Editing Explosive (section)

==Properties==
To determine the suitability of an explosive substance for a particular use, its [[physics|physical]] [[Physical property|properties]] must first be known. The usefulness of an explosive can only be appreciated when the properties and the factors affecting them are fully understood. Some of the more important characteristics are listed below:

===Sensitivity===
{{Main|Sensitivity (explosives)}}
Sensitivity refers to the ease with which an explosive can be ignited or detonated, i.e., the amount and intensity of [[electric shock|shock]], [[friction]], or [[heat]] that is required. When the term [[wikt:Sensitivity|sensitivity]] is used, care must be taken to clarify what kind of sensitivity is under discussion. The relative sensitivity of a given explosive to impact may vary greatly from its sensitivity to friction or heat. Some of the test methods used to determine sensitivity relate to:
* '''[[Impact (mechanics)|Impact]]''' – Sensitivity is expressed in terms of the distance through which a standard weight must be dropped onto the material to cause it to explode.
* '''[[Friction]]''' – Sensitivity is expressed in terms of the amount of pressure applied to the material in order to create enough friction to cause a reaction.
* '''[[Heat]]''' – Sensitivity is expressed in terms of the temperature at which decomposition of the material occurs.

Specific explosives (usually but not always highly sensitive on one or more of the three above axes) may be idiosyncratically sensitive to such factors as pressure drop, acceleration, the presence of sharp edges or rough surfaces, incompatible materials, or {{nowrap|even{{hsp}}{{mdash}}{{hsp}}}}in rare {{nowrap|cases{{hsp}}{{mdash}}{{hsp}}}}nuclear or electromagnetic radiation. These factors present special hazards that may rule out any practical utility.

Sensitivity is an important consideration in selecting an explosive for a particular purpose. The explosive in an armor-piercing projectile must be relatively insensitive, or the shock of impact would cause it to detonate before it penetrated to the point desired. The explosive lenses around nuclear charges are also designed to be highly insensitive, to minimize the risk of accidental detonation.

===Sensitivity to initiation===
The index of the capacity of an explosive to be initiated into detonation in a sustained manner. It is defined by the power of the detonator, which is certain to prime the explosive to a sustained and continuous detonation. Reference is made to the [[Sellier-Bellot]] scale that consists of a series of 10 detonators, from {{nowrap|n.{{hsp}}1}} to {{nowrap|n.{{hsp}}10}}, each of which corresponds to an increasing charge weight. In practice, most of the explosives on the market today are sensitive to an {{nowrap|n.{{hsp}}8}} detonator, where the charge corresponds to 2&nbsp;grams of [[mercury fulminate]].

===Velocity of detonation===
{{Main|Detonation velocity}}
The velocity with which the reaction process propagates in the mass of the explosive. Most commercial mining explosives have detonation velocities ranging from 1,800&nbsp;m/s to 8,000&nbsp;m/s. Today, the velocity of detonation can be measured with accuracy. Together with [[density]], it is an important element influencing the yield of the energy transmitted through both atmospheric over-pressure and ground acceleration. By definition, a "low explosive", such as black powder, or smokeless gunpowder has a burn rate of 171–631&nbsp;m/s.<ref>{{Cite book|url=https://books.google.com/books?id=PmuqCHDC3pwC&pg=PA106|title=History of Shock Waves, Explosions and Impact: A Chronological and Biographical Reference|last=Krehl|first=Peter O.K.|date=2008-09-24|publisher=Springer Science & Business Media|isbn=978-3-540-30421-0|page=106|language=en}}</ref> In contrast, a "high explosive", whether a primary, such as [[detonating cord]], or a secondary, such as TNT or C-4, has a significantly higher burn rate about 6900–8092&nbsp;m/s.<ref>{{Cite book|title=History of Shock Waves, Explosions and Impact: A Chronological and Biographical Reference|last=Krehl|first=Peter O.K.|publisher=Springer Science & Business Media|year=2008|isbn=978-3-540-30421-0|page=1970}}</ref>

===Stability===
{{Main|Chemical stability}}
'''Stability ''' is the ability of an explosive to be stored without [[chemical decomposition|deterioration]].

