Black Powder

Background

Black powder is a world-wide recognized mixture. It was first used by the chinese for use in fireworks and was first used in weapons and explosives in the 1100s. Since then it has been used for years as a projectile propellant in guns, cannons, fireworks, shells, and the like. It is no longer used in firearms and was replaced by chordite (nitro cellulose and nitroglycerine) soon after its discovery in 1889.

Composition

There are many different composition for Black powder which vary depending on the application. Listed are just a few possibilities.

Ingredient Formula Standard Sulfurless Ammonium Based
potassium nitrate KNO3 75% 80%
ammonium nitrate NH4NO3 85%
sulfur S 10%
charcoal C 15% 20% 15%

There are a number of reasons for variation in the composition. Below is a list of reason and effects of the variations.

Oxidiser

Generally speaking, the more oxidiser the faster the powder will burn. This of course is only true to a certain extent, but for the burn rate to decrease as a result of too much oxidiser, the would have to be a very large quantity of oxidiser.

Different oxidisers are used for different reasons. Potassium nitrate is the usual oxidiser, but other oxidisers such as ammonium nitrate and sodium nitrate are often used.

Sodium nitrate is often used for fireworks and blasting applications because it is often cheaper than potassium nitrate. Sodium nitrate, like most sodium salts, is hygroscopic and so when in the hydrous state, mixtures containing it do not burn as fiercely. For this reason black powder containing sodium nitrate is often held in a water-proof casing or treated in a certain way, for example, given a graphite glaze. Sodium nitrate also emits yellow-orange light of wavelength 589nm when it decomposes, making it the oxidiser of choice for certain light producing applications.

Ammonium nitrate is normally used to make smokeless powders because all of its decomposition products are gasses. Smokeless powder was useful on the battle field because, there being no smoke, the enemy could not see where you were. Another advantage of smokeless powders in general is that a greater percentage of a composition is converted into hot gasses which produces a better propellant effect. This does not apply to ammonium nitrate so much as it is not as efficient an oxidiser as other oxidisers. Ammonium nitrate is also very hygroscopic. It must be sealed from air other wise it will absorb so much moisture that it will not work at all.

Fuels

Sulfur was sometimes omitted from a composition because the compounds it formed corroded the barrel. The absence of sulfur in a composition increased the ignition temperature. This caused a progressive burning, each grain only bursting into flame when incontact of the flame from an adjacent grain, rather than a more symultaneous burning of the grains.

Although that when sulfur burns by its self, when it burns as part of a composition (such as black powder), it largely formes compounds which are solids. For this reason, smokeless powders containing ammonium nitrate often did not contain sulfur.

Other additives

Some other ingredients sometimes found in black powders might be resins, binders, starch and parafin. These perform function such as binding and smoke producing which could be important in certain blasting applications.

Procedure

Unfortunately I have had to remove the procedure explaning how to make this (see bottom of main page). Soon, however, I will have some information on how it was/is made by large scale industrial manufacturers.

Equations

Just one example of the equation for BP is:

20KNO3(s) + 32C(s) +8S(s) ---> 5K2CO3(s) + K2SO4(s) + K2SO3(s) + 3K2S(s) + 2S(s) + 11CO2(g) + 16CO(g) + 10N2(g)

Under different conditions, a whole new equation pops up.

The best results do not always come from balanced equations. For example, kinetics might require extra fuel for faster a reaction and so an equation is rarely accurately represented by the starting composition.

According to "The Chemistry of Powder and Explosives", by T. L. Davis, from a black powder consisting of:

Name Percentage
Potassium nitrate 74.430
Potassium sulfate 0.133
Sulfur 10.093
Charcoal Consisting of...
Carbon 12.398
Hydrogen 0.41
Oxygen 1.272
Ash 0.215
14.286
Moisture 1.058

the average product composition is:

Gaseous (by volume) Solid (by weight)
Carbon dioxide 49.29 % Potassium carbonate 61.03 %
Carbon monoxide 12.47 % Potassium sulfate 15.10 %
Nitrogen 32.9 % Potassium sulfide 14.45 %
Hydrogen sulfide 2.65 % Potassium thiocyanate 0.22 %
Methane 0.43 % Potassium nitrate 0.27 %
Hydrogen 2.19 % Ammonium carbonate 0.08 %
Sulfur 8.74 %
Carbon 0.08 %

Ignition

Potassium nitrate black powder can be ignited with a low temperature flame, but ignites more readily with a hotter flame closer to the decomposition temperature of potassium nitrate which is about 400°C. It is ignited in firearms using concussion and friction.

Other Information

Black powder is not a particularly brilliant propellant as only about 50% of it gets converted to hot gasses and the rest becomes smoke (very fine burned particles suspended in the atmosphere). Black powder is not to be confused with gun powder, which is usually cordite.