Basic Explosives Theory

[7.62mm [FullMetalJacket]]

I thought I'd start out here with some basic explosives theory. From there, I'll introduce you to a very basic high explosive composition.

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Firstly: There are two main classes of explosives. High and Low.

High explosives are either stand alone chemicals or a combination of two - three other chemicals in stoichiometric proportions. When they are initiated, their total average Brownian energy is pushed beyond a certain point. This can be from fire, friction, shock... Anything that sufficiently increases molecular kinetic energy. This is usually either in the form of fuse or blasting cap, however some (nitroglycerine, most organic peroxides, most fulminates) can be set off by shock alone, like being hit with a hammer or dropping from a certain height. Fulminates, for example, are the primers used in firearms that the hammer strikes to set off the bullet. The major point of a high explosive is that when it detonates, a shockwave propogates through it at supersonic speeds, breaking it down to component substances and a supersonic cloud of gas and debris (the actual explosion).

High explosives are normally employed in mining, demolition, and military warheads. They undergo detonation at rates of 1,000 to 9,000 meters per second. High explosives are conventionally subdivided into two classes differentiated by sensitivity:

Primary explosives are extremely sensitive to any kind of energy increase (shock, friction, heat)... So no smoking, disco dancing on, or chewing these! Primary explosives include fulminates, organic peroxides, some double salts and a few other special ones.

* Nitroglycerin: a highly unstable and sensitive liquid.
* Fulminates: Fulminates are chemical compounds which include the fulminate anion. Due to the instability of the anion, they are friction-sensitive explosives. The best known is mercury fulminate which has been used as a primary explosive in detonators. Fulminates can be formed from metals, like silver and mercury, dissolved in nitric acid and reacted with alcohol.
* Organic Peroxides: Such as AP (acetone peroxide, aka TATP), MEKP (methyl-ethyl ketone peroxide), HMTD (hexamethylene triperoxide diamine) and others can detonate when hit with a hammer..

Secondary explosives, also called base explosives, are relatively insensitive to shock, friction, and heat. They may burn when exposed to heat or flame in small, unconfined quantities, but detonation can occur. These are sometimes added in small amounts to blasting caps to boost their power.

* TNT: Yellow insensitive crystals that can be melted and cast without detonation.
* Nitrocellulose: A nitrated polymer which can be a high or low explosive depending on nitration level and conditions.
* RDX, PETN, HMX: Very powerful explosives which can be used pure or in plastic explosives.
o G-1 (or Composition G-1): An RDX plastic explosive plasticized to be adhesive and malleable, invented by yours truly

PETN is often considered a benchmark compound, with materials that are more sensitive than PETN being classified as primary explosives.

Some definitions add a third category:

Tertiary explosives, also called blasting agents, are so insensitive to shock that they cannot be reliably detonated by practical quantities of primary explosive, and instead require an intermediate explosive booster of secondary explosive. Examples include an Ammonium Nitrate/Fuel Oil mixture (ANFO) and slurry or 'Wet Bag' explosives. These are primarily used in large-scale mining and construction operations, and are usually initiated by a 'train detonation', where a fuse or e-cap initiates a primary explosive which initiates a secondary, finally inducing supersonic decomposition in the mjority portion explosive.

Note that many if not most explosive chemical compounds may usefully deflagrate as well as detonate, and are used in high as well as low explosive compositions. This also means that under extreme conditions, a propellant can detonate. For example, nitrocellulose deflagrates if ignited, but detonates if initiated by a detonator.

A low explosive is a combustible substance that decomposes rapidly (deflagration), but does not explode under normal conditions. Under certain conditions, though, it is possible for them to detonate, usually through initiation with high explosives.

Low explosives are often employed as propellants or visual explosives (pyrotechnics e.g flares, fireworks). Most low explosives are mixtures; most high explosives are compounds, but to both there are notable exceptions. Low explosives undergo deflagration at rates that vary from a few centimeters per second to approximately 400 metres per second. Included in this group are smokeless powders, black powders and flash powders (sort of). Flash Powder is debated because sufficient quantities of a powerful mixture (e.g KMnO4/Mg will detonate instead of deflagrating, however average theatric or recreational volumes will not. To reflect this, the U.S BATFE lists flash powders as high explosives and has subsequently restricted the purchase of precursors.

