Shock Wave Science and Technology Reference Library, Vol.4 Heterogen
This book, as a volume of the Shock Wave Science and Technology Reference Library, is primarily concerned with detonation waves or compression shock waves in reactive heterogeneous media, including mixtures of solid, liquid and gas phases. The topics invo
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1 Introduction In this chapter, we consider the theoretical and practical aspects of shock wave processes in condensed media, including solid–solid detonations (SSDs), i.e., conversion of solid-phase reactants to solid-phase products [1]. Numerous experimental data imply that shock processing may be used to induce very fast chemical reactions in compacted reactive powder mixtures. It is known [2] that a shock wave process is a kind of motion in a continuous medium which is accompanied by propagation of special waves (shocks) at a hypersound velocity. A shock (sudden change) represents a thin, relatively stable zone within which elementary volumes of matter spasmodically change their velocity and density. Depending on the properties of the medium, either compression or rarefaction shocks can be formed. Since rarefaction shocks are encountered infrequently, in further discussion we will deal only with compression shocks. Within the shock, the medium may undergo various physicochemical transformations (chemical reaction, phase transition, collapse of pores, etc.). Shocks without transformations and shocks in chemically inert porous media are normally termed “shock waves.” The shocks accompanied by physicochemical transformations are termed either “shock waves” or “detonation waves,” depending on the type of transformation. The difference between shock waves and detonation waves will be discussed later. Now let us only note that a leading shock in a self-propagating shock wave process in condensed explosives or reactive gaseous mixtures can be classified as a detonation wave. Concerning other shock wave processes, the difference between shock and detonation waves is a subject of controversy and argument. The width of shocks without transformation of matter is comparable to the free path of molecules in gases or to intermolecular distance in condensed matter [2]. As a mathematical image of such a shock, the notion of a traveling finite discontinuity surface can be used. The width of a shock accompanied by transformations of matter is greater by several orders of magnitude. For F. Zhang (ed.), Shock Wave Science and Technology Reference Library: Heterogeneous Detonation, DOI: 10.1007/978-3-540-88447-7 5, c 2009 Springer-Verlag Berlin Heidelberg
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instance, in powder mixtures the shock width is comparable to the particle size. Nevertheless, in some cases the shock with transformation can also be modeled as a surface of finite discontinuity. It is believed that a self-sustained shock wave process (detonation) may develop only in condensed explosives or reactive gaseous mixtures where the reaction is accompanied by vigorous gas evolution. The possibility of detonation in systems that react without evolution of gases (so-called gas-free detonation) has been predicted theoretically [3], and a quantitative thermodynamic criterion for this to occur in any condensed media was suggested in [3] and then specified in [4] (see Sect. 5.4.4).
5.2 Shock-Induced Solid–Solid Reactions 5.2.1 Experimental Obse
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