The following factors affect the stability of an explosive:
* '''[[Chemical constitution]].''' In the strictest technical sense, the word "stability" is a thermodynamic term referring to the energy of a substance relative to a reference state or to some other substance.<!--vague, needs better def--> However, in the context of explosives, stability commonly refers to ease of detonation, which is concerned with [[chemical kinetics]] (i.e., rate of decomposition). It is perhaps best, then, to differentiate between the terms thermodynamically stable and kinetically stable by referring to the former as "inert." Contrarily, a kinetically unstable substance is said to be "labile." It is generally recognized that certain groups like nitro (–NO<sub>2</sub>), [[nitrate]] (–ONO<sub>2</sub>), and [[azide]] (–N<sub>3</sub>), are intrinsically labile. Kinetically, there exists a low activation barrier to the decomposition reaction. Consequently, these compounds exhibit high sensitivity to flame or mechanical shock. The chemical bonding in these compounds is characterized as predominantly covalent and thus they are not thermodynamically stabilized by a high ionic-lattice energy. Furthermore, they generally have positive enthalpies of formation and there is little mechanistic hindrance to internal molecular rearrangement to yield the more thermodynamically stable (more strongly bonded) decomposition products. For example, in [[lead azide]], Pb(N<sub>3</sub>)<sub>2</sub>, the nitrogen atoms are already bonded to one another, so decomposition into Pb and N<sub>2</sub><sup>[1]</sup> is relatively easy.
* '''[[Temperature]] of storage.''' The rate of decomposition of explosives increases at higher temperatures. All standard military explosives may be considered to have a high degree of stability at temperatures from –10 to +35&nbsp;°C, but each has a high temperature at which its rate of [[thermal decomposition]] rapidly accelerates and stability is reduced. As a rule of thumb, most explosives become dangerously unstable at temperatures above 70&nbsp;°C.
* '''Exposure to [[sunlight]].''' When exposed to the [[ultraviolet]] rays of sunlight, many explosive compounds containing [[nitrogen]] groups rapidly decompose, affecting their stability.
* '''[[Electrical discharge]].''' [[Electrostatic discharge|Electrostatic]] or [[electric spark|spark]] sensitivity to initiation is common in a number of explosives. Static or other electrical discharge may be sufficient to cause a reaction, even detonation, under some circumstances. As a result, safe handling of explosives and [[pyrotechnics]] usually requires proper [[ground (electricity)|electrical grounding]] of the operator.

===Power, performance, and strength===
{{Main|Power (physics)|Strength (explosive)}}
The term '''power''' or '''performance''' as applied to an explosive refers to its ability to do work. In practice it is defined as the explosive's ability to accomplish what is intended in the way of energy delivery (i.e., fragment projection, air blast, high-velocity jet, underwater shock and bubble energy, etc.). Explosive power or performance is evaluated by a tailored series of tests to assess the material for its intended use. Of the tests listed below, cylinder expansion and air-blast tests are common to most testing programs, and the others support specific applications.
* '''Cylinder expansion test.''' A standard amount of explosive is loaded into a long hollow [[cylinder (geometry)|cylinder]], usually of copper, and detonated at one end. Data is collected concerning the rate of radial expansion of the cylinder and the maximum cylinder wall velocity. This also establishes the [[Gurney equations|Gurney energy]] or 2''E''.
* '''Cylinder fragmentation.''' A standard steel cylinder is loaded with explosive and detonated in a sawdust pit. The [[fragmentation (weaponry)|fragments]] are collected and the size distribution analyzed.
* '''Detonation pressure ([[Chapman–Jouguet condition]]).''' [[Detonation]] pressure data derived from measurements of shock waves transmitted into water by the detonation of cylindrical explosive charges of a standard size.
* '''Determination of critical diameter.''' This test establishes the minimum physical size a charge of a specific explosive must be to sustain its own detonation wave. The procedure involves the detonation of a series of charges of different diameters until difficulty in detonation wave propagation is observed.
* '''Massive-diameter detonation velocity.''' Detonation velocity is dependent on loading density (c), charge diameter, and grain size. The hydrodynamic theory of detonation used in predicting explosive phenomena does not include the diameter of the charge, and therefore a detonation velocity, for a massive diameter. This procedure requires the firing of a series of charges of the same density and physical structure, but different diameters, and the extrapolation of the resulting detonation velocities to predict the detonation velocity of a charge of a massive diameter.
* '''Pressure versus scaled distance.''' A charge of a specific size is detonated and its pressure effects measured at a standard distance. The values obtained are compared with those for TNT.
* '''Impulse versus scaled distance.''' A charge of a specific size is detonated and its impulse (the area under the pressure-time curve) measured as a function of distance. The results are tabulated and expressed as [[TNT equivalent]]s.
* '''Relative bubble energy (RBE).''' A 5 to 50&nbsp;kg charge is detonated in water and piezoelectric gauges measure peak pressure, time constant, impulse, and energy.
::The RBE may be defined as ''K''<sub>''x''</sub> 3
::RBE = ''K''<sub>''s''</sub>
::where ''K'' = the bubble expansion period for an experimental (''x'') or a standard (''s'') charge.

===Brisance===
{{Main|Brisance}}
In addition to strength, explosives display a second characteristic, which is their shattering effect or brisance (from the French meaning to "break"). Brisance is important in determining the effectiveness of an explosion in fragmenting shells, bomb casings, and [[grenade]]s. The rapidity with which an explosive reaches its peak pressure ([[power (physics)|power]]) is a measure of its brisance. Brisance values are primarily employed in France and Russia.

The sand crush test is commonly employed to determine the relative brisance in comparison to TNT. No test is capable of directly comparing the explosive properties of two or more compounds; it is important to examine the data from several such tests (sand crush, [[trauzl lead block test|trauzl]], and so forth) in order to gauge relative brisance. True values for comparison require field experiments.

===Density===
Density of loading refers to the mass of an explosive per unit volume. Several methods of loading are available, including pellet loading, cast loading, and press loading, the choice being determined by the characteristics of the explosive. Dependent upon the method employed, an average density of the loaded charge can be obtained that is within 80–99% of the theoretical maximum density of the explosive. High load density can reduce [[sensitivity (explosives)|sensitivity]] by making the [[mass]] more resistant to internal [[friction]]. However, if density is increased to the extent that individual [[crystal]]s are crushed, the explosive may become more sensitive. Increased load density also permits the use of more explosive, thereby increasing the power of the [[warhead]]. It is possible to compress an explosive beyond a point of sensitivity, known also as ''dead-pressing'', in which the material is no longer capable of being reliably initiated, if at all.{{citation needed|date=November 2023}}

===Volatility===
[[Volatility (chemistry)|Volatility]] is the readiness with which a substance [[vaporization|vaporizes]]. Excessive volatility often results in the development of pressure within rounds of ammunition and separation of mixtures into their constituents. Volatility affects the chemical composition of the explosive such that a marked reduction in stability may occur, which results in an increase in the danger of handling.

===Hygroscopicity and water resistance===
The introduction of [[water]] into an explosive is highly undesirable since it reduces the sensitivity, strength, and velocity of detonation of the explosive. [[Hygroscopicity]] is a measure of a material's moisture-absorbing tendencies. Moisture affects explosives adversely by acting as an inert material that absorbs heat when vaporized, and by acting as a solvent medium that can cause undesired chemical reactions. Sensitivity, strength, and velocity of detonation are reduced by inert materials that reduce the continuity of the explosive mass. When the moisture content evaporates during detonation, cooling occurs, which reduces the temperature of reaction. Stability is also affected by the presence of moisture since moisture promotes decomposition of the explosive and, in addition, causes corrosion of the explosive's metal container.

Explosives considerably differ from one another as to their behavior in the presence of water. Gelatin dynamites containing nitroglycerine have a degree of water resistance. Explosives based on [[ammonium nitrate]] have little or no water resistance as ammonium nitrate is highly soluble in water and is hygroscopic.

===Toxicity===
Many explosives are [[toxicity|toxic]] to some extent. Manufacturing inputs can also be organic compounds or hazardous materials that require special handling due to risks (such as [[carcinogen]]s). The decomposition products, residual solids, or gases of some explosives can be toxic, whereas others are harmless, such as carbon dioxide and water.

Examples of harmful by-products are:
* Heavy metals, such as lead, mercury, and barium from primers (observed in high-volume firing ranges)
* Nitric oxides from TNT
* Perchlorates when used in large quantities

"Green explosives" seek to reduce environment and health impacts. An example of such is the lead-free primary explosive copper(I) 5-nitrotetrazolate, an alternative to [[lead azide]].<ref>{{cite magazine |url=https://www.newscientist.com/article/dn8903-green-explosive-is-a-friend-of-the-earth.html |title=Green explosive is a friend of the Earth |magazine=New Scientist |date=27 March 2006 |access-date=12 November 2014 |url-status=live |archive-url=https://web.archive.org/web/20141112220348/http://www.newscientist.com/article/dn8903-green-explosive-is-a-friend-of-the-earth.html |archive-date=12 November 2014 |df=dmy-all}}</ref>

===Explosive train===
{{Main|Explosive train}}
Explosive material may be incorporated in the explosive train of a device or system. An example is a pyrotechnic lead igniting a booster, which causes the main charge to detonate.

===Volume of products of explosion===
The most widely used explosives are condensed liquids or solids converted to gaseous products by explosive chemical reactions and the energy released by those reactions. The gaseous products of complete reaction are typically [[carbon dioxide]], [[steam]], and [[nitrogen]].<ref name="z&k">{{cite book |title=Theory of Detonation |last1=Zel'dovich |first1=Yakov |author-link=Yakov Borisovich Zel'dovich |first2=Alexander Solomonovich |last2=Kompaneets |author-link2=Alexander Solomonovich Kompaneyets |publisher=Academic Press |year=1960|pages=208–210}}</ref> Gaseous volumes computed by the [[ideal gas law]] tend to be too large at high pressures characteristic of explosions.<ref>{{cite book |title=Chemical Process Principles |last1=Hougen |first1=Olaf A. |first2=Kenneth |last2=Watson |first3=Roland |last3=Ragatz |publisher=John Wiley & Sons |year=1954|pages=66–67}}</ref> Ultimate volume expansion may be estimated at three orders of magnitude, or one liter per gram of explosive. Explosives with an oxygen deficit will generate soot or gases like [[carbon monoxide]] and [[hydrogen]], which may react with surrounding materials such as atmospheric [[oxygen]].<ref name="z&k"/> Attempts to obtain more precise volume estimates must consider the possibility of such side reactions, condensation of steam, and aqueous solubility of gases like carbon dioxide.<ref>{{cite book |title=Chemical Calculations |last=Anderson |first=H.V. |publisher=McGraw-Hill |year=1955|page=206}}</ref>

===Oxygen balance (OB% or ''Ω'')===
{{Main|Oxygen balance}}
[[Oxygen balance]] is an expression that is used to indicate the degree to which an explosive can be oxidized. If an explosive molecule contains just enough oxygen to convert all of its carbon to carbon dioxide, all of its hydrogen to water, and all of its metal to metal oxide with no excess, the molecule is said to have a zero oxygen balance. The molecule is said to have a positive oxygen balance if it contains more oxygen than is needed, and a negative oxygen balance if it contains less oxygen than is needed.<ref>{{cite book |last1= Meyer |first1= Rudolf |first2=Josef |last2=Köhler|first3=Axel |last3=Homburg |title= Explosives |edition=6th |publisher= Wiley VCH |year= 2007 |isbn= 978-3-527-31656-4}}</ref> The sensitivity, [[strength (explosive)|strength]], and [[brisance]] of an explosive are all somewhat dependent upon oxygen balance and tend to approach their maxima as oxygen balance approaches zero.

===Chemical composition===
A chemical explosive may consist of either a chemically pure compound, such as [[nitroglycerin]], or a mixture of a [[fuel]] and an [[oxidizer]], such as [[black powder]] or [[grain dust]] and air.

====Pure compounds====
Some chemical compounds are unstable in that, when shocked, they react, possibly to the point of detonation. Each molecule of the compound dissociates into two or more new molecules (generally gases) with the release of energy.
* '''[[Nitroglycerin]]''': A highly unstable and sensitive liquid
* '''[[Acetone peroxide]]''': A very unstable white [[organic peroxide]]
* '''[[TNT]]''': Yellow insensitive crystals that can be melted and cast without detonation
* '''[[Cellulose nitrate]]''': 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
** '''[[C4 explosive|C-4]]''' (or Composition C-4): An [[RDX]] [[plastic explosive]] plasticized to be adhesive and malleable

The above compositions may describe most of the explosive material, but a practical explosive will often include small percentages of other substances. For example, [[dynamite]] is a mixture of highly sensitive nitroglycerin with [[sawdust]], powdered [[silica]], or most commonly [[diatomaceous earth]], 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; [[aluminium]] powder may be introduced to increase total energy and blast effects. Explosive compounds are also often "alloyed": HMX or RDX powders may be mixed (typically by melt-casting) with TNT to form [[Octol]] or [[Cyclotol]].

====Oxidized 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 [[Chemical element|element]], such as [[gas state|gaseous]] or [[liquid]] [[oxygen]].
* '''[[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 [[potassium perchlorate|perchlorate]])
* '''[[Ammonal]]''': [[Ammonium nitrate]] and aluminium powder
* '''[[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 of the phosphorus to slightly decrease sensitivity.
* '''[[Sprengel explosive]]s''': A very general class incorporating any strong oxidizer and highly reactive fuel, although in practice the name was most commonly applied to mixtures of [[chlorate]]s and [[nitroaromatic]]s.
** '''[[ANFO]]''': Ammonium nitrate and [[fuel oil]]
** '''[[Cheddite]]s''': [[Chlorate]]s or [[perchlorate]]s and oil
** '''[[Oxyliquit]]s''': Mixtures of organic materials and [[liquid oxygen]]
** '''[[Panclastite]]s''': Mixtures of organic materials and [[dinitrogen tetroxide]]

===Availability and cost===
The availability and cost of explosives are determined by the availability of the raw materials and the cost, complexity, and safety of the manufacturing operations.