A contact explosive is a chemical substance that explodes violently when it is exposed to a relatively small amount of energy (e.g. friction, pressure, sound, light). Though different contact explosives have varying amounts of energy sensitivity, they are all much more sensitive relative to other kinds of explosives. Contact explosives are a part of a group of explosives called primary explosives, which are also very sensitive to stimuli but not to the degree of contact explosives. The extreme sensitivity of contact explosives is due to either chemical composition, bond type, or structure.
These are some common contact explosives.
Compound | Sensitivity | Sensitive to | Type of explosion |
---|---|---|---|
Acetone peroxide | Very high | Heat, flame, shock, friction | Entropic |
Chlorine azide [1] | Extreme | Friction, shock, chemicals | Energy, entropic |
Copper(II) azide | Extreme | Shock, static | Energy |
Fulminates | Very high | Friction, static, heat, flame, shock | Energy |
Lead(II) azide | High | Shock, static | Energy |
Nitrogen triiodide | Extreme [2] | Shock, [3] friction, pressure, sound, light, alpha radiation [4] | Energy, entropic |
Picric acid (dry) | Moderate | Shock, friction | Energy |
Tetrasulfur tetranitride | Moderate | Shock, friction | Energy, entropic |
Flash powder like Armstrong's mixture | High | Static, flame, friction | Energy, light |
Silver nitride | Extreme | Shock | Energy |
Explosives that are nitrogen-based are incredibly volatile due to the stability of nitrogen in its diatomic state, N2. [5] [6] Most organic explosives are explosive because they contain nitrogen. They are defined as nitro compounds.
Nitro compounds are explosive because although the diatomic form of nitrogen is very stable - that is, the triple bond that holds N2 together is very strong, and therefore has a great deal of bond energy - the nitro compounds themselves are unstable, as the bonds between nitrogen atoms and other atoms in nitro compounds are weak by comparison. Therefore, little energy is required to overcome these weak bonds, but a great deal of energy is released in the exothermic process in which the strong triple bonds in N2 are formed. The rapidity of the reaction, due to the weakness of the bonds in nitro compounds, and the high quantity of overall energy released, due to the much higher strength of the triple bonds, produce the explosive qualities of these compounds.
Some contact explosives contain an oxidizer and a fuel in their composition. [6] Chemicals like gasoline, a fuel, burn instead of explode because they must come into contact with oxygen in the combustion reaction. However, if the compound already contains both the oxidant and fuel, it produces a much faster and violent reaction.
The structures and bonds that make up a contact explosive contribute to its instability. Covalent compounds that have a large unequal sharing of electrons have the capability to fall apart very easily and explosively. Nitrogen triiodide is a perfect example of this property. The three huge iodine atoms try to attach themselves to one small nitrogen ion, which means that the atoms are holding on to each other through a very weak bond. The weak bond between each atom is like a thread just waiting to break. Therefore, any small amount of applied energy cuts this thread and releases the iodine and nitrogen atoms to react with the fuel, allowing the reaction to occur quickly and release a large amount of energy. [2]
The shape of the contact explosive molecule plays a role in its instability as well. Using nitrogen triiodide as an example again, its pyramidal shape forces the three iodine atoms to be incredibly close to each other. The shape further strains the already weak bonds that holds together this molecule.
Compound | Reason for instability |
---|---|
Acetone peroxide | Composition allows for initiation reaction |
Chlorine azide | Nitrogen |
Copper(II) azide | Nitrogen |
Fulminates | Instability of fulminate ion |
Lead(II) azide | Nitrogen |
Nitrogen triiodide | Unstable intramolecular bonds |
Nitroglycerin | Nitrogen, Oxidizer and fuel |
Picric acid (dry) | Nitrogen |
Tetrasulfur tetranitride | Nitrogen, Unstable intramolecular bonds |
Flash Powder | Oxidizer and metallic fuel |
Silver nitride | Unstable intramolecular bonds |
Contact explosives are used in a variety of fields.
