Pyrotechnic compositions are usually homogenized mixtures of small particles of fuels and oxidizers. The particles can be grains or flakes. Generally, the higher the surface area of the particles, the higher the reaction rate and burning speed. For some purposes, binders are used to turn the powder into a solid material.
Fuels Typical fuels are based on metal or
metalloid powders. A flash powder composition may specify multiple different fuels. Some fuels can also serve as binders. Common fuels include: •
Metals •
Aluminium – most common fuel in many classes of mixtures, also a combustion instability suppressant. Less energy per mass than carbon but less gas evolution, retaining heat in the reaction mixture. High-temperature flame with solid particles, which interfere with flame colorants. Reacts with nitrates, except ammonium nitrate, yielding nitrogen oxides, ammonia, and heat (the reaction is slow at room temperature but violent at above 80 °C and may spontaneously ignite); the reaction can be inhibited by a weak acid, e.g.
boric acid. Corroded by alkaline substances. Flake particles easier to ignite and better for pyrotechnics than spherical ones. In presence of moisture reacts with potassium chlorate and perchlorate, yielding hydrogen. Particle size selected according to the required burn rate. •
Magnesium – more sensitive and violent than aluminium, increases probability of spontaneous ignition in storage. Used in fireworks to increase flame temperature. Less interference with flame color than aluminium. •
Magnalium – aluminium-magnesium alloy, more stable and less expensive than magnesium; less reactive than magnesium, easier to ignite than aluminium •
Iron – makes gold sparks, frequently used •
Steel – an alloy of iron and carbon, makes branching yellow-orange sparks •
Zirconium – produces hot particles, good for ignition mixtures, e.g. the
NASA Standard Initiator, also a combustion instability suppressant •
Titanium – produces hot particles, increases sensitivity to impact and friction; sometimes the Ti4Al6V alloy is used which gives a bit brighter white sparks; together with potassium perchlorate it is used in some
pyrotechnic igniters; coarse powder produces branching blue-white sparks •
Ferrotitanium – iron-titanium alloy, produces bright yellow-white sparks, used in pyrotechnic stars, rockets, comets, and fountains •
Ferrosilicon – iron-silicon alloy, used in some mixtures, sometimes replacement of calcium silicide •
Manganese – used to control burn rates, e.g. in delay compositions •
Zinc – used in some
smoke compositions, together with sulfur used in some early amateur rocket fuels, also in pyrotechnic stars; heavy, zinc-based compositions may require additional lift to fly high enough; moisture-sensitive; can spontaneously ignite; rarely used as primary fuel except in smoke compositions, can be encountered as a secondary enhancement fuel •
Copper – used as a blue colorant with other fuels •
Brass – a zinc-copper alloy used in some fireworks formulas, as a blue colorant for its copper content •
Tungsten – used to control and slow down burn rates of compositions, also in delay compositions • Zirconium-
nickel alloy – used in some military delay compositions •
Metal hydrides (lower
heat of combustion than pure metals, but increased sensitivity/reactivity to water): •
Titanium(II) hydride – together with potassium perchlorate it is used in some igniters •
Zirconium(II) hydride – together with potassium perchlorate it is used in some igniters •
Aluminum hydride – unstable for storage (decomposes easily with humidity) and reacts dangerously in contact with water •
Decaborane – experimented with for some rocket fuels • Metal carbides •
Zirconium carbide – used in some rocket fuels, also a combustion instability suppressant •
Metalloids •
Silicon – high flame temperature, burns producing molten glass, used in some ignition compositions and delay charges, commonly with
lead tetroxide •
Boron – used in some ignition mixtures •
Antimony – used in some fireworks for
glitter effects, toxic, burns bright white; usually used as 200–300 mesh; with potassium nitrate and sulfur produces white fires • Non-metallic inorganic •
Sulfur – ignition promoter, increases burn rate; increases sensitivity to temperature, impact and friction, dangerous in combination with chlorates; commonly used with nitrates; used as an additive; may contain residual acids, combination with carbonates or other alkaline stabilizers is advised in acid-sensitive compositions •
Red phosphorus – extremely dangerous, especially in combination with chlorates (
Armstrong's mixture); used in
caps; also used in
matches and some military infrared flares; toxic •
White phosphorus – used in
incendiary weapons and to make some military
smoke screens, ignites spontaneously in air; even more toxic •
