8
Potassium Chlorate 5
Shellac Powder 5
Sulfur 3
Bind with alcohol
Purple (ingredients must be very pure)
Potassium Chlorate 36 This one has more of a lilac color
Strontium Sulfate 10 Potassium Chlorate 38
Copper Sulfate 5 Strontium Carbonate 18
Lead Chloride 2 Copper Chloride 4
Charcoal 2 Lead Chloride 2
Sulfur 12 Sulfur 14
Bind with dextrin in Bind with dextrin in water
water
Brilliant White
Potassium Perchlorate 12
Aluminum Dust 4
Dextrin 1
Bind with water
Golden Twinkler Stars
Falls through the air and burns in an on and off manner. The effect is
spectacular. A pumped or cut star.
Potassium Nitrate 18
Sulfur 3
Lampblack 3
Aluminum Powder 3
Antimony Sulfide 3
Sodium Oxalate 4
Dextrin 2
Bind with water
Zinc Spreader Stars
Shoot out pieces of burning zinc and charcoal.These stars are much heavier
than usual, and require larger charges if they're
to be fired from a tube.
Zinc Dust 72
Potassium Chlorate 15
Potassium Dichromate 12
Granular Charcoal 12
Dextrin 2
bind with water
Electric Stars
Stars that contain aluminum powder
Potassium Nitrate 15 Potassium Chlorate 60
Aluminum, fine 2 Barium Nitrate 5
Aluminum, medium 1 Aluminum, fine 9
Black Powder 2 Aluminum, medium 4
Antimony Sulfide 3 Aluminum, coarse 3
Sulfur 4 Charcoal 2
bind with dextrin in Dextrin 5
water bind with red gum in
water
Potassium Perchlorate 6
Barium Nitrate 1 Potassium Perchlorate 4
Aluminum 20 Aluminum, medium 2
Dextrin 1 Dextrin 1
bind with shellac in bind with shellac in alcohol
alcohol
Simpler Zinc Spreaders
Potassium Nitrate 14 Potassium Chlorate 5
Zinc Dust 40 Potassium Dichromate 4
Charcoal 7 Charcoal, medium 4
Sulfur 4 Zinc Dust 24
bind with dextrin in bind with dextrin in water
water
Willow Tree Stars
Use large amounts of lampblack -- too much to burn fully. Gives a
willow tree effect.
Potassium Chlorate 10
Potassium Nitrate 5
Sulfur 1
Lampblack 18
bind with dextrin in water
As always, don't forget that it's just plain stupid to go buying
all these materials from one chemical supply house. When you buy it
all as a group, they know what you plan to do with it, and they
keep records. If anyone goes investigating the source of homemade
fireworks and checks with your supplier, there will be a lead straight to
you. Be sure to cover your
tracks
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