Secondary explosives products

High Explosives (HE). A high explosive is a substance that undergoes extremely rapid chemical reaction, when properly initiated, to produce gaseous products at high temperature and pressure. These products are then capable of doing useful work as they expand. It has been customary to divide HE into two categories primary explosives and secondary explosives. 

The thermodynamic path presented in Figure 5.1 will most likely not be the same as the kinetic path . For instance, the reaction may take place in several stages involving complex systems of reaction chains, etc. Nevertheless, the energy evolved depends only on the initial and final states and not on the intermediate ones. Once the reaction is completed, the net heat evolved is exactly the same as if the reactant molecules were first dissociated into their atoms, and then reacted directly to form the final products (Hess s Law). The heats of formation of some primary and secondary explosive substances are presented in Table 5.11. 

Above we presented the question of non-steady combustion applied to secondary explosive materials. With respect to the combustion of smokeless powder, a possible complicating factor is its multicomponent composition. Of interest in this connection is the fact cited by Andreev [15] of steady combustion of nitroglycerin gelated by 1% nitrocellulose. In the case of smoky powders and pipe mixtures the role of condensed combustion products which adhere to the burning surface and accumulate heat may be important. 

Generally, it can be said that the damaging effect of a shockwave produced by a detonation is proportional to its impulse (impulse = mass x velocity of the gaseous explosion products) and its maximum pressure, with the impulse being the most influential factor at smaller distances and the pressure being most important at larger distances. As a rule of thumb , the distance D, which offers a chance of survival, is proportional to the cube route of the mass w of an explosive, while for typical secondary explosives at larger distances, the proportionality constant is approximately 2 ... 

A chemical research laboratory is different from an industrial production facility for many reasons. First of all, only much smaller quantities of energetic materials are handled in a chemical research laboratory and secondly, during research, the properties of new, energetic materials are not known and therefore particular care must be taken. One of the most important safety rules can be worked out from the rule of thumb , which relates the distance D (in m), which offers a chance of survival, to the mass w (in kg) of the explosive. For a typical secondary explosive at large distances, the proportionality constant is approximately 2 ... 

The energy, or heat, released from the chemical reaction that occurs during the burning of a propellant or detonation of an explosive is called the heat of explosion or heat of detonation. This is the heat of reaction for the reaction of the explosive itself going to the explosive products. It does not include any heat generated by secondary reactions of the explosive or its products with air. Usually the term heat of explosion is used for propellants and heat of detonation for explosives. These are designated as A//e p and A//3-... 

Table Vll shows how the process used to manufacture lead azide, or the consequent product, significantly affects the quantity required to initiate a standard secondary explosive, RDX, in the stab-sensitive detonator (Figure la). Dextrinated lead azide has a lower output because it is less compressible and has more diluent namely, 8.5% dextrin compared to the 3.5% carboxymethyl cellulose (CMC) [34] in RD 1333, 2% polyvinyl alcohol in PVA lead azide, and no binder in Service lead azide (see Chapters 1 and 2). This situation is shown quantitatively in Table VII, which shows the minimum charge weights of each...

With the approval of the DOD Explosives Safety Board, the Army considers incineration of materials containing less than 10% explosives by weight to be a nonexplosive operation. Soil with less than 10% explosives by weight has been shown by AEC to be nonreactive, that is, not to propagate a detonation throughout the mass of soil. (The military explosives to which this limit applies are secondary explosives such as TNT and RDX, and their manufacturing by-products.)... 

The safety production is always threatened by the gas explosion in coal mine. Due to the participation of coal dust, gas explosion will be endowed with a new ability called continuity. The first explosion maybe flowed by secondary explosion or repeated explosion, so that the region of disaster and damage will been enlarged greatly. Therefore, It is necessary and urgent to develop an effective barrier device to avoid secondary and repeated gas explosion. 

The reaction level of aluminum depends on its particle size and the scattering conditions of explosion products. The decrease of aluminum powder grain size can increase the stability of explosive detonation, but it can cover other particles to hinder the reaction transmission if its size is too small. The typical used aluminum particle is 3-200 pm in diameter. Since aluminum are oxidized during its secondary reaction with oxygen-containing gas products from the first stage of explosion, the temperature of gas explosion products, the distribution of unreacted aluminum particles in the product, and the extended phase-contacting time all play important roles in the reaction level of aluminum powder. 

The emission spectra of irradiated secondary explosives reveal the immediate presence of the decomposition products which remain present at later times. This suggests for HMX and RDX that the N-N bond is broken upon decomposition rather than the C-N bond. The spectra very closely resemble the emission spectra and its characteristics which have been observed during and after irradiation of polymers and biological tissues such as vascular tissues, the myocardium etc. This ablation process induced by UV laser light has been explained by the promotion of an electron into a dissociative state through intersystem crossing or internal conversion. Similar mechanisms are probably also operative in explosives. To obtain more insight into the decomposition reactions of explosives, more experimental results are needed. 

By far the largest grouping is secondary explosives, which includes all of the major military and industrial explosives. They are much less easily brought to detonation than primary explosives and are less hazardous to manufacture. Beyond that, however, generalizations are difficult because their sensitivity to initiation covers a very wide range. Generally the military products tend to be more sensitive and the industrial products less sensitive, but all are potentially hazardous and should be handled and stored as prescribed by law. Table 30.3 lists some of the more prominent explosives of each type, along with a few of their properties. 

Esters of nitro alcohols with primary alcohol groups can be prepared from the nitro alcohol and an organic acid, but nitro alcohols with secondary alcohol groups can be esterified only through the use of an acid chloride or anhydride. The nitrate esters of the nitro alcohols are obtained easily by treatment with nitric acid (qv). The resulting products have explosive properties but are not used commercially. 

The released energy might result from the wanted reaction or from the reaction mass if the materials involved are thermodynamically unstable. The accumulation of the starting materials or intermediate products is an initial stage of a runaway reaction. Figure 12-6 illustrates the common causes of reactant accumulation. The energy release with the reactant accumulation can cause the batch temperature to rise to a critical level thereby triggering the secondary (unwanted) reactions. Thermal runaway starts slowly and then accelerates until finally it may lead to an explosion. 

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