Calcium silicide – used in some special compositions •
Antimony trisulfide – ignition promoter; fine powder increases sensitivity, sharpens the boom of salutes; toxic and sensitive to static electricity; emits bright white light, crystals also used as a fuel in glitter compositions and in white comets and pyrotechnic stars. Sensitive to friction and impact; the degree of sensitisation depends on the oxidizer (sensitive to friction and impact with potassium chlorate, friction with potassium perchlorate, impact with ammonium perchlorate, and insensitive to either with potassium nitrate). •
Arsenic sulfide (
realgar) – toxic, sensitive to impact and friction. Used for
report compositions due to its sensitivity with chlorate even in small amounts. Used in yellow
smoke compositions due to its low boiling point. •
Phosphorus trisulfide – used to make
matches •
Calcium phosphide – liberates
phosphine when wet, used in some naval
signal flares •
Potassium thiocyanate • Carbon-based •
Carbon •
Charcoal – makes dim gold sparks •
Graphite – also used as
opacifier in rocket fuels to prevent heat transfer by radiation into lower layers of fuels and avoid the related explosions •
Carbon black – produces long lasting fine gold sparks in fireworks, also used as opacifier in rocket fuels •
Asphaltum – carbon-based fuel, also used as a binder. Some forms contain ammonia; should not be combined with chlorates. decomposes at higher temperatures than nitrates of lighter metals and promotes higher burning temperatures. With aluminium produces bright silver sparks; when used with aluminium, addition of boric acid as stabilizer is advised. Not very hygroscopic. At lower temperatures (with organic fuels) produces strontium nitrite ash which can smother the flame; decomposes completely at higher temperatures (with magnesium). Colorant for low-temperature flames, colorant and oxidizer for hot flames. •
Caesium nitrate – used in some military infrared flare compositions •
Permanganates: •
Potassium permanganate – used in early mixtures, now considered to be sensitive and unstable •
Ammonium permanganate – a moderately powerful explosive •
Chromates: •
Barium chromate – used in delay compositions, e.g. in fireworks rockets •
Lead chromate – used in delay compositions •
Potassium dichromate – used infrequently as an oxidizer; can be used as a surface treatment for passivation of magnesium particles, also as a catalyst and in some matches; potassium perchlorate often added •
Oxides and
peroxides: •
Barium peroxide – unstable, spontaneously decomposes, compositions containing it should not be stored •
Strontium peroxide •
Lead tetroxide – versatile but toxic •
Lead dioxide – used in friction-sensitive compositions, e.g.
matches •
Bismuth trioxide – used as a safe alternative to lead tetroxide in some compositions •
Iron(III) oxide – a high temperature oxidizer, a catalyst •
Iron(II,III) oxide – an oxidizer in
Thermite and
Thermate •
Manganese(IV) oxide – an oxidizer in manganese thermite, a catalyst •
Chromium(III) oxide – an oxidizer in chromium thermite •
Tin(IV) oxide – an oxidizer in some delay charges •
Sulfates (reactions require high temperatures and strongly reducing fuels): •
Barium sulfate – a high-temperature oxidizer for e.g. strobe compositions, a green colorant •
Calcium sulfate – a high-temperature oxidizer for e.g. strobe compositions, a red-orange colorant. •
Potassium sulfate – a high-temperature oxidizer, a purple colorant •
Sodium sulfate – a high-temperature oxidizer, a yellow colorant •
Strontium sulfate – a high-temperature oxidizer, a red colorant • Organic chemicals •
Guanidine nitrate – used in some high power rocket fuels, propellants, and blue firework compositions •
Hexanitroethane – used in some special military compositions •
Cyclotrimethylene trinitramine – used in some
double-base propellants •
Cyclotetramethylene Tetranitramine – used in some double-base propellants • Others •
Sulfur – oxidizer for zinc in zinc-sulfur fuels •
Teflon – oxidizer for some metal fuels •
Boron – oxidizer for titanium, forming
titanium diboride Corresponding sodium salts can be substituted for potassium ones.
Additives •
Coolants. For some purposes it is necessary to lower the burning temperature of the mixture, and/or slow down the reaction rate. For such purpose, inert materials (e.g.
clay,
diatomaceous earth,
alumina,
silica,
magnesium oxide, or others) or endothermically decomposing materials (e.g.
carbonates) are added.
Oxamide is used as a high performance burning rate suppressant in some propellant compositions.
Strontium carbonate is used as a fire retardant in some gunpowders. •
Flame suppressants.
Potassium nitrate and
potassium sulfate are commonly used. •
Opacifiers. Some solid rocket propellants have problems with radiative heat transfer through the material, which may lead to explosion.
