Explosion, heat of—

In a chemical reaction involving explosives, energy is initially required to break the bonds of the explosive into its constituent elements as shown in Eq. (12.22) for RDX [4]. 

These elements quickly form new bonds with the release of a greater quantity of energy as shown in Eq. (12.23) [4]. 

When an explosive is initiated either to burning or detonation, its energy is released in the form of heat. The liberation of heat under adiabatic conditions is called the heat of explosion, denoted by the letter Q. The heat of explosion provides information about the work capacity of the explosive, where the effective propellants and secondary explosives generally have high values of Q. For propellants burning in the chamber of a gun, and secondary explosives in detonating devices, the heat of explosion is conventionally expressed in terms of constant volume 

Consider an explosive that is initiated by a stimulus of negligible thermal proportions. The explosion can be represented by the irreversible process that includes the initiation followed by the explosion to give gaseous products with a heat Q ultimately lost to the surroundings. 

Under constant volume conditions Qy can be calculated from the standard internal energies of formation for the products AU°f(producis) and the standard internal energies of formation for the explosive components 

A similar expression is given for the heat of explosion under constant pressure conditions as shown in Equation 5.5, where AHet represents the corresponding standard enthalpies of formation  

In considering the thermochemistry of solid and liquid explosives, it is usually adequate, for practical purposes, to treat the state functions AH and A U as approximately the same. Consequently, heats, or enthalpy terms, tend to be used for both constant pressure and constant volume conditions. 

Therefore, the heat of explosion Q can be calculated from the difference between the sum of the energies for the formation of the explosive components and the sum of the energies for the formation of the explosion products, as shown in Equation 5.6. 

Therefore, the heat of explosion Q can be calculated from the difference between the sum of the energies for the formation of 

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Table 7-26 [49] has been developed by ratio of relative heats of explosion. For close explosion, i.e., (Z < 3.0 ft./lb / ) and for shapes other than spherical, the TNT equivalent factor can be much greater than those from relative heats of explosion [49]. 

Heat of Combustion. 102.9kcal/mole (Ref 22) Heat of Explosion. From a differential therm analysis exotherm at 310° the Qe at 227° was calcd to be 557cal/g (Ref 39)... 

Petrin. The earliest reference to its prepn and use appears to be in German patents (Ref 1). Ref 15 gives its heat of explosion as 1204cal/g, and its impact sensitivity as 5 to 10 inches on the PicArsn impact machine (or roughly equivalent to Tetryl)... 

Heat of Explosion. 1138.5 keal/kg (w as vapor) Heat of Formation. 78.1kcal/mole Power. 540ml or 92% NG by Trauzl Pb block test with w tamping... 

Solyentless powder without nitroglycerine (G powder) has a lower heat of explosion, and consequently causes less wear on the bore... 

Gallwitz (Ref 16) reports the following data on the influence of the heat of explosion upon the bore wear. With a nitroglycerine powder containing no solvent and giving a heat of explosion of 950 kcal, the barrel stands up to 1700 rounds while with a similar powder giving a heat of explosion of 820 kcal, it withstands 3500 rounds. The reduction of the calorific value of the powder by 130 kcal therefore doubles the useful life of the barrel... 

Further reduction of the calorific value of nitroglycerine powder proved to be impossible. But by using nitrodiglycol instead of nitroglycerine, a powder was obtained with a heat of explosion of 690 kcal, which prolonged the life of the barrel considerably, i.e. to 15,000-17,000... 

H0 can be calculated from the propellant composition, but He must be obtained by successive approximation, assuming that the final state of the exhaust gases is known. For present purposes, it is sufficient to note that H0 — He correlates well with the heat of explosion of the solid explosive. In order to obtain the maximum thrust from a rocket it is therefore necessary to achieve the highest combustion temperature, but also necessary to produce gases with the lowest mean molecular weight. 

The authors of Ref. 18 fitted data from over 175 experiments to the scaled vented pressure parameters, using total heats of explosion for W. Graphs from that paper will be shown later. 

The heat of explosion is then calculated as the difference between the sum of the heats of formation of the products, and the sum of the heats of formation of the reactants, using the usual thermodynamic convention that heat evolved is negative. 

Berthelot s approximation is then employed whereby the explosive output is assumed to be proportional to the product of the heat of explosion and the volume change. 

The heat produced by a chemical reaction is expressed by the heat of explosion , Hexp- Hgxp is determined by the difference between the heat of formahon of the reactants, AHj-r, and the heat of formation of the products, AHj p, as represented by... 

Table 2.5 Heats of explosion and nitrogen concentrations of energetic materials.

Nitroguanidine (NQ) is a nitramine compound containing one N-NOj group in its molecular structure. In contrast to cyclic nitramines such as HMX and RDX, its density is low and its heat of explosion is also comparatively low. However, the Mg of its combustion products is low because of the high mass fraction of hydrogen contained within the molecule. Incorporating NQ particles into a double-base propellant forms a composite propellant termed a triple-base propellant, as used in guns. 

Fig. 6.2 The burning rates of NC-NG double-base propellants increase as the heat of explosion increases at constant pressure.

Fig. 8.7 shows the adiabatic flame temperatures and the heats of explosion of HMX-CMDB propellants as a function of KNOj) under conditions of thermal equilibrium. The adiabatic flame temperatures, Tg, and the heats of explosion increase... 

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