Thermal decomposition correlations with impact sensitivity

On the other hand, the characteristics of detonation, electric spark sensitivity, and thermal decomposition correlate with the N NMR chemical shifts of nitrogen atoms of the most reactive nitro groups. The basis of initiation by electric spark could lie in a thermal stimulus [35,39,52,53]. However, thermal stimuli cannot be considered in the process of detonation initiation by shock (also by impact) [115]. This also agrees with the finding that the detonation characteristics of energetic materials correlate with the characteristics of their low-temperature decomposition, which means that the primary fragmentation of polynitro compounds in their detonation transformation proceeds at milder conditions than those present at the front of detonation wave or in its reaction zone. That also means that the detonation transformation itself of the given substance should be preceded by an induction period [120]. 

Impurities, such as grit, shreds of cotton, even in small quantities, sensitize an expl to frictional impact. That is why utmost cleanliness must be exercised in the preparation of expls. There are differences in the sensitivity of azides to mechanical and thermal influences. They have been correlated with the structure of the outer electronic orbits, the electrochemical potential, the ionization energy and the arrangement of atoms within the crystal. Functions of the polarizability of the cation are the plastic deformability of the crystals, and their surface properties. The nature of cation in an azide, such as Pb(Nj)2, has little effect on the energy released by the decomposition, which is vested in the N ion. The high heat of formation of the N2 molecule accounts... 

A key point, with regard to both issues, is the decomposition process of the compound What are its energetics and how readily does it occur Our emphasis in this chapter shall be upon factors that influence the ease with which decomposition can be initiated by unwanted external stimuli, i.e. sensitivity. These stimuli may be of various types, including impact, shock, friction, heat and electrostatic charge [8]. Relative vulnerabilities to these different effects need not be the same for example, the onset temperatures for the thermal decomposition of TNT (1) and HMX (2) are quite similar, but the latter is much more likely to undergo detonation upon impact [8]. It has been shown, however, that there is a general correlation between impact and shock sensitivities [10], which are the ones upon which we will focus. 

Correlations of the oxygen balance of a parent energetic compound and its impact sensitivity (a thermal decomposition phenomenon) are well known 11-31. Hammett correlations with the explosive sensitivity in arylammonium perchlorate salts have been uncovered [4]. Relationships between the composition [5] and decomposition [6,7] of explosives and their detonation velocity are known. Extensive studies have been made relating molecular structure to the kinetics and thermolysis trends for aliphatic nitro compounds [8J, azides [9,10], and nitramines [11]. Correlations of the melting point with burn-rate [12], functional group with decomposition temperature [13], and various structural parameters with stability [14] have been proposed. 

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