Mixtures of an oxidizer and a fuel

An oxidizer is a pure substance (molecule) that in a chemical reaction can contribute some atoms of one or more oxidizing elements, in which the fuel component of the explosive burns. On the simplest level, the oxidizer may itself be an oxidizing element, such as gaseous or liquid oxygen, or an ionic compound (such as nitrate-containing salt).

* Black powder: potassium nitrate, charcoal and sulfur
* Flash powder: fine metal powder (usually aluminium or magnesium) and a strong oxidizer (e.g. potassium chlorate or perchlorate or permanganate).
* Ammonal: ammonium nitrate and aluminium powder. Also known as ANAl, much to the hilarity of the younger pyros.
* Ammonpulver: Ammonium nitrate and charcoal
* Armstrong's mixture: potassium chlorate and red phosphorus. This is a very sensitive mixture. It is a primary high explosive in which sulfur is substituted for some or all phosphorus to slightly decrease sensitivity.
* Sprengel explosives: a very general class incorporating any strong oxidizer and highly reactive fuel, although in practice the name most commonly was applied to mixtures of chlorates and nitroaromatics
o ANFO: ammonium nitrate and fuel oil (diesel, hydrazine, No. 3 lube oil, etc).
o Cheddites: chlorates or perchlorates and oil
o Oxyliquits: mixtures of organic materials and liquid oxygen
o Panclastites: mixtures of organic materials and dinitrogen tetroxide


The above compositions may describe the majority of the explosive material, but a practical explosive will often include small percentages of other materials. For example, nitroglycerin becomes dynamite when mixed into sawdust, powdered silica, powdered ammonium nitrate or most commonly diatomaceous earth (known then as guhr dynamite), which act as stabilizers. Plastics and polymers may be added to bind powders of explosive compounds; waxes may be incorporated to make them safer to handle; aluminum powder may be introduced to increase total energy and blast effect. Explosive compounds are also often "alloyed": HMX or RDX powders maybe mixed (typically by melt-casting) with TNT to form octol or cyclotol.

That's all from me today - Watch out for more in the next issue, or keep your ears open - Soldier Science may be coming to a Guerilla Radio Station near you!

[drbroccoli]

I thought ammonal had TNT in it too.

[Douchermann]

Hmmm, well this is a good add. I don't think we have any explosives theory on this board (until now of course). A few things to add, ammonpulver does not contain TNT, but it is not ammonium nitrate and aluminum, it's ammonium nitrate and charcoal. Secondaries can also be broken up into final charges and/or blasting agents. High power/velocity furan explosives reach above 9000m/s in velocity, nitroglycerin isn't something to be feared as it is depicted, however it should be treated with respect. Not all secondary explosives are base explosives, it's most often stated that the explosives that require a booster are a base. Blasting agents are also things that can be mixed on site in ungodly large quantities, such as ANFO. Everything else is great and I thank you for this add.

[masonjar chemist]

I am not so sure that nitroglycerin should be classified as a primary. While it is sensitive to shock, it is not exactly fuse sensitive, and in all practical applications, it is set off by a detonator. Also the bar was raised a few years back when hexanitroisowurtzitane (Cl-20) was measured with a VoD over 10,000 mps (10,060 IIRC). I believe Oxyliquits are technically also classified a Sprengal explosives and I am pretty sure the most common oxidizer used was nitric acid not chlorates.

I don't mean to critique your post so harshly, it is very well written for the most part, and an excellent compilation of information for beginners. By the way, If you don't mind, could you post the formulation for "G-1"?

[7.62mm [FullMetalJacket]]

Good lord, I made this post a while ago... I think it's time to update.

[nme]

Na NG's a secondary. I'll only ever throw explosive theory into Introduction threads or newb threads... Tis pretty simple tbh.. A grounding in school taught chemistry or just balancing equations is a good start.