Sound propagation, chemical reaction

An exothermic chemical reaction that propagates with such rapidity that the rate of advance of the reaction zone into the unreacted material exceeds the velocity of sound in the unreacted material, that is the advancing reaction zone is preceded by a shock wave. The rate of advance of the reaction zone is termed detonation rate or detonation velocity. When this rate of advance attains such a value that it will continue without diminution thru the unreacted material, it is termed a stable detonation velocity. The exact value of this term is dependent upon a number of factors, principally the chemical and physical properties of the material. When the detonation rate is equal to or greater than the stable detona-... 

The first difference in a detonation wave which is favorable for stability is the fact that due to the decrease in the speed of sound (added to the mass velocity) to less than the propagation velocity, independence is achieved from the conditions behind the wave. On the other hand, application of small perturbations also leads to variation in the rate of the chemical reaction. It is impossible now to foresee the result of a calculation of stability with respect to small perturbations which might prove dependent on peculiarities of the chemical kinetics (autocatalysis, activation heat). 

In Chapter 1.3 we defined a detonation as the propagation of a chemical reaction through an energetic material under the influence of a shock-wave at speeds faster than the speed of sound in the material. The velocity at which the energetic material decomposes is therefore only dependent on the velocity of the shock-wave. It is not determined by a heat-transfer process as it is the case for deflagration or combustion. 

Propagation of sound is an established method of studying irreversible thermodynamics. Sound propagation is accompanied by heat production, viscous flow, relaxation phenomena and chemical reactions, each of which is determined by a particular relaxation time. 

Appendix 3A Sound Propagation in Liquid/Fluid Disperse systems and Chemical Reaction... 

Surface chemistry can be restricted simply to bulk chemistry if we assume that a "reaction" is characterised by a time-dependent change of components A and B. In terms of surfaces science A can be the monomer and B the associated state of an adsorbed species. In other words, sound propagation in bulk phases and hydrodynamic stresses act in the same way. Considering only one chemical reaction the plot In e -1 with V and e as independent variables obtains the form... 

A critical characteristic of energetic materials is the Chapman-Jouguet (CJ) state. This describes the chemical equilibrium of the products at the end of the reaction zone of the detonation wave before the isentropic expansion. In the classical ZePdovich-Neumann-Doring (ZND) detonation model, the detonation wave propagates at constant velocity. This velocity is the same as at the CJ point which characterizes the state of reaction products in which the local speed of sound decreases to the detonation velocity as the product gases expand. 

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