Militaries use a variety of contact explosives in combat. Some can be manufactured into different types of bombs, tactical grenades, and even explosive bullets. Dry picric acid, which is more powerful than TNT, was used in blasting charges and artillery shells. A lot of contact explosives are used in detonators. For explosives that use secondary explosives, contact explosives are used in the detonators to set off an energy chain reaction that will eventually set off the secondary explosive.
Compounds like lead azide are used to manufacture bullets that explode into shrapnel on impact.
Flash powders are used in a variety of military and police tactical pyrotechnics. [7] Stun grenades , flash bangs, and flares all use flash powder to create bright, flashing lights and loud noise that disorients the enemy.
On the other hand, many of these cheap, volatile contact explosives are also used in improvised explosive devices (IEDs) created by terrorists and suicide bombers. [8] For example, acetone peroxide passes through explosive detectors and is incredibly powerful, unstable, and deadly. Evidence for the instability of these IEDs lies in the multiple reports of premature or wrongful IED explosions. However, when these explosives are used correctly, they have devastating consequences. The July 7, 2005, London bombings, the 2015 Paris attacks, and the 2016 Brussels bombings all used explosives that contained acetone peroxide.
Angina pectoris, a symptom of Ischaemic heart disease, is treated with nitroglycerin. [9] Nitroglycerin is known as a vasodilator. Vasodilators work by relaxing the heart's blood vessels so the heart does not need to work as hard. Picric acid specifically has been used for burn treatment and as an Antiseptic. [10]
The same flash powder used for military tactical pyrotechnics can also be used for several theatrical special effects. [11] They are used to produce loud, bright flashes of light for effect. Though some flash powders are too volatile and dangerous to be safely used, there are milder compounds that are still incorporated into performances today.
Silver Fulminate is used to make noise-makers, small contact poppers, and several other novelty fireworks. [12] It is most widely used in bang snaps. In these small explosives, a minuscule amount of silver fulminate is encased in gravel and cigarette paper. Even with this small amount of silver fulminate, it produces a loud, sharp bang.
An explosive is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An explosive charge is a measured quantity of explosive material, which may either be composed solely of one ingredient or be a mixture containing at least two substances.
Nitrogen is a chemical element; it has symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bond to form N2, a colorless and odorless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant chemical species in air. Because of the volatility of nitrogen compounds, nitrogen is relatively rare in the solid parts of the Earth.
Nitroglycerin (NG), also known as trinitroglycerol (TNG), nitro, glyceryl trinitrate (GTN), or 1,2,3-trinitroxypropane, is a dense, colorless or pale yellow, oily, explosive liquid most commonly produced by nitrating glycerol with white fuming nitric acid under conditions appropriate to the formation of the nitric acid ester. Chemically, the substance is an organic nitrate compound rather than a nitro compound, but the traditional name is retained. Discovered in 1846 by Ascanio Sobrero, nitroglycerin has been used as an active ingredient in the manufacture of explosives, namely dynamite, and as such it is employed in the construction, demolition, and mining industries. It is combined with nitrocellulose to form double-based smokeless powder, used as a propellant in artillery and firearms since the 1880s.
A detonator is a device used to make an explosive or explosive device explode. Detonators come in a variety of types, depending on how they are initiated and details of their inner working, which often involve several stages. Types of detonators include non-electric and electric. Non-electric detonators are typically stab or pyrotechnic while electric are typically "hot wire", exploding bridge wire or explosive foil.
Nitrogen triiodide is an inorganic compound with the formula NI3. It is an extremely sensitive contact explosive: small quantities explode with a loud, sharp snap when touched even lightly, releasing a purple cloud of iodine vapor; it can even be detonated by alpha radiation. NI3 has a complex structural chemistry that is difficult to study because of the instability of the derivatives.
In organic chemistry, nitration is a general class of chemical processes for the introduction of a nitro group into an organic compound. The term also is applied incorrectly to the different process of forming nitrate esters between alcohols and nitric acid. The difference between the resulting molecular structures of nitro compounds and nitrates is that the nitrogen atom in nitro compounds is directly bonded to a non-oxygen atom, whereas in nitrate esters, the nitrogen is bonded to an oxygen atom that in turn usually is bonded to a carbon atom.
