Explosives: How They’re Made & What They Are
These may include Propellants, but they’re all DEFLAGRATORY explosives. Black powder is the oldest and most familiar. It is nearly impossible to get it to truly “detonate,” i.e. develop a supersonic overpressure wave. (“Air waves?” Gimme’ a break!) Deflagration is a rapid burning (Oxidation) reaction. It generally requires a fuel, such as an organic substance or a finely divided metal, and an Oxidizer, such as a Nitrate, Chlorate or Perchlorate, although there are others. In fact, several comps don’t carry any Oxygen at all, perhaps the best known being a Zinc/Sulfur propellant (although the impetus and therefore the specific impulse are rather weak).
Perhaps the best known, outside of Blackpowder, is a flash comp known as M-80 mix (70/30 KClO4/dark Aluminum). (That’s the official arsenal designation. M-100, M-1,000 and the rest are all bullshit. The actual designation is “Composition-Pyrotechnic-M-80.” using the above formula.)
Deflagration can best be described as the rapid oxidation/combustion of two or more elements into another product by rapid reorganization of constituent materials, resulting in an equally rapid energy release, usually heat and gaseous expansion.
When contained in a vessel such as a heavy walled, paper tube, suffucient pressure accumulates to burst it in such a manner that it develops an overpressure wave which can be loosely described as an “explosion.” If the force released is sufficient to create an overpressure with enough shock and gaseous expansion, work can be accomplished. Before the advent of Nitroglycerin and other high explosives, this is how blasting operations were accomplished, such as mining and road building. They would drill holes in the geologic structures to be disrupted, light a fuse that was placed in the charge and run like hell.
And of course, this deflagatory reaction created sufficient pressure to propel a projectile out of a tube with enough force to push a small pellet of lead into an opposing combatant, or a stone, Iron ball or explosive vessel into a castle wall, a ship’s hull or a formation of troops.
In the late 19th century, Alfred Nobel discovered that cellulose fibers could be subjected to a mixed acid Nitration to produce a substance (Nitrocellulose) which could propel a projectile with much more force than blackpowder. This so-called “smokeless” propellant was capable of acheiving much higher velocities than the ancient, nitrate-based propellants that people used to kill each other with for all of those hundreds of years. Nowadays, propellants may include Nitroglycerine , as both a plasticizer and inhibitor(believe it or not) to keep the NC from detonating under pressure. Ethyl Centralite may also be employed for this purpose. Nitroguanidine may also be employed, primarily as a bulking agent, and doeesn’t add much to the kinetic impetus, but does “fluff” the charge for ease of ignition, and does at least “carry its own weight” as far as power. In recent years, Nitramines (think RDX) and Nitric Esters (think PETN & HMX) have added substantially to velocity (& hence KE), but at the expense of bore erosion problems.
This is a different animal entirely. Instead of a fuel and an Oxidizer rearranging themselves, the reaction is based on the ability of Nitrogen to combine (but only barely) with other elements in a tenuous fashion which makes the resulting molecules hang together until they are somehow jarred apart.
High explosives are rated according to comparison with TNT (Trinitrotoluene) in terms of expansion, brisance (primarily measured as Velocity of Detonation, or VOD), and reactive pressure, sesiitivity to shock, friction and heating on a percentage basis. For instance, PETN (Pentaerythritol Tetranitrate) has an overall energy release of 160% of TNT, and Nitroglycerine about 120. There are other parameters as well, such as Oxygen balance when blending with other compounds. For instance, PETN has a negative OB (-8%), and Ammonium Nitrate a positive one. So when the two are mixed in the correct proportions and properly detonated, they compliment each other, and some of the brizance (shattering effect) of the PETN is combined with the “heave” (gaseous expansion & therefore work)of the AN is combined.
Unless you really know what you’re doing, these are nothing to mess with. Especially Organic Peroxides. Some are super easy to make, but that doesn’t mean that just anybody can go fucking around with this stuff.
Silver Fulminate was the original initiator compound for NG/Dynamite, but it’s so sensitive that it has been relegated to cigarette loads, throwdown “poppers” and the like. Soon after, it was found that Mercury, subjected to the same Nitration process, would produce an initiator (Mercury Fulminate)that was as powerful as the Silver-based compound, but much less sensitive, making it safer to handle.
Still, the Hg-based primary had its problems. Today, the standard layout is Lead Azide, which is much less sensitive than its predecessors, and delivers sufficient force to shoot most Gelatin Dynamites. ANFO, however, is still so insensitive, and so commonly used, that a booster between the primary & secondary charges is required. This usually takes the form of a small amount of PETN, RDX or HMX. With Primaries, the main concern is not just the VOD, but the pressure developed. However, Detonation velocity is still important, and PETN (7,800 MPS), RDX (8,400) and HMX (9,000) will certainly take care of that. For large charges, seperate boosters are used which are significantly larger than the caps themselves, sometimes weighing several pounds. Also, nowadays the primary is dispensed with entirely, and an “exploding bridgewire” consisting of a small diameter wire or strip of foil, usually gold,is subjected to a quick(400usec), high energy(800vdc @400-600ma) burst of electricity, which actually vaporizes with sufficient force to initiate a booster charge, usually a Nitric Ester or Nitramine.