Image By Senior Airman Rusty Frank – https://www.dvidshub.net/image/1060499, Public Domain, https://commons.wikimedia.org/w/index.php?curid=39209997
How does C-4 work? It rapidly produces gases at an explosive velocity.
C-4 is a plastic explosive called Composition C-4 and it is the fourth in the series. Composition C was discovered in World War II and the first type was only called Composition C. Each variation had problems that were ironed out by the time C-4 was produced. For example, C-1 couldn’t be stored at high temperatures, C-2 was toxic, and C-3 wasn’t soft enough at low temperatures. C-4 was introduced in 1956 and it is so good that it has remained the same since then.
So, how does C-4 work? All explosives work by producing gases at an explosive rate. TNT, for example, produces 1 liter of carbon monoxide, carbon dioxide, and nitrogen gas for every 1 gram of TNT in about 15 milliseconds. C-4 words on the same principle, but it is moldable.
Any explosive needs an explosive chemical and a binder to hold it together. C-4 also needs something to make it plasticky. The explosive chemical in C-4 is cyclotrimethylene-trinitramine (RDX – Royal Demolition Explosive). The binder is polyisobutylene and the plasticizer is dioctyl sebacate. Cyclotrimethylene-trinitramine is a common explosive. The trinitramine part is often shortened to TNT. It has a very high concentration of nitrogen and oxygen, which is what makes it explosive. It is also a very stable compound. Polyisobutylene is an organic polymer that is often used in rubber products, such as sealants and adhesives. Dioctyl sebacate is a liquid that is often used to make compounds plasticky.
When C-4 is made, the RDX is in powder form and it is mixed with water to make a paste. Then the binders are added and mixed with a solvent to keep them liquid. Once everything has been added, the mixture is dried to evaporate the solvent and the water. Motor oil is also added. This is used as a marker so that the army know if an explosion has been caused by C-4. When the C-4 is dried, it has the consistency of modeling clay and is very stable. The plasticizer keeps the explosive component in a far more stable state than solid explosive. You can throw it on the floor, jump on it, and even shoot it with a gun and it won’t detonate.
How does C-4 detonate? The explosion comes about because of the chemical reaction and a detonator is needed to start that reaction. The detonator needs to release a shockwave large enough to start decomposing the RDX. This is usually done with an electric detonator. An electric detonator has a detonator wire that is heated up so quickly by the electric current that it vaporizes and explodes with a velocity of about 6000 m/s. An average bullet only reaches about 1000 m/s, which is why a gun won’t set it off. The shockwave forces the RDX to undergo decomposition, which means that it is broken down into its component parts. It releases all of the nitrogen, carbon dioxide, and carbon monoxide in a rush. The gases expand at a rate of 8,050 meters per second. When the gases expand, two things happen. The first is that a shockwave is produced because the rapidly expanding gases compress the air around the explosion. The second thing is that a lot of heat is produced. This heat comes from the chemical reaction itself because the molecules release thermal energy when they undergo decomposition. The heat is also produced by the high pressure that the expanding gases create. This pressure and heat is what causes the destruction from the explosion.
Plastic explosives have an advantage over solid explosives because they can be shaped, and their explosive force can be directed. When TNT is detonated, the explosive force comes out equally in every direction. C-4 can be shaped to direct its explosive force. For this reason, it can be used as a general explosive, or to remove specific obstacles, such as door locks, or cut through things, such as steel beams. C-4 also burns slowly when lit and some soldiers in the Second World War, Korean War, and Vietnam War used it to cook food on.
One disadvantage of C-4 is something that also is an advantage for the army. The fact that it is light and moldable, means that it is very useful for terrorists. It has been used in multiple terrorist attacks.
So, C-4 is a very stable explosive that is detonated with a shockwave. The shockwave releases all of the gases and heat contained within the explosive chemical in milliseconds, causing the destruction. And this is what I learned today.
Sources
http://www.chm.bris.ac.uk/motm/tnt/tntjs.htm
https://en.wikipedia.org/wiki/Polybutene
https://en.wikipedia.org/wiki/Composition_C
https://en.wikipedia.org/wiki/Dioctyl_sebacate
https://en.wikipedia.org/wiki/RDX
https://www.osti.gov/servlets/purl/3648
https://www.chem.fsu.edu/chemlab/chm1020c/Lecture%207/04.php
https://science.howstuffworks.com/c-4.htm
https://www.quora.com/How-is-a-C4-detonated
https://www.fema.gov/pdf/plan/prevent/rms/426/fema426_ch4.pdf