In organic chemistry, free-radical addition is an addition reaction which involves free radicals. Radical additions are known for a variety of unsaturated substrates, both olefinic or aromatic and with or without heteroatoms.
Smokeless powder is a type of propellant used in firearms and artillery that produces less smoke and less fouling when fired compared to black powder. Because of their similar use, both the original black powder formulation and the smokeless propellant which replaced it are commonly described as gunpowder. The combustion products of smokeless powder are mainly gaseous, compared to around 55% solid products for black powder. In addition, smokeless powder does not leave the thick, heavy fouling of hygroscopic material associated with black powder that causes rusting of the barrel.
In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups. The nitro group is one of the most common explosophores used globally. The nitro group is also strongly electron-withdrawing. Because of this property, C−H bonds alpha (adjacent) to the nitro group can be acidic. For similar reasons, the presence of nitro groups in aromatic compounds retards electrophilic aromatic substitution but facilitates nucleophilic aromatic substitution. Nitro groups are rarely found in nature. They are almost invariably produced by nitration reactions starting with nitric acid.
Silver fulminate (AgCNO) is the highly explosive silver salt of fulminic acid.
Fulminates are chemical compounds which include the fulminate ion. The fulminate ion is a pseudohalic ion because its charge and reactivity are similar to those of the halogens. Due to the instability of the ion, fulminate salts are friction-sensitive explosives. The best known is mercury(II) fulminate, which has been used as a primary explosive in detonators. Fulminates can be formed from metals, such as silver and mercury, dissolved in nitric acid and reacted with ethanol. The weak single nitrogen-oxygen bond is responsible for their instability. Nitrogen very easily forms a stable triple bond to another nitrogen atom, forming nitrogen gas.
The cyanate ion is an anion with the chemical formula OCN−. It is a resonance of three forms: [O−−C≡N] (61%) ↔ [O=C=N−] (30%) ↔ [O+≡C−N2−] (4%).
Phosphorus triiodide (PI3) is an inorganic compound with the formula PI3. A red solid, it is too unstable to be stored for long periods of time; it is, nevertheless, commercially available. It is widely used in organic chemistry for converting alcohols to alkyl iodides. It is also a powerful reducing agent.
Borazine, also known as borazole, is an inorganic compound with the chemical formula B3H6N3. In this cyclic compound, the three BH units and three NH units alternate. The compound is isoelectronic and isostructural with benzene. For this reason borazine is sometimes referred to as “inorganic benzene”. Like benzene, borazine is a colourless liquid with an aromatic odor.
The chemical element nitrogen is one of the most abundant elements in the universe and can form many compounds. It can take several oxidation states; but the most common oxidation states are -3 and +3. Nitrogen can form nitride and nitrate ions. It also forms a part of nitric acid and nitrate salts. Nitrogen compounds also have an important role in organic chemistry, as nitrogen is part of proteins, amino acids and adenosine triphosphate.
Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name the compound has the formula Al2(C2H5)6 (abbreviated as Al2Et6 or TEA). This colorless liquid is pyrophoric. It is an industrially important compound, closely related to trimethylaluminium.
Mass spectral interpretation is the method employed to identify the chemical formula, characteristic fragment patterns and possible fragment ions from the mass spectra. Mass spectra is a plot of relative abundance against mass-to-charge ratio. It is commonly used for the identification of organic compounds from electron ionization mass spectrometry. Organic chemists obtain mass spectra of chemical compounds as part of structure elucidation and the analysis is part of many organic chemistry curricula.
Explosophores are functional groups in organic chemistry that give organic compounds explosive properties.
In organic chemistry, a nitrate ester is an organic functional group with the formula R−ONO2, where R stands for any organyl group. They are the esters of nitric acid and alcohols. A well-known example is nitroglycerin, which is not a nitro compound, despite its name.
1-Diazidocarbamoyl-5-azidotetrazole, often jokingly referred to as azidoazide azide, is a heterocyclic inorganic compound with the formula C2N14. It is a highly reactive and extremely sensitive explosive.