In ballistics and pyrotechnics, a propellant is a generic name for chemicals used for propelling projectiles from guns and other firearms. Propellants are usually made from low explosive materials, but may include high explosive chemical ingredients that are diluted and burned in a controlled way (deflagration) rather than detonation. The controlled burning of the propellant composition usually produces thrust by gas pressure and can accelerate a projectile, rocket, or other vehicle. In this sense, common or well known propellants include, for firearms, artillery and solid propellant rockets: Gun propellants, such as:
Ø Gunpowder (black powder)
Ø Nitrocellulose-based powders
Ø Smokeless powders
Composite propellants made from a solid oxidizer such as ammonium perchlorate or ammonium nitrate, a rubber such as HTPB, or PBAN (may be replaced by energetic polymers such as polyglycidyl nitrate or polyvinyl nitrate for extra energy) , optional high explosive fuels (again, for extra energy) such as RDX or nitroglycerin, and usually a powdered metal fuel such as aluminum.
Some amateur propellants use potassium nitrate, combined with sugar, epoxy, or other fuels / binder compounds.
Potassium perchlorate has been used as an oxidizer, paired with asphalt, epoxy, and other binders.
Propellants are used in forms called grains. A grain is any individual particle of propellant regardless of the size or shape. The shape and size of a propellant grain determines the burn time, amount of gas and rate produced from the burning propellant and consequently thrust vs time profile.
There are three types of burns that can be achieved with different grains.
Ø Progressive Burn:
Usually a grain with multiple perforations or a star cut in the center providing a lot of surface area.
Ø Digressive Burn
Usually a solid grain in the shape of a cylinder or sphere.
Ø Neutral Burn
Usually a single perforation; as outside surface decreases the inside surface increases at the same rate.
There are four different types of solid propellant compositions:
Single Based Propellant:
A single based propellant has nitrocellulose as its chief explosives ingredient. Stabilizers and other additives are used to control the chemical stability and enhance the propellant’s properties.
Double Based Propellant:
Double based propellants consist of nitrocellulose with nitroglycerin or other liquid organic nitrate explosives added. Stabilizers and other additives are used also. Nitroglycerin reduces smoke and increases the energy output. Double based propellants are used in small arms, cannons, mortars and rockets.
Triple Based Propellant
Triple based propellants consist of nitrocellulose, nitroquanidine, nitroglycerin or other liquid organic nitrate explosives. Triple based propellants are used in cannons.
Composites contain no nitrocellulose, nitroglycerin, nitroquanidine or any other organic nitrate. Composites usually consist of a fuel such as metallic aluminum, a binder such as synthetic rubber, and an oxidizer such as ammonium perchlorate. Composite propellants are used in large rocket motors.