Detonation, deflagrative reaction

Figure 6-13 shows the physical differences between a detonation and a deflagration for a combustion reaction that occurs in the gas phase in the open. For a detonation the reaction front moves at a speed greater than the speed of sound. A shock front is found a short distance in front of the reaction front. The reaction front provides the energy for the shock front and continues to drive it at sonic or greater speeds. 

A physical explosion, for example, a boiler explosion, a pressure vessel failure, or a BLEVE (Boiling Liquid Expanding Vapor Explosion), is not necessarily caused by a chemical reaction. Chemical explosions are characterized as detonations, deflagrations, and thermal explosions. In the case of a detonation or deflagration (e.g., explosive burning), a reaction front is present that proceeds through the material. A detonation proceeds by a shock wave with a velocity exceeding the speed of sound in the unreacted material. A... 

For a detonation, the reaction front moves faster than the speed of sound, pushing the pressure wave or shock front immediately ahead of it. For a deflagration, the reaction front moves at a speed less than the speed of sound, resulting in a pressure wave that moves at the speed of sound, moving away from the reaction front. A noticeable difference is found in the resulting pressure-time or pressure-distance plots. 

Permitted explosives with a higher grade of safety are powder explosives. They contain a minimum percentage of nitroglycerine-ni-troglycol to ensure reliable initiation and transmission of detonation and to exclude slow deflagration reactions. The mechanism of salt-pair... 

Detonation Deflagration Thermal explosion Hypergolic reaction... 

For self—reactive substances typical dangerous reactions are detonation, deflagration... 

We have now seen how deflagration can be initiated thermally, and also that detonation requires a shock for initiation. Under certain circumstances and conditions, a burning or deflagration reaction can grow into a full steady-state detonation. 

Decomposition Hazards. The main causes of unintended decompositions of organic peroxides are heat energy from heating sources and mechanical shock, eg, impact or friction. In addition, certain contaminants, ie, metal salts, amines, acids, and bases, initiate or accelerate organic peroxide decompositions at temperatures at which the peroxide is normally stable. These reactions also Hberate heat, thus further accelerating the decomposition. Commercial products often contain diluents that desensitize neat peroxides to these hazards. Commercial organic peroxide decompositions are low order deflagrations rather than detonations (279). 

The latter method typically requires less severe conditions than the former because of the labile nature of the organic anhydride (87,137). Both of these reactions can result in explosions and significant precautions should be taken prior to any attempted synthesis of a peracid (87). For soHd peracids the reaction mixture can be neutralized with sodium hydroxide and the resulting fUtercake washed with water. In the case of the sulfuric acid mediated reaction the peracid has sodium sulfate incorporated in the cake (135). The water of hydration present in the sodium sulfate is desirable to prevent detonation or deflagration of the soHd peracid when isolated in a dry state (87,138,139). 

Deflagration to Detonation Transition A reaction front that starts out with velocities below the speed of sound and subsequently accelerates to velocities higher than the speed of sound in the unreacted material is said to have undergone a Deflagration to Detonation Transition. The possibility of transition is enhanced by confinement/turbulence generators in the path of the reaction front. 

Nichols (1999) describes a nnmber of reaction forces that are generated dnring deflagrations and detonations in piping systems snch as ... 

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