Carbon black and
graphite are often used to inhibit this effect. •
Colorants, sometimes in combination with sources of
chlorine. Usually salts of suitable metals, often
barium,
strontium,
calcium,
sodium,
copper, etc. The salt may simultaneously serve as an oxidizer.
Copper metal can be also used.
Copper acetoarsenite with potassium perchlorate provides richest blue. •
Chlorine donors. Used together with colorants. In some cases, the color emitting species is molecular and not atomic. Such is the case for blue pyrotechnic flames where the emitting species is copper monochloride. Also, some chloride molecular emitters are much stronger than oxides of the same element, as in the case of Barium and Strontium.
Polyvinyl chloride,
polyvinylidene chloride,
Saran,
chlorinated paraffins, chlorinated
rubber (e.g.
Parlon),
hexachloroethane,
hexachlorobenzene (most common chlorine donor until the 1970s, now rarely used), and some other
organochlorides and inorganic
chlorides (e.g.
ammonium chloride,
mercurous chloride) are used as chlorine donors. Perchlorates and chlorates play this role together with their main use as oxidizers. Chlorine donors are often used also in
smoke compositions, e.g.
hexachloroethane together with
zinc oxide to produce
smoke based on
zinc chloride. •
Catalysts. Propellant formulas often require a catalyst to burn faster and more stably.
Transition metal ions and complexes tend to be used. Certain oxidizers often serve as catalysts. E.g.
ammonium dichromate is used as a catalyst in ammonium nitrate based propellant formulas. Other catalysts are e.g.
iron(III) oxide, hydrated ferric oxide,
manganese dioxide,
potassium dichromate,
copper chromite,
lead salicylate,
lead stearate,
lead 2-ethylhexoate,
copper salicylate,
copper stearate,
lithium fluoride,
n-butyl ferrocene,
di-n-butyl ferrocene. •
Stabilizers. Some mixtures, e.g. containing chlorates, tend to degrade and create acidic byproducts.
Carbonates (e.g.
sodium,
calcium, or
barium carbonate) or other mildly alkaline materials can be added to scavenge such acids.
Boric acid can be used to inhibit the sensitivity of aluminium to moisture, and to stabilize mixtures of metals with nitrates (which can otherwise form amides which react exothermically with metals and can cause spontaneous initiation). Many organic nitrated amines are used as stabilizers as well, e.g.
2-nitrodiphenylamine.
Petroleum jelly,
castor oil,
linseed oil, etc. can be used as stabilizers, also to add hydrophobicity to particles and protect metals (especially iron and magnesium) from corrosion.
Ethyl centralite and
2-nitrodiphenylamine are used in some rocket propellants. •
Anticaking agents. E.g.
fumed silica. For powder compositions, e.g.
flash powder or
gunpowder.
Graphite is used in some cases to coat the grains, lubricate them, and dissipate
static electricity.
Magnesium carbonate used too, together with its function as carbonate stabilizer. •
Binders. Often
gums and
resins, e.g.
gum arabic,
red gum,
guar gum,
copal,
carboxymethyl cellulose,
nitrocellulose, rice
starch,
cornstarch,
shellac,
dextrin. Binders can also serve as fuels.
Camphor can be used as a
plasticizer. Binders are used in manufacture of compact compositions, e.g.
pyrotechnic stars. Polymers like
HTPB and
PBAN are often used for rocket fuels. Other polymers used are e.g.
polyethylene or
polyvinyl chloride can be encountered as well. •
Plasticizers. Improve the mechanical properties of the propellant particles. For composite rocket propellants,
dioctyl adipate,
isodecyl pelargonate, and
dioctyl phthalate are often used. Plasticizers can also be
other energetic materials (common in smokeless powders), e.g.
nitroglycerine,
butanetriol trinitrate,
dinitrotoluene,
trimethylolethane trinitrate,
diethylene glycol dinitrate,
triethylene glycol dinitrate,
bis(2,2-dinitropropyl)formal,
bis(2,2-dinitropropyl)acetal,
2,2,2-trinitroethyl 2-nitroxyethyl ether, and others. •
Curing and crosslinking agents. Used to harden the polymer component of composite rocket propellants. They include
paraquinone dioxime,
toluene-2,4-diisocyanate,
tris(1-(2-methyl) aziridinyl) phosphine oxide,
N,N,O-tri(1,2-epoxy propyl)-4-aminophenol, and
isophorone diisocyanate. •
Bonding agents. Used to increase the level of bonding between the binder and the fuel/oxidizer particles. They include
tris(1-(2-methyl) azirinidyl) phosphine oxide and
triethanolamine. ==See also==