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Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion does not always result in fire, because a flame is only visible when substances undergoing combustion vaporize, but when it does, a flame is a characteristic indicator of the reaction. While activation energy must be supplied to initiate combustion, the heat from a flame may provide enough energy to make the reaction self-sustaining.
The following outline is provided as an overview of and topical guide to chemistry:
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.
In chemistry, thermodynamics, and other related fields, a phase transition is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of matter: solid, liquid, and gas, and in rare cases, plasma. A phase of a thermodynamic system and the states of matter have uniform physical properties. During a phase transition of a given medium, certain properties of the medium change as a result of the change of external conditions, such as temperature or pressure. This can be a discontinuous change; for example, a liquid may become gas upon heating to its boiling point, resulting in an abrupt change in volume. The identification of the external conditions at which a transformation occurs defines the phase transition point.
A discrete element method (DEM), also called a distinct element method, is any of a family of numerical methods for computing the motion and effect of a large number of small particles. Though DEM is very closely related to molecular dynamics, the method is generally distinguished by its inclusion of rotational degrees-of-freedom as well as stateful contact and often complicated geometries. With advances in computing power and numerical algorithms for nearest neighbor sorting, it has become possible to numerically simulate millions of particles on a single processor. Today DEM is becoming widely accepted as an effective method of addressing engineering problems in granular and discontinuous materials, especially in granular flows, powder mechanics, and rock mechanics. DEM has been extended into the Extended Discrete Element Method taking heat transfer, chemical reaction and coupling to CFD and FEM into account.
Ammonium nitrate is a chemical compound with the chemical formula NH4NO3. It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is predominantly used in agriculture as a high-nitrogen fertilizer.
In physics, a shock wave, or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a medium but is characterized by an abrupt, nearly discontinuous, change in pressure, temperature, and density of the medium.
Detonation is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with speeds in the range of 1 km/sec and differ from deflagrations which have subsonic flame speeds in the range of 1 m/sec.
The shock tube is an instrument used to replicate and direct blast waves at a sensor or a model in order to simulate actual explosions and their effects, usually on a smaller scale. Shock tubes can also be used to study aerodynamic flow under a wide range of temperatures and pressures that are difficult to obtain in other types of testing facilities. Shock tubes are also used to investigate compressible flow phenomena and gas phase combustion reactions. More recently, shock tubes have been used in biomedical research to study how biological specimens are affected by blast waves.
An entropic explosion is an explosion in which the reactants undergo a large change in volume without releasing a large amount of heat. The chemical decomposition of triacetone triperoxide (TATP) may be an example of an entropic explosion. It is not a thermochemically highly favored event because little energy is generated in chemical bond formation in reaction products, but rather involves an entropy burst, which is the result of formation of one ozone and three acetone gas phase molecules from every molecule of TATP in the solid state.
Detonation nanodiamond (DND), also known as ultradispersed diamond (UDD), is diamond that originates from a detonation. When an oxygen-deficient explosive mixture of TNT/RDX is detonated in a closed chamber, diamond particles with a diameter of c. 5 nm are formed at the front of the detonation wave in the span of several microseconds.
Explosive velocity, also known as detonation velocity or velocity of detonation (VoD), is the velocity at which the shock wave front travels through a detonated explosive. Explosive velocities are always faster than the local speed of sound in the material.
The Chapman–Jouguet condition holds approximately in detonation waves in high explosives. It states that the detonation propagates at a velocity at which the reacting gases just reach sonic velocity as the reaction ceases.
In pyrotechnics, a pyrotechnic initiator is a device containing a pyrotechnic composition used primarily to ignite other, more difficult-to-ignite materials, such as thermites, gas generators, and solid-fuel rockets. The name is often used also for the compositions themselves.
The Voitenko compressor is a shaped charge adapted from its original purpose of piercing thick steel armour to the task of accelerating shock waves. It was proposed by Anatoly Emelyanovich Voitenko, a Soviet scientist, in 1964. It slightly resembles a wind tunnel.
An explosion is a rapid expansion in volume of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Explosions may also be generated by a slower expansion that would normally not be forceful, but is not allowed to expand, so that when whatever is containing the expansion is broken by the pressure that builds as the matter inside tries to expand, the matter expands forcefully. An example of this is a volcanic eruption created by the expansion of magma in a magma chamber as it rises to the surface. Supersonic explosions created by high explosives are known as detonations and travel through shock waves. Subsonic explosions are created by low explosives through a slower combustion process known as deflagration.
Deflagration to detonation transition (DDT) refers to a phenomenon in ignitable mixtures of a flammable gas and air when a sudden transition takes place from a deflagration type of combustion to a detonation type of explosion.
The ZND detonation model is a one-dimensional model for the process of detonation of an explosive. It was proposed during World War II independently by Y. B. Zel'dovich, John von Neumann, and Werner Döring, hence the name.
A shock-induced combustion ramjet engine (abbreviated as shcramjet; also called oblique detonation wave engine; also called standing oblique detonation ramjet (sodramjet); or simply referred to as shock-ramjet engine) is a concept of air-breathing ramjet engine, proposed to be used for hypersonic and/or single-stage-to-orbit propulsion applications.
The photoacoustic effect or optoacoustic effect is the formation of sound waves following light absorption in a material sample. In order to obtain this effect the light intensity must vary, either periodically or as a single flash. The photoacoustic effect is quantified by measuring the formed sound with appropriate detectors, such as microphones or piezoelectric sensors. The time variation of the electric output from these detectors is the photoacoustic signal. These measurements are useful to determine certain properties of the studied sample. For example, in photoacoustic spectroscopy, the photoacoustic signal is used to obtain the actual absorption of light in either opaque or transparent objects. It is useful for substances in extremely low concentrations, because very strong pulses of light from a laser can be used to increase sensitivity and very narrow wavelengths can be used for specificity. Furthermore, photoacoustic measurements serve as a valuable research tool in the study of the heat evolved in photochemical reactions, particularly in the study of photosynthesis.
References
- ↑ Boslough, M. B. (1989). "A thermochemical model for shock-induced chemical reactions in porous solids: Analogs and contrasts to detonation". 9. International Symposium on Detonation. Portland, OR. OSTI 5978092.
- ↑ Boslough, M.B. (1990). "A thermochemical model for shock‐induced reactions (heat detonations) in solids". Journal of Chemical Physics. 92 (3): 1839–1848.
- ↑ Graham, R. A.; Anderson, M. U.; Horie, Y.; You, S.-K.; Holman, G. T. (1993). "Pressure measurements in chemically reacting powder mixtures with the Bauer piezoelectric polymer gauge". Shock Waves. Berlin / Heidelberg: Springer. 3 (2): 79–82. Bibcode:1993ShWav...3...79G. doi:10.1007/BF02115887. S2CID 120624871.
- ↑ Xu, X.; Thadhani, N. N. (2004). "Investigation of shock-induced reaction behavior of as-blended and ball-milled Ni + Ti powder mixtures using time-resolved stress measurements". Journal of Applied Physics. 96 (4): 2000–2009. Bibcode:2004JAP....96.2000X. doi:10.1063/1.1773380.
- ↑ Boslough, M.B.; Silling, S.A.; Fischer, S.H.; Cox, D.E.; Vandermolen, W.B. (2017). "Shock-Induced Solid-State reactions in Powders: An Experimentally-Based Reassessment". Sandia Report. SAND